Telescope Mirror

It is actually quite easy to make a timeline with regards to the invention of the telescope as well as how it has evolved over the years. Much has been written about the telescope and good records have been kept with regards to new technologies and inventions. Basically, the telescope timeline looks something like this:

1609 - Galileo first invented the telescope. Though it was crude, it still did the trick and allowed him to look into space for the very first time other than with the naked eye. Galileo's telescope was a reflecting one causing light to bounce off a mirror when looked at through a lens.

Mid-1600's - Johannes Keplar came up with the idea of a refracting telescope that would widen the field of view as well as improve the quality of the image. He did this by changing the shape and the placement of the lenses, but doing this caused little circles of color that would surround bright objects - chromatic aberration.

Late 1600's - As the century began to draw to a close, telescope makers were realizing that with a bigger lens, you could see much more. With a bigger lens, the telescope had to be bigger to accommodate it. Eventually, telescopes were being built that we as long as a hundred feet!

It was at this point in the telescope timeline that Sir Isaac Newton began to change telescope lenses so that there would be no chromatic aberration. He also found a way to add mirrors to improve images without having to make the telescope longer. This appealed to people as Newton's telescope was small but had the same power as the larger ones.

Mid-1800's - The first photographic telescope is introduced. John William Draper found a way to focus the Moon's image on a light-sensitive photographic plate. He used a clockwork device to keep the light in place even as the Earth rotated and the moon moved through the sky. After an exposure of 20 minutes, he had taken the first ever photograph of the moon! After the introduction of the photographic telescope came about, we were able to see the skies up close and personal. And what a great accomplishment!

The early timeline of telescopes shows that many advances were made even before we advanced into what we think of as modern times. Since the 1800's, so many advancements were made in the field of producing telescopes that documenting each and every one would be able to fill up pages and pages of text.

Suffice it to say that now we are graced with telescopes that can see even the minutest parts of Saturn's rings and even realize that Pluto is just a little too small to be a real planet. The timeline of telescopes will continue. All we have to do now is sit back, watch, and document the advancements.

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Why concave mirror is used in telescope?

Why concave mirror is used in telescope?Give answer with explaination.

From my studies, i knew that there r two types of telescopes:
1) Refracting telescope (doesn't need concave mirror)
2) Reflecting telescope ( need concave mirror, & its has 2 types)

Refracting telescope:
----------------------------
Construction:
- Objective lens
- The eyepiece

How it works:
- The objective lens forms a real, inverted, (diminished) small image of the object, which lies at the focus becouse the incident rays r parallel
- The eyepiece forms a virtual, erect, magnified image of the object, inverted (with respect to the original object), this image lies at a distance from the eye = 25 cm in normal person

Reflecting telescope:
---------------------------
1st type:
-----------
Construction:
- Concave mirror
- Plane mirror
- converging lens

How it works:
- The concave mirror recieves the parallel rays emitted from the object to be observed & reflected them towards the focus
- The path of the reflected rays is changed before reaching the focus of the plane mirror to fall on the eyepiece (lens)
- The eyepiece recieves the rays reflected from the plane mirror & the final image is seen through it (or mirror recorded on a sensitive film)

2nd type:
------------
Construction:
- Concave mirror
- Convex mirror
- Converging lens

How it works:
- The concave mirror recieves the parallel rays emitted from the object to be observed & reflected them towards its focus
- The path of the reflectedrays is changed before reaching the focus by the convex mirror, which reflect them once again towards a hole in the concave mirror to fall on the eyepiece (lens)
- The eyepiece recieves the rays reflected from the convex mirror & the final image is seen through it (or recorded on a sensitive film)

Also the real reasons behind using concave mirrors in reflecting telescope:
1) Decrease its mass
2) Get rid of defects of lens
3) recieve parallel rays & reflect them to a plane mirror or convex mirror, which also reflect them to the eyepiece

i hope u got ur point from my explanation

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