This is a unique question in that it's the
subject of ongoing research in the astrophysics
community. At the size of galaxies and stars, the
main driving force toward alignment is gravity.
The gravity of a large star can be felt for
millions of miles. When a galaxy forms, over a
very long time they take different shapes.
Galaxies were originally formed from massive,
massive clouds of star material dust, so big that
if you moved at the speed of light it would take
you hundreds of thousands of years to cross them.
As this "star stuff" clumped together, stars were
born and began releasing energy and glowing.
Astronomers can watch this still happen today
in nebulas (like this one: click
here to see a nebula
from NASA : ).
As the other stars nearby form, they push and
pull on each other until they are jumbled together
in the sky. There isn't a lot of order to the way
stars are located, it's mostly random in the sky,
based on these interactions as they formed. The
gravity of all the stars together though leads to
galaxies forming, which are clumps of hundreds of
thousands of stars. These can have many shapes
here to see galaxies.
Our galaxy is a spiral shape. That is why if
you look in the sky in the middle of the desert it
looks like this: click
here to see our galaxy .
We are actually inside one of the bands on that
Fun fact: there are more stars in the
universe than there are grains of sand on all the
beaches of the world.
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