Diagrams of the Orbits of the Planets
The diagrams on this page show the positions of the major planets, and the two brightest asteroids, in their orbits. The orbits are in correct relative scale. Planetary orbits are elliptical with the Sun at one focus of the ellipse. On the diagrams the position on the orbit where a planet is closest to the Sun, that is at Perihelion, is marked with a P The position of Aphelion, when the planet is furthest from the Sun is marked A.
The diagrams for the inner planets, as far out as Mars, are for the periods December 2011 to April 2012, May to September 2012 September to December 2012 The diagrams cover four months, rather more than the time Mercury takes to complete one orbit round the Sun. The positions of the planets are marked every 10 days.
The last diagram shows the orbits of the outer planets as far as Saturn for 2012. The orbits of the Earth and Mars are also indicated as are the orbits of the two brightest Asteroids, (1) Ceres and (4) Vesta. The diagrams cover a year, with the positions of the Asteroids, Jupiter and Saturn marked at the start of every other month. The positions of the Earth and Mars are shown at the start of each month.
Also indicated on this diagram are the directions to Uranus, Neptune and Pluto at the beginning and end of the year. The distance of Uranus from the Sun is over twice that of Saturn, whilst the distances of Neptune and Pluto are over three times the distance of Saturn.
Using the charts to find where a planet is in the sky
For the date you are interested in, imagine a line from the Earth to the Sun. If the planet lies to the left of this line, that is clockwise from the line, then the planet is in the evening sky. On the other hand, if the planet is to the right of the line, that is anti-clockwise from it, then the planet is in the morning sky.
Mercury and Venus, the inner planets, are at inferior conjunction when they are between the Earth and Sun and at superior conjunction when the Sun is between the Earth and the planet. In either case they will be too close to the Sun to observe. Mercury is first at superior conjunction on February 7 and inferior conjunction on March 22. Venus is at inferior conjunction on June 6 when it will transit across the face of the Sun. There is no superior conjunction of Venus in 2012.
The inner planets are at their best position for observing when the line from the Earth to the planet is at right angles to the line from the planet to the Sun. They are then at greatest elongation from the Sun. Examples occur for Mercury on March 5 and Venus on March 27 when they are east of the Sun. Venus is at an westerly elongation on August 15.
The outer planets, Mars, Jupiter, Saturn etc, can never be at inferior conjunction with the Sun, only at superior conjunction (just called "conjunction"). On the other hand they can be on the opposite side of the Earth to the Earth. This is known as "opposition" and is the time when the planet is in the sky all night, rising close to sunset and setting close to sunrise. An opposition of Saturn occurs on 15 April 2012.
Two planets will appear close together in the sky when a line from the Earth passes close to both of them. One of the best examples of such a planetary conjunction during 2012 occurs on August 15, when Mars and Saturn are less than 3° apart. A straight line drawn on the outer planet from the Earth's position to Saturn will then pass through the position of Mars. The other planetary conjunction in 2012 all involve one of the inner and one of the outer planets.
Inner Planets December 2011 to May 2012
Inner Planets May to September 2012
Inner Planets September to December 2012
Outer Planets in 2012