The telescope is an optical instrument which allows to observe distant and confusing objects as it would be more bright and close to the observer. The telescopes are used in astronomy to observe the distant celestial elements. For hundreds of years, they were the only tools used to observe the planets and the galaxies.
Most telescopes work by collecting reflected light emitted from stars or by the planets surface. These are called optical telescopes. They use a curved lens or a spherical or parabolic mirror to collect light rays and sends them to a small lens placed in the center which makes the observation of the objects possible.
Visible light telescope collected radiation is split into components with a spectroscope, thus achieving information about the temperature of the object, motion, chemical composition or the presence of magnetic fields.
Many telescopes are built astronomical observatories around the Earth but only radio waves, visible light and infrared radiation can penetrate Earth's atmosphere and can reach the planet.
To overcome this problem in the space were launched telescopes that can collect waves from other regions of the electromagnetic spectrum.
There are several types of telescopes: I. The main optical telescopes: reflected and refractory.
The reflected telescopes
They use a glass lens to form the image in focus. The lens is convex and the power to gather the light rays of such a telescope is proportional with the size of the target. These telescopes are hampered by chromatic aberration which changes each coming color and has its own angle of refraction.
Another fundamental limitation of these telescopes is represented by the fact that the lenses with the diameters greater than 1 meter are hard to use because they weigh more than a half of ton and collapse under their own weight. They may not be supported below by the mirrors.
The other category of telescopes, the refractory telescopes use a concave mirror to collect light rays and are forming a focal image above the mirror. The refractory telescopes are particularly useful to gather light from dark objects. Light sensitivity of this category of telescope increases by the square of the mirror’s diameter of the telescope.
The resolution of an optical telescope increases because of the size of the mirror or of the lens, but the Earth’s atmosphere imposes a limit to this because the light rays are being clouded. Other element that is brought in discussion when it comes to telescopes is the optical interferometer. This is being used to see the shiny and very closed objects, like doubles stars.
Infrared telescope allows the exploration of the dark and dusty regions of the space.
Ultraviolet telescopes are similar to optical refractory telescopes but their mirrors have special coatings that reflects very well the ultraviolet light.
