
HOW FAR IS A STAR?
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.
Problem:
How far is the star?
Estimate this distance in three different
ways.
The answer is
3*10^{13}km.
In centimeters, it has
eighteen zeros after 3.
This distance which
the light flies in three
years is called
PARSEC (parallaxsecond). It's three light
years. Both parsec and
light
year are standard units
of measurement in Astronomy!
WOW!


