At the age of eight I decided that writing was for me. Knowing what you want to be from an early age is useful.
I missed most of my schooling at Eton because of a heart condition, but I managed to pass my exams. A place at Cambridge was secured for me, but the war broke out and at 16 I joined the RAF. I pretended to be 18.
When the war ended, I still intended to go to university, but I wrote a book first. It was called Guide to the Moon and it turned out to be very successful. (I never did get to university but I have managed to acquire six honorary degrees.) I find the moon fascinating so I managed to combine my hobby with my work, and that's important. Enjoying what you do, no matter what the subject, is vital for success - it's as simple as that. Find your interest and make it work for you.
Then the BBC approached me to present a monthly programme on astronomy, and 42 years later its still going strong. If anything, my enthusiasm has increased.
A confidence in my ability to speak and write fluently have helped me to acheive my goals. I also happen to have the nerves of a rhinoceros - virtually none.
The effect my own career has had on so many other people is enormously satisfying and the ultimate barometer of my success.