Microscopium
What is Microscopium?
Constellations· Southern spring · faint stars south of Capricornus. Microscopium is Lacaille's tribute to the microscope. Its stars are around fifth magnitude, so it looks like empty sky to the eye, but it holds AU Microscopii, a young star with a dusty disk that planet researchers study often.
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Stars of the figure
| Star | Magnitude |
|---|---|
| Alpha Microscopii | 4.9 |
The 1 brightest of the 2 stars used in the figure (1 lines). Lower magnitude means brighter.
Constellation basics
| Season | Aug–Oct evenings, low south; low from New York; only its northern part from London |
|---|---|
| Brightest star | γ Microscopii, mag 4.7 |
| How to find | directly south of Capricornus, west of Piscis Austrinus |
| Area rank | 66th of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Lacaille 8760 in Microscopium, a red dwarf at the naked-eye limit
About three quarters of the stars in the Milky Way are red dwarfs. They are smaller and cooler than the Sun and very dim, so although they are the commonest stars, the naked eye can hardly see any of them. Lacaille 8760 in Microscopium is the brightest of these red dwarfs in the night sky. It is about 13 light-years away and shines at magnitude 6.7.
Magnitude 6.7 is close to the faintest the human eye can see. So this star may be glimpsed without optical aid only under a very dark, clear sky, and usually needs binoculars or a telescope. It is also a flare star, whose surface occasionally erupts and briefly brightens it. That is why it also carries the variable-star name AX Microscopii.
The star's name includes Lacaille's own. It is there because Lacaille listed it in his catalogue while recording southern stars from the Cape of Good Hope in the 1750s. So inside the constellation he made to honour a scientific instrument, a star he himself recorded still carries his name. His catalogue listed about 10,000 stars of the southern sky.
The constellation in depth
Microscopium is one of the scientific-instrument constellations Lacaille added to the southern sky in the 1750s. It honours the compound microscope, which uses several lenses and was invented in the 17th century. Its brightest star is only magnitude 4.7, making it one of the faintest of the 88 constellations. From a city it can be hard to see even one of its stars.
Small and dim as it is, it holds a scientifically interesting star. AU Microscopii is a young red dwarf about 32 light-years away. It is surrounded by a thin disk of dust, which we see edge-on, so Hubble photographed it as a narrow line. Two planets have been confirmed inside the disk. Because it shows how planets form, it is studied often.
Gamma Microscopii is calculated to have come fairly close to the Sun long ago. About 3.8 million years ago it seems to have been only about 6 light-years away. The nearest star to the Sun today is a little over 4 light-years off, so back then Gamma would have shone very brightly in the night sky. Over long ages, stars keep approaching the Sun and then moving away again.
From mid-northern latitudes the northern part of Microscopium rises low above the southern horizon on September nights. Look directly below Capricornus, to the right of the bright star Fomalhaut. In the Sky view, set New York on a September night and scan the southern horizon, or pick a southern city. Turn on the constellation lines to see how its faint stars connect.
Frequently asked
- When can I see Microscopium?
- Microscopium is best seen in Aug–Oct evenings, low south; low from New York; only its northern part from London.
- How do I find Microscopium?
- To find Microscopium, look for directly south of Capricornus, west of Piscis Austrinus.
- What is the brightest star in Microscopium?
- The brightest star in Microscopium is Alpha Microscopii, at magnitude 4.9.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.