Star Constellation Facts: Telescopium

Telescopium Constellation
Image Credit: IAU and Sky&Telescope magazine

Telescopium (“telescope”) is a small, faint southern sky constellation that was devised by French astronomer Nicolas-Louis de Lacaille following his expedition to South Africa (1751-53). He named it in honor of the scientific instrument that helped revolutionize the study of astronomy, with the constellation’s brightest star, Alpha Telescopii, a blue-white subgiant found 278 light years from Earth with an apparent visual magnitude of +3.51.


Telescopium is the 57th largest constellation, taking up an area of 252 square degrees of the southern celestial hemisphere. It can be seen by observers located between +40° and -90°of latitude, although best viewed from June to August. Its neighboring constellations include Indus to its east, Ara to its west, Sagittarius and Corona Australis to its north, and Pavo to its south.

Lacaille Constellation Family

Telescopium is a member of the Lacaille family of constellations, together with Antlia, Caelum, Circinus, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Reticulum and Sculptor.


Following his study of the stars of the southern hemisphere from an observatory in Cape Town during the mid-18th century, Nicolas Louis de Lacaille created 14 new constellations. One of these he named Telescopium, in honor of the aerial telescope, a long “tubed” type of refracting telescope that was invented in the latter part of the 17th century, and was still very popular during Lacaille’s time.

Principal Stars

Image Credit: Torsten Bronger

– Alpha Telescopii, the constellation’s brightest star, is a blue-white subgiant (B3 IV) situated 278 light years from our solar system that shines with an apparent visual magnitude of 3.51. It is around 3 times bigger than the Sun, with 5 times its mass, and almost 800 times its luminosity. Alpha Telescopii is believed to be a slow pulsating variable star, and is also a slow rotator at just 35 km/s.

– Zeta Telescopii, the second brightest star in Telescopium, is an orange giant (K1III-IV) located 127 light-years away of magnitude 4.13. It is around 7.7 times bigger than our sun, with 1.53 times its mass, and 512 times its brightness.

– Epsilon Telescopii, the constellation’s third brightest star, is a binary system found 420 light years from the Sun with an apparent magnitude of 4.52. The main component of the system, Epsilon Telescopii A, is an orange giant star separated from its fainter 13th magnitude companion, Epsilon Telescopii B, by 21 arcseconds.

Other stars of interest in Telescopium includes the binary system Delta Telescopii; the white giant Nu Telescopii; the white main sequence star Eta Telescopii; the white dwarf Lambda Telescopii; the yellow giant Kappa Telescopii and HIP 92367; the orange giant Iota Telescopii; and the red giant Xi Telescopii.

Notable Deep-Sky Objects

There are no Messier objects in Telescopium, but it does contain a number of interesting deep-sky objects.

– Telescopium Group (AS0851) is a grouping of 12 galaxies situated 120 million light-years away that can be found in the northeastern area of the constellation. Its two brightest members, the elliptical galaxy NGC 6868 and the spiral galaxy NGC 6861, are interacting and expected to merge at some stage in the future.

– NGC 6845 is a system of 4 interacting galaxies with its largest member located 325 million light years distant. There are two spiral galaxies (NGC 6845A and NGC 6845B), and two lenticular galaxies (NGC 6845C and NGC 6845D) in this group.

– NGC 6584 is a globular cluster 45,000 light-years from Earth of magnitude 7.9. It contains thousands of stars, of which at least 69 are of the variable type.

Other objects of interest in Telescopium includes the 12.6. magnitude spiral galaxy NGC 6850; and the 13 magnitude planetary nebula IC 4699.

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