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.
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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.
- Twilight
The period when the sky darkens after sunset. It is civil until the Sun is 6° below the horizon (you can read outside), nautical until 12° (the horizon fades) and astronomical until 18°. Only then is the night truly dark for deep-sky objects.
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