Jupiter is the third brightest object in the night sky after the Moon and Venus so it can easily be seen without optical aid, appearing as a very bright star. Technically speaking, the Galilean moons should just about be visible to the unaided eye as well but tend to get overwhelmed by Jupiter’s brightness. Even so, in former times it was said that those with exceptional eyesight could just about resolve Ganymede given ideal conditions. It would be interesting to find out if anyone can repeat this feat today!
Binoculars will resolve Jupiter as a small bright cream-coloured disc and show the Galilean moons as bright dots on either side. Depending on their relative positions in orbit when you observe them you might only see two or three but if you look again over successive nights you’ll soon see all four, arranged in various positions. The innermost, Io, whizzes around Jupiter in less than two Earth days. The outermost, Callisto, takes over 16 days so will just about complete half an orbit during NAW.
Small telescopes with magnifications up to about 100 times will show the main cloud bands, especially the dark north and south equatorial belts which show up distinctly either side of the bright equatorial zone. It will also be possible to track the movements of the Galilean moons.
Medium to large telescopes with magnifications of a few hundred times and above will show the Great Red Spot, Oval BA and other weather systems. It will also be possible to detect coloration of the Galilean moons and observe transits, when the moons cross the face of Jupiter.
When is Jupiter visible?
Apart from a couple of months each year when Jupiter is near the Sun or behind it as seen from Earth, it’s easy to find in the night sky and can even be seen in twilight. The planet easily outshines any star. There’s a host of astronomy websites and magazines out there that publish regular tables or maps of positions detailing when to observe.
For an easy-to-follow guide to this month’s sky, try the Society for Popular Astronomy’s Young Stargazers’ guide, for example.
Jupiter will be prominent in the southern night sky during the first quarter of 2013, just above the prominent constellation of Orion the Hunter. From the onset of spring, it will sink gradually westward after the Sun until lost from view during June and July. During mid-September, Jupiter rises during late evening so the best time to observe will not be until just before dawn. However, it rises progressively earlier as the year draws to an end. By mid-December it will rise by 6.00pm and be high in the south-east by midnight.
Throughout NAW, Jupiter will be visible high in the south as soon as the sky darkens, progressing gradually west until setting at around 3.30 am. Jupiter will be best placed during the evening so it won’t be necessary to stay out until the small hours unless you want to!