Circinus Constellation


Circinus constellation is located in the southern sky. Its name means “the compass” in Latin, referring to the tool for drawing circles.

Circinus was created and first catalogued by the French astronomer Nicolas Louis de Lacaille in the 18th century.

Lacaille created the constellation to bridge the void between Triangulum Australe and the stars marking Centaurus‘ forefeet.

Circinus contains two well-known deep sky objects, the Circinus Galaxy and the x-ray source Circinus X-1.

FACTS, LOCATION & MAP

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Circinus Constellation Map, by IAU and Sky&Telescope magazine

Circinus is the fourth smallest constellation in the sky, 85th in size, occupying an area of only 93 square degrees.

It lies in the third quadrant of the southern hemisphere (SQ3) and can be seen at latitudes between +30° and -90°.

The neighboring constellations are Apus, Centaurus, Lupus, Musca, Norma, and Triangulum Australe.

Circinus has one star with known planets and contains no Messier objects.

The brightest star in the constellation is Alpha Circini.

There are no meteor showers associated with the constellation.

Circinus belongs to the Lacaille family of constellations, along with Antlia, Caelum, Fornax, Horologium, Mensa, Microscopium, Norma, Octans, Pictor, Reticulum, Sculptor, and Telescopium.


STORY

There are no myths associated with Circinus. The constellation was named after the drafting tool used for drawing circles (not after a mariner’s compass, which is represented by the constellation Pyxis).

It is depicted as a pair of dividing compasses used by draughtsmen to measure distances.

Lacaille originally named the constellation le Compas and placed it next to Triangulum Australe, which he depicted as a surveyor’s level, to fill the void between several existing constellations in the south.

MAJOR STARS IN CIRCINUS

α Circini (Alpha Circini)

Alpha Circini is the brightest star in the constellation, with an apparent visual magnitude of 3.19. It is a visual binary, with a faint companion. It is classified as a variable star, belonging to the class of rapidly oscillating Ap stars. It lies about 53.5 light years from Earth.

β Circini (Beta Circini)

Beta Circini is the second brightest star in Circinus, with an apparent magnitude of 4.069. It is a main sequence star belonging to the spectral class A3Va. It is approximately 97 light years distant.

γ Circini (Gamma Circini)

Gamma Circini is another binary star in the constellation. It is composed of a pair of blue and yellow stars.

HD 129445

HD 129445 is a star belonging to the spectral class G6V, notable for having a planet in its orbit. The planet was named HD 129445 b. Its existence was confirmed by 17 doppler velocity tests conducted as part of the Magellan Planet Search Program. The star has an apparent magnitude of 8.8 and is 220 light years distant.

DEEP SKY OBJECTS IN CIRCINUS

Circinus Galaxy

The Circinus Galaxy is a spiral galaxy approximately 13 million light years distant. The galaxy is notable for the motions of gas that form two rings inside it. One of the rings is a site of massive star forming activity.

The galaxy was discovered in 1975. It is an active galaxy with a black hole-powered core.

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Supernova SN 1996cr in the Circinus Galaxy, photo: Smithsonian Institution

Circinus X-1

Circinus X-1 is an X-ray double star composed of a neutron star and a main sequence star, with the former orbiting the latter. The system is located approximately 20,000 light years away. The X-ray source was discovered on June 14, 1969, during a scan of the region of the sky occupied by the constellations Circinus, Norma and Lupus.

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Circinus X-1, photo: X-ray: NASA, CXC, Univ. of Wisconsin-Madison, S.Heintz et al.; Illustration: NASA, CXC, M.Weiss

NGC 5315

NGC 5315 is a bright planetary nebula in Circinus. Like all other planetary nebulae, it was created when a star in the final stages of its life shed its outer layers and cast them off into space.

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NGC 5315, photo: Hubble Space telescope, NASA, ESA