Space Exploration: Going Further

Distances, orbits and how anybody knows what a star is made of.

8 questions, free, marked as you go with a worked explanation on every one.

What this covers

Light travels about 9.5 trillion km in a year. A star is 4 light years away. How many trillion kilometres is that?
Astronomers say a star is made mostly of hydrogen and helium. How can they know that without going there?
What keeps a satellite in orbit around Earth rather than flying off or falling down?
Which technologies developed for space exploration are used on Earth? Select all that apply.
A radio signal travels at 300000 km per second. Mars is about 78 million km away at its closest. How many seconds does a one-way signal take, to the nearest second?
Why does that delay mean Mars rovers have to be partly autonomous?
Which best explains why we see phases of the Moon?
A telescope in orbit sees more detail than the same telescope on the ground. Why?