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The Planet Saturn
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Amateur Astronomy
The Stars
Our sun is a star. It is one of the billions of stars in the Milky Way Galaxy. On a clear night, when you look up at the sky, you can see thousands of stars with your naked eye. If you have a pair of binoculars or a telescope, you can see more stars than you could ever hope to count.
Each star is unique, but they all share things in common as well. Stars are born from interstellar gas clouds, nuclear fusion causes them to shine and stars die. Sometimes the death of a star is a very dramatic event.
Cold interstellar clouds or nebula, like the Orion Nebula and the Eagle Nebula, are the incubators and nurseries from which stars are born. An extremely simplified description is that gravitational collapse happens and forms a rotating gas globule. The resulting globule spins faster and faster. The central core becomes a star while the other material becomes planets or asteroids.
The life of a star begins and ends with a battle between two forces: gravity and pressure. It takes energy for a star to live, and this energy comes almost entirely from nuclear fusion of lighter elements into heavier elements. This is the energy through which a star can shine for millions or billions of years.
Stars fuse hydrogen to helium for most of their lifetime. This is referred to as the "main sequence" of a star's life. Our sun, Vega, Sirius, and Spica are all stars that are in their main sequence. Once the hydrogen in the core of a star has been used up, the star becomes a red giant like Betelguese, Arcturus, Aldebaran and Antares.
A star's life is limited because the hydrogen at the core is not self-replenishing and will eventually be used up. A star cannot depend upon thermal energy to resist the pull of gravity forever, and a star's final fate depends on whether something other than thermal pressure manages to halt the relentless crush of gravity. |
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Mirrors and Lenses
Many people believe that the main function of a telescope is just to make distant celestial objects appear bigger so that astronomers (even amateur astronomers) can see them better, but that really is a misconception. The fact is that telescopes work by gathering light. Magnifying distant objects is secondary. Telescopes gather light basically in two ways: through the use of lenses, and through the use of mirrors. The third way that telescopes gather light is by using a combination of lenses and mirrors.
A telescope that gathers light through the use of a lens is called a refractor telescope. The truth is that how much you spend on a refractor telescope is the determining factor of how well you will be able to see celestial objects. Inexpensive refractor telescopes (2.4 inch) have not-so-good optics and low light grasp. High-end refractor telescopes (3.5 inch) have almost perfect optics and much, much better light grasp.
Telescopes that gather light through the use of a mirror are called reflector telescopes. Refractors cost less per inch of aperture. They are less costly to manufacture because there is only one optical surface, and they lend themselves well to different designs and uses. Also, because the light doesn't have to pass through glass, the images are basically color free. Probably the best telescope for a novice astronomer is the Newtonian reflector. The cost factor is a plus for the refractor telescope, but the corresponding minus (there always is one) is that the primary mirror is ground to a concave shape, so the outside zone has a little longer focal length than the inner zone.
A catadioptic telescope is a compromise between a refractor and a reflector, because both lens and a mirror are used. Catadioptic telescopes are portable. They do not cost as much as a high-quality refractor telescope, but they cost a little more than a good-quality reflector telescope. Still, they are the best of both worlds.
Related Topics: History of Astronomy,
NASA, Telescope Jargon
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