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The Planets : Just the basic facts What is the definition of a Planet? From wikipedia: Share Tweet
Where are the planets today?
The definition of planet set in 2006 by the International Astronomical Union (IAU) states that in the Solar System a planet is a celestial body that: 1. is in orbit around the Sun, 2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and 3. has "cleared the neighbourhood" around its orbit. So in layman's : 1. It's a body which is in orbit around the sun and not a satellite of a planet. e.g. the moon is ruled out as being a planet because it orbits the earth. 2. It's shape is close to being the shape if it was made of water - e.g. close to a sphere. If the object is spinning then centrifugal force will cause it to flatten in the middle - so it's never a perfect sphere. 3. It has a clear area around it. In other words it has sucked up or pushed away any other objects to become the dominant body in the area. It has been argued that Neptune should be a dwarf planet for the reason that objects like Pluto keep wandering through it's orbit space. However Pluto has been locked into a phase in which it orbits the sun twice for every three orbits of Neptune. If this were not the case Pluto's orbit would be unstable. Therefore Neptune's much larger gravitational force is in control.
When is a satellite a satellite? You may wonder how to define when one object is a satellite of another. When two objects are locked together by gravity then both objects can be said to be circling each other. The point about which they circle is called the barycenter. If one object is heavier than the other then the barycenter will be closer to that object. When one object is much much heavier then the barycenter can lie inside that object - which is an unofficial definition of a satellite. E.g. in the case of the earth and the moon, they orbit each other around a point about 1700km under the surface of the earth, hence the moon is a satellite of the earth. It is known that Pluto and it's moon Charon orbit about a barycenter outside of both objects. They are in fact a binary system - but currently the classification remains that Charon is a satellite of Pluto.
So if it's not a planet... what is it? What's an SSSB? If an object fulfills only the first criteria - e.g. it orbits the sun and is not a satellite of a planet - is not spherical and doesn't dominate it's orbit then its a "Small Solar System Body" (SSSB).
What's a Dwarf Planet? If an object fulfills the first and second criteria - e.g. it orbits the sun and is spherical, but doesn't dominate the space around it then it's a "Dwarf Planet".
So... Which objects are planets, and which are dwarf planets? The 8 planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The 6 dwarf planets are: Ceres, Pluto, Charon, Haumea, Makemake, Eris. In 2008 it was decided to have a sub classification of Plutoids which means dwarf planets which orbit outside (mostly) of Neptune. There are 4 Plutoids : Pluto, Haumea, Makemake and Eris. And SSSB's? Well there are loads of them, and they include all the asteroids and comets.
Mercury Mercury is the closest planet to the Sun. It orbits in a highly elliptical orbit ranging from 46 million km (29 million miles) from the Sun out to 70 million km (43.5 million miles). It takes about 88 earth days to orbit the sun but rotates on it's axis once every 59 earth days. Because of the slow rotation, a single day on Mercury (mid day to mid day) takes 176 Earth days. It's axial tilt is remarkably small at 3/100ths of a degree. Much smaller than any other planet. Mercury is quite small with a diameter of 4,878km, (2/5ths that of earth) and only 5% of earths mass. It's gravity on the surface is 1/3rd of earths. Mercury has almost no atmosphere and is blasted by the Sun during the day and exposed to cold space during the night. This means that it undergoes some of the widest temperature swings of any body in the Solar System with temperatures reaching +430 C and dipping down to -180 C. It has a highly cratered rocky surface and is known to have an iron core. However it's magnetic field is much weaker than the earths (1% as strong). RADAR waves reflected from the surface of Mercury have indicated that water ice might be present at the poles. It is thought that areas of the surface permanently protected in deep craters from the fierce heat of the sun may be able to preserve large quantities of ice. Because mercury is so close to the sun, it is only ever seen with the naked eye just before sunrise and just after sunset. At all other times it is masked by the brightness of the sun.
Mercury and Man The Greeks had two names for Mercury, "Apollo" when it appeared in the morning and "Hermes" when it appeared in the evening.
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In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky. Before 2011 It had only been visited by 1 spacecraft - the Mariner 10 spacecraft which performed 3 fly-pasts in 1974/75 mapping about 45% of it's surface.
Mercury Latest: Mercury is currently being studied by the Messenger Spacecraft. Messenger entered Mercury's Orbit on 18th March 2011, the first man made object ever to do so. It is hoped that by studying Mercury, and it's ancient surface, it will help to answer many questions about the formation of the solar system. Because of it's inhospitable environment, mercury has been one of the least explored of the inner solar system planets.
Venus Venus is the second closets planet to the Sun and orbits in an almost circular orbit at 108 million km. As it orbits, Venus comes closer to earth than any other planet in the solar system and can come to within about 40 million km. Venus takes about 225 earth days to orbit the Sun and rotates at the incredibly slow rate of once every 243 days - and in a clockwise direction (as seen from looking down on the Suns north pole). Only Neptune (which almost spins on it's side) also has a clockwise spin. A day on Venus (sunrise to sunrise) lasts 117 earth days. Venus has a gentle axial tilt of 3 degrees. Venus, with a diameter of 12100 km, it is very nearly the same size as earth (1000km smaller), and has 80% of earths mass. It's gravity on the surface is 90% that of earths. Venus has a very dense atmosphere with pressures at the surface over 90 times that of earths. The atmosphere is comprised of carbon dioxide with thick clouds of suplhur dioxide. This atmosphere has the stongest greenhouse effect known in the solar system which keeps the planet at a reasonably constant temperature of 460 degrees C. This makes Venus the hottest planet in the solar system, far hotter even then mercury which is twice as close to the sun. The surface of venus, although hidden from view by thick clouds, has been mapped using radar and it is known that is is covered by large flat volcanic plains with two higher areas of land (continents) with mountains and valleys. The surface also shows impact craters and volcano like structures. Venus has a very weak magnetic field.
Venus and Man Because Venus so close to the Sun, it is often the first star to appear in the evening and the last to disappear in the morning. hence it has long been known as the "evening star" and the "morning star". The early Greeks named them Phosphorus and Hesperus and the Romans Lucifer, (literally "Light-Bringer"), and the evening aspect as Vesper. Attempts to send probes to the planet started in the infancy of space flight. In 1961, the russian probe Venera 1 was sent to impact with the planet, but communications were lost in transit. The USA then launched mariner 1 in 1962, but it was destroyed by a command from the control cent er a few minutes after launch as it veered of course. Mariner 2 was launched a month later and made a fly past of Venus in December of 1962 and was the first successful robotic interplanetary mission. It successfully measured the atmosphere, surface temperature magnetic field and radiation levels. The Russians sent the probe Venera 3 in 1966 which became the first probe to enter the atmosphere of another planet. Unfortunately it returned no planetary data. It was followed by Venera 4 which did return data which showed among other things, that the atmosphere was much denser than expected. Using the data from Venera 4, improved probes Venera 5 and 6 were also sent the the planet in the 60's neither surviving long enough to reach the surface. Mariner 5 also performed a fly-by and data was shared between Russian and American scientists. During the 70's and 80's many more missions were sent to the planet with Venera 7 being the first probe to send data from the surface of another planet. The Venera 13 analysing luna soil samples and Venera 15 and 16 entering orbit to map the surface using radar. The Americans sent Mariner 10 to photograph the planet in detail and the Pioneer Venus project sent an Orbiters and 4 atmospheric probes to the surface. In the 90's the magellan spacecraft mapped the planet before deliberately crashing into the planet. Currently Venus is being studied by Europe's Venus Express Spacecraft which has been orbiting the planet since 2005. The Messenger probe also made measurements during two fly-pasts in 2006/7 on it's way to mercury.
Earth and the Moon The third closest planet to the sun is earth and is the largest and densest of the inner planets. Earth orbits in a reasonably circular at 150 million km and is the first of the planets to have a moon. Earth is of course the only place that we know of that has life. Earth takes 365.25 earth days to orbit the Sun and rotates once every 23 hours, 56 minutes and 4 seconds. Because it rotates around the sun the length of a day on earth (sunrise to sunrise) takes 24 hours. The earth has an axial tilt of 23.4 degrees and a diameter of 12742km. The earth is thought to be 4.54 billion years old and has been accompanied by the moon for most of that time. It is believed that the moon was formed when a large mars sized body impacted the earth causing enough material to be ejected which eventually coalesced into the moon. The moon has had the effect of stabilising Earths axial tilt and is the source of the earths ocean tides. The moon is 3,474km in diameter (27% that of earth) and orbits at a distance of between about 362,000 to 405,000 km. It has also been affected by the gravitational pull of the earth which has over time caused the moons rotation to be slowed until it matches the time it takes to orbit the earth. This is why the same side of the moon always faces the earth. Earth is protected from solar radiation by a strong magnetic field generated by movement of it's core which is mainly comprised of molten iron.
