What is the 'background' when measuring using parallax?

25 September 2013

Question

I've just been listening to this week's programme, with the piece about mapping the milky way using parallax. This left me with two questions:
- To observe something moving because of parallax, you need to see the movement against a more distant background. What are they using as background?
- Are there still significant risks with launches into orbit. It was made to sound so mundane!
Thanks,
Derek McComiskey

Answer

Transcript to follow.

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