Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille.

[2] Bordered by Centaurus, Musca, Apus, Triangulum Australe, Norma and Lupus, Circinus lies adjacent to the Alpha and Beta Centauri stars.

It has the unusual spectral type A7 Vp SrCrEu, showing increased emissions of strontium, chromium and europium.

[8] Alpha Circini forms a binary star system with an orange dwarf companion of spectral type K5 and magnitude 8.5,[8] which with a separation of 5.7 arcseconds is only discernible with a telescope.

[6] Delta Circini is also a multiple star whose components have magnitudes of 5.1 and 13.4 and orbit around a common centre of gravity every 3.9 days.

The brighter component is a close eclipsing binary (specifically, a rotating ellipsoidal variable),[6] with a minor dip of magnitude (0.1).

[11] The two main components are separated by 50 arcseconds, resolvable to the naked eye for individuals with good vision and easily discernible with a telescope.

[6] T Circini has a B-type spectrum, ranging in magnitude from 10.6 to 9.3 over a period of 3.298 days,[19] although it is actually an eclipsing binary system rather than a pulsating star.

[27] Its two planets were discovered in 2011 through the radial velocity method: the smaller, HD 134060 b, has a mass of 0.0351 MJ (Jupiter masses) and orbits its star every 3.27 days, at 0.0444 AU;[28] the larger, HD 134060 c (0.15 MJ), orbits farther out at 2.226 AU, with a period of approximately 1161 days.

HD 129445 b, a Jupiter-like planet (1.6 MJ) discovered in 2010 via the radial velocity method, orbits this star at a distance of 2.9 AU, approximately every 1840 days.

Three open clusters and a planetary nebulae are found within the borders of Circinus, all visible with amateur telescopes of varying sizes.

NGC 5823, also called Caldwell 88,[6] is an 800-million-year-old open cluster, located 3500 light-years away and spanning a 12-light-year region along the constellation's northern border.

The dark nebula component is easily visible in a large amateur telescope, and it measures 12 by 5 arcminutes.

Observations of Circinus X-1 in July 2007 revealed the presence of X-ray jets normally found in black hole systems.

Recorded by Chinese observers in 185 AD, SN 185 was visible in the night sky for around eight months; its remnants, known as RCW 86, cover an area larger than the typical full moon.

[42] A white dwarf star in a close binary system can accumulate material from its companion until it ignites and blows off in a thermonuclear explosion, known as a nova.

[48][49] In 2011, Peter Jenniskens proposed that the debris trail of comet C/1969 T1 could intersect with the Earth's orbit and generate a meteor outburst coming from a radiant close to Beta Circini.