|Pronunciation||//, genitive //|
|Area||210 sq. deg. (66th)|
|Stars with planets||2|
|Stars brighter than 3.00m||0|
|Stars within 10.00 pc (32.62 ly)||2|
|Brightest star||γ Mic (4.67m)|
|Nearest star||Lacaille 8760
(12.87 ly, 3.95 pc)
|Visible at latitudes between +45° and −90°.
Best visible at 21:00 (9 p.m.) during the month of September.
Microscopium // is a minor constellation in the southern celestial hemisphere, one of twelve created 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 microscope. Its stars are very faint and hardly visible from most of the non-tropical northern hemisphere.
The brightest star is Gamma Microscopii of apparent magnitude 4.68, actually a yellow giant located around 381 light-years distant. Two star systems—WASP-7 and HD 205739—have been found to have planets, while two others—the young red dwarf star AU Microscopii and the sunlike HD 202628—have debris disks. AU Microscopii and the binary red dwarf system AT Microscopii are probably a wide triple system and members of the Beta Pictoris moving group. Nicknamed "Speedy Mic", BO Microscopii is a star with an extremely fast rotation period of 9 hours 7 minutes.
The stars that comprise Microscopium may previously been seen as the hind feet of the Sagittarius, a neighboring constellation. John Ellard Gore wrote that although Al-Sufi seemed to report the stars as having been seen by Ptolemy, he did not pinpoint their positions.
Microscopium was introduced in 1751–52 by Nicolas Louis de Lacaille with the French name le Microscope, after he had observed and catalogued 10,000 southern stars during a two-year stay at the Cape of Good Hope. He devised fourteen new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. All but one honored instruments that symbolised the Age of Enlightenment. Commemorating the compound microscope, the Microscope's name had been Latinised by Lacaille to Microscopium by 1763.
Microscopium is a small constellation bordered by Capricornus to the north, Piscis Austrinus and Grus to the west, Sagittarius to the east, Indus to the south, and touching on Telescopium to the southeast. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'Mic'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between 20h 27.3m and 21h 28.4m, while the declination coordinates are between −27.45° and −45.09°. The whole constellation is visible to observers south of latitude 45°N.[a] Given that its brightest stars are of fifth magnitude, the constellation is invisible to the naked eye in areas with polluted skies.
Lacaille charted and designated ten stars with the Bayer designations Alpha through to Iota in 1756. A star in neighbouring Indus that Lacaille had labelled Nu Indi turned out to be in Microscopium, so Gould renamed it Nu Microscopii. Francis Baily considered Gamma and Epsilon Microscopii to belong to the neighbouring constellation Piscis Austrinus, but this was not followed by subsequent cartographers. Within the constellation's borders, there are 43 stars brighter than or equal to apparent magnitude 6.5.[b]
Depicting the eyepiece of the microscope is Gamma Microscopii, which—at apparent (visual) magnitude of 4.68—is the brightest star in the constellation. Having spent much of its 620 million-year lifespan as a blue-white main sequence star, it has swollen and cooled to become a yellow giant of spectral type G6III, with a diameter ten times that of the Sun. Measurement of its parallax yields a distance of 229±4 light years from Earth. Alpha Microscopii is also an ageing yellow giant star of spectral type G7III with an apparent magnitude of 4.90. Located 380±30 light-years away from Earth, it has swollen to 17.5 times the diameter of the Sun. Alpha has a 10th magnitude companion, visible in 7.5 cm telescopes, though this is a coincidental closeness rather than a true binary system. Epsilon Microscopii lies 182±2 light years away, and is a white star of apparent magnitude 4.7, and spectral type A1V. Theta1 and Theta2 Microscopii make up a wide double whose components are splittable to the naked eye. Both are white A-class magnetic spectrum variable stars with strong metallic lines, similar to Cor Caroli. They mark the constellation's specimen slide.
Many notable objects are too faint to be seen with the naked eye. AX Microscopii, better known as Lacaille 8760, is a red dwarf which lies only 12.9 light-years from our solar system. At magnitude 6.68, it is the brightest red dwarf in the sky. BO Microscopii is a rapidly rotating star that has 80% the diameter of the Sun. Nicknamed "Speedy Mic", it has a rotation period of 9 hours 7 minutes. An active star, it has prominent stellar flares that average 100 times stronger than those of the Sun, and are emitted mainly in X-ray and ultraviolet spectra. AT Microscopii is a binary star system, both members of which are flare star red dwarfs. The system lies close to and may form a very wide triple system with AU Microscopii, a young star which appears to be a solar system in the making with a debris disk. The three stars are candidate members of the Beta Pictoris moving group, one of the nearest associations of stars that share a common motion through space.
The Astronomical Society of Southern Africa in 2003 reported that observations of four of the Mira variables in Microscopium were very urgently needed as data on their light curves was incomplete. Two of them—R and S Microscopii—are challenging stars for beginners, while the other two U and RY Microscopii are more difficult. Another red giant, T Microscopii, is a semiregular variable that ranges between magnitudes 7.7 and 9.6 over 344 days. Of apparent magnitude 11, DD Microscopii is a symbiotic star system composed of a orange giant of spectral type K2III and white dwarf in close orbit, with the smaller star ionizing the stellar wind of the larger star. The system is metal-poor. Combined with its high galactic latitude, this indicates that the star system has its origin in the galactic halo of the Milky Way.
HD 205739 is a yellow-white main sequence star of spectral type F7V that is around 1.22 times as massive and 2.3 times as luminous as the Sun. It has a Jupiter-sized planet with an orbital period of 280 days that was discovered by the radial velocity method. WASP-7 is a star of spectral type F5V and about 1.28 times as massive as the Sun, which has an apparent magnitude of 9.54. Its hot Jupiter planet—WASP-7b—was discovered by transit method and found to orbit the star every 4.95 days. HD 202628 is a sunlike star of spectral type G2V with a debris disk that ranges from 158 to 220 AU distant. Its inner edge is sharply-defined, indicating a probable planet orbiting between 86 and 158 AU from the star.
Deep sky objects
Describing Microscopium as "totally unremarkable", astronomer Patrick Moore concluded there was nothing of interest for amateur observers. NGC 6925 is a barred spiral galaxy of apparent magnitude 11.3 which is lens-shaped as it lies almost edge on to observers on Earth. It lies 3.7 degrees westnorthwest of Alpha Microscopii. NGC 6923 lies nearby and is a magnitude fainter still.
- While parts of the constellation technically rise above the horizon to observers between 45°N and 62°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.
- Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.
- Rubie, G. (1830). The British Celestial Atlas. London, United Kingdom: Baldwin & Cradock. pp. 36–37.
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- Wagman 2003, pp. 6-7.
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- Ridpath, Ian; Tirion, Wil (2007). Stars and Planets Guide. Princeton: Princeton University Press. pp. 184–85. ISBN 978-0-691-13556-4.
- "Epsilon Microscopii". SIMBAD. Retrieved 15 July 2012.
- Croswell, Ken (July 2003). "The Brightest Red Dwarf". Sky & Telescope. p. 32. Retrieved 15 July 2012.
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- Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. ISBN 978-0-939923-78-6.
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