Choosing GCSEs and A Levels or Highers
Astronomy is mainly about the physics of the Universe - the way stars and galaxies and so on actually work. It is quite an unusual science because it deals with lots of extremes - very big things like galaxies and very small things like atoms and sub-atomic particles; very hot things like the middles of stars and very cold things like the spaces between galaxies and so on. So, astronomers need to understand lots of different bits of science - that is what makes it so interesting!
Therefore, it is important to get good qualifications (GCSEs and A-Levels or Highers) in Physics and Mathematics. You may also find that you will need to know quite a lot of Chemistry.
On to University
With those qualifications, you can then go on to do a degree at University. It is often difficult to choose where to do your degree, but the teachers and careers advisors at your school or college will be able to help you. However, if you do want to become an astronomer, then you will probably need a degree in either Astronomy itself or Physics. Since astronomy contains a lot of physics, many universities now offer degrees in Astrophysics, which combine Physics and Astronomy. Good knowledge in both these subjects will help you to see the way in which they fit together.
Of course, all of these are very useful qualifications to have whatever you eventually decide to do. Even if you finally decide that you do not want to be an astronomer, you can still be confident that you will find an interesting and well paid job. In fact, people leaving University with degrees in science are among the best paid in the country. Graduates with Astrophysics or Physics degrees are often sought out by businesses because of the very useful skills that they have learnt.
Because astronomers are doing research, they need to have a lot of knowledge and experience. Therefore, nearly all will have not one, but two or more degrees! So, as well as your first, "normal" degree, you will probably then go on to get a Doctorate or PhD. This is where you would be able to do some research of your own and begin to specialise in a particular area of Astronomy.
Once you have got your PhD, you can then look around for a job as a professional astronomer. Astronomers work in all sorts of places, not just universities, but observatories and space-agencies like NASA as well. Because astronomy is very popular all over the world, many British astronomers are actually working in other countries and there are a lot of chances to travel.