The constellation's brightest star isGamma Microscopii ofapparent magnitude 4.68, a yellow giant 2.5 times the Sun's mass located 223 ± 8 light-years distant. It passed within 1.14 and 3.45 light-years of the Sun some 3.9 million years ago, possibly disturbing the outer Solar System. Three star systems—WASP-7,AU Microscopii andHD 205739—have been determined to haveplanets, while other star —the Sun-like starHD 202628— has adebris disk. AU Microscopii and the binary red dwarf systemAT Microscopii are probably a wide triple system and members of theBeta Pictoris moving group. Nicknamed "Speedy Mic",BO Microscopii is a star with an extremely fast rotation period of 9 hours, 7 minutes.
Microscopium is a small constellation bordered byCapricornus to the north,Piscis Austrinus andGrus to the east,Sagittarius to the west, andIndus to the south, touching onTelescopium to the southwest. The recommended three-letter abbreviation for the constellation, as adopted by theInternational Astronomical Union in 1922, is "Mic".[1] The official constellation boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined by a polygon of four segments (illustrated in infobox). In theequatorial coordinate system, theright ascension coordinates of these borders lie between20h 27.3m and21h 28.4m, while thedeclination coordinates are between −27.45° and −45.09°.[2] The whole constellation is visible to observers south of latitude45°N.[3][a] Given that its brightest stars are of fifth magnitude, the constellation is invisible to the naked eye in areas with light polluted skies.[4][b]
French astronomerNicolas-Louis de Lacaille charted and designated ten stars with theBayer designationsAlpha through toIota in 1756. A star in neighbouring Indus that Lacaille had labelled Nu Indi turned out to be in Microscopium, so Gould renamed itNu Microscopii.Francis Baily considered Gamma and Epsilon Microscopii to belong to the neighbouring constellation Piscis Austrinus, but subsequent cartographers did not follow this.[6] In his 1725Catalogus Britannicus, John Flamsteed labelled the stars 1, 2, 3 and 4 Piscis Austrini, which became Gamma Microscopii,HR 8076,HR 8110 and Epsilon Microscopii respectively.[7] Within the constellation's borders, there are 43 stars brighter than or equal toapparent magnitude 6.5.[c][3]
Depicting the eyepiece of the microscope isGamma Microscopii,[8] which—at magnitude of 4.68—is the brightest star in the constellation. Having spent much of its 620-million-year lifespan as a blue-whitemain sequence star, it has swollen and cooled to become a yellowgiant ofspectral type G6III, with a diameter ten times that of the Sun.[9] Measurement of its parallax yields a distance of 223 ± 8 light years from Earth.[10] It likely passed within 1.14 and 3.45 light-years of the Sun some 3.9 million years ago, at around 2.5 times the mass of the Sun, it is possibly massive enough and close enough to disturb theOort cloud.[11]Alpha Microscopii is also an ageing yellow giant star of spectral type G7III with an apparent magnitude of 4.90.[12] Located 400 ± 30 light-years away from Earth,[13] it has swollen to 17.5 times the diameter of the Sun.[14] Alpha has a 10th magnitude companion, visible in 7.5 cm telescopes,[15][16] though this is a coincidental closeness rather than a true binary system.[14]Epsilon Microscopii lies 166 ± 5 light-years away,[17] and is a white star of apparent magnitude 4.7,[16] and spectral type A1V.[18]Theta1 andTheta2 Microscopii make up a wide double whose components are splittable to the naked eye. Both are white A-classmagnetic spectrum variable stars with strong metallic lines, similar toCor Caroli. They mark the constellation's specimen slide.[8]
Many notable objects are too faint to be seen with the naked eye. AX Microscopii, better known asLacaille 8760, is ared dwarf which lies only 12.9 light-years from theSolar System. At magnitude 6.68, it is the brightest red dwarf in the sky.[19]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.[20] An active star, it has prominentstellar flares that average 100 times stronger than those of the Sun, and are emitting energy mainly in the X-ray and ultraviolet bands of the spectrum.[21] It lies 218 ± 4 light-years away from the Sun.[22]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 withAU Microscopii,[23] a young star which has aplanetary system in the making with adebris disk. The three stars are candidate members of theBeta Pictoris moving group, one of the nearestassociations of stars that share a common motion through space.[24]
