How a Telescope Works - Part 2 - Light conferrence Power

The human eye has a diameter of seven millimetres; a 250 mm gap ,break reflecting telescope has 1275 times as much covering area (250 divided by 7, squared), which means that it collects 1275 times as much light. Celestial objects will therefore appear 1275 times as bright as with the unaided eye.

Astronomers portion the glow of stars in terms of a magnitude scale, which is essentially derived from an old classification of stellar glow as classes 1, 2, 3, and so on. The brightest stars are those of first magnitude and the faintest stars descriptive with the unaided eye are of magnitude six. There are a estimate of stars that are brighter than first magnitude; Sirius, the brightest star, shines at magnitude minus 1.4; the planet Venus, at its brightest, shines at nearby magnitude minus 4. The Sun, being the brightest object in the sky, shines at nearby magnitude minus 26.

Telescope

Now, the magnitude scale is a logarithmic one, which basically means that if the glow is divided by a estimate x, then 2.5 times log to the base 10 is added to the magnitude. For example, a 250 mm telescope makes celestial objects appear 1275 times brighter, which means it makes them 2.5 xlog1275 which equals 7.8 magnitudes brighter. This means that such an instrument can theoretically expand the observer's optic limit to magnitude 7.8 + 6.0 which equals magnitude 13.8.

In reality however, telescopes do a small best than this calculation suggests; with a 250 mm instrument in good looking conditions, it is possible to see objects down to a magnitude 14.5. This is due to the fact that a telescope can be focused perfectly, with all the light being captured going straight into the observer's eye. The actual formula to use is 7.5 + 5 x log10 times the telescope gap ,break in centimetres. So, for the 250 mm telescope, the limiting magnitude is 7.5 + 5log10 x 25, which equals 14.49.

However, reflecting telescopes have a central obstruction caused by the possessor of the secondary mirror. This covers nearby 16 per cent of the total covering area, which costs 0.2 magnitudes. So the limiting magnitude under exquisite looking conditions with a 250 mm reflector will be nearby 14.3.

Telescopes will brighten point-like objects, such as stars, but not extended objects, like the Moon, the planets, nebulae and galaxies. The fancy for this is because the telescope spreads the collected light over a wider area of the eye's retina. This means that the higher the power being used, the dimmer the image becomes. This is a phenomenon that always disappoints those who use a telescope on the night sky for the first time. They expect to see more, but struggle to do so.

However, the telescope is convention more light than the eye ever can, and an extended object like a galaxy at magnitude 10 will be descriptive through a telescope, but not as bright as hoped for. This is why astronomers use long exposure photography in order to capture and collect all the photons of light coming from extended celestial objects. It is the only way that we can truly appreciate the attractiveness and the colour of the night sky. scrutinize the overwhelming images obtained by the amateur astronomers from all nearby the world, and of course by the Hubble Space Telescope.

How a Telescope Works - Part 2 - Light conferrence Power

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