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.

Oppositions occur when an outer planet is in the opposite side of the sky from the Sun as viewed from the Earth. At opposition the planets are at their brightest. 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. The brightest times for Mercury and Venus are close to greatest elongations.

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.

The outer planets are morning objects after conjunction with the Sun, rising earlier each day until reaching opposition. At this time they are closest to Earth and on the meridian at midnight, due south in northern latitudes (due north in southern latitudes). Following opposition the planets become evening objects, setting earlier each night until setting in the west with the Sun at the next conjunction. The distance in brightness betwen oppositions is most noticeable with Mars, whose distance from Earth varies considerably and rapidly.

In the northern hemisphere, oppositions are best in December when the ecliptic (the path that the planets follow) is high and the planets can be at an altitude of more than 60º in the constellations of Taurus or Gemini. During summer oppositions, the planet might be only 15º above the southern horizon and less impressive. In southern latitudes the reverse applies and a June opposition in Sagitarrius can have the planet as high as 80º above the northern horizon for observors in South Africa. A demonstration of the movement of the ecliptic can be seen on our seasons page.

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. Oppositions o Mars occur at average intervals of 780 days.

Jupiter, always a bright planet, comes to opposition a month later each year after moving approximately from one zodiacal constellation to the next.

Saturn moves much slower than Jupiter and may stay in the same constellation for several years. Its brightness depends on the aspect of its rings as well as the distance from Earth and the Sun.

During 2011:
Mars - no opposition during 2011.
Jupiter - October 29th in Aries.
Saturn - April 3rd in Virgo.
Uranus - September 26th in Pisces.
Neptune - August 22nd in Aquarius.
Pluto - June 28th in Sagittarius.

During 2010:
Mars - January 29th in Cancer.
Jupiter - September 21st in Pisces.
Saturn - March 22nd in Virgo.
Uranus - September 21st in Pisces.
Neptune - August 20th in Capricorn.
Pluto - June 25th in Sagittarius.

During 2009:
Mars - no opposition during 2009.
Jupiter - August 14th in Capricorn.
Saturn - March 8th in Leo.
Uranus - September 17th in Pisces.
Neptune - August 17th in Capricorn.
Pluto - June 23rd in Sagittarius.

During 2008:
Jupiter - July 9th at -2.7 magnitude in Sagittarius.
Saturn – February 24th at +0.2 magnitude in Leo.
Uranus - September 13th at +5.7 magnitude in Aquarius.
Neptune - August 15th at +7.8 magnitude in Capricorn.
Pluto - June 20th at +14 magnitude in Sagittarius.

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.