An object that uses lenses or reflecting surfaces to collect light from a distant object.
A Telescope collects photons, so fainter objects can be seen.
A telescope magnifies angular sizes.
It gathers light from faint distant objects and magnifies these objects.
There are different telescope designs but the basic idea remains the same in all of them.
Topics covered in this snack-sized chapter:
- A lens or mirror gathers light and concentrates it so the image can be examined by a magnifying eyepiece.
A flat surface reflects incident light at the same angle.
A curved surface can focus light.
A telescope uses mirrors or lenses to collect and focus light.
The area of the lens or mirror can be considerably larger than the area of the eye’s pupil. Hence, much fainter objects can be seen.
The largest lenses that can be built have a diameter of about 1 m, and have very long focal lengths.
A lens must be held by its edges, and large lenses sag under their own weight. Also lots of light is lost in the glass.
For these and more reasons, all modern telescopes use mirrors.
Using an objective mirror, and some additional mirrors and lenses, light are collected and focused to a point.
A telescope’s main job is collecting photons.
The light gathering power is proportional to the area of the mirror or lens.
There are two main types of telescopes:
- Refracting Telescopes use lenses to focus light to a point.
- Reflecting Telescopes use mirrors to focus the light.
There are many types of telescopes; all have some basic key parts:
The Aperture is simply the part of the telescope that lets light in.
The Primary bends the light, bringing the rays to a point.
The Secondary aids in this process.
The Optical Tube protects the rest of the telescope and blocks stray rays of light.
The Finder is a small telescope used for locating an object.
The Detector is the thing that actually records the light.
The idea of focusing light is important-
- Catadioptric Telescopes are a combination of the two.
- Telescopes collect light from a large area.
The Focal Plane is the plane where the light rays meet.
The Focal Length is the distance from the primary lens to the focal plane.
- By focusing the light, we concentrate its power.
The resolution of a telescope defines how much detail can be seen.
All optical systems have some resolution limit.
- The separation between the objects becomes too small for us to see.
- Telescopes have a much improved resolution, but there is a limit.
The separation of objects is measured in terms of angles.
- The resolving power of a telescope cannot be greater than R= (1.22×λ)/D
- There are 360° in a full circle.
- There are 60 arc minutes in a degree, and 60 arc seconds in an arc minute.