Mounts
When using a telescope to observe stars, it is important to be able to keep track of the star being viewed as the Earth is of course, moving. If a telescope’s position is not altered, celestial objects will move out of its field of view within minutes. Astronomers often need to observe a star for longer than this if they plan on photographing of analysing it.
To enable Astronomers to keep track of a star, a mount can be used. One type of mount is the altitude-azimuth system. The altitude of the telescope is the angle it is above the horizon. It can be adjusted by tilting the telescope along a horizontal axis. The azimuth is the compass bearing with north at 0 degrees. It is altered by twisting the telescope on a horizontal axis. Another type of mount is the equatorial mount. It uses declination and right ascension to keep track of a star. One of the mount’s axes is parallel to the Earth's axis of rotation, meaning it is pointing towards the closest pole. This axis keeps declination steady whilst changing the right ascension. The declination axis is perpendicular to the polar axis. It keeps the right ascension the same whilst the declination is adjusted. The Earth's polar axis is parallel to declination, so the declination of a star does not change. By moving just the declination axis, an astronomer can easily keep their telescope focused on a star. If a telescope is rotated around the polar axis at 360 degrees every 23 hours and 56 minutes, it will track a star's movement. |
Optical system
Telescopes can be categorised as either refracting or reflecting.
A refracting telescope consists of two lenses. The eyepiece lens controls the magnifying power and the objective lens adjusts the the size of the image. There are two major problems with refracting telescopes. Firstly, the diameter of the objective lens must be lengthened to increase the amount of light on an image. As a result, the thickness of the lens must also be increased to keep its curvature. This creates distortion as the light is refracted when entering and exiting the lens. Also, different colours focus at different points. This is called chromatic aberration and can be fixed with a glass lens but not completely erased.
In the reflecting telescope, the objective lens is replaced with a parabolic mirror. It is referred to as the objective or primary mirror and made of a silver or aluminium coated surface. Light is reflected by the mirror and cannot be influenced by a faulty lens or chromatic aberration. The mirror can be placed outside of the telescope, allowing for a large mirror with a better light-gathering power.
The Gregorian telescope was developed in 1663 and contains two concave mirrors. The primary mirror collects light and focuses it onto the secondary mirror. This reflects it back through an eyepiece in the middle of the primary mirror. The Newtonian telescope was invented in 1668. In other reflecting telescopes, it was difficult to view an image, without blocking out the light. The Newtonian's secondary mirror was adjusted to 45 degrees, and angled the light's path up, through an eyepiece at the top of the telescope.
A refracting telescope consists of two lenses. The eyepiece lens controls the magnifying power and the objective lens adjusts the the size of the image. There are two major problems with refracting telescopes. Firstly, the diameter of the objective lens must be lengthened to increase the amount of light on an image. As a result, the thickness of the lens must also be increased to keep its curvature. This creates distortion as the light is refracted when entering and exiting the lens. Also, different colours focus at different points. This is called chromatic aberration and can be fixed with a glass lens but not completely erased.
In the reflecting telescope, the objective lens is replaced with a parabolic mirror. It is referred to as the objective or primary mirror and made of a silver or aluminium coated surface. Light is reflected by the mirror and cannot be influenced by a faulty lens or chromatic aberration. The mirror can be placed outside of the telescope, allowing for a large mirror with a better light-gathering power.
The Gregorian telescope was developed in 1663 and contains two concave mirrors. The primary mirror collects light and focuses it onto the secondary mirror. This reflects it back through an eyepiece in the middle of the primary mirror. The Newtonian telescope was invented in 1668. In other reflecting telescopes, it was difficult to view an image, without blocking out the light. The Newtonian's secondary mirror was adjusted to 45 degrees, and angled the light's path up, through an eyepiece at the top of the telescope.
Data collection System
Optical telescopes magnifies an object by collecting the light that is reflected or emitted off of it. The image can be viewed straight away or photographed. The three types of optical telescopes are refracting telescope, reflecting telescopes and catadioptric telescopes (these combine mirrors and lenses). Optical telescopes rely on their light-gathering power, as to be able to see an object through a telescope, the telescope must be able to collect the object's light. Optical telescopes gather light from the visual section of the electromagnetic spectrum.
A radio telescope is an example of a telescope that collects data electronically. It uses a radio antenna to receive information from satellites and space probes. They are different to optical telescopes as they operate in the radio frequency section of the electromagnetic spectrum. Radio telescopes are large, concave antennas located far from cities, due to electromagnetic interference.
A radio telescope is an example of a telescope that collects data electronically. It uses a radio antenna to receive information from satellites and space probes. They are different to optical telescopes as they operate in the radio frequency section of the electromagnetic spectrum. Radio telescopes are large, concave antennas located far from cities, due to electromagnetic interference.