Radio Telescope vs Optical Telescope | Difference between Radio Telescope and Optical Telescope

This page compares Radio Telescope vs Optical Telescope and mentions difference between Radio Telescope and Optical Telescope. It mentions basic working of both radio telescope and optical telescope.

Radio Telescope

radio telescope

The figure-1 depicts radio telescope block diagram. As shown in the figure, radio telescope gather radio frequency waves.
• The telescope concentrates radio frequency (RF) waves which fall on the dish part of it.
• It reflects the RF waves from dish to a RF receiver.
• The concentration of RF waves will provide information with more definition and resolution.
• The captured RF signals from distant radio source is passed to the control room for further processing.
• The control room houses receiver, filter, computer, recording devices, display and analysis system etc.
• As electronics used in the radio telescope themselves emit RF waves. This need to be reduced in order to reproduce image with good quality. The coolant such as liquid nitrogen ot liquid helium is used in order to cool the receiver.
• It can be used as single antenna or multiple antennas are linked together electronically stacked as an array.
• They are used in the daytime as well as in the night time.

Optical Telescope

The optical telescope works on collection of light rather than RF waves as does by radio telescope. Following properties of light is being used in the design of optical telescope.
➨Law of Reflection:
• Angle of Incidence = Angle of reflection
➨Law of Refraction:
• Light beam is bent towards the normal when passing into a medium of higher Index of Refraction. Here the "normal" is the ray path perpendicular to the mirror's surface.
• Light beam is bent away from the normal when passing into a medium of lower Index of Refraction.
➨Inverse Square Law:
• Light intensity diminishes with square of the distance from source.
➨ As light passes from one medium (e.g. air) to the another (e.g. glass or water), the speed of light changes. This will cause the light to be "bent" or refracted. The amount of refraction is called the index of refraction. It is expressed as follows.
• Index of refraction (n) = speed of light in vacuum/speed of light in medium.

There are two main types of optical telescope viz. refractor telescope and reflector telescope. Optical telescope is used in the daytime unlike radio telescope which is used in both day and night.

optical telescope refractor type

The figure-2 depicts refractor optical telescope. Following are the features of this type.
• It uses lens to gather light to a point.
• It provides sharpest view of planets and moon.
• It is most expensive for any given aperture.
• Usually tube is quite long. The shorter length tube based telescopes are now available.
• The in-expensive models will have problem known as chromatic aberration.

Optical Telescope reflector type

The figure-3 depicts reflector optical telescope. Following are the features of this type.
• It uses mirror to collect the light to a point.
• It requires periodic alignment of mirrors.
• It is least expensive for any given aperture.
• It is available in both long as well as short tube designs.
• Generally there is no chromatic aberration.
• The smallest angle or angular resolution of reflecting telescope depends on following equation.
θ = 1.22*λ/D ,
λ = Wavelength of light being viewed
D = Diameter of the primary mirror.

There is third type called compound optical telescope. It uses both mirrors and lens to gather the light to a point. It has moderate cost for any given aperture. It is the most portable type for any given aperture.

Large Optical Telescope

Large telescopes are preferable due to following features.
➨It will have large collection of light compare to small telescope. The amount of light collection depends on mirror area which is π*(D/2)2.
➨It will produce brighter images.
➨It will detect fainter objects.
➨It will increase sharpness of the produced image. This will help in distinguishing fine details of the image.
➨Will have good amount of magnifying power so that larger image can be produced in the field of view.

Optical Components

Following are the links to useful optical components:
Optical Isolator   Optical Circulator   Optical Amplifier   Optical Filter   Optical Coupler   Optical MUX DEMUX   Optical Equalizer   Optical Switch   Wavelength converter

Radio Frequency Components

Following are the links to useful radio frequency components:
rf connector   RF Terminologies   what is RF   RF circulator basics   RF isolator basics   RF Power Amplifier   RF Mixer basics   RF Switch basics   RF MMIC   RF Transceiver basics   rf synthesizer design   waveguide basics tutorial

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