Mars Mars is the fourth closets planet to the Sun and orbits in an fairly eccentric orbit at around 230 (+-20) million km. Mars takes about 686 earth days to orbit the Sun. It has a tilt (25.1 degrees) and rotational period (24 hour 37 minutes) which are both similar to the earth with a day (sunrise to sunrise) lasting 24 hours, 39 mins. Because of the tilt it also has seasons in the same way as the earth does. Mars is about half the size of the earth with a diameter of 6,792km. However it's mass is only a tenth of earths with gravity on the surface
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being around 37% that of earths. Because Mars no longer has a magnetic field to protect it, Mars has lost it's original atmosphere due to the effects of the solar wind interacting with the atmosphere causing atoms to be lost into space. Spacecraft have detected streams of atoms trailing off into space behind Mars. As a result the atmospheric pressure on mars is 1% that on earth. It is comprised of mostly (95%) carbon dioxide. Mars is very cold. Not only is it about 1.5 times further from the Sun than earth, it also has a thin atmosphere which cannot store much heat. Because of this the temperature ranges from about -87 degrees C in winter up to a maximum of -5 degrees C in summer. Mars is very dusty and prone to huge dust storms which can envelop the entire planet. These are more likely to occur when the planet is closest to the Sun.
Moons : Phobos and Deimos Mars is lucky enough to have 2 small moons - both discovered in August 1877 by Asaph Hall. Phobos is tiny - only about 22km across- orbiting very close to Mars (9300km) every 7 hours. It can be described as a non symmetrical, heavily cratered, dirty rock. Deimos however, is even smaller. It is only 12km across and orbits at 23,000 km every 30 hours. The origins of the moons are disputed but it is likely they are captured asteroids. However their near perfect circular orbits which align with the planets equator could point toward them originating on or with Mars.
Mars and Man Mars is named after the Roman god of war and has been known since before babylonian times where it was associated with Nergul, a god of war, fire and destruction - possibly inspired by its red colour. Possibly because Mars has a more benign environment than that any of the other inner planets (other than Earth of course) it has received quite a few robotic explorers. The first successful fly-by of Mars was performed by Mariner 4 in 1965. Mariner 9 in 1971 became the first probe to orbit another planet when it entered Mars orbit. Shortly after 2 Soviet probes Mars2 and Mars3 became the first to successfully land on another planet - even though they ceased functioning very shortly after. 1976 saw the US Viking mission in with two orbiters and two landers. The landers successfully re laid images of the Mars surface and other measurements and continued working for up to 6 years. In 1988 the soviets sent 2 probes (phobos 1 and 2) to photograph and land on the moons. One lost communications in transit and the other successfully photographed the phobos but failed before deploying it's landers. Mars Global Surveyor entered the Mars orbit in 1997 and spent 4 years mapping the Mars in detail. Also in 1997 Mars Pathfinder landed on the surface with its robotic vehicle Sojourner which was able to wander up to 0.5 km from the lander and took many photographs and measurements from the rocks and soil. Another lander, Phoenix, landed in the polar regions of Mars and confirmed the presence of water on Mars. Since the year 2000, many additional probes have reached Mars and now provide detailed monitoring of the planets atmosphere and geography. The Mars Exploration Rovers, Spirit and Opportunity landed in 2004 for their 90 day mission. They both exceeded their mission objectives with Sprit eventually failing 2010 and Opportunity still performing - "Opportunity is in good health, although the robotic arm elbow t potentiometer is acting up." (June 2013) Mars is currently host to five functioning spacecraft: three in orbit – the Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter; and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity. Defunct spacecraft on the surface include MER-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
Asteroid Belt Between Mars and Jupiter lies the Asteroid belt which is comprised of thousands of rocks left over from the formation of the solar system. These rocks vary in size from microscopic up to Ceres (950km diameter) which is classified as a dwarf planet. It is thought that jupiter's strong gravitational influence may have prevented the asteroids coalescing into larger objects such as a planet. Outside of the asteroid belt itself there are also three clusters of asteroids which are very much in Jupiter's influence. These are the Trojan asteroids which orbit ahead and behind Jupiter and the Hilda Asteroids which orbit twice for every 3 Jupiter orbits. These asteroids are in Jupiter's Lagrange points - areas of gravitational stability. Although the asteroid belt has many bodies within it, it is still very thinly populated with many unmanned spacecraft having successfully ed through it without incident.
Jupiter Jupiter is the fifth closest planet to the Sun and is the first of what are called the outer planets (being outside the asteroid belt). It is by far the largest planet in the solar system having two and a half times as much mass as all the other planets put together and one thousandth the mass of the Sun. This is so large that the Sun and Jupiter actually orbit each other about a point just outside of the Suns surface. Jupiter orbits the Sun once very 12 years (at about 780 million km) and is comprised of gas (75% hydrogen and 24% helium) and is presumed to have a rocky core surrounded by a sea of liquid metallic hydrogen which forms a ball 110,000km in diameter. Jupiter's total diameter is 142,984 km. In the upper atmosphere is a cloud layer 50km thick. The clouds are comprised of ammonia crystals and other compounds which are arranged into bands moving at different speeds at different latitudes. The Great Red Spot is a large stable storm vortex laying between two layers. Considering it's size, Jupiter rotates very quickly at one rotation at just under once every 10 hours. This means that at the equator there is quite a large centrifugal force which means the planet has a pronounced bulge - it's diameter around the equator is 9000km greater than the diameter measured at the poles.
Moons : Io, Europa, Ganymede and Callisto Jupiter has many satellites (more than 60) but most of these are quite small (less than 10km diameter). The four largest moons (named above) which were discovered by Galileo Galilei in 1610 are named after the lovers of Zeus. These moons are generally larger than the earths moon with diameters ranging from 3100km to 5200km. Three of the moons are locked together in an orbital resonance in which for every orbit Ganymede takes, Europa takes exactly two orbits and Io exactly four orbits. The closest to Jupiter, Io, has over 400 volcano's and is incredible geologically active. This is thought to be due to Jupiter's strong gravitational field constantly squeezing the moon as it orbits which warms the moons interior. The next of the Galilean Moons is Europa. It's surface is very smooth and comprised of water ice, possibly floating on a sea of liquid water. It's thought to have a rocky centre and has a thin oxygen atmosphere. Because of the presence of water it is thought to be a good candidate to find life outside of the earth.
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Ganymede is the largest satellite in the solar system and is larger than the planet Mercury. It is also covered in ice but is less geologically active with it's surface marked by craters and ridges. Callisto, the last of the Galilean moons is comprised of even quantities of rock and ice and a thin atmosphere of carbon dioxide and oxygen. It is possible it has liquid water buried 100km below it's surface.
Jupiter and Man Jupiter is named after the Roman king of the gods also known as Jove who was based on the greek god Zeus. Jupiter was first visited by the Pioneer 10 spacecraft in 1973 closely followed by Pioneer 11 in 1974. These spacecraft obtained the first close-up images of jupiter and it's red spot and moons and also measured Jupiter's massive magnetic field. They are still traveling out of the solar system, but have lost communications with earth. The next visitors were Voyager 1 and 2 in 1979 and discovered, among other things, the faint Jovian ring system, several new natural satellites, volcanic activity on Io. The Ulysses spacecraft which was designed to study the Sun used jupiter's gravitational field (1992) to swing it out of the plane of the ecliptic to allow it to orbit over the Suns poles. Galileo became the first (and only) spacecraft to orbit jupiter in 1995, orbiting the planet for 7 years before being deliberately crashed into the planet in order to ensure that it did not crash into, and contaminate, Europa. During it's mission it collected a huge amount of data on the entire Jovian system and even witnessed the Shoemaker-Levy 9 comet impact in Jupiter's southern hemisphere. The Cassini probe flewpast in 2000 and imaged Jupiter's atmosphere revealing many unknown features. The New Horizons probe flew past in 2007 on it's way to pluto and studied the Jovian moons, magnetic field and ring system. NASA currently has a mission underway to study Jupiter in detail from a polar orbit. Named Juno, the spacecraft launched in August 2011, and will arrive in late 2016. The next planned mission to the Jovian system will be the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. Cassini Images of Jupiter Voyager Images of Jupiter
Saturn Saturn is the sixth closest planet to the Sun. It is the second largest planet in the solar system having a radius 9 times that of earth (57,000 km) and a mass 95 times that of earth. Saturn orbits the Sun once very 29 years (at about 1400 million km) and is mainly comprised of gas (96% hydrogen and 3% helium) and is presumed to have a rocky core surrounded by a sea of liquid metallic hydrogen which forms a ball some 56,000km in diameter. The upper layers are thought to comprise of liquid water, ammonium hydrosulfide, hydrogen and helium. Saturn's core is quite hot (11,700 degrees C) and it generates more heat than it receives from the sun. It cools the further from the centre with only the top 350km being cooler than freezing - it's upper atmosphere being around -180 degrees C. The cloud layers of Saturn are similar to those of Jupiter except that the banding is weaker and wider. Saturn also has a short lived but periodical storm called the great white spot which seems to occur every Saturnian year. Saturn rotates at around 10 hours 39 minutes. The precise figure (like that of all gas giants) is not certain since there are several ways of measuring the rotation of a body which has no fixed visual references.
