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Asked by M+P to Deborah, Euan, Maheen, Rob, Stu on 18 Jun 2016.
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Deborah Prunty answered on 18 Jun 2016:
They use trigonometry. The Earth’s orbit around the sun has a diameter of about 186 million miles. By looking at a star one day and then looking at it again 6 months later, an astronomer can see a difference in the viewing angle for the star. With a little trigonometry, the different angles yield a distance!
Will we ever be able to travel to them? Research is being done on suspended animation. That is basically freezing people, literally or otherwise, so that they haven’t aged when they wake up. Or there’s the possibility of us sending a huge ship with enough people on it that it has a sustainable population. The people who eventually arrived at the new start would then not be the same people who left, but their decendents.
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Euan Allen answered on 19 Jun 2016:
There are many ways we can guess how far they are away from us. One is how Deborah said, but we can also look at the colour of the light that the star is producing.
Because of the way the universe is expanding, it turns out that stars that are further from use are actually travelling faster away from us. When stars move away from us, their starlight gets shifted from being more blue in colour to being more red. The faster they are going the more red they are. This is called the “Doppler effect”, and is actually why a fire engine siren sounds high pitched when its coming towards you, and low pitched as it goes past and away from you.
We can measure the colour of light that a star produces, and then make an estimate of how fast it must be moving away from us to get that colour. We can then use how fast it is moving away to make an estimate of how far away it is!
I don’t think we’d be able to travel a million years to one. But I hope eventually we’d be able to make it to another star.
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