TheAstronomical Society of Southern Africa in 2003 reported that observations of four of theMira variables in Microscopium were very urgently needed as data on their light curves was incomplete.[25] Two of them—R andS Microscopii—are challenging stars for novice amateur astronomers,[26] and the other two,U andRY Microscopii, are more difficult still.[25] Another red giant,T Microscopii, is asemiregular variable that ranges between magnitudes 7.7 and 9.6 over 344 days.[27] Of apparent magnitude 11,DD Microscopii is asymbiotic star system composed of an orange giant of spectral type K2III andwhite dwarf in close orbit, with the smaller star ionizing the stellar wind of the larger star. The system has a lowmetallicity. Combined with its high galactic latitude, this indicates that the star system has its origin in thegalactic halo of theMilky Way.[28]
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 theradial velocity method.[29]WASP-7 is a star of spectral type F5V with an apparent magnitude of 9.54, about 1.28 times as massive as the Sun. Itshot Jupiter planet—WASP-7b—was discovered bytransit method and found to orbit the star every 4.95 days.[30]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.[31]
Describing Microscopium as "totally unremarkable", astronomerPatrick Moore concluded there was nothing of interest for amateur observers.[33]NGC 6925 is abarred spiral galaxy of apparent magnitude 11.3 which is lens-shaped, as it lies almost edge-on to observers on Earth, 3.7 degrees west-northwest of Alpha Microscopii.[34]SN 2011ei, aType II Supernova in NGC 6925, was discovered by Stu Parker in New Zealand in July 2011.[35]NGC 6923 lies nearby and is a magnitude fainter still.[36] TheMicroscopium Void is a roughly rectangular region of relatively empty space, bounded by incomplete sheets of galaxies from other voids.[37] TheMicroscopium Supercluster is an overdensity of galaxy clusters that was first noticed in the early 1990s. The component Abell clusters3695 and3696 are likely to be gravitationally bound, while the relations of Abell clusters3693 and3705 in the same field are unclear.[38]
Microscopium lies in a region where Ptolemy had listed six 'unformed' stars behind the tail of Piscis Austrinus.[40]Al-Sufi did not include these stars in his revision of theAlmagest, presumably because he could not identify them.[41] Microscopium was introduced in 1751–52 by Lacaille with the French namele Microscope,[42][43] after he had observed and catalogued 10,000 southern stars during a two-year stay at theCape of Good Hope. He devised fourteen new constellations in uncharted regions of theSouthern Celestial Hemisphere not visible from Europe. All but one honoured instruments that symbolised theAge of Enlightenment.[44] Commemorating thecompound microscope,[40] the Microscope's name had been Latinised by Lacaille toMicroscopium by 1763.[42]
^While parts of the constellation technically rise above the horizon to observers between 45°N and62°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.[3]
^Objects of magnitude 5.0 are barely visible to the unaided eye in the night skies of city-suburban transition areas.[5]
^Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.[5]
^abMotz, Lloyd; Nathanson, Carol (1991).The Constellations: An Enthusiast's Guide to the Night Sky. London: Aurum Press. pp. 369–370.ISBN978-1-85410-088-7.
^Kaler, James B."Gamma Mic".Stars. Retrieved13 July 2012.
^abCooper, Tim (2003). "Presidential address: Amateur Observations – Successes and Opportunities".Monthly Notes of the Astronomical Society of Southern Africa.62:234–240.Bibcode:2003MNSSA..62..234C.
^Maurellis, A.; Fairall, A.P.; Matravers, D.R.; Ellis, G.F.R. (1990). "A two-dimensional sheet of galaxies between two southern voids".Astronomy and Astrophysics.229 (1):75–79.Bibcode:1990A&A...229...75M.ISSN0004-6361.
^Molau, Sirko; Kac, Javor; Berko, Erno; Crivello, Stefano; Stomeo, Enrico; Igaz, Antal; Barentsen, Geert (July 2012). "Results of the IMO Video Meteor Network".WGN, Journal of the International Meteor Organization.40 (5):181–186.Bibcode:2012JIMO...40..181M.
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.ISBN978-0-939923-78-6.
