On January 29 Mars reached opposition, when it was opposite the Sun in the sky. Martian oppositions happen every 26 months and feature close approaches of Mars to Earth, making this a good time to observe the Red Planet. Though the exact time of opposition is past, Mars still shines brightly in the current night sky and is a breathtaking object to view through a telescope.
Mars Oppositions
The planets’ orbits are not perfect circles, so the distance between Mars and Earth varies with each opposition. During the 2003 Mars opposition, Mars made its closest approach to Earth in 60,000 years, coming within 56 million kilometers (35 million miles) of us.
During the 2010 opposition, which occurred January 29, Mars is much further away - 99 million kilometers (62 million miles) - but still fascinating to see through a telescope. Features such as the north polar ice cap may be picked out under the right conditions.
It was during such an opposition of Mars that its two moons were discovered by American astronomer Asaph Hall in 1877. While much has been written about the Red Planet, these moons, Phobos and Deimos, are rarely discussed. They are named for the sons of Ares, the Greek god of war, as described in Homer's Iliad.
Mars' Moons Phobos and Deimos
Scientists believe these potato-shaped bodies were once part of the asteroid belt, a collection of small bodies between Mars and Jupiter. Perhaps the immense gravity of Jupiter threw Phobos and Deimos out of their orbits, only to be captured by Mars.
Phobos and Deimos are two of the smallest known moons in the solar system. Phobos, which is Greek for fear (and the root of “phobia”) is about 22 kilometers (14 miles) in diameter. Phobos is so close to the surface of Mars - about 6,000 kilometers (3,720 miles) - that Mars would cover half of the sky as seen from Phobos.
Because of Phobos’ small size and proximity to Mars, it is eclipsed by Mars 1,330 times every Martian year (one Martian year equals 687 days). While our moon takes about 27 days to orbit Earth, Phobos only takes about 7 ½ hours to orbit Mars, meaning it circles Mars three times per day. Not only that, but Phobos also rises in the west and sets in the east - opposite the motion of our moon around Earth.
The other Martian moon, Deimos (Greek for panic), is only about 12 kilometers (seven miles) across. Ethiopian running legend Haile Gebrselassie could cover the entire diameter of Deimos in about 30 minutes; our moon, 3,500 kilometers (2,170 miles) across, is about 310 times wider than Deimos.
Viewing Mars
Because Phobos and Deimos are so small, they are difficult to see even through a telescope. Mars, however, shines brightly in the current night sky and is easily seen in the southeast just after sunset. Through a telescope, Mars is a fairly small object. However, it continues to fascinate observers of all ages because it is one of just a few celestial objects whose surface features, such as changing surface markings due to dust storms, may be seen with even a moderate-sized telescope.
References
Sheehan, William and Stephen O'Meara. 2001. The Planet Mars: A History of Observation and Discovery, Prometheus Books.
Kevin Schindler - I have worked at scientific institutions for more than 20 years written more than 200 articles about science, history, and baseball.
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