Opposition

Opposition has a different meaning astronomically than its common every day usage. As everyone knows, the planets in our Solar System orbit the Sun. Therefore the planetary positions are constantly changing relative to one other. Opposition occurs when the Earth is located directly in-between the Sun and a superior planet (superior or having an orbit further from the Sun than Earth).

Opposition dates are of particular interest to astronomers as that is when the planet will appear to be the largest (as measured in arc seconds), brightest, highest in the sky and be fully illuminated as seen from the Earth. For these reasons, the weeks before and after opposition represent the most favorable times to view or image a planet. That does not mean that the night of opposition will give the best views of the season. The affects of seeing dictate when the best views will occur.

Opposition does not occur with any of the inner or inferior planets. These are the planets that are closer to the Sun than Earth (Mercury & Venus). The use of ‘superior’ and ‘inferior’ as astronomical terms date back to the Roman Empire as coined by Claudius Ptolemy.