Mars, oppositions

Mars, oppositions

Oppositions recur at an average interval of 2 years 50 days, although this varies by 30 days either way because of the eccentricity of Mars' orbit. Favorable oppositions for observation of surface features recur every 15–17 years when Mars is near perihelion and may approach within 56 million km of the Earth, attaining an apparent diameter of 25.7 arc seconds. Perihelion oppositions are, however, much less frequent than aphelion ones. The most favorable perihelion opposition of the 21st century occurred in August 2003, when Mars and Earth came within 55.8 million km of each other. This was estimated to be the closest proximity the two planets had achieved in 60 000 years. But even closer oppositions are due in 2287, 2650, 2729, 2808, and 2934, when the planetary distances will in each case be less than 55.7 million km. At aphelion oppositions Mars may be as much as 101 million km distant with an apparent diameter of 14 arc seconds.
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