Mars in 2008
There will be no close approach between Mars and Earth in August 2008, despite a variety of messages circulating on the internet to the contrary. Some of these messages might be well intentioned misinformation; others might be deliberate hoaxes. While we constantly encourage going out to observe and to admire the sky, we also want the public to be aware of incorrect information.

Mars and Earth approach each other closely about every 26 months. These close approaches occur around a time of an event that astronomers call an opposition, which happens when Earth lies on a straight light between a planet (Mars, in this case) and the sun. We saw a superb close approach in August 2003, followed by close approaches in October 2005 and December 2007. The next close approach is thus not August 2008 but January 2010.

Closest Approaches of Mars, 2001-2012 (Data from seds.org)
Date	Distance from Earth (millions of kilometers)	Apparent size of Mars (arc seconds - see below)
2001 June 21	67.34	20.79
2003 August 27	55.76	25.11
2005 October 30	69.42	20.19
2007 December 18	88.17	15.88
2010 January 27	99.33	14.10
2012 March 5	100.78	13.89

Whether misinformation or hoax, the internet messages stating the Mars will appear as large as the full Moon in August 2008 offer considerable detail, which seems to lend them credibility. However, most of the details are mere repetitions of the dates and distances that correspond to the historic opposition of August 2003. Some of them also repeat the incorrect notion that Mars will appear to the naked eye as large as the full moon, which never happens. In fact, in late August 2008, the apparent disk of Mars will be so small that you would have to line up 450 of them to equal the apparent diameter of the moon! Other versions of the hoax are more plausible in stating that seen through a telescope with a certain magnification Mars will appear as large as the full moon does to the naked eye. This is not wrong, in principle, if you were to use sufficient magnification: you would need a 450x telescope.

Astronomers use the concept of angular size to describe how large an object appears in the sky. The angle between the two opposite sides of an object determines its angular size, which depends upon the actual size of the object and how far away it is. For example, the angular size of the moon is approximately 1/2 degree, or 30 arc minutes (1 degree = 60 arc minutes; 1 arc minute = 60 arc seconds). Magnification increases the angular size of an object, making it appear larger. The current angular size of Mars is about 4 arc seconds, or 1/450 the apparent size of the moon. Even at its closest approaches Mars seldom appears larger than 26 arc seconds, or about 1/69 the apparent size of the moon.

This diagram shows the disposition of the inner solar system near the end of August 2008. Notice that Mars is actually over six times further from Earth than it was in August 2003, when it was only 56 million kilometers away. Throughout 2008 and 2009, Earth, because it orbits faster than Mars, will "catch up" with Mars as both revolve counterclockwise around the sun. On January 29, 2010, Earth will be directly between Mars and the sun, which is how astronomers define an opposition. The closest approach between Earth and Mars will occur two days earlier on January 27. The reason that opposition and closest approach occur on different days is a result of the facts that both planets have orbits that are not perfect circles and that these orbits are inclined slightly with respect to each other. At the point of closest approach Earth and Mars will be 99 million kilometers apart, with Mars appearing about 1/128 the size of the full Moon to the naked eye.

Please do go out to observe the night sky on August 27 or any other clear night. At the beginning of August Mars will set in the west shortly after sunset, along with Saturn: both planets are currently in the constellation Leo. Mars and Saturn become increasingly lost in the glare of the sun as the month progresses. In the middle of August you will probably also see some Perseid meteors. The Perseid shower peaks in the predawn hours of the 12th; the meteor activity is evident for a week or so on either side of the peak. Throughout August you will also see brilliant Jupiter in the southern part of the evening sky, which will be near the waxing moon on August 12 and 13 (the moon is full on the 16th). And high overhead you can find the three bright stars of the "Summer Triangle," which are good guides to finding many other stars, constellations, and interesting objects in the summer sky.

For more information about the August sky, feel free to download a pdf copy of our August Eyes on the Skies newsletter