The apparent meeting of two objects in the sky, such as the Moon and Venus, while they stay far apart in space. A planet is also said to be in conjunction with the Sun when it is lost in its glare and invisible. Close planetary conjunctions are lovely naked-eye sights.
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Related terms
- Opposition
The moment an outer planet (Mars, Jupiter, Saturn…) lies opposite the Sun in the sky. It rises at sunset, is highest around midnight and is at its closest to Earth, so at its largest and brightest. Mars only reaches opposition about every 26 months.
- Elongation
The angle between a planet and the Sun as seen from Earth. Mercury and Venus, being closer to the Sun, never stray far from it: at most about 28° for Mercury and 47° for Venus. They are best seen around greatest elongation, in the west after sunset or in the east before dawn.
- Occultation
One object passing in front of another and hiding it completely, most often the Moon in front of a star or planet. A star vanishes instantly at the Moon’s edge, since the Moon has no atmosphere. Timing these moments precisely is a useful amateur contribution.
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