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.
ToolsWhat to see tonight?, Eyepieces
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.
- 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.
- 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.
- Ecliptic
The Sun’s apparent path among the stars over the year, mirroring the plane of the Earth’s orbit. It is tilted by 23.4° to the celestial equator. The Moon and planets always stay close to it, which helps to recognise them.
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