Opposition, conjunction and elongation explained
Three words from the planet calendar, and what they mean for when you can see each planet.
Planet calendars are full of words like opposition, conjunction and elongation. They describe where a planet is compared with the Sun, as seen from Earth, and that decides whether you can see it.
Inferior and superior planets
Mercury and Venus orbit closer to the Sun than Earth: NASA calls them inferior planets. They always appear near the Sun, in the evening or morning sky. Mars, Jupiter, Saturn, Uranus and Neptune orbit farther out: they are superior planets and can appear anywhere along the ecliptic, including opposite the Sun.
Opposition
A superior planet is at opposition when it and the Sun are on opposite sides of Earth. The planet then:
- rises around sunset and sets around sunrise, so it is visible all night
- is near its closest to Earth, so it is at its brightest and largest in a telescope
- appears fully lit.
Opposition is the best time to see an outer planet. How often it comes round, from Astronomy Engine for 2026 to 2035:
| Planet | Time between oppositions | Next oppositions |
|---|---|---|
| Mars | 765 to 810 days (about 26 months) | 19 Feb 2027, 25 Mar 2029 |
| Jupiter | 396 to 403 days (about 13 months) | 11 Feb 2027, 12 Mar 2028 |
| Saturn | about 379 days | 18 Oct 2027, 30 Oct 2028 |
Mars’s gap varies the most because its orbit is quite elongated. The events calendar lists every opposition with times for your location.
Conjunction
Two objects are in conjunction when they appear to pass closest together in the sky. Two planets, or a planet and the Moon, can be in conjunction: a nice sight, though they are not physically close, only lined up from our point of view.
When a planet passes closest to the Sun as seen from Earth, it is in solar conjunction and invisible in the Sun’s glare. Mercury and Venus have two kinds:
- Inferior conjunction: the planet passes roughly between Earth and the Sun. If it crosses exactly in front of the Sun, that is a transit.
- Superior conjunction: the planet is on the far side of the Sun.
Superior planets can only have superior conjunctions, when they are hidden in the Sun’s glare for a while.
Elongation
Elongation is a planet’s apparent angle from the Sun in our sky. For Mercury and Venus it never gets very large, and greatest elongation is when they appear farthest from the Sun, the best time to see them:
- Eastern (evening) elongation: the planet is east of the Sun and visible after sunset in the west.
- Western (morning) elongation: west of the Sun, visible before sunrise in the east.
| Planet | Greatest elongation, 2026 to 2035 |
|---|---|
| Mercury | 17.9° to 27.8° |
| Venus | 45.4° to 47.2° |
Mercury’s elongations vary a lot because its orbit is very elongated. How high the planet appears also depends on the angle of the ecliptic to your horizon, so some elongations are much better than others for a given place. The guide to finding planets and the planets page show what that means for you.
Sources
- NASA, Basics of Space Flight: The Solar System (inferior and superior planets, conjunction, opposition, elongation)
- Dates, intervals and elongations: Astronomy Engine, checked against NASA JPL Horizons. See methodology.
Frequently asked questions
What is a planet at opposition?
A superior planet (Mars, Jupiter, Saturn, Uranus or Neptune) is at opposition when it is on the opposite side of Earth from the Sun. It is then up all night, near its closest to Earth and at its brightest.
What is the greatest elongation of Mercury or Venus?
The moment when Mercury or Venus appears farthest from the Sun in our sky. Around then they are easiest to see, in the evening (eastern elongation) or in the morning (western elongation).
How often is Mars at opposition?
About every 26 months. Between 2026 and 2035 the gaps range from 765 to 810 days.