Hubble Space Telescope

Visible Astronomy: Space Observatories, Telescope Types, Refracting, Reflecting, Hubble, Etc.

Visible light astronomy encompasses a wide variety of observations via telescopes that are sensitive to the range of visible light. Visible light ranges from 380nm to 750nm in wavelength.

Space-based Observatories

Hubble Space Telescope
Hubble Space Telescope

In ancient times, visible-light astronomy was solely limited to the unaided eye. Visible light observatories are present both on Earth and in Space, with observatories in Space having several advantages over Earth-based ones. The Space-based observatories allow for much clearer observations, as the Earth’s atmosphere is not disrupting the image and viewing quality of the telescope, meaning objects can be observed in much greater detail, and much more distant or low-light objects may be observed.

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Types of Telescopes

There are three main types of telescopes used in visible-light astronomy; Refracting telescopes, Reflecting telescopes, and Catadioptric telescopes.

Refracting Telescope

A refracting Telescope
A refracting Telescope

In a refracting telescope, the light first passes through a large lens, called the objective lens. The objective is the part that intercepts the incoming light, so it determines the light-gathering power of the telescope. The light passing through the objective is concentrated on a second lens, called the eyepiece. The eyepiece is used to inspect the image formed by the objective.

Refracting telescopes suffer from Chromatic aberration, which causes colors to be shown on edges separating light and dark parts of the image, this is due to the lens being unable to focus all the colors to the same convergence point.

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Reflecting Telescope

The largest reflecting telescope in the World, Gran Telescopio Canarias in Canaries, Spain.
The largest reflecting telescope in the World is Gran Telescopio Canarias in Canaries, Spain. Credits – Pachango. Source. License – CC BY-SA 3.0

In the Reflecting telescopes, the objective mirror is used instead of the lens. Almost all major telescopes used in astronomy research are reflectors.

Reflecting telescopes also suffer several types of optical inaccuracies, such as off-axis aberrations near the edges of the field of view.

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Catadioptric Telescope

A catadioptric Maksutov telescope.
A catadioptric Maksutov telescope. Credits – Halfblue. Source. CC BY-SA 3.0.

Catadioptric telescopes use a combination of lenses and mirrors to form the image.

The celestial objects commonly observed using visible light astronomy are the Moon, meteors, planets, stars, and constellations.

The Hubble Space Telescope observes in the visible region.

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