Observing Space Telescopes — Maharashtra (SSC) Class 9 Science Solutions (Free)

A telescope is an optical instrument used to observe distant objects in space by magnifying their size and brightness. Two types: 1) Refracting telescope - uses a convex lens to focus light. 2) Reflecting telescope - uses a concave mirror to focus light and is preferred for large telescopes.

A refracting telescope has two convex lenses: the objective lens (larger, at one end) focuses light from a distant object to form a real image. The eyepiece lens (smaller, at the other end) acts as a magnifying glass, creating a magnified virtual image visible to the observer.

A reflecting telescope uses a large concave primary mirror to collect and focus light, and a small plane mirror directs the image to the eyepiece. Advantages: Can be made much larger without optical defects, produces sharper images, doesn't suffer from chromatic aberration, and is less expensive.

Light year is the distance light travels in one year in vacuum, approximately 9.46 trillion km. Used to measure vast distances between stars and galaxies. Astronomical unit (AU) is the average distance between Earth and Sun, approximately 150 million km, used for distances within the solar system.

The eight planets in order are: 1) Mercury - smallest, closest to Sun. 2) Venus - hottest planet. 3) Earth - our home. 4) Mars - red planet. 5) Jupiter - largest planet. 6) Saturn - has prominent rings. 7) Uranus - rotates on its side. 8) Neptune - farthest from Sun.