Stars, comets, planets
The stars that twinkle in the sky at night are tremendously far away.
Even the closest one, called Proxima Centauri [(prahk]{.smallcaps} suh
muh sen [tawr]{.smallcaps} eye), is some twenty-five million million
miles (forty million million kilometers) away! No one could measure that
great a distance. So how do we know how far away Proxima Centauri is?
Astronomers use mathematics to figure out the distances to stars and to
work out star movements. This astronomer is inside a telescope that can
take pictures of large parts of the sky.
We know because of the work of scientists called astronomers (uh
[strahn]{.smallcaps} uh muhrs). The word astronomer means something
like, “one who studies the ways of stars.” Astronomers study stars,
comets, planets, and everything else in space, to help us know as much
as we can about the wonderful universe we’re all part of. And to find
out many things, astronomers use mathematics.
For example, to find the distance to a star, astronomers use the kind of
mathematics called trigonometry (trihg uh NAHM uh tree), which means
“triangle measurement.” Trigonometry gives us a way to measure angles
and find distances by figuring out triangles.
A triangle has three sides and three angles. If you know three parts of
a triangle, one of which must be a side, you can figure out each of the
other three parts. And, as you can see in the diagram, this is the way
astronomers find the distance to a star.
Most things in space are so far away that astronomers don’t usually
measure distance in miles. They use light-years. A light-year is the
distance light travels in one year.
Light moves at a speed of 186,282 miles (299,792 kilometers) a second.
This means that in one year light travels 5.88 million million miles
(9.46 million million kilometers). At this speed, light from Proxima
Centauri takes 4.3 years to reach Earth. So an astronomer would say that
this star is 4.3 light-years away.
Astronomers use mathematics for a great many other things, too, such as
figuring out the sizes of things in space, the movements of stars and
planets, and so on. Mathematics is a big part of an astronomer’s job.
Astronomers know how far Earth is from the Sun, so they know one side
of the triangle, the distance from A to B. Measuring angles a and b,
they can figure out the distance to the star.
