how do scientists know stars are millions of light years away??? have they been there and back , do they have a tape

Question: how do scientists know stars are millions of light years away??? have they been there and back , do they have a tape measure that strechs that long????
- Keywords:
  light years,
  stars,
  universe
Asked by nicenadia to Alessandro, Angela, Claudia, Marina, Phil on 9 Mar 2013.
- Marina De Vos answered on 9 Mar 2013:
  
  A measuring tape would have been fun. You do not need to travel to a place to know how far it is. Some clever mathematics and some observation will give you the answer.
  
  See http://science.howstuffworks.com/question224.htm for a detailed explenation
- Alessandro Guazzi answered on 10 Mar 2013:
  
  This is one of my favourite topics, which always takes my breath away when I think about it. What stars are and how far they are is a question that was haunting scientists for hundreds of years – there’s just really so little for us to hold onto or measure when we talk about stars (we even have to stay awake at night just to get a good look at them)! But what happened was that scientists realised that stars were a bit like our own sun (and that only happened about 400 years ago!) and it took another 200-odd years for astronomers to realise they could estimate the distance by using the method given by Marina. And it took all this time because astronomers had to collect their data by patiently observing the sky night in and night out, not really knowing what they’d end up doing with it – experimental science at its best!

Question: how do scientists know stars are millions of light years away??? have they been there and back , do they have a tape measure that strechs that long????