The sun is a star of a type known as a G2 dwarf, a sphere of hydrogen and helium 870,000 miles (1.4 million km) in diameter. It is about 1/3 inside the outside edge of the Milky Way Galaxy. In the expanding Universe, there are millions of galaxies that have suns. Humbling, n'esp pas! Is there life somewhere outside? While we are on the edge of this galaxy - the sun is the central body in our solar system. It is the big Shamababa that holds life and everything we know together.
Until about 500 years ago the depth of space was not understood. The stars were a canopy that came out when it was dark. It was assumed that the earth held the central position because of a bias that Plato had. He loved the perfection of a sphere which has the minimum possible surface area relative the volume of space it encloses. This misconception was taught at his academy and continued until the Renaissance when Nicholas Copernicus, Galileo and Kepler put the sun in the right place. The planets revolve around the sun-heliocentric as contrasted to the planets and sun revolving around the earth - geocentric. If you are someday in Florence; check out an amazing museum in a little obscure building behind the Pitti Palace. It is the Science Museum. There you can see and look through Galieo's telescope. You can see the incline planes that were created to understand gravity and Newtons three laws. And relative to the SUN are all the models of planets and the sun revolving around the earth. The convolutions of planets to fit the observations (epicycles) did not fit the data. The astroglobes became more complicated until Kepler had a flash of inspiration about the elliptic nature of the planets revolving around the sun. Planets revolve in an elliptical orbits around two foci, the Sun being one of the two foci.
The earth revolves around the sun on a tilted axis. Think of a top spinning while at the same time it is magically held by a string (gravity) as it revolves around the sun. The axis determines the four seasons. In the winter, the earth is close to the sun but tilted so that the direct rays of the sun are focused on the southern hemisphere. The days are short in the northern hemisphere and we subconsciously crave the sunlight. Joy to the World, the lord has come, let earth redeem it's King.
Space is full of dust and matter. It starts to condense as gravity pulls it together. This is the birth of a star. Some starry night find Andromeda. With a telescope, look at the Horse Head Nebula. It is truly amazing the first time you see it with your own eyes.
Gravity is described as Force of attraction = G (M1xm2)/r2. AND, Gravity compacts the hydrogen so tightly together that tremendous heat results. Boyle's law describes this simply PV = nrT. Pressure times the volume equals the temperature. Imagine the volume as somewhat constant which is about the volume of the sun, as gravity continues to pull more dust and hydrogen into the sphere the pressure increases and the temperature rises correspondingly. The interior temperature is about 15 million C and the surface is a little under 6,000 C. At these tremendous temperatures, two hydrogen atoms fuse into a helium atom. Our sun is one great big fusion reactor.
When Helium is created, it has two highly excited electrons orbiting in valence shells far, far outside their first shell comfort zone. As they relax, they give off a big sigh in the form of energy. We call this unit of energy a photon and we experience it as light. Think of it like having a Martini or glass of wine after a big day - one relaxes. When GOD said "Let there be light" it would seem he was referring to the photon of energy being emitted. About 2% of the Sun's photons reach the earth. If you were at the edge of our atmosphere with 100 % efficient solar cells, you would have 1 kilowatt of energy in one meter square of space and enough electricity to power the earth many times.
Our earth is unique in that we have the right combination of water, gravity and temperature for life as we know it to exist. Throw into the mix; Kate Hudson, Frank Sinatra, Face Book, U-Tube, Kobe Bryant, Nicholas Sarkozy, Divine Secrets of the Ya Ya Sisterhood, DW-TV, 4 billion people, Lady Gaga, plus all the animals and fish. Do we even need to look beyond the earth for extraterrestrial life? Yet, looking up at the millions of stars on a clear night outside the light pollution of a city one cannot help wonder if we are alone in the vastness of space. It is an ageless question and we are a curious bunch.
S.E.T.I. which is an anonym for Search for Extraterrestrial Intelligence has great listening ears located behind Mt Shasta. They listen for any transmissions which would indicate that we are not alone in the Universe. Wiki-leaks provided recently a mountain of material about unidentified flying objects in England. While 95% is likely a hoax, the other 5% is real and unknown. There is quite an interesting history in the question including a movie with Jody Foster playing Dr. Eleanor Ellie Arroway in Contact 1997.
