Lens, Mirror and Telescope

 Lecture 11 Lens, Mirror and Telescope

Lens

An optical tool that converges and diverges a light beam by refraction. Lenses are of mainly two types called concave and convex.

Mirror

Polished and smooth reflecting surface with two types- plain mirror and spherical mirror. 

Spherical mirror have the spherical reflecting surface and are of two types- concave mirrors and convex mirrors.

Telescope

Device used to observe distant things by gathering electromagnetic radiation like visible light, UV wave, X ray etc.

Types of telescopes(Based on location) 

• Ground based telescope- Telescope installed on earth surface. 
• Space based telescop- Atmosphere is opaque for most of the electromagnetic spectrum, only a few bands can be observed from the Earth's surface. So for telescope with operating frequency higher than visible light are installed in space only. For visible light and lower frequency telescope can be installed either at ground or space with space based telescope have advantage of no atmospheric interference. 

Types of telescopes(Based on operating frequency) 

• Gamma ray telescope(Space based) 
• X ray telescope(Space based) 
• UV telescope(Space based) 
• Visible light telescope(Space & Ground based)- three type 1. Reflecting(Mirror based) 2. Refracting(Lense based) 3. Catadioptric/Compound(Lens + Mirror based) 
• Infrared telescope(Space & Ground based) 
• Microwave telescope(Space & Ground based) 
• Radio wave telescope(Space & Ground based) 

 

Major Telescope around the world

Square Kilometre Array(Radio telescope)- A global effort to construct the Square Kilometre Array(SKA) with rays collecting area larger than one square kilometre(one million square metres). SKA is installed at Australia and South Africa. 

Thirty Meter Telescope(Visible light)- Largest visible light telescopes in the world with a 30 m prime mirror diameter installed with collaboration of many countries at Mauna Kea, Hawaii. 

Hubble Space Telescope(Visible light)- The first optical telescope installed by NASA in the space was Hubble with operating frequency of viable and UV light. 

James Webb Space Telescope(Infrared)- Successor of Hubble Space Telescope with operating frequency of Infrared and installed at Sun Earth L2 orbit. 

Chandra X ray Observatory(X ray)- Chandra is the world’s most powerful X ray telescope launched by NASA. Chandra, named for Indian-American physicist Subrahmanyan Chandrasekhar.

Major Telescope in India

ARIES telescope(Visible light)-  A joint collaboration between Indian, Russian, and Belgian scientists. The telescope is located at Devasthal, Nainital at a height of 2,500 metres. 

Astrosat(Multi wavelength)- India’s first space telescope operating as multi-wavelength space telescope.

PRATUSH space telescope(radio telescope)- PRATUSH is a radio telescope designed to be placed on the far side of the moon. It is built by Raman Research Institute(RRI), Bengaluru and Indian Space Research Organisation(ISRO). Aims to uncover the timing and characteristics of the first star formation in the universe, including the colour of the light during Cosmic Dawn.

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