Saturn's Rings Saturn is of course best known for it's ring system. These were first seen by Galileo Galilei in 1610 who, quite understandably, was confused by them and thought Saturn was being accompanied by two other planets which sat either side of it. In 1655 Christian Huygens using an improved telescope was able to see enough detail to suggest that there was a ring around Saturn. The rings extend from 7000km to 120,000km above the surface of Saturn. Incredibly, they are under 20m thick comprising of mainly ice particles ranging in size from dust to boulders a few meters across. The gaps in the rings are caused by the gravitational effects of Saturn's moons, and also by larger "moonlets" which inhabit the rings causing particles to be nudged into banded orbits. Recent observations have discovered that there are some distortions in the rings causing particles to rise some 4km out of the normal ring plane due to the tilted orbit of certain moons. The rings are thought to be either the remnants of a moon destroyed in orbit or simply by material left over by the formation of the solar system.
Moons : Titan... and the others Saturn has 62 moons with only seven being large enough to become spherical in shape. By far the largest of all of Saturn's moons is Titan which is larger than the planet Mercury, and the second largest moon in the solar system (Jupiter's Ganymede being the largest). Titan is 5,150 km in diameter and has a dense atmosphere of nitrogen with traces of methane. It has large lakes of liquid methane/ethane on it's surface and may have a subsurface ocean of liquid water which occasionally erupts to the surface. The next largest moon to Titan is Rhea which has a diameter of 1,530km (30% Titans diameter). It is an icy body (75% ice, 25% rock) with a heavily cratered surface. The other moons of Saturn tend to have similar characteristics being comprised mainly of ice and rock and all being heavily cratered. Two notable moons include Mimas which shows an impact crater with a radius 1/3rd that of the moon, Iapetus which has remarkable colouring with one side being black as soot and the other as white as snow. This colouring is thought to be the result particles being kicked up from impacts on the moon Phoebe which lay Iapetus's orbit. As Iapetus ed through these particles they were deposited on Iapetus's leading hemisphere causing it to darken.
Saturn and Man Saturn is named after the Roman gods Saturnus (equivalent to the Greek god Cronus) which was the god of agricultural and harvest. Saturn was first visited by the Pioneer 11 spacecraft in 1979 which discovered among other things additional rings in the ring system, and the moon Epimetheus which it almost (within 4000km) collided with. The Voyager probes were the next to study Saturn with Voyager 1 taking the first high resolution images of Saturn, it's rings and moons in 1980. Voyager 2 took more images in 1981 but a failure in it's camera pointing ability resulted in losing some expected imagery. in 2004 the Cassini spacecraft became the first probe to enter into orbit around Saturn releasing the Huygens probe which entered Titans atmosphere early in January 2005. The Huygens probe successfully landed on the surface of Titan sending back images and data during it's descent and from the surface. Cassini has made many fly-pasts of Saturn's moons and ring systems making many new discoveries including new rings and weather systems. The Cassini spacecraft is intended to continue to study the Saturnian system until 2017 when it will be
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deliberately to crashed into Saturn. Cassini-Huygens Images of Saturnian System Voyager Images of Saturn
Uranus Uranus is the seventh closest planet to the Sun and the third largest and fourth heaviest of the planets. It diameter (50,000km) is four times that of earth with a mass over 14 times that of earth. Uranus orbits the Sun once very 84 years (at about 2900 million km) but is unusual in that it spins on its side (with an axial tilt of 97 degrees). This means that it's moons and also it's faint ring system also orbit in plane perpendicular to the plane of the ecliptic. It is believed to be comprised of a small rocky core surrounded by a beep mantle of water, ammonia and methane. This is in turn surrounded by an atmosphere of hydrogen, helium and methane with an upper cloud layer. Another oddity in Uranus is the fact that it is very cold. All the other gas giant planets emit more heat radiation than they receive due to very hot cores, but Uranus does not. A temperature of -224 degrees C and been measured in Uranus's atmosphere - the coldest in the solar system.
Uranus's Rings Uranus has the second most extensive ring system of the solar system after Saturn. The rings, which are very difficult to see from ground based observations, were first discovered in 1977 by measuring the intensity of a star as Saturn and it's rings ed in front of it. There are 13 known rings with radii of 38,000km to 98,000km. They are comprised of ice and some darker material which results in them being much darker than the rings of Saturn.
Moons Uranus has 27 known moons with sizes ranging from over 1500 km diameter down to under 20km. The moons consist of ice, rock and other trace elements. Some of the inner moon undergo gravitation interactions with each other which may in many millions of years lead to un stabilities and collisions.
Uranus and Man Uranus, under clear dark skies, is actually visible to the naked eye. However it is very dim and it's 84 year periodicity means that it moves slowly across the sky. However it is interesting that it was not noticed by the ancients and was only observed for the first time by Sir William Herschel in 1781 using a telescope. It was initially named Georgium Sidus (George's Star) by Herschel after King George III. However this unpopular name was eventually discarded and it was renamed Uranus after the greek god of the sky. Uranus is the only planet to be named after a greek god, rather than a roman deity. To date Uranus has been visited only once - by the Voyager 2 spacecraft. The fly-by occurred in 1986 and resulted in the discovery of 10 new moons and 2 rings. It also measured the chemical compostion of the atmosphere and photographed the planet and it's moons. A "Uranus Orbiter and Probe" mission is in the study stages. Voyager Images of Uranus
Neptune Neptune is the eighth closest planet to the Sun and is (since the relegation of Pluto) the last Planet in the Solar System. It is similar in size and composition to Uranus with a diameter of 49,000km and a mass of over 17 times that of earth. Uranus orbits the Sun once very 165 years at about 4500 million km. This is 30 times the distance from the Sun to the Earth which means that the strength of sunlight at Neptune is 1% of its strength at Earth. Neptune spins on an axis with a tilt of 28 degrees which is quite similar to that of the Earth every 16 hours. Unlike Uranus's almost completely bland cloud layer, Neptune's weather systems are more pronounced with great dark spot storm systems being seen in the southern and northern hemispheres and other visible banding. Wind speeds of up to 600m/s have also been observed. Due to it's great distance from the sun, it is not surprising that the planet is one of the coldest with temperatures of -220 degrees C in the upper atmosphere. The core is thought to be at around 5200 degrees C.
Neptune's Rings Neptune has a ring system comprised of three main rings with radii between 63,000 km and 42,000km which appear to have a clumpy structure in which they form arcs rather than complete rings. It is believed that gravitational effects from Neptune's moons may cause the clumping.
Moons - Triton Uranus has 13 known moons of which only Triton (2700km diameter) is the most significant. The next largest moon Proteus is only 420km in diameter. Triton is the only large moon to orbit in retrograde (e.g. in the opposite direction to most orbits) and is thought to be a an captured object rather than created in orbit. It has avery thin atmosphere of Nitrogen, Carbon Dioxide and methane. Although it has a surface temperature of around -230 degrees C, it is thought to be geologically active with cryovolcanism (low temperature volcano's) producing eruptions of water and ammonia which freeze to form complex valleys and ridges.
Neptune and Man Neptune is invisible to the naked eye and was unknown to the ancients. It was first discovered when astronomers noticed anomalies in the orbit of Uranus and suggested that an as yet undiscovered planet could be the cause. In 1846 Neptune was observed near the position predicted by Urbain Le Verrier. This was the first planet to be discovered by mathematical prediction. Le Verrier proposed the name Neptune (roman god of the sea) for the planet since it was in keeping with naming planets after Roman deities (other than Uranus which is greek). To date Neptune (like Uranus) has been visited only once - again by the Voyager 2 spacecraft. The fly-by occurred in 1989 and resulted in many discoveries including Neptune's weather systems, rings and 6 more moons. It also provided an accurate measurement of Neptune's mass which allowed discrepancies in the orbits of Uranus and Neptune to be solved. There are currently no missions planned to visit Neptune, since the Neptune Orbiter and Probe mission was dropped in favour of the Uranus Orbiter and Probe mission. Voyager Images of Neptune
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th to see the planets as they were. For full information on all the Where are the planets today?
