The Microscopium Constellation

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 Latinised form of the Greek word for a microscope. Its stars are faint and hardly visible from most of the non-tropical Northern Hemisphere. The constellation is bordered by Capricornus to the north, Piscis Austrinus and Grus to the west, Sagittarius to the east, and Indus to the south touching on Telescopium to the southeast. 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 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.

French astronomer Nicolas Louis de 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 subsequent cartographers did not follow this. In his 1725 Catalogus 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. Within the constellation’s borders, there are 43 stars brighter than or equal to apparent magnitude 6.5. Depicting the eyepiece of the microscope is Gamma Microscopii, which—at a 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. At around 2.5 times the mass of the Sun, it likely passed within 1.14 and 3.45 light-years of the Sun some 3.9 million years ago, possibly massive enough and close enough to disturb the Oort cloud. 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.

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 with an apparent magnitude of 9.54, about 1.28 times as massive as the Sun. 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 sun-like 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.

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, 3.7 degrees west-northwest of Alpha Microscopii. SN 2011ei, a Type II Supernova in NGC 6925, was discovered by Stu Parker in New Zealand in July 2011. NGC 6923 lies nearby and is a magnitude fainter still. The Microscopium Void is a roughly rectangular region of relative space, bounded by incomplete sheets of galaxies from other voids. The Microscopium Supercluster is an overdensity of galaxy clusters that was first noticed in the early 1990s. The component Abell clusters 3695 and 3696 are likely to be gravitationally bound, while the relations of Abell clusters 3693 and 3705 in the same field are unclear.

The Microscopids are a minor meteor shower that appears from June to mid-July. Credit: Wikipedia.