The nearest star to us is the Sun.

It is One Hundred Fifty Million kilometers away.

The next closest star is Sirius, the brightest star in the sky. It is so far that when the Earth orbits the Sun from one end to another in half a year the change of the angle to the star in these two positions is less than 1 second. Not degree, not even minute, but one angular second.

It is 3600 times smaller than 1 degree angle.

Can you imagine that? And this is the closest star!

The base of the triangle shown in the pictures equals 300,000,000km. It's called parallax.


How far is the star? Estimate this distance in three different ways.

The answer is 3*1013km.

In centimeters, it has eighteen zeros after 3.

This distance which the light flies in three years is called PARSEC (parallax-second). It's three light years. Both parsec and light year are standard units of measurement in Astronomy!