Circinus

by Tammy Plotner on October 28, 2008

Circinus

Circinus

The small, faint southern constellation Circinus was created by Nicholas de Lacaille during his stay at the Cape of Good Hope in the mid-18th century and has endured into the 88 modern constellation recognized by the IAU. It has no bright stars and consists of only 3 main stars and 9 Bayer/Flamsteed designated stars and is bordered by the constellations Centaurus, Musca, Apus, Triangulum Australe, Norma and Lupus. Circinus is visible for observers at latitudes between +10° and ?90° and is best seen at culmination during the month of June.

Because Circinus was unknown to the ancient Greeks and Romans, it has no mythology associated with it. The three brightest stars form a narrow triangle. The shape is reminiscent of a drawing (or drafting) compass of the sort used to plot sea and sky charts. Nicolas Louis de Lacaille had a fascination with secular science and the thought of naming a constellation – or asterism of stars – after a science tool fascinated him. In this case, Circinus represents a drafting tool used in navigation, mathematics, technical drawing, engineering drawing, in cartography (drawing maps) – and which many elementary school age children use to learn to draw circles and in geometry to bi-sect lines, draw arcs and so forth. In this case, the device should not be confused with Pyxis, a constellation associated with a ship’s compass… despite the similarity in names with the Latin language!

Now take out your binoculars for a look at Alpha Circini – a great visual double star. Located about 53.5 light years from Earth, this stellar pair isn’t physically related but does make a unique target. The brighter of the two, Alpha, is a F1 Bright Yellow Dwarf that is a slight variable star. This contrasts very nicely with the fainter, red companion.

For the telescope, take a look at Gamma Circini – a faint star a little over five hundred light years from the Solar System. In the sky, it lies in the Milky Way, between bright Alpha Centauri and the Southern Triangle. Gamma Circini is a binary system, containing a blue giant star with a yellow, F-type, companion. Gamma is unique because it possess a stellar magnetic buoyancy!

For larger binoculars and telescopes, have a look at galactic star cluster NGC 5823 (RA 15 : 05.7 Dec -55 : 36). This dim cluster will appear to have several brighter members which are actually foreground stars, but does include Mira-type variable Y Circini. While it will be hard to distinguish from the rich, Milky Way star fields, you will notice an elliptical shaped compression of stars with an asterism which resembles and open umbrella.

For large telescopes, check out ESO 97-G13 – the “Circinus Galaxy”. Located only 4 degrees below the Galactic plane, and 13 million light-years away (RA 14h 13m 9.9s Dec 65° 20? 21?), this Seyfert Galaxy is undergoing tumultuous changes, as rings of gas are being ejected from the galactic core. While it can be spotted in a small telescope, science didn’t notice it until 25 years ago!

Sources: Chandra Observatory, Wikipedia
Charts Courtesy of Your Sky.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

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