Jupiter

The Galilean moons

Io, Europa, Ganymede and Callisto were the first objects proven to orbit something other than Earth. They are individually bright enough to see in 10×50 binoculars, appearing as four points of light in a straight line either side of the planet.

Their positions change noticeably within hours. Over a single evening you can watch a moon disappear behind the planet or emerge from its shadow. These events are predictable to the minute and are worth looking up before setting up.

Europa is the one to watch for transits — its shadow is small and sharp, and much easier to see than the moon itself against the cloud tops.

Cloud belts

In a small telescope Jupiter shows two dark equatorial belts as its most obvious feature, with a brighter zone between them. Larger apertures add the temperate belts and, at moments of steady air, finer detail within the belts themselves.

The detail is not constant. Atmospheric steadiness varies second by second, so the standard technique is to watch patiently and take the brief sharp moments rather than expecting a steady image.

The Great Red Spot

The storm is real, but it is not always easy. It is distinctly pale now compared with historical descriptions, and it is only on the Earth-facing side for about half of Jupiter's ten-hour rotation.

It is also often better seen as a notch or bay in the southern edge of the belt than as a distinct oval. Knowing when it is due to cross the centre of the disc makes it far easier to catch.