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The sky is divided up into 12 areas - the 12 signs of the zodiac. Each of these signs covers an equal area of the sky and always align to the same stars. (Over millennia the zodiac could be said to move as the earth's axis rotates - but it's best to ignore this whilst learning the basics). So when looking at the sky, the stars are fixed when compared with the zodiac, but the planets, as they orbit the sun, change position and "wander" about. Astrology tries to use the movements of the stars to understand our personalities and to some extent control our destinies. Each of the 12 signs is also associated with an element (earth, air, fire and water) and also a mode (cardinal, fixed and mutable). More about this later.
The Planets Each of the planets (which for astrology includes the sun and the moon) control a different aspect. In general they can be listed as: Sun = Ego / Self Moon = Emotion / Moods Mercury = Communication / Thinking Venus = Harmony / Affections Mars = Confidence / Energy Jupiter = Prosperity / Good Fortune Saturn = Limitations / Practicality Uranus = Individuality / Inventiveness Neptune = Idealism / Comion Pluto = Transformation / Power The Sun, Moon, Mercury, Venus and Mars are the personal planets which affect our personalities and immediate relationships. The more distant planets affect how we interact with the world in a more general way. When planets are in retrograde (e.g. they appear to be traveling backwards to their normal motion in the sky) their effect can be reversed to be directed inwards. When they again start to move forward again their effect can be enhanced.
Planets and Signs Each planet is the ruler of a particular sign (or signs). Whilst in that sign the planets influence is enhanced. The rulerships for each of the planets are as below:
Sun Moon Mercury Venus Mars Jupiter Saturn Uranus Neptune Pluto
Leo Cancer Gemini and Virgo Libra and Taurus Aries (and* Scorpio) Sagittarius (and* Pisces) Capricorn (and* Aquarius) Aquarius Pisces Scorpio
* before the invention of telescopes, these signs were also assigned to these planets. Since telescopes the three outer planets have been discovered and assigned these signs. This information is useful since if you know what influence a planet has, then you will know what influence that signs ruled by that planet have.
Elements Signs are allocated a different element in turn. This means that every fourth sign has the same element as follows: Fire Signs : Aries, Leo, Sagittarius Earth Signs: Taurus, Virgo, Capricorn Air Signs : Gemini, Libra, Aquarius Water Signs : Cancer, Scorpio, Pisces Fire signs represent a persons ion, energy,enthusiasm, inspiration. Earth signs represent a persons practicality, stability, materialism, realism. Air signs represent language, intellect, communication and social relationships. Water Signs represent emotion, mysticism, intuition. Generally speaking, the more planets someone has in a particular sign at the time of their birth, the stronger that signs personality traits will be in them.
Modes Rather like elements, each sign also has a mode allocated to it. Every 3rd sign has the same mode as follows: Cardinal Signs: Aries, Cancer, Libra, Capricorn Fixed Signs: Taurus, Leo, Scorpio, Aquarius Mutable Signs: Gemini. Virgo, Sagittarius, Pisces Cardinal signs are energetic, dynamic and proactive. Fixed signs are persistence, perseverant, stabile. Mutable signs are flexible, changeable, adaptable, suggestible. Again, the more planets you have in a particular Mode, the more your personality has those traits.
Working out the planets influences? It takes quite a lot of skill to determine one's personality traits accurately. However, a simple rule of thumb is to count at the time of birth how many planets fall in each sign and then work out how many are in each element and mode (perhaps counting the sun and moon as 2 due to their extra influence). The greater the score for each indicates how much of an influence each element and mode are on that person.
What are the Houses Just when you thought you might have got some sort of a grip on astrology, in come the houses. Whereas signs indicate what personality traits one has, houses indicate where they will exhibited themselves.
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Like the signs, there are 12 houses which divide up the sky. However the alignment of the houses is defined by the position of the horizon on the time of your birth. This means in order to calculate the houses, one must know not only what date one was born but also what time (to within a few minutes) and at what location on earth.
If one were to the set the application above to the time of ones birth and then set the lat and long to the place of ones birth, then the lowest slider will then bring up a display of the horizon at that time and location. Using this horizon one can ascertain how the houses are defined. The first house is located just under the western horizon, and the others follow consecutively in an anti-clockwise direction - e.g. the first 6 are in the black area (below the horizon), the last 6 are in the sky area (above the horizon). Once one knows where the houses lie, one can again see which sign lies in which house. Since there are 12 signs and 12 houses one can see that normally each house will overlay parts of 2 signs. The sign used is the sign which overlays the cusp of the house. The lines which separate each of the houses are called the cusps. The cusp of a house is the line preceding.
What do the houses mean? The following chart from wikipedia shows how the houses are interpreted.
House
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Sign
Latin motto
Translation
Modern title of house
1st
Aries
Vita
Life
House of Self
2nd
Taurus
Lucrum
Wealth
House of Value
3rd
Gemini
Fratres
Brothers
House of Communications
4th
Cancer
Genitor
Parent
House of Home and Family
5th
Leo
Nati
Children
House of Pleasure
6th
Virgo
Valetudo
Health
House of Health
Interpretation Physical appearance, traits and characteristics. First impressions. General outlook into the world. Ego. Beginnings and initiatives. Material and immaterial things of certain value. Money. Belongings, property, acquisitions. Cultivation and growth. Substance. Self-Worth. Higher education and childhood environment. Communication. Happiness. Intelligence. Achievements. Siblings. Neighbourhood matters. Short, local travel and transportations. Ancestry, heritage, roots. Early foundation and environment. Mother or mothers as figure. The caretaker of the household. Cyclic end of matters. Recreational and leisure activities. Things which makes for enjoyment and entertainment. Games and gambling. Children. Love and sex. Creative self-expression. Routine tasks and duties. Skills or training acquired. Jobs and Employments. Health and overall well-being. Service performed for others. Caretaking. Pets and small domestic animals.
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7th
Libra
Uxor
Spouse
House of Partnerships
8th
Scorpio
Mors
Death
House of Reincarnation
9th
Sagittarius
Iter
Journeys
House of Philosophy
10th
Capricorn
Regnum
Kingdom
House of Social Status
11th
Aquarius
Benefacta
Friendship
House of Friendships
12th
Pisces
Carcer
Prison
House of Self-Undoing
Close, confidante-like relationships. Marriage and business partners. Agreements and treaties. Matters dealing with diplomatic relations of all kinds, including open (known) enemies. Attraction to qualities we ire from the other partner. Cycles of Deaths And Rebirth. Sexual relationships and deeply committed relationships of all kinds. t funds, finances. Other person's resource. Occult, psychic and taboo matters. Regeneration. Self-transformation. Foreign travel and foreign countries. Culture. Long distance travels and journeys. Religion. Law and ethics. Higher education. Knowledge. Experience through expansion. Ambitions. Motivations. Career. Status in society. Government. Authority. Father or father figure. The breadwinner of the household. One's public appearance/impression at large(audience). Friends and acquaintances of like-minded attitudes. Groups, clubs and societies. Higher associations. Benefits and fortunes from career. One's hopes and wishes. Mysticism. Places of seclusion such as hospitals, prisons and institutions, including self-imposed imprisonments. Things which are not apparent to self, yet clearly seen by others. Elusive, clandestine, secretive or unbeknownst matters. Retreat, reflection and self-sacrifice. Unconscious/subconscious. Unknown enemies.
Many modern astrologers assume that the houses relate to their corresponding signs, i.e. that the first house has a natural affinity with the first sign, Aries, and so on.
And there's more... The houses can also be classified as Angular, Succedent and Cadent and are ruled by signs according to the astrological modality. And... well there are many many more aspects to astrology which seem almost designed to confuse and complicate. As you can see, astrology is not a simple area of study. The above is just skimming the surface of a subject that could (and does) take up volumes and volumes of books. There are many systems of astrology and many variations between individual astrologers that use the same basic principles. Some astrologers also use astronomical objects which have never been seen by the unaided eye (such as chiron - an asteroid/comet cross discovered in 1977) and others objects that have never even been detected. Some prefer to align the zodiac to the night time sky as seen by astrologers thousands of years ago. All in all, with astrology, one must pick and choose the astrologer and the style of astrology that suits one best. Follow @ThePlanetsToday
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The Planets : Just the basic facts What is the definition of a Planet? From wikipedia: Share Tweet
Where are the planets today?
