Collecting Electromagnetic Radiation through telescopes

Introduction »

Except for rock samples brought back from the Moon by Apollo astronauts, cosmic rayparticles that reach the atmosphere, and meteorites and comet dust that fall to Earth,           

 the only information about objects in space comes to Earth in the form of electromagnetic radiation. How astronomers collect this radiation determines what they learn from it.

The most basic collector is the human eye. The retina at the back of the eye is covered with visible electromagnetic radiation stimulates nerve endings, which send messages tiny antennae called rods and cones that resonate with incoming light. 

   Galileo's telescope two of Galileo's first telescopes; in the Museum Galileo, Florence. 

Resonance colors of the visible spectrum, while the rods are most sensitive to black and white. To the brain that are interpreted as visual images. Cones in the retina are sensitive.

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 Until the early 1600s, astronomers had only movements of planets and transient objects their eyes and a collection of geometric devices to observe the universe and measure locations such as comets and meteors. 

However,when of interstellar objects. They concentrated on the Jupiter, craters on the Moon, phases of Venus, Galileo Galilei used the newly invented tele- scope to study the Moon, planets, and the Sun, our knowledge of the universe changed dramat-

Galileo’s telescope and all optical telescopes that ically. 

He was able to observe moons circling and spots on the Sun.

Note :-Galileo did his solar observations by projecting light through his telescope on to a white surface -a technique that is very effective even today. Never look directly at the sun!

Lens were bent and concentrated into a narrow have been constructed since are collectors of electromagnetic radiation. The objective or front lens of Galileo’s telescope was only a few cen- beam that emerged through a second lens, timeters in diameter. Light rays falling on that distant objects three times.

entered his eye, and landed on his retina.The lens diameter was much larger than the diameter of the pupil of Galileo’s eye, so it collected much more light than Galileo’s unaided eye could gather

The famous 5-meter-diameter Hale Telescope on The telescope’s lenses magnified the images of Since Galileo’s time, many huge telescopes have

rors as the light collector.

 The bigger the mirror been constructed. Most have employed big mir-

fainter the source that the astronomer can detect. or lens, the more light could be gathered and the power is two and a half million times that of the

Mt. Palomar is able to gather 640,000 times the amount of light a typical eye could receive. The to the human eye is its light gathering power amount of light one telescope receives compared (LGP). Much larger even than the Haletive diameter of 10 meters. Its light gathering
Telescope is the Keck Telescope that has an effec- typical eye. Although NASA’s Hubble Space

lectors, not detectors. Like all other telescopes,

Telescope, in orbit above Earth’s atmosphere, has

only a LGP of 144,000, it has the advantage of

its sensitivity extends into infrared and ultravio- an unfiltered view of the universe. Furthermore, let wavelengths.

the mirror of the Hubble Space Telescope is a Once a telescope collects photons, the detection method becomes important. Telescopes are col images can be made at specific wavelengths.

photon collector that gathers the photons to a focus so a detector can pick them up. It has several filters that move in front of the detector ...

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