Telescopes are instruments designed for observing distant objects by collecting electromagnetic radiation. They are fundamental tools in astronomy, allowing us to see objects far beyond the resolution of the naked eye.

Types of Optical Telescopes

Optical telescopes are the most common type and are categorized based on how they form an image:

Refracting Telescopes (Refractors)

Refracting telescopes use lenses to gather and focus light.

• Key components: Objective lens (at the front) and an eyepiece (for viewing).
• Pros: Produce clear, steady images; typically low-maintenance.
• Cons: Suffer from chromatic aberration (color fringing); objective lenses become very expensive and difficult to manufacture for large apertures.

Reflecting Telescopes (Reflectors)

Reflecting telescopes use mirrors to gather and focus light.

• Key components: Primary mirror (at the back) and a secondary mirror (to direct light to the eyepiece).
• Pros: No chromatic aberration; mirrors are easier and cheaper to manufacture than large lenses; can be built with very large apertures.
• Cons: Require more frequent alignment (collimation); the secondary mirror can cause diffraction spikes.

Catadioptric Telescopes

These telescopes combine lenses and mirrors to form an image, offering a compact design and correcting for some aberrations.

• Examples: Schmidt-Cassegrain and Maksutov-Cassegrain.
• Characteristic: Use a large lens (a corrector plate) at the front of the tube.

Non-Optical Telescopes

Telescopes are not limited to visible light. They are used to observe the entire electromagnetic spectrum:

• Radio Telescopes: Detect radio waves from space. They often consist of large dish antennas located in remote, radio-quiet place.
• Infrared Telescopes: Detect infrared radiation. They are often placed in space or on high mountains to minimize atmospheric interference.
• X-ray and Gamma-ray Telescopes: Detect high-energy radiation. These must be placed in space, as Earth's atmosphere absorbs most X-rays and gamma rays.