How do you calculate the distance to a star?

我们提出了this question to Author, Physicist and Campaigner, Simon Singh...

你这样做的方式是通过使用一种叫做parallax. Now that means that you measure the angle to a star using a telescope and then you move your telescope to a different position and you look for a shift in the angle to the star. The problem is, the stars are so very, very far away, you need to move your telescope a long way in order to get a perceptible shift in angle. A few meters, a few kilometres, a few hundred kilometres just isn't enough. It wasn't until the 19th century that an astronomer, Friedrich Bessel, moved his telescope to the other side of the Sun. He took a measurement in July from the Earth and then he waited six months for the Earth to go right around the other side of the Sun, he took another measurement. Even though the Earth and his telescope had moved such a vast distance, the shifting angles of the star was just 1/6000th of a degree, a tiny shift, but that tiny shift was enough for him to work out the distance to the local stars around us. Now to give you an idea how far away those stars are, it takes about 8 minutes for light from the Sun to reach us on Earth. It takes over 4 years for light from our closest star to reach us. That's how you measure the distances to the stars.