The definition of planet set in 2006 by the International Astronomical Union (IAU) states that in the Solar System a planet is a celestial body that: 1. is in orbit around the Sun, 2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and 3. has "cleared the neighbourhood" around its orbit. So in layman's : 1. It's a body which is in orbit around the sun and not a satellite of a planet. e.g. the moon is ruled out as being a planet because it orbits the earth. 2. It's shape is close to being the shape if it was made of water - e.g. close to a sphere. If the object is spinning then centrifugal force will cause it to flatten in the middle - so it's never a perfect sphere. 3. It has a clear area around it. In other words it has sucked up or pushed away any other objects to become the dominant body in the area. It has been argued that Neptune should be a dwarf planet for the reason that objects like Pluto keep wandering through it's orbit space. However Pluto has been locked into a phase in which it orbits the sun twice for every three orbits of Neptune. If this were not the case Pluto's orbit would be unstable. Therefore Neptune's much larger gravitational force is in control.
When is a satellite a satellite? You may wonder how to define when one object is a satellite of another. When two objects are locked together by gravity then both objects can be said to be circling each other. The point about which they circle is called the barycenter. If one object is heavier than the other then the barycenter will be closer to that object. When one object is much much heavier then the barycenter can lie inside that object - which is an unofficial definition of a satellite. E.g. in the case of the earth and the moon, they orbit each other around a point about 1700km under the surface of the earth, hence the moon is a satellite of the earth. It is known that Pluto and it's moon Charon orbit about a barycenter outside of both objects. They are in fact a binary system - but currently the classification remains that Charon is a satellite of Pluto.
So if it's not a planet... what is it? What's an SSSB? If an object fulfills only the first criteria - e.g. it orbits the sun and is not a satellite of a planet - is not spherical and doesn't dominate it's orbit then its a "Small Solar System Body" (SSSB).
What's a Dwarf Planet? If an object fulfills the first and second criteria - e.g. it orbits the sun and is spherical, but doesn't dominate the space around it then it's a "Dwarf Planet".
So... Which objects are planets, and which are dwarf planets? The 8 planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The 6 dwarf planets are: Ceres, Pluto, Charon, Haumea, Makemake, Eris. In 2008 it was decided to have a sub classification of Plutoids which means dwarf planets which orbit outside (mostly) of Neptune. There are 4 Plutoids : Pluto, Haumea, Makemake and Eris. And SSSB's? Well there are loads of them, and they include all the asteroids and comets.
Mercury Mercury is the closest planet to the Sun. It orbits in a highly elliptical orbit ranging from 46 million km (29 million miles) from the Sun out to 70 million km (43.5 million miles). It takes about 88 earth days to orbit the sun but rotates on it's axis once every 59 earth days. Because of the slow rotation, a single day on Mercury (mid day to mid day) takes 176 Earth days. It's axial tilt is remarkably small at 3/100ths of a degree. Much smaller than any other planet. Mercury is quite small with a diameter of 4,878km, (2/5ths that of earth) and only 5% of earths mass. It's gravity on the surface is 1/3rd of earths. Mercury has almost no atmosphere and is blasted by the Sun during the day and exposed to cold space during the night. This means that it undergoes some of the widest temperature swings of any body in the Solar System with temperatures reaching +430 C and dipping down to -180 C. It has a highly cratered rocky surface and is known to have an iron core. However it's magnetic field is much weaker than the earths (1% as strong). RADAR waves reflected from the surface of Mercury have indicated that water ice might be present at the poles. It is thought that areas of the surface permanently protected in deep craters from the fierce heat of the sun may be able to preserve large quantities of ice. Because mercury is so close to the sun, it is only ever seen with the naked eye just before sunrise and just after sunset. At all other times it is masked by the brightness of the sun.
Mercury and Man The Greeks had two names for Mercury, "Apollo" when it appeared in the morning and "Hermes" when it appeared in the evening.
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In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky. Before 2011 It had only been visited by 1 spacecraft - the Mariner 10 spacecraft which performed 3 fly-pasts in 1974/75 mapping about 45% of it's surface.
Mercury Latest: Mercury is currently being studied by the Messenger Spacecraft. Messenger entered Mercury's Orbit on 18th March 2011, the first man made object ever to do so. It is hoped that by studying Mercury, and it's ancient surface, it will help to answer many questions about the formation of the solar system. Because of it's inhospitable environment, mercury has been one of the least explored of the inner solar system planets.
Venus Venus is the second closets planet to the Sun and orbits in an almost circular orbit at 108 million km. As it orbits, Venus comes closer to earth than any other planet in the solar system and can come to within about 40 million km. Venus takes about 225 earth days to orbit the Sun and rotates at the incredibly slow rate of once every 243 days - and in a clockwise direction (as seen from looking down on the Suns north pole). Only Neptune (which almost spins on it's side) also has a clockwise spin. A day on Venus (sunrise to sunrise) lasts 117 earth days. Venus has a gentle axial tilt of 3 degrees. Venus, with a diameter of 12100 km, it is very nearly the same size as earth (1000km smaller), and has 80% of earths mass. It's gravity on the surface is 90% that of earths. Venus has a very dense atmosphere with pressures at the surface over 90 times that of earths. The atmosphere is comprised of carbon dioxide with thick clouds of suplhur dioxide. This atmosphere has the stongest greenhouse effect known in the solar system which keeps the planet at a reasonably constant temperature of 460 degrees C. This makes Venus the hottest planet in the solar system, far hotter even then mercury which is twice as close to the sun. The surface of venus, although hidden from view by thick clouds, has been mapped using radar and it is known that is is covered by large flat volcanic plains with two higher areas of land (continents) with mountains and valleys. The surface also shows impact craters and volcano like structures. Venus has a very weak magnetic field.
Venus and Man Because Venus so close to the Sun, it is often the first star to appear in the evening and the last to disappear in the morning. hence it has long been known as the "evening star" and the "morning star". The early Greeks named them Phosphorus and Hesperus and the Romans Lucifer, (literally "Light-Bringer"), and the evening aspect as Vesper. Attempts to send probes to the planet started in the infancy of space flight. In 1961, the russian probe Venera 1 was sent to impact with the planet, but communications were lost in transit. The USA then launched mariner 1 in 1962, but it was destroyed by a command from the control cent er a few minutes after launch as it veered of course. Mariner 2 was launched a month later and made a fly past of Venus in December of 1962 and was the first successful robotic interplanetary mission. It successfully measured the atmosphere, surface temperature magnetic field and radiation levels. The Russians sent the probe Venera 3 in 1966 which became the first probe to enter the atmosphere of another planet. Unfortunately it returned no planetary data. It was followed by Venera 4 which did return data which showed among other things, that the atmosphere was much denser than expected. Using the data from Venera 4, improved probes Venera 5 and 6 were also sent the the planet in the 60's neither surviving long enough to reach the surface. Mariner 5 also performed a fly-by and data was shared between Russian and American scientists. During the 70's and 80's many more missions were sent to the planet with Venera 7 being the first probe to send data from the surface of another planet. The Venera 13 analysing luna soil samples and Venera 15 and 16 entering orbit to map the surface using radar. The Americans sent Mariner 10 to photograph the planet in detail and the Pioneer Venus project sent an Orbiters and 4 atmospheric probes to the surface. In the 90's the magellan spacecraft mapped the planet before deliberately crashing into the planet. Currently Venus is being studied by Europe's Venus Express Spacecraft which has been orbiting the planet since 2005. The Messenger probe also made measurements during two fly-pasts in 2006/7 on it's way to mercury.
Earth and the Moon The third closest planet to the sun is earth and is the largest and densest of the inner planets. Earth orbits in a reasonably circular at 150 million km and is the first of the planets to have a moon. Earth is of course the only place that we know of that has life. Earth takes 365.25 earth days to orbit the Sun and rotates once every 23 hours, 56 minutes and 4 seconds. Because it rotates around the sun the length of a day on earth (sunrise to sunrise) takes 24 hours. The earth has an axial tilt of 23.4 degrees and a diameter of 12742km. The earth is thought to be 4.54 billion years old and has been accompanied by the moon for most of that time. It is believed that the moon was formed when a large mars sized body impacted the earth causing enough material to be ejected which eventually coalesced into the moon. The moon has had the effect of stabilising Earths axial tilt and is the source of the earths ocean tides. The moon is 3,474km in diameter (27% that of earth) and orbits at a distance of between about 362,000 to 405,000 km. It has also been affected by the gravitational pull of the earth which has over time caused the moons rotation to be slowed until it matches the time it takes to orbit the earth. This is why the same side of the moon always faces the earth. Earth is protected from solar radiation by a strong magnetic field generated by movement of it's core which is mainly comprised of molten iron.
