By Jove! - Jupiter

There are so many people who want to find out more about the universe but are put off astronomy for one reason or another.Well re-write your resolutions because, by the end of this year, if you follow this weekly blog you’ll have grasped the basics of observational astronomy. You don’t need a telescope (Binoculars are handy), you can do this from a city and all you need is half an hour a week and some warm clothes.

Dipping your toe into the wonders of the universe can be daunting. The sky is a bewildering place, and finding your way around does take practise. People are also often put off because they’re expecting to see an image that looks something like this:

Credit: NASA/JPL

Of course through even a decent sized Earth-based telescope you'll never get that level of detail, but there's still lots to enjoy out there.

It happens that we’re going to start off with Jupiter. There are two reasons for this – firstly because it’s easy to find, and secondly because it’s pretty damned cool, even if it doesn’t look quite like the image above.

So, how to find it:

Naked Eye

At 9.30pm, look up high towards the West – Jupiter is the brightest thing you can see. In fact it’s the fourth brightest thing in the sky, after the Sun, Moon and Venus. Its colour is striking with the naked eye, a vivid yellow.

There are two ways to recognise something bright and shiny in the sky as being a planet:

1 – Stars twinkle, due to the movements of our atmosphere. Planets do not.

2 – Planets move around the sky, relative to the stars. That’s why they’re called Planets; the word means “Wanderer.” As a consequence of this, if you read this article after January 2014, Jupiter won’t be in the same position – it moves by roughly one zodiacal constellation per year. At the moment it’s in the constellation of Gemini, but in 2015 it’ll be moving through Cancer and Leo. We won’t worry too much about constellations for now – Jupiter is bright enough that it’s hard to mistake for anything else.

Binoculars

Look at Jupiter through a pair of binoculars and things get interesting. You’ll see four small pin-pricks of light strung out in a line beside it. These are the four brightest moons of Jupiter: Io, Europa, Ganymede and Callisto.

Every time you look at Jupiter they’ll have shifted around slightly with some of them occasionally going behind or in front of the planet. The Voyager space probes revealed a wealth of information about these worlds, but they were first discovered by Galileo using a telescope.

Telescope

Jupiter is by far my favourite planet for telescopic observation. The moons are clearly there and, with a big enough telescope, it is possible to watch them silhouetted against the disc of the planet when they pass across it – a transit.

The disc itself reveals a lot of detail – even relatively small instruments show a series of dark bands running across the planet’s surface - the cloud belts. In my 3’’ refractor the largest of these, the north and south equatorial belts, are most easily seen. The bigger the ‘scope the more detail you get, and it’s possible to see the wisps and curls of the clouds of gas as they interact with each other, and the famous Great Red Spot, an enormous storm the size of our own planet.

Jupiter is the largest planet in our solar system. In fact it weighs two and half times as much as all the other planets combined. Landing there would be tough – it’s mostly made up of a mixture of gases, all of which are rather unpleasant. For example its clouds are full of hydrogen sulphide, the gas that gives rotten eggs and flatulence their characteristic smell. Even if you went a little way into the clouds, your body would swiftly be crushed by the weight of gas above you. The gravity of the planet is so intense that it squeezes the core of its closest moon, Io, causing massive vulcanism. It's not a place to consider for a holiday either - the intense radiation would bake you if you were to get too close to it. Probably worse for you even than sunbeds.

That's it for this week - next time I'm going to describe how to find the most useful star in the entire night sky: Polaris.