What’s Out Tonight?

Stars Galore 
In the Universe, there are more stars than anything else and since the beginning of time, their births have represented a natural process that is repeated over and over. When you think of a galaxy, think of stars. Galaxies are the home of stars—they are collections of billions of stars all held together by their collective gravity. There are no stars between galaxies. 

Shining Brightly 
Stars shine from light created as a by-product of nuclear fusion that occurs at their centers when hydrogen atoms are converted into helium atoms. For a star the size of our Sun, this process takes place in an area equal to 1.6% of the total volume of the star, but containing half of its total mass. The density in this region is so great that a photon (a packet of light) ricochets for about 170,000 years before reaching the surface. Star shine brightly and give off tremendous amounts of energy because they convert massive quantities of hydrogen into helium. In our Sun, 700 million tons of hydrogen are converted to helium every second, but even at this rate our Sun can produce light for billions of years.

Normal size, Mass, Brightness, Temperature and Life 
Stars come in all sizes, but even the smallest are large and massive. Our Sun is an average-size star. It has a diameter of 865,000 miles and a mass 330,000 times that of Earth. The diameter of normal-size stars varies from about 1/3 to 10 times the diameter of our Sun. Star mass, or the amount of matter that a star contains, varies from 1/10 to 40 times that of our Sun. Their brightness varies from 1/100 to over 1,000,000 times that of our Sun and the smallest stars have surface temperatures of just 5,000°F while the largest reach 70,000°F. Our Sun will last about 10 billion years, while the smallest stars may last a trillion and the largest only a million. These ranges apply to normal stars. There are stars that are much smaller or much larger than mentioned above, but they represent special cases of stars that are at the ends of their lives. This includes stars known as white dwarfs, neutron stars, black holes, giants and supergiants.

Giants and Supergiants 
Really large stars are “puffed up” stars near the ends of their lives. Towards the end of our Sun’s life, it will expand to about the size of Mercury’s orbit and will be considered a red giant. Stars that are much more massive than our Sun become supergiants. Their outer atmospheres can expand to at least 1,500 times the diameter of our Sun (the diameter of Earth’s orbit is equal to 200 Suns). The outer atmosphere of the supergiant Betelgeuse in the constellation Orion would almost reach the orbit of Jupiter.

Galactic Alchemy
When the Universe was formed, it created just two elements — hydrogen and helium. The other elements of the periodic table were produced by stars. These include metals and the various silicates or materials that make up rocks. Our Sun is a “second generation” star, and like the planets it contains elements created from stars that have lived and died. Some of the heavy elements, like gold, could only have been formed by supernova explosions.

The Closest Stars
Our Sun is the closest star at just 93 million miles away. The closest nighttime star visible to the naked eye is Alpha Centauri in the constellation CENTARUS (Southern Hemisphere star) and it is also known as Rigel Kent or Rigel Kentaurus. Alpha Centauri shines brightly at magnitude –0.01 and is just 4.4 light years away. One light year (ly) is about 6 trillion miles. The very closest star is Proxima in CENTARUS at just 4.22 ly away. It is too faint to see with the eyes because it shines at magnitude +11. The second closest star visible to the naked eye is Sirius at 8.6 ly followed by Epsilon Eridani at 10.5 ly and Procyon at 11.4 ly. There are several stars closer than these three but they are too faint to be seen with the naked eye.