Mars Mars is the fourth closets planet to the Sun and orbits in an fairly eccentric orbit at around 230 (+-20) million km. Mars takes about 686 earth days to orbit the Sun. It has a tilt (25.1 degrees) and rotational period (24 hour 37 minutes) which are both similar to the earth with a day (sunrise to sunrise) lasting 24 hours, 39 mins. Because of the tilt it also has seasons in the same way as the earth does. Mars is about half the size of the earth with a diameter of 6,792km. However it's mass is only a tenth of earths with gravity on the surface
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being around 37% that of earths. Because Mars no longer has a magnetic field to protect it, Mars has lost it's original atmosphere due to the effects of the solar wind interacting with the atmosphere causing atoms to be lost into space. Spacecraft have detected streams of atoms trailing off into space behind Mars. As a result the atmospheric pressure on mars is 1% that on earth. It is comprised of mostly (95%) carbon dioxide. Mars is very cold. Not only is it about 1.5 times further from the Sun than earth, it also has a thin atmosphere which cannot store much heat. Because of this the temperature ranges from about -87 degrees C in winter up to a maximum of -5 degrees C in summer. Mars is very dusty and prone to huge dust storms which can envelop the entire planet. These are more likely to occur when the planet is closest to the Sun.
Moons : Phobos and Deimos Mars is lucky enough to have 2 small moons - both discovered in August 1877 by Asaph Hall. Phobos is tiny - only about 22km across- orbiting very close to Mars (9300km) every 7 hours. It can be described as a non symmetrical, heavily cratered, dirty rock. Deimos however, is even smaller. It is only 12km across and orbits at 23,000 km every 30 hours. The origins of the moons are disputed but it is likely they are captured asteroids. However their near perfect circular orbits which align with the planets equator could point toward them originating on or with Mars.
Mars and Man Mars is named after the Roman god of war and has been known since before babylonian times where it was associated with Nergul, a god of war, fire and destruction - possibly inspired by its red colour. Possibly because Mars has a more benign environment than that any of the other inner planets (other than Earth of course) it has received quite a few robotic explorers. The first successful fly-by of Mars was performed by Mariner 4 in 1965. Mariner 9 in 1971 became the first probe to orbit another planet when it entered Mars orbit. Shortly after 2 Soviet probes Mars2 and Mars3 became the first to successfully land on another planet - even though they ceased functioning very shortly after. 1976 saw the US Viking mission in with two orbiters and two landers. The landers successfully re laid images of the Mars surface and other measurements and continued working for up to 6 years. In 1988 the soviets sent 2 probes (phobos 1 and 2) to photograph and land on the moons. One lost communications in transit and the other successfully photographed the phobos but failed before deploying it's landers. Mars Global Surveyor entered the Mars orbit in 1997 and spent 4 years mapping the Mars in detail. Also in 1997 Mars Pathfinder landed on the surface with its robotic vehicle Sojourner which was able to wander up to 0.5 km from the lander and took many photographs and measurements from the rocks and soil. Another lander, Phoenix, landed in the polar regions of Mars and confirmed the presence of water on Mars. Since the year 2000, many additional probes have reached Mars and now provide detailed monitoring of the planets atmosphere and geography. The Mars Exploration Rovers, Spirit and Opportunity landed in 2004 for their 90 day mission. They both exceeded their mission objectives with Sprit eventually failing 2010 and Opportunity still performing - "Opportunity is in good health, although the robotic arm elbow t potentiometer is acting up." (June 2013) Mars is currently host to five functioning spacecraft: three in orbit – the Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter; and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity. Defunct spacecraft on the surface include MER-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
Asteroid Belt Between Mars and Jupiter lies the Asteroid belt which is comprised of thousands of rocks left over from the formation of the solar system. These rocks vary in size from microscopic up to Ceres (950km diameter) which is classified as a dwarf planet. It is thought that jupiter's strong gravitational influence may have prevented the asteroids coalescing into larger objects such as a planet. Outside of the asteroid belt itself there are also three clusters of asteroids which are very much in Jupiter's influence. These are the Trojan asteroids which orbit ahead and behind Jupiter and the Hilda Asteroids which orbit twice for every 3 Jupiter orbits. These asteroids are in Jupiter's Lagrange points - areas of gravitational stability. Although the asteroid belt has many bodies within it, it is still very thinly populated with many unmanned spacecraft having successfully ed through it without incident.
Jupiter Jupiter is the fifth closest planet to the Sun and is the first of what are called the outer planets (being outside the asteroid belt). It is by far the largest planet in the solar system having two and a half times as much mass as all the other planets put together and one thousandth the mass of the Sun. This is so large that the Sun and Jupiter actually orbit each other about a point just outside of the Suns surface. Jupiter orbits the Sun once very 12 years (at about 780 million km) and is comprised of gas (75% hydrogen and 24% helium) and is presumed to have a rocky core surrounded by a sea of liquid metallic hydrogen which forms a ball 110,000km in diameter. Jupiter's total diameter is 142,984 km. In the upper atmosphere is a cloud layer 50km thick. The clouds are comprised of ammonia crystals and other compounds which are arranged into bands moving at different speeds at different latitudes. The Great Red Spot is a large stable storm vortex laying between two layers. Considering it's size, Jupiter rotates very quickly at one rotation at just under once every 10 hours. This means that at the equator there is quite a large centrifugal force which means the planet has a pronounced bulge - it's diameter around the equator is 9000km greater than the diameter measured at the poles.
Moons : Io, Europa, Ganymede and Callisto Jupiter has many satellites (more than 60) but most of these are quite small (less than 10km diameter). The four largest moons (named above) which were discovered by Galileo Galilei in 1610 are named after the lovers of Zeus. These moons are generally larger than the earths moon with diameters ranging from 3100km to 5200km. Three of the moons are locked together in an orbital resonance in which for every orbit Ganymede takes, Europa takes exactly two orbits and Io exactly four orbits. The closest to Jupiter, Io, has over 400 volcano's and is incredible geologically active. This is thought to be due to Jupiter's strong gravitational field constantly squeezing the moon as it orbits which warms the moons interior. The next of the Galilean Moons is Europa. It's surface is very smooth and comprised of water ice, possibly floating on a sea of liquid water. It's thought to have a rocky centre and has a thin oxygen atmosphere. Because of the presence of water it is thought to be a good candidate to find life outside of the earth.
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Ganymede is the largest satellite in the solar system and is larger than the planet Mercury. It is also covered in ice but is less geologically active with it's surface marked by craters and ridges. Callisto, the last of the Galilean moons is comprised of even quantities of rock and ice and a thin atmosphere of carbon dioxide and oxygen. It is possible it has liquid water buried 100km below it's surface.
Jupiter and Man Jupiter is named after the Roman king of the gods also known as Jove who was based on the greek god Zeus. Jupiter was first visited by the Pioneer 10 spacecraft in 1973 closely followed by Pioneer 11 in 1974. These spacecraft obtained the first close-up images of jupiter and it's red spot and moons and also measured Jupiter's massive magnetic field. They are still traveling out of the solar system, but have lost communications with earth. The next visitors were Voyager 1 and 2 in 1979 and discovered, among other things, the faint Jovian ring system, several new natural satellites, volcanic activity on Io. The Ulysses spacecraft which was designed to study the Sun used jupiter's gravitational field (1992) to swing it out of the plane of the ecliptic to allow it to orbit over the Suns poles. Galileo became the first (and only) spacecraft to orbit jupiter in 1995, orbiting the planet for 7 years before being deliberately crashed into the planet in order to ensure that it did not crash into, and contaminate, Europa. During it's mission it collected a huge amount of data on the entire Jovian system and even witnessed the Shoemaker-Levy 9 comet impact in Jupiter's southern hemisphere. The Cassini probe flewpast in 2000 and imaged Jupiter's atmosphere revealing many unknown features. The New Horizons probe flew past in 2007 on it's way to pluto and studied the Jovian moons, magnetic field and ring system. NASA currently has a mission underway to study Jupiter in detail from a polar orbit. Named Juno, the spacecraft launched in August 2011, and will arrive in late 2016. The next planned mission to the Jovian system will be the European Space Agency's Jupiter Icy Moon Explorer (JUICE), due to launch in 2022. Cassini Images of Jupiter Voyager Images of Jupiter
Saturn Saturn is the sixth closest planet to the Sun. It is the second largest planet in the solar system having a radius 9 times that of earth (57,000 km) and a mass 95 times that of earth. Saturn orbits the Sun once very 29 years (at about 1400 million km) and is mainly comprised of gas (96% hydrogen and 3% helium) and is presumed to have a rocky core surrounded by a sea of liquid metallic hydrogen which forms a ball some 56,000km in diameter. The upper layers are thought to comprise of liquid water, ammonium hydrosulfide, hydrogen and helium. Saturn's core is quite hot (11,700 degrees C) and it generates more heat than it receives from the sun. It cools the further from the centre with only the top 350km being cooler than freezing - it's upper atmosphere being around -180 degrees C. The cloud layers of Saturn are similar to those of Jupiter except that the banding is weaker and wider. Saturn also has a short lived but periodical storm called the great white spot which seems to occur every Saturnian year. Saturn rotates at around 10 hours 39 minutes. The precise figure (like that of all gas giants) is not certain since there are several ways of measuring the rotation of a body which has no fixed visual references.
