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Starscapes In The Earth Sky
Starscapes. A star is formed out of cloud of cool, dense molecular gas. In order for it to become a potential star, the cloud needs to collapse and increase in density. There are two common ways this can happen: it can either collide with another dense molecular cloud or it can be near enough to encounter the pressure caused by a giant supernova. Several stars can be born at once with the collision of two galaxies. In both cases, heat is needed to fuel this reaction, which comes from the mutual gravity pulling all the material inward. Starscapes
What happens next is dependent upon the size of the newborn star; called a protostar. Small protostars will never have enough energy to become anything but a brown dwarf (think of a really massive Jupiter). A brown dwarf is sub-stellar object that cannot maintain high enough temperatures to perpetuate hydrogen fusion to helium. Some brown dwarfs can technically be called stars depending upon their chemical composition, but the end result is the same; it will cool slowly over billions of years to become the background temperature of the universe. Starscapes
Medium to large protostars can take one of two paths depending upon their size: if they are smaller than the sun, they undergo a proton-proton chain reaction to convert hydrogen to helium. If they are larger than the sun, they undergo a carbon-nitrogen-oxygen cycle to convert hydrogen to helium. The difference is the amount of heat involved.
The CNO cycle happens at a much, much higher temperature than the p-p chain cycle. Whatever the route – a new starscapes has formed. The life cycle of a star is dependent upon how quickly it consumes hydrogen. For example, small, red dwarf stars can last hundreds of billions of years, while large supergiants can consume most of their hydrogen with a comparably short few million years. Once the star has consumed most of its hydrogen, it has reached its mature state. This is how a star forms. We have written many articles about star formation on Universe Today. Here’s an article about star formation in the Large Magellanic Cloud, and here’s another about star formation in NGC 3576. Starscapes
If you look at the stars on a clear night, you will notice that they seem to twinkle and that they differ greatly in brightness. A much slower movement also takes place in the night sky: If you map the location of several stars for a few hours, you will observe that all the stars revolve slowly about a single point in the sky.
Twinkling of stars is caused by movements in Earth’s atmosphere. Starlight Starscapes enters the atmosphere as straight rays. Twinkling occurs because air movements constantly change the path of the light as it comes through the air. You can see a similar effect if you stand in a swimming pool and look down. Unless the water is almost perfectly still, your feet will appear to move and change their shape. This “twinkling” occurs because the moving water constantly changes the path of the light rays that travel from your feet to your eyes.
Brightness of stars. How bright a star looks when viewed from Earth depends on two factors: (1) the actual brightness of the star — that is, the amount of light energy the star emits (sends out) — and (2) the distance from Earth to the star. A nearby star that is actually dim can appear brighter than a distant star that is really extremely brilliant. For example, Alpha Centauri A seems to be slightly brighter than a star known as Rigel. But Alpha Centauri A emits only 1/100,000 as much light energy as Rigel. Alpha Centauri A seems brighter because it is only 1/325 as far from Earth as Rigel is — 4.4 light-years for Alpha Centauri A, 1,400 light-years for Rigel. Starscapes
About the Author
Freddy Demetrio
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