The Planets
Jupiter is at opposition on 9 May, a time when the planet is in the opposite part of the sky to the Sun. This means that May is an excellent month to observe Jupiter. On 9 May, Jupiter shines at mag. –2.4 and presents a disc that appears 44 arcseconds across. At this apparent size there is plenty of detail up for grabs through the eyepiece of a telescope. A small scope will clearly show the planet’s oblate shape, the result of its rapid rotation. In addition, its two main belts are easily seen either side of the Jovian equator.
The Great Red Spot is one of the observing highlights on Jupiter and can be seen through a telescope with a 100mm or greater aperture. The spot represents a persistent storm in Jupiter’s atmosphere. The Jovian atmosphere is very dynamic. For example, earlier this year, a storm outbreak in the south temperate belt (STB) was observed.
The four largest moons of Jupiter – Io, Europa, Ganymede and Callisto – are also fascinating to watch. As they pass between Jupiter and the Sun they cast vast shadows on the atmosphere below, which can be seen with relatively small telescopes. Before opposition it’s interesting to watch how the moons chase their shadows, catching up with them on opposition day and then leading them after opposition. There are a number of such events visible this month (see pages 50, 51 and 52 for more information), which spectacularly illustrate the effect. From the UK, Jupiter is now sadly losing altitude as it heads east towards a more southerly part of the ecliptic. Its maximum height from the centre of the UK is around 21°. By the end of the month, Jupiter will have nudged west enough to sit within a degree of Zubenelgenubi (Alpha (_ Librae).