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  Telescope Type: Astronomy: Telescope Type - APERTURE NOT POWER
Posted on Saturday, December 11 @ 01:03:48 CST by astronomy
  Telescope Type


The key specification of any telescope is its aperture—the diameter of the lens or mirror that collects the light. The magnification is unimportant— by changing eyepieces it is possible to make any telescope magnify any amount. But the maximum power any telescope can deliver is equal to about 50 times its aperture in inches.

A 2.4 inch (60 mm) telescope cannot operate much higher than 120 power. The limit for a 4.5 inch (110 mm) scope is 225 power. Exceed these limits and the image will indeed get bigger, but it will also look faint and fuzzy.

The critical factor is the light-gathering power of the instrument. The greater the aperture of the telescope, the more light it can collect. In fact, for every doubling of aperture, light-gathering power goes up by a factor of four. For example, a 6 inch (150 mm) mirror has four times the surface area of a 3 inch (75 mm) mirror. It collects four times the light, making the images appear four times brighter.

Doubling the aperture of a telescope also doubles its resolving power—the ability to see fine details on planets or split closely spaced stars. Under excellent seeing conditions, a 4 inch (100 mm) telescope can resolve stars about 1 arcsecond apart, while an 8 inch (200 mm) telescope's resolving power is 0.5 arc-second. (By comparison, the human eye can resolve only about 60 arcseconds.)

So when you are shopping, consider the telescope in your price range with the largest aperture. Then again, the biggest telescope you can afford is not necessarily the best for you. Think about where you will store it, and where and how you will use it. A smaller, portable instrument may get used more frequently than a large, unwieldy one. The best telescope for you is the one you will use most often.




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