|Area||252 sq. deg. (57th)|
|Stars with planets||0|
|Stars brighter than 3.00m||0|
|Stars within 10.00 pc (32.62 ly)||2|
|Brightest star||α Tel (3.49m)|
|Nearest star||Gliese 754
(19.35 ly, 5.93 pc)
|Visible at latitudes between +40° and −90°.
Best visible at 21:00 (9 p.m.) during the month of August.
Telescopium is a minor southern constellation created in the 18th century by Nicolas Louis de Lacaille, a French astronomer and student of the southern skies. Its name is a Latinized form of the Greek word for telescope. One of several constellations depicting scientific instruments drawn up by Lacaille, it was later much reduced in size by Francis Baily and Benjamin Gould.
The brightest star in the constellation is Alpha Telescopii, a blue-white subgiant with an apparent magnitude of 3.5, followed by the orange giant star Zeta Telescopii at magnitude 4.1. Eta and PZ Telescopii are two young star systems with debris disks and brown dwarf companions. Telescopium hosts two unusual stars with very little hydrogen that are likely to be the result of two merged white dwarfs: HD 168476, also known as PV Telescopii, is a hot blue extreme helium star, while RS Telescopii is an R Coronae Borealis variable. RR Telescopii is a cataclysmic variable that brightened as a nova to magnitude 6 in 1948.
Telescopium was introduced in 1751–52 by Nicolas Louis de Lacaille with the French name le Telescope, depicting an aerial telescope. Covering 40 degrees of the night sky, it stretched out northwards between Sagittarius and Scorpius. Lacaille had Latinised its name to Telescopium by 1763. It was also known as Tubus Astronomicus in the 18th Century, during which time three constellations depicting telescopes were recognised—Tubus Herschelii Major between Gemini and Auriga and Tubus Herschelii Minor between Taurus and Orion, both of which had fallen out of use by the 19th Century. Johann Bode called it the Astronomische Fernrohr in his 1805 Gestirne and kept its size, but later astronomers Francis Baily and Benjamin Gould subsequently shrank its boundaries. The much-reduced constellation lost several brighter stars to neighbouring constellations: Beta Telescopii became Eta Sagittarii, which it had been before Lacaille placed it in Telescopium, Gamma was placed in Scorpius and renamed G Scorpii by Gould, Theta Telescopii reverted to its old appellation of d Ophiuchi, and Sigma Telescopii was placed in Corona Australis. Initially unnamed, it is now known as HR 6875. The original object Lacaille had named Eta Telescopii—the open cluster Messier 7—was also in what is now Scorpius, and Gould used the Bayer designation for a magnitude 5 star, which he felt warranted a letter.
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 three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'Tel'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments. 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.[a]
With an apparent 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. Close by Alpha are the two blue-white stars sharing the designation of Delta Telescopii. Delta¹ is of spectral type B6IV and apparent magnitude 4.9, while Delta² is of spectral type B3III and magnitude 5.1. They form an optical double, as the stars are 800 and 1120 light-years away respectively. However, allowing the margin of error in their distances just overlaps, indicating there is a slim chance they are a true binary system.
At least four of the fifteen stars visible to the unaided eye are orange giants of spectral class K. The second brightest star in the constellation is Zeta Telescopii of apparent magnitude 4.1 and spectral type K1III-IV. 127 light years distant, it has been described as yellow, or reddish in appearance. Epsilon Telescopii is another double star, though this time a true binary system. Epsilon Telescopii A is an orange giant of spectral type K0III with an apparent magnitude of +4.52, with a 13th magnitude companion, Epsilon Telescopii B, 21 arcseconds away from the primary, and just visible with a 15 cm telescope on a dark night. The system is 409 light-years away. Iota Telescopii and HD 169405—magnitude 5 orange giants of spectral types K0III and K0.5III respectively—make up the quartet.
Kappa Telescopii is a yellow giant with a spectral type G9III and apparent magnitude of 5.18. It is approximately 293 light-years from Earth, and is another optical double. RR Telescopii, also designated Nova Telescopium 1948, often called a slow nova is now classified as a symbiotic nova system composed of an M5III pulsating red giant and a white dwarf; between 1944 and 1948 it brightened by about 7 magnitudes before being noticed at apparent magnitude 6.0 in mid-1948. It has since faded slowly to about apparent magnitude 12.
