Can you tell how old people are just by looking at them?  Babies are easy.  They are small and pudgy and have that soft baby glow.  Teenagers are taller and a little shiny.  Adults are bigger with more hair and they have lost a little of that glow and shininess.  Older people might be a little more wrinkled with white hair, but they have the glow again.  People are easy.  Now look into the night sky.  Can you figure out how old a star is just by looking at it?


Stars let off a lot more light than humans.  While they do have spots and wrinkles and fire that sticks out like arms sometimes, we cannot really see these things from way down here.  We have to figure out a star's age by its light.  The youngest stars are the hardest to spot.  That's because they are still coming together.  Nebulae are giant clouds of dust and gas that are about to turn into a star.  Since they are not a star yet, they look kind of like a very big fuzziness in space.  There's an easy way to compare dust and gas to a person's age, but let's just say this is like when you were still just a twinkle in your mom and dad's eyes.

Nebulae, not quite a twinkle twinkle little star yet.


Just as your mom and dad get along (or at least they did once upon a time), things in space get along, as well.  All of that gas and dust is pulled into each other.  As they are pulled in, they begin to crash into each other.  This makes heat.  The dust and gas start to melt as they gather into a big ball of fire.  A protostar is the beginning of a of a star, when gas and dust are pulling together and heating up.  They make what you know as a little twinkling in the sky.  Protostars do not glow much, but they are a lot prettier than a person being born.

Protostar, a star being born.


We are going to skip ahead a bit.  They next stages of a star's life are not boring, but you know about them.  Just look at our sun.  WAIT!  Do not look at our sun or else you will burn your eyes.  Just think about our sun's bright light.  These are like the sun's teen years (one that's billions of years old, that is).  Do not pinch its cheeks.  You will burn your fingers off.  Like a teenager and adult, stars spend a lot of energy during these times.  You can see it burning off as light and heat.  Soon, all the stuff that the star used to make all of its light and heat starts to go away when they get a little older.  A red giant is a star that has spent most of its energy and is now growing.  Its middle gets colder while the fire around it cools down a lot.  Just like people, as a star gets a little bit bigger in the middle as it gets older.

Red giants start to get a little heavy around the waist.


A star cannot burn forever.  Once all of that stuff has been spent, the core starts to go away.  Just like little old men and ladies, it will start to shrink.  A white dwarf is a very small, hot star that is at the end of its life.  Since all of its energy is going away, these stars are very hot to the touch, but it's also a lot smaller than it once was and it does not burn as brightly as it once did.  In a way it has returned to that baby glow.

White dwarfs burn brightly as they die out.


Stars may seem like they will last forever.  Like people, they have different stages of life.  If you know what to look for you can tell about how old they are.  Nebulae are a lot of gas and dust floating around, getting ready to become a star.  A protostar is when all of that stuff comes together, just like a baby being born.  A red giant is when a lot of the gas that made up the star has been burned up and it starts to grow very big.  At last, a white dwarf is when that has been spent and it starts to shrink back to something smaller.  It's sad to see a star go, but remember they were around for billions of years.  While people might not be, at least we get to see the beauty of a star's twinkle.

References:

Cain, Fraser. "Life Cycle of Stars"  Universetoday.Com, 2009.  <www.universetoday.com/24629/life-cycle-of-stars/>

NASA.  "Imagine the Universe: The Life Cycle of Stars"  NASA, 2008.  <http://imagine.gsfc.nasa.gov/teachers/lifecycles/LC_main_p1.html>

Kids Astronomy.  "Nebulae"  Kids Astronomy, 2011. <http://www.kidsastronomy.com/nebulae.htm>