Constellations: Telescopium 'the Telescope' Content from the guide to life, the universe and everything

Constellations: Telescopium 'the Telescope'

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The shield of the Science, Mathematics and Engineering faculty of the h2g2 University.Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
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A telescope

Meaning:The Telescope
Short form:Tel
Area:252 square degrees
Co-ordinates1:Right Ascension 19h 30', Declination −50°
Origin:18th Century

Telescopium is a faint, unremarkable southern constellation that was first imagined by the French astronomer Abbé Nicolas Louis de Lacaille (1713 - 1762). It is not fully visible at latitudes north of 30°N, so it is best observed from the Southern Hemisphere. Telescopium borders Sagittarius and Corona Australis to the north, Ara to the west, Pavo to the south and Indus to the east. The brightest star in Telescopium has a magnitude of +3.5, which means it is pretty dim.

Telescopium does not have a lot to offer the amateur observer. There are no meteor showers and the few deep sky objects are quite faint, requiring a very large telescope to see them. In addition, there are no known extrasolar planets, so those of us searching for extra-terrestrial life should look elsewhere.

The main feature of the constellation is the small 'L' shape formed by the stars epsilon, alpha and zeta Telescopii, representing the horizontal tube of the telescope and the vertical stand. To the east of these stars lies an apparently empty patch of sky which is included in Telescopium. Big telescopes, however, see it as a rich field of galaxies.


Because, due to its southerly location, Telescopium is not visible from Europe or the Middle East, it was never seen by the ancient Greeks and Babylonians, who devised the ancient constellations. As a result, it has no mythological associations.

Lacaille went on an expedition to the Cape of Good Hope at the southern tip of Africa, where he set up an observatory and observed the stars for two years from 1751 - 1753. The results of his observations were published posthumously as Coelum Australe Stelliferum (The Star-bearing Southern Heavens). He included proposals for 15 new constellations, the breaking up of the massive Argo Navis constellation into three parts, and details of 10,000 stars and 42 'nebulous objects'. Some 14 of Lacaille's new constellations were adopted as standard by the IAU, including Telescopium.

In Lacaille's original plan, the telescope was much bigger than it is now. The stand stretched across neighbouring Corona Australis as far as Sagittarius, while the tube of the telescope stretched across Scorpius and ended as far away as Ophiuchus. When the final definitions of the constellations were fixed by the IAU, it did not approve of one constellation stretching across another, so the telescope and stand were truncated and became rather small and insignificant.


None of the stars in Telescopium are bright enough to merit a proper name, so they use 'Bayer designations': a Greek letter followed by the constellation name in the genitive form. The alpha star is the brightest and the others should follow in (Greek) alphabetical order. But in Telescopium there are no beta, gamma or theta stars. These are stars of Lacaille's original extended telescope which have since been re-assigned to other constellations as eta Sagittarii, G Scorpii and 45 Ophiuchi.

Stars in Telescopium

Delta Telescopii is easily discernible as two stars side by side, and they are given the names delta1 and delta2. They are not actually related to each other at all; they just happen to look close to each other from our viewpoint. In fact, delta1 is 800 light years away, while delta2 is about 40 per cent further away again, at 1,100 light years. Such a pairing is known as an 'optical double'.

Star Table

StarDesignationBrightness (m)Distance
(light years2)
α TelAlpha Telescopii+3.51250B3IV
ζ TelZeta Telescopii+4.13120G8-K0III
ε TelEpsilon Telescopii+4.53140K0III
λ TelLambda Telescopii+4.87530A0V
ι TelIota Telescopii+4.91,600K0III
ξ TelXi Telescopii+4.94230M1IIab
δ1 TelDelta1 Telescopii+4.96800B6IV
η TelEta Telescopii+5.05160A0Vn
δ2 TelDelta2 Telescopii+5.071,100B3III

New General Catalogue (NGC)

The New General Catalogue (NGC) is a list of interesting deep-space objects (that is, objects outside our solar system). It was compiled by John Louis Emil Dreyer at Armagh Observatory, based on the observations of Sir William Herschel. Telescopium has a large number of objects in the catalogue. We will only list the principal ones here.

Deep Space Objects

CatalogueTypeBrightness (m)Distance
(light years)
NGC 6584Globular cluster7.943,700
NGC 6868Elliptical galaxy10.887.4 million
NGC 6861Elliptical galaxy11.1130 million
NGC 6893Lenticular galaxy11.6140 million
NGC 6909Elliptical galaxy11.7125 million
NGC 6851Lenticular galaxy11.9140 million

NGC 6868 is an elliptical galaxy, but the stars in it are of the type normally found in spiral galaxies. One explanation is that the galaxy has collided with a spiral one and fused with it.

Voyager 2

One object which is in Telescopium but you will not be able to see is Voyager 2, the unmanned space probe which enthralled us all in the 1980s with its photographs of the outer planets. Voyager 2 was launched on 20 August, 1977. It followed a path out of the solar system which took it past Jupiter (July 1979), Saturn (August 1981), Uranus (January 1986) and Neptune (August 1989). Scientific discoveries included the rings of Jupiter, the volcanoes on Jupiter's moon Io, and the only close-up photos of Uranus and Neptune. Voyager 2 ended its tour of the gas giant planets and carried on into the outer reaches of the solar system. It is currently in the constellation of Telescopium, heading away from the Sun. It has not yet reached the orbit of dwarf planet Eris, but unfortunately Eris will not be anywhere nearby when Voyager 2 reaches that milestone.

Other Celestial Telescopes

Telescopium is now the only constellation which represents a telescope, but there were two others in the past. In 1789, a Hungarian astronomer called Maximillian Hell invented two constellations commemorating Sir William Herschel's discovery of the planet Uranus. Hell called his constellations 'Tubus Herschelii Major' (Herschel's Big Tube) and 'Tubus Herschelii Minor' (Herschel's Small Tube), representing Herschel's 20ft and 7ft telescopes. The bigger constellation was published in Johann Bode's Uranographia star atlas as 'Telescopium Herschelii', Herchel's Telescope, and was positioned between Lynx and Auriga.

1Current International Astronomical Union (IAU) guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.2A light year is the distance light travels in one year, roughly 10,000,000,000,000km.

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