Gliese 754, a red dwarf of spectral type M4.5V, is one of the nearest 100 stars to Earth at 19.3 light-years distant. Its eccentric orbit indicates that it may have an origin in the Milky Way's Thick Disk.
Although no star systems in Telescopium have confirmed planets, several have been found to have brown dwarfs. 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 has a common proper motion with (and is hence 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) as massive as the Sun, and is 2.69 times as luminous and has around 1.62 times its radius. Using the ESO-HARPS instrument, it was found to have a brown dwarf around 38 times as massive as Jupiter orbiting at an average distance of 1.35 AU in a period of 505 days. This is an unusual distance from the star and has been termed the 'brown dwarf desert'.
Xi Telescopii is a red giant of spectral type M1II that is an irregular variable, ranging between magnitudes 4.89 and 4.94. Another irregular variable, RX Telescopii is red supergiant that varies between magnitudes 6.45 and 7.47, just visible to the unaided eye under good viewing conditions. Dipping from its baseline magnitude of 9.6 to 16.5, BL Telescopii is an Algol-like eclipsing binary system that varies between apparent magnitudes 7.09 and 9.08 over a period of just over 778 days (2 years 48 days). The primary is a yellow supergiant that is itself intrinsically variable. RS Telescopii is a rare R Coronae Borealis variable—an extremely hydrogen-deficient supergiant thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012. The dimming is thought to be caused by carbon dust expelled by the star. As of 2012, four dimmings have been observed. HD 168476, also known as PV Telescopii, is a class B-type (blue) extreme helium star that is the prototype of a class of variables known as PV Telescopii variables. First discovered in 1952, it was found to have a very low level of hydrogen. One theory of its origin is that it is the result of a merger between a helium- and carbon-oxygen white dwarf. If the combined mass does not exceed the Chandrasekhar limit, the former will accrete onto the latter star and ignite to form a supergiant. Later this will become an extreme helium star before cooling to become a white dwarf.
Deep sky objects
The globular cluster NGC 6584 lies near Theta Arae and is 45000 light-years distant. It is an Oosterhoff type I cluster, and contains at least 59 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.
There are a group of twelve galaxies spanning three degrees in the northeastern part of the constellation. They lie around 120 million light-years from our own galaxy. This group is known as the Telescopium group or AS0851. The brightest is the elliptical galaxy NGC 6868. To the west lies the spiral 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' x 2', NGC 6845 is an interacting system of four galaxies—two spiral and two lenticular galaxies—that is estimated to be around 88 megaparsecs (287 million light-years) distant. SN 2008DA was a type II supernova observed in one of the spiral galaxies, NGC 6845A in June 2008.
- While parts of the constellation technically rise above the horizon to observers between 33°N and 44°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.
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- Zsoldos, E. (1994). "The pulsations of yellow semi-regular variables II. The F supergiant in the high-latitude binary BL Telescopii". Astronomy and Astrophysics 286: 870–74. Bibcode:1994A&A...286..870Z.
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- Otero, Sebastian Alberto (13 February 2014). "RS Telescopii". AAVSO Website. American Association of Variable Star Observers. Retrieved 3 July 2014.
- Otero, Sebastian Alberto (11 November 2011). "RX Telescopii". AAVSO Website. American Association of Variable Star Observers. Retrieved 26 June 2014.
- Watson, Christopher (3 May 2013). "NSV 12783". AAVSO Website. American Association of Variable Star Observers. Retrieved 2 July 2014.
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- "Eta Telescopii". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 2 July 2014.
- "HD 169405". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 26 June 2014.
- "HD 181327". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 2 July 2014.
- "HR 6934". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 29 September 2012.
- "HR 6938". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 29 September 2012.
- "Iota Telescopii". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 26 June 2014.
- "Kappa Telescopii". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 30 September 2012.
- "LTT 7332". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 29 September 2012.
- Streicher, Magda (August 2009). "A Spyglass Telescope" (PDF). Deepsky Delights. The Astronomical Society of Southern Africa. Retrieved 29 September 2012.
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