One of the most beloved, well-known, and beautiful members of the solar system is its very heart; the Sun.  You see it every day, you learn about it in school, and you know that life itself couldn’t exist on Earth without it.  We now have the STEREO spacecrafts, and can see exactly what the Sun looks like right this minute.  It’s fascinating.  Of course, I think everything about the Sun is fascinating.

For one thing, just look at it:

NASA/STEREO

Gorgeous, isn’t it?  We know a lot about our sun — as well we should.  We’ve been thinking about it every since we had the brain capacity to “think” about anything.  This near-perfect sphere accounts for over 99% of all the mass in the solar system, its spectral class is G2V (we went over that, remember?), and it generates energy through nuclear fusion.  That’s the fusion of two atomic nuclei to form one “heavier” nucleus.  It takes a lot of energy to force two nuclei close enough together for them to fuse, but the process releases more energy (in the form of “free” neutrons) than it uses (until you get to iron).  The end result is this continuous outpouring of the energy which fuels all life on Earth.

Life cycle of the Sun, by Oliver Beatson - image released to public domain by author

Our understanding of the Sun hasn’t always been so neat and scientific, of course.  The Sun was worshiped as a god by early civilized man; and probably back into prehistory.  Solar eclipses were occasions of horror.  When we gave up on the idea that the Earth was the center of the universe, the Sun was the next logical choice.

Ancient Chinese print - Chinese solar diety Tai Yang Xing Jun

Once it became clear that the Sun was a physical thing and not a deity, early man pondered the mystery of its energy source.  After figuring out that it couldn’t be a huge fire burning off in the distance (hey, it makes sense if you know next to nothing about the universe around you), it wasn’t until the 20th century that the true nature of the Sun was known.  The Pioneer spacecrafts gave us our first really good look, returning detailed information about the solar wind and magnetic field.  Now we’ve had SolarMax, SOHO, and STEREO to give us a greater understanding, and appreciation, of our parent star.

Egyptian god Ra in his solar barge

Our Sun, at 4.6 billion years old, is still a relatively young star.  It is about one-half way through its time as a main sequence star (the time it fuses hydrogen into helium).  After about 5 billion more years, it will enter a red giant phase.  Our star doesn’t have enough mass to supernova.  It will end its life as a white dwarf, slowly releasing its remaining heat into space.  The very end of its life is theorized to be as a “black dwarf”, a cold, burned-out cinder.  Such a thing is purely theoretical since the universe isn’t old enough for one to have formed yet.  Still, it makes sense.

NASA/STEREO Behind - the Sun today, March 3, 2011

The more we know about the Sun, the more fascinating and mysterious it becomes.  We have always looked to the stars in awe, and lest we forget, the Sun is a star.  In every sense of the word.