The planets travel in elliptical, rather than circular, orbits around the Sun which means the
distance to the Sun varies. Oppositions can occur when a planet is closest to the Sun (at perihelion) or when a planet is
furthest from the Sun (at aphelion), or at any time between the two. The most favourable oppositions for viewing are at
perihelic opposition as this is also the time the opposing planet is closest to Earth.
Mars appears almost twice as large at perihelic opposition at 56.3 million kilometres from the
Earth, as at aphelic opposition when it is 100 million kilometres from the Earth.
At opposition:
-The planet is visible almost all night, rising at about sunset and setting about sunrise.
-The planet´s orbit brings it closest to the Earth, making it appear bigger and brighter.
-The opposition effect increases reflected light from the planet.
During 2007:
Mars – December 24th at –1.7 magnitude in Gemini.
Jupiter – 5th June at -2.6 magnitude in Ophiuchus.
Saturn - 10th February at 0.0 magnitude in Leo.
Uranus – 9th September at 5.7 magnitude in Aquarius.
Neptune - 13th August at 7.8 magnitude in Capricorn.
During 2006:
Jupiter - 4th May at -2.5 magnitude in Libra.
Saturn - 27th January at –0.1 magnitude in Cancer.
Uranus - 5th September at 5.7 magnitude in Aquarius.
Neptune - 11th August at 7.8 magnitude in Capricorn.
The Moon, which orbits the Earth rather than the Sun, is in opposition to the Sun at full Moon. When it is in exact opposition a lunar
eclipse occurs.
Oppositions occur when an outer planet is in the opposite side of the sky from the Sun as viewed from the
Earth. Mercury and Venus can never be at opposition since they are inside of the Earth's orbit and, therefore, remain
relatively close to the Sun.
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