The picture, created from a series of Hubble Space Telescope images of Mars, shows the variation of the apparent size of Mars, during its recent close approaches to Earth. Mars is closest to Earth every 26 months.
Image credit: NASA, http://hubblesite.org/

On 27 January 2010, Mars will come to within nearly 100 million km from Earth, the shortest distance between the two planets, in 26 months. In the evening, Mars will shine as a brilliant reddish star, with a brightness similar to that of Sirius, the brightest naked-eye star. Mars is the second closest planet to Earth, following Venus, our “Twin Planet”, which comes to within about 38 million km from Earth, at its closest.

Every 26 months, Mars is closest to Earth, but its minimum distance from our planet is variable. Under the most favorable conditions, the minimum distance to Mars is approximately 55 million km. This occurred on 27 August 2003, and will not recur until 2287.

On 29 January 2010, Mars will be in opposition, a fascinating phenomenon that occurs when Mars and the Sun are on opposite sides of Earth. Therefore, on the opposition day, Mars will be opposite the Sun in the sky, and will be visible throughout the night. It will rise from the eastern sky, at sunset, and will set in the western sky, around sunrise.

Mars is a small rocky planet, whose diameter is approximately 6,800 km. With a diameter of 12,756  km, Earth is about twice larger than Mars, in size. Interestingly, the ratio of the size of Earth to the size of Mars is similar to that between the sizes of the tennis ball and the ping pong ball. Earth is about 10 times more massive than Mars.

Further Reading

Mars: Closest Approach 2007

http://hubblesite.org/newscenter/archive/releases/2007/45/image/h/

The Eight Planets

www.nineplanets.org/