QUESTION: 
Why is it important to learn about the stars?

ANSWER from Scott Sandford on May 5:
Good question!  There are a LOT of good reasons to study stars.  In fact, if 
I were to try to explain all the reasons for studying stars, this letter 
would be much too long!  Nonetheless, I'll give a starting list of four 
reasons why I personally think studying stars is important.


(1) Most scientist think that the universe started out containing only a few 
atomic elements, mostly hydrogen and helium.  However, when we look 
around the universe today, we see all the other elements are now also 
present.  [And it's a good thing too, since without elements like oxygen, 
carbon, nitrogen, etc. life as we know it wouldn't be able to exist!]

So where did the new elements come from?  We think that most of the 
atoms heavier than hydrogen and helium were made in stars by a process 
called "fusion."  This can be a complicated process, so I won't explain it in 
detail, but basically it's a process in which hydrogen and helium in the 
center of a star are 'squashed' together to make heavier elements.  This 
process of fusion liberates energy and it's what makes the stars shine.  
Sometimes this process proceeds in a relatively stable fashion, like in our 
Sun, and sometimes it proceeds in a very violent way, like when a star 
explodes in a nova or supernova. 

So... the first answer to your question is that studying stars is important 
because it helps tell us how we got all the other elements that make up 
things around us (and in us!).  By the way, since your bodies are made of 
elements like carbon, oxygen, etc., that means that you are made up of 
atoms that used to be part of a star!


(2) Another reason to study stars is that what we learn from other stars may 
help us understand our own Sun, which is also a star.  The Sun only seems 
different to us because it is so much closer to us than other stars.  
Understanding our own Sun is important since it is ultimately the source of 
most of the energy we use on earth.  It is what keeps the Earth warm 
enough for us to live on and it provides the light needed for plants and 
animals to stay healthy.


(3) When we study stars, we also learn something about how they are born 
and die.  This helps us understand how our own solar system was formed.  
We now think that our solar system was formed about 4.55 billion years 
ago and that it was created from a big interstellar cloud of gas, dust, and ice 
that slowly collapsed into the shape of a disk.  The materials in this disk 
then clumped together to form the Sun and planets.  Disks like the one we 
think formed our Solar System have now been detected around other stars 
in our galaxy.


(4) Understanding stars is also important because stars contain a large 
fraction of all the visible mass in galaxies.  As a result, their combined 
gravitational forces affect the 'dynamics' of galaxies, i.e. the ways in which 
galaxies move and evolve in shape.  Our own galaxy is shaped like a disk 
with a central 'bulge.'.  Since our Solar System is in the disk, the galaxy 
looks like a stripe of stars to us.  We call the stripe the "Milky Way."  You 
can easily see the Milky Way at night if the sky is dark where you live.

The gravitational pull of one particular star, our Sun, is especially important 
since it is the Sun's gravitational attraction that keeps the Earth in orbit.  
Without the Sun's gravity, the Earth would fly off into space and freeze!


There are other good reasons to study stars as well, but I hope this list gives 
you an idea of why astronomers think stars are important.

Scott Sandford
Astrophysics Branch
NASA/Ames Research Center