Saturn's Rings Saturn is of course best known for it's ring system. These were first seen by Galileo Galilei in 1610 who, quite understandably, was confused by them and thought Saturn was being accompanied by two other planets which sat either side of it. In 1655 Christian Huygens using an improved telescope was able to see enough detail to suggest that there was a ring around Saturn. The rings extend from 7000km to 120,000km above the surface of Saturn. Incredibly, they are under 20m thick comprising of mainly ice particles ranging in size from dust to boulders a few meters across. The gaps in the rings are caused by the gravitational effects of Saturn's moons, and also by larger "moonlets" which inhabit the rings causing particles to be nudged into banded orbits. Recent observations have discovered that there are some distortions in the rings causing particles to rise some 4km out of the normal ring plane due to the tilted orbit of certain moons. The rings are thought to be either the remnants of a moon destroyed in orbit or simply by material left over by the formation of the solar system.
Moons : Titan... and the others Saturn has 62 moons with only seven being large enough to become spherical in shape. By far the largest of all of Saturn's moons is Titan which is larger than the planet Mercury, and the second largest moon in the solar system (Jupiter's Ganymede being the largest). Titan is 5,150 km in diameter and has a dense atmosphere of nitrogen with traces of methane. It has large lakes of liquid methane/ethane on it's surface and may have a subsurface ocean of liquid water which occasionally erupts to the surface. The next largest moon to Titan is Rhea which has a diameter of 1,530km (30% Titans diameter). It is an icy body (75% ice, 25% rock) with a heavily cratered surface. The other moons of Saturn tend to have similar characteristics being comprised mainly of ice and rock and all being heavily cratered. Two notable moons include Mimas which shows an impact crater with a radius 1/3rd that of the moon, Iapetus which has remarkable colouring with one side being black as soot and the other as white as snow. This colouring is thought to be the result particles being kicked up from impacts on the moon Phoebe which lay Iapetus's orbit. As Iapetus ed through these particles they were deposited on Iapetus's leading hemisphere causing it to darken.
Saturn and Man Saturn is named after the Roman gods Saturnus (equivalent to the Greek god Cronus) which was the god of agricultural and harvest. Saturn was first visited by the Pioneer 11 spacecraft in 1979 which discovered among other things additional rings in the ring system, and the moon Epimetheus which it almost (within 4000km) collided with. The Voyager probes were the next to study Saturn with Voyager 1 taking the first high resolution images of Saturn, it's rings and moons in 1980. Voyager 2 took more images in 1981 but a failure in it's camera pointing ability resulted in losing some expected imagery. in 2004 the Cassini spacecraft became the first probe to enter into orbit around Saturn releasing the Huygens probe which entered Titans atmosphere early in January 2005. The Huygens probe successfully landed on the surface of Titan sending back images and data during it's descent and from the surface. Cassini has made many fly-pasts of Saturn's moons and ring systems making many new discoveries including new rings and weather systems. The Cassini spacecraft is intended to continue to study the Saturnian system until 2017 when it will be
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deliberately to crashed into Saturn. Cassini-Huygens Images of Saturnian System Voyager Images of Saturn
Uranus Uranus is the seventh closest planet to the Sun and the third largest and fourth heaviest of the planets. It diameter (50,000km) is four times that of earth with a mass over 14 times that of earth. Uranus orbits the Sun once very 84 years (at about 2900 million km) but is unusual in that it spins on its side (with an axial tilt of 97 degrees). This means that it's moons and also it's faint ring system also orbit in plane perpendicular to the plane of the ecliptic. It is believed to be comprised of a small rocky core surrounded by a beep mantle of water, ammonia and methane. This is in turn surrounded by an atmosphere of hydrogen, helium and methane with an upper cloud layer. Another oddity in Uranus is the fact that it is very cold. All the other gas giant planets emit more heat radiation than they receive due to very hot cores, but Uranus does not. A temperature of -224 degrees C and been measured in Uranus's atmosphere - the coldest in the solar system.
Uranus's Rings Uranus has the second most extensive ring system of the solar system after Saturn. The rings, which are very difficult to see from ground based observations, were first discovered in 1977 by measuring the intensity of a star as Saturn and it's rings ed in front of it. There are 13 known rings with radii of 38,000km to 98,000km. They are comprised of ice and some darker material which results in them being much darker than the rings of Saturn.
Moons Uranus has 27 known moons with sizes ranging from over 1500 km diameter down to under 20km. The moons consist of ice, rock and other trace elements. Some of the inner moon undergo gravitation interactions with each other which may in many millions of years lead to un stabilities and collisions.
Uranus and Man Uranus, under clear dark skies, is actually visible to the naked eye. However it is very dim and it's 84 year periodicity means that it moves slowly across the sky. However it is interesting that it was not noticed by the ancients and was only observed for the first time by Sir William Herschel in 1781 using a telescope. It was initially named Georgium Sidus (George's Star) by Herschel after King George III. However this unpopular name was eventually discarded and it was renamed Uranus after the greek god of the sky. Uranus is the only planet to be named after a greek god, rather than a roman deity. To date Uranus has been visited only once - by the Voyager 2 spacecraft. The fly-by occurred in 1986 and resulted in the discovery of 10 new moons and 2 rings. It also measured the chemical compostion of the atmosphere and photographed the planet and it's moons. A "Uranus Orbiter and Probe" mission is in the study stages. Voyager Images of Uranus
Neptune Neptune is the eighth closest planet to the Sun and is (since the relegation of Pluto) the last Planet in the Solar System. It is similar in size and composition to Uranus with a diameter of 49,000km and a mass of over 17 times that of earth. Uranus orbits the Sun once very 165 years at about 4500 million km. This is 30 times the distance from the Sun to the Earth which means that the strength of sunlight at Neptune is 1% of its strength at Earth. Neptune spins on an axis with a tilt of 28 degrees which is quite similar to that of the Earth every 16 hours. Unlike Uranus's almost completely bland cloud layer, Neptune's weather systems are more pronounced with great dark spot storm systems being seen in the southern and northern hemispheres and other visible banding. Wind speeds of up to 600m/s have also been observed. Due to it's great distance from the sun, it is not surprising that the planet is one of the coldest with temperatures of -220 degrees C in the upper atmosphere. The core is thought to be at around 5200 degrees C.
Neptune's Rings Neptune has a ring system comprised of three main rings with radii between 63,000 km and 42,000km which appear to have a clumpy structure in which they form arcs rather than complete rings. It is believed that gravitational effects from Neptune's moons may cause the clumping.
Moons - Triton Uranus has 13 known moons of which only Triton (2700km diameter) is the most significant. The next largest moon Proteus is only 420km in diameter. Triton is the only large moon to orbit in retrograde (e.g. in the opposite direction to most orbits) and is thought to be a an captured object rather than created in orbit. It has avery thin atmosphere of Nitrogen, Carbon Dioxide and methane. Although it has a surface temperature of around -230 degrees C, it is thought to be geologically active with cryovolcanism (low temperature volcano's) producing eruptions of water and ammonia which freeze to form complex valleys and ridges.
Neptune and Man Neptune is invisible to the naked eye and was unknown to the ancients. It was first discovered when astronomers noticed anomalies in the orbit of Uranus and suggested that an as yet undiscovered planet could be the cause. In 1846 Neptune was observed near the position predicted by Urbain Le Verrier. This was the first planet to be discovered by mathematical prediction. Le Verrier proposed the name Neptune (roman god of the sea) for the planet since it was in keeping with naming planets after Roman deities (other than Uranus which is greek). To date Neptune (like Uranus) has been visited only once - again by the Voyager 2 spacecraft. The fly-by occurred in 1989 and resulted in many discoveries including Neptune's weather systems, rings and 6 more moons. It also provided an accurate measurement of Neptune's mass which allowed discrepancies in the orbits of Uranus and Neptune to be solved. There are currently no missions planned to visit Neptune, since the Neptune Orbiter and Probe mission was dropped in favour of the Uranus Orbiter and Probe mission. Voyager Images of Neptune
30-05-2014 22:08
Planets of the Solar System :: The Planets Today
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Astrology :: The Planets Today
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th to see the planets as they were. For full information on all the Where are the planets today?
