If you're travelling to Neptune, or you're planning a short holiday to Mars, you'll need to know the weather forecast before you pack. Will you need raincoats and warm woollen socks? Or will you just be needing a hat, a t-shirt and a couple of litres of sunscreen? on some planets, there have been gigantic storms that have lasted for over 500 years - so you might want to pack a good bock o read, too, just in case you're stuck inside!