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.
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Related terms
- Conjunction
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.
- Planet
A body that orbits the Sun and shines by reflecting its light. Mercury, Venus, Mars, Jupiter and Saturn are visible to the naked eye; they move slowly among the stars, near the ecliptic, and twinkle less than stars. Uranus (magnitude 5.7) and Neptune (7.8) need binoculars or a telescope.
- Culmination
An object’s crossing of the meridian, at the highest point of its path; the best time to observe it. For an object south of the zenith, its altitude then is 90° − latitude + declination. From London (51.5°), the Orion Nebula (−5.4°) culminates at about 33°.
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