Telescopium is a minor constellation in the southern celestial hemisphere, one of twelve named in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. Its name is a Latinized form of the Greek word for the telescope. Telescopium was later much reduced in size by Francis Baily and Benjamin Gould. A small constellation, Telescopium is bordered by Sagittarius and Corona Australis to the north, Ara to the west, Pavo to the south, and Indus to the east cornering on Microscopium to the northeast. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a quadrilateral. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 18h 09.1m and 20h 29.5m, while the declination coordinates are between −45.09° and −56.98°. The whole constellation is visible to observers south of latitude 33°N.
With a magnitude of 3.5, Alpha Telescopii is the brightest star in the constellation. It is a blue-white subgiant of spectral type B3IV which lies around 250 light-years away. It is radiating nearly 800 times the Sun’s luminosity, and is estimated to be 5.2±0.4 times as massive and have 3.3±0.5 times the Sun’s radius. The second brightest star in the constellation—at apparent magnitude 4.1—is Zeta Telescopii, an orange subgiant of spectral type K1III-IV. Around 1.53 times as massive as the Sun, it shines with 512 times its luminosity. Located 127 light years away from Earth, it has been described as yellow or reddish in appearance.
Although no star systems in Telescopium have confirmed planets, several have been found to have brown dwarf companions. A member of the 12-million-year-old Beta Pictoris moving group of stars that share a common proper motion through space, Eta Telescopii is a young white main sequence star of magnitude 5.0 and spectral type A0V. It has a debris disk and brown dwarf companion of spectral type M7V or M8V that is between 20 and 50 times as massive as Jupiter. The system is complex, as it has a common proper motion with (and is gravitationally bound to) the star HD 181327, which has its own debris disk. This latter star is a yellow-white main sequence star of spectral type F6V of magnitude 7.0. PZ Telescopii is another young star with a debris disk and substellar brown dwarf companion, though at 24 million years of age appears too old to be part of the Beta Pictoris moving group. HD 191760 is a yellow subgiant—a star that is cooling and expanding off the main sequence—of spectral type G3IV/V. Estimated to be just over four billion years old, it is slightly (1.1 to 1.3 times) more massive as the Sun, 2.69 times as luminous, and has around 1.62 times its radius. It was found to have a brown dwarf around 38 times as massive as Jupiter orbiting at an average distance of 1.35 AU with a period of 505 days. This is an unusually close distance from the star, within a range that has been termed the brown-dwarf desert.
The globular cluster NGC 6584 lies near Theta Arae and is 45,000 light-years distant from Earth. It is an Oosterhoff type I cluster and contains at least 69 variable stars, most of which are RR Lyrae variables. The planetary nebula IC 4699 is of 13th magnitude and lies midway between Alpha and Epsilon Telescopii. IC 4889 is an elliptical galaxy of apparent magnitude 11.3, which can be found 2 degrees north-north-west of 5.3-magnitude Nu Telescopii. The Telescopium Group is a group of twelve galaxies spanning three degrees in the northeastern part of the constellation, 120 million light-years from our own galaxy. The brightest member is the elliptical galaxy NGC 6868, and to the west lies the spiral galaxy (or, perhaps, lenticular galaxy) NGC 6861. These are the brightest members of two respective subgroups within the galaxy group and are heading toward a merger in the future. Occupying an area of around 4‘ × 2′, NGC 6845 is an interacting system of four galaxies—two spiral and two lenticular galaxies—that is 287 million light-years distant. SN 2008da was a type II supernova observed in one of the spiral galaxies, NGC 6845A, in June 2008. NGC 6850 is a spiral galaxy in Telescopium. It was discovered by the English astronomer John Herschel in June 1836. It has an apparent magnitude of 12.6. SN 1998bw was a luminous supernova observed in the spiral arm of the galaxy ESO 184-G82 in April 1998 and is notable in that it is highly likely to be the source of the gamma-ray burst GRB 980425. Credits: Constellation Guide, Wikipedia.