30-05-2014 22:10
Astrology :: The Planets Today
http://www.theplanetstoday.com/astrology.html
The sky is divided up into 12 areas - the 12 signs of the zodiac. Each of these signs covers an equal area of the sky and always align to the same stars. (Over millennia the zodiac could be said to move as the earth's axis rotates - but it's best to ignore this whilst learning the basics). So when looking at the sky, the stars are fixed when compared with the zodiac, but the planets, as they orbit the sun, change position and "wander" about. Astrology tries to use the movements of the stars to understand our personalities and to some extent control our destinies. Each of the 12 signs is also associated with an element (earth, air, fire and water) and also a mode (cardinal, fixed and mutable). More about this later.
The Planets Each of the planets (which for astrology includes the sun and the moon) control a different aspect. In general they can be listed as: Sun = Ego / Self Moon = Emotion / Moods Mercury = Communication / Thinking Venus = Harmony / Affections Mars = Confidence / Energy Jupiter = Prosperity / Good Fortune Saturn = Limitations / Practicality Uranus = Individuality / Inventiveness Neptune = Idealism / Comion Pluto = Transformation / Power The Sun, Moon, Mercury, Venus and Mars are the personal planets which affect our personalities and immediate relationships. The more distant planets affect how we interact with the world in a more general way. When planets are in retrograde (e.g. they appear to be traveling backwards to their normal motion in the sky) their effect can be reversed to be directed inwards. When they again start to move forward again their effect can be enhanced.
Planets and Signs Each planet is the ruler of a particular sign (or signs). Whilst in that sign the planets influence is enhanced. The rulerships for each of the planets are as below:
Sun Moon Mercury Venus Mars Jupiter Saturn Uranus Neptune Pluto
Leo Cancer Gemini and Virgo Libra and Taurus Aries (and* Scorpio) Sagittarius (and* Pisces) Capricorn (and* Aquarius) Aquarius Pisces Scorpio
* before the invention of telescopes, these signs were also assigned to these planets. Since telescopes the three outer planets have been discovered and assigned these signs. This information is useful since if you know what influence a planet has, then you will know what influence that signs ruled by that planet have.
Elements Signs are allocated a different element in turn. This means that every fourth sign has the same element as follows: Fire Signs : Aries, Leo, Sagittarius Earth Signs: Taurus, Virgo, Capricorn Air Signs : Gemini, Libra, Aquarius Water Signs : Cancer, Scorpio, Pisces Fire signs represent a persons ion, energy,enthusiasm, inspiration. Earth signs represent a persons practicality, stability, materialism, realism. Air signs represent language, intellect, communication and social relationships. Water Signs represent emotion, mysticism, intuition. Generally speaking, the more planets someone has in a particular sign at the time of their birth, the stronger that signs personality traits will be in them.
Modes Rather like elements, each sign also has a mode allocated to it. Every 3rd sign has the same mode as follows: Cardinal Signs: Aries, Cancer, Libra, Capricorn Fixed Signs: Taurus, Leo, Scorpio, Aquarius Mutable Signs: Gemini. Virgo, Sagittarius, Pisces Cardinal signs are energetic, dynamic and proactive. Fixed signs are persistence, perseverant, stabile. Mutable signs are flexible, changeable, adaptable, suggestible. Again, the more planets you have in a particular Mode, the more your personality has those traits.
Working out the planets influences? It takes quite a lot of skill to determine one's personality traits accurately. However, a simple rule of thumb is to count at the time of birth how many planets fall in each sign and then work out how many are in each element and mode (perhaps counting the sun and moon as 2 due to their extra influence). The greater the score for each indicates how much of an influence each element and mode are on that person.
What are the Houses Just when you thought you might have got some sort of a grip on astrology, in come the houses. Whereas signs indicate what personality traits one has, houses indicate where they will exhibited themselves.
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30-05-2014 22:10
Astrology :: The Planets Today
http://www.theplanetstoday.com/astrology.html
Like the signs, there are 12 houses which divide up the sky. However the alignment of the houses is defined by the position of the horizon on the time of your birth. This means in order to calculate the houses, one must know not only what date one was born but also what time (to within a few minutes) and at what location on earth.
If one were to the set the application above to the time of ones birth and then set the lat and long to the place of ones birth, then the lowest slider will then bring up a display of the horizon at that time and location. Using this horizon one can ascertain how the houses are defined. The first house is located just under the western horizon, and the others follow consecutively in an anti-clockwise direction - e.g. the first 6 are in the black area (below the horizon), the last 6 are in the sky area (above the horizon). Once one knows where the houses lie, one can again see which sign lies in which house. Since there are 12 signs and 12 houses one can see that normally each house will overlay parts of 2 signs. The sign used is the sign which overlays the cusp of the house. The lines which separate each of the houses are called the cusps. The cusp of a house is the line preceding.
What do the houses mean? The following chart from wikipedia shows how the houses are interpreted.
House
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Sign
Latin motto
Translation
Modern title of house
1st
Aries
Vita
Life
House of Self
2nd
Taurus
Lucrum
Wealth
House of Value
3rd
Gemini
Fratres
Brothers
House of Communications
4th
Cancer
Genitor
Parent
House of Home and Family
5th
Leo
Nati
Children
House of Pleasure
6th
Virgo
Valetudo
Health
House of Health
Interpretation Physical appearance, traits and characteristics. First impressions. General outlook into the world. Ego. Beginnings and initiatives. Material and immaterial things of certain value. Money. Belongings, property, acquisitions. Cultivation and growth. Substance. Self-Worth. Higher education and childhood environment. Communication. Happiness. Intelligence. Achievements. Siblings. Neighbourhood matters. Short, local travel and transportations. Ancestry, heritage, roots. Early foundation and environment. Mother or mothers as figure. The caretaker of the household. Cyclic end of matters. Recreational and leisure activities. Things which makes for enjoyment and entertainment. Games and gambling. Children. Love and sex. Creative self-expression. Routine tasks and duties. Skills or training acquired. Jobs and Employments. Health and overall well-being. Service performed for others. Caretaking. Pets and small domestic animals.
30-05-2014 22:10
Astrology :: The Planets Today
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http://www.theplanetstoday.com/astrology.html
7th
Libra
Uxor
Spouse
House of Partnerships
8th
Scorpio
Mors
Death
House of Reincarnation
9th
Sagittarius
Iter
Journeys
House of Philosophy
10th
Capricorn
Regnum
Kingdom
House of Social Status
11th
Aquarius
Benefacta
Friendship
House of Friendships
12th
Pisces
Carcer
Prison
House of Self-Undoing
Close, confidante-like relationships. Marriage and business partners. Agreements and treaties. Matters dealing with diplomatic relations of all kinds, including open (known) enemies. Attraction to qualities we ire from the other partner. Cycles of Deaths And Rebirth. Sexual relationships and deeply committed relationships of all kinds. t funds, finances. Other person's resource. Occult, psychic and taboo matters. Regeneration. Self-transformation. Foreign travel and foreign countries. Culture. Long distance travels and journeys. Religion. Law and ethics. Higher education. Knowledge. Experience through expansion. Ambitions. Motivations. Career. Status in society. Government. Authority. Father or father figure. The breadwinner of the household. One's public appearance/impression at large(audience). Friends and acquaintances of like-minded attitudes. Groups, clubs and societies. Higher associations. Benefits and fortunes from career. One's hopes and wishes. Mysticism. Places of seclusion such as hospitals, prisons and institutions, including self-imposed imprisonments. Things which are not apparent to self, yet clearly seen by others. Elusive, clandestine, secretive or unbeknownst matters. Retreat, reflection and self-sacrifice. Unconscious/subconscious. Unknown enemies.
Many modern astrologers assume that the houses relate to their corresponding signs, i.e. that the first house has a natural affinity with the first sign, Aries, and so on.
And there's more... The houses can also be classified as Angular, Succedent and Cadent and are ruled by signs according to the astrological modality. And... well there are many many more aspects to astrology which seem almost designed to confuse and complicate. As you can see, astrology is not a simple area of study. The above is just skimming the surface of a subject that could (and does) take up volumes and volumes of books. There are many systems of astrology and many variations between individual astrologers that use the same basic principles. Some astrologers also use astronomical objects which have never been seen by the unaided eye (such as chiron - an asteroid/comet cross discovered in 1977) and others objects that have never even been detected. Some prefer to align the zodiac to the night time sky as seen by astrologers thousands of years ago. All in all, with astrology, one must pick and choose the astrologer and the style of astrology that suits one best. Follow @ThePlanetsToday
Flash animations copyright 2011-2014 : Hayling Graphics.
30-05-2014 22:10
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