-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 60║ in the constellations of Taurus or Gemini. During summer oppositions, the planet might be only 15║ 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 80║ 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.
Mars - March 3rd in Leo, at -1.2 magnitude.
Jupiter - December 3rd in Taurus, at -2.8 magnitude.
Saturn - April 15th in Virgo, at +0.3 magnitude.
Uranus - September 29th in Pisces, at +5.7 magnitude.
Neptune - August 24th in Aquarius, at +7.8 magnitude.
Pluto - June 29th in Sagittarius, at +14.0 magnitude.
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.
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.
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.
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.
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.
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