Jupiter’s four large moons, Io, Europa, Ganymede and Callisto, discovered by Galileo in 1610. Small, steadily held binoculars show them as points lined up on either side of the planet. Their dance changes hour by hour: eclipses, transits across the disc, shadows.
ToolsWhat to see tonight?, Eyepieces
Related terms
- 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.
- Transit
A small object passing in front of a larger one without hiding it: Mercury across the Sun (next on 13 November 2032), one of Jupiter’s moons across the planet, or the ISS across the Sun or the Moon. For the Sun, a solar filter is essential.
- 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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