Theory:

Have you caught a glimpse of the recent lunar eclipse?
 
We can't see the phenomena clearly with our naked eyes. So, how can we get a better view of the distant object? With a telescope, this is possible.
 
A telescope is an optical device that allows you to see distant objects. Johann Lippershey invented the first telescope in 1608. To observe distant stars, Galileo built a telescope. He got the idea from a spectacle maker who noticed how the distant weather cock appeared magnified through his shop's lens system. Galileo used his telescope to observe Jupiter's satellites and Saturn's rings. In \(1611\), Kepler invented the telescope, which was essentially the same as the astronomical telescope.
 
Based on optical property, it is classified into two groups:
  • Refracting telescope
  • Reflecting telescope
 
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Refracting telescope
 
Lenses are used in refracting telescopes. Achromatic refractors, Galilean telescopes, and Keplerian telescopes are examples of refracting telescopes. Gregorian, Newtonian, and Cassegrain telescopes are examples of reflecting telescopes that use parabolic mirrors.
 
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Reflecting telescope