PlanetStar Wiki
Constellations (11)
Ara, Centaurus, Chamaeleon, Circinus, Corona Australis, Crux, Lupus, Musca, Norma, Scorpius, Triangulum Australe
Abbreviation Sim
Genitive Simiani
Pronunciation Name: /'sim•ē•yon•is/
Genitive: /'sim•ē•yon•ē/
Symbolism the monkey
Midpoint right ascension 13h 22.84m
Midpoint declination −45° 41.98'
Northernmost border −08° 17.75'
Southernmost border −83° 07.20'
Westernmost border 07h 26.61m
Easternmost border 19h 19.08m
Quadrant SQ3
Crossed by Ecliptic
Autumn meridian
Winter meridian
Bordering caelregios Felis (N (W))
Malus (W)
Noctua (N (E))
Solarium (SE/S/SW)
Tarandus (NE)
Segments 33
Area 2962.656 sq. deg. (9th)
Proportion of the sky 71.817‰
Average constellation area 269.332 sq. deg. (10th)
Named stars 18
Stars in the figure 7
Naked eye stars
(m < 6.50)
BF stars 565
Bright stars
(m < 3.00)
Brightest star Alpha Centauri A (−0.01m)
Nearby stars
(D < 10.00 pc, 32.62 ly)
Nearest star Proxima Centauri (1.30 pc, 4.24 ly)
Messier objects 4
Full visibility range 6°N–90°S
Partial visibility range 81°N–6°N
Midnight culmination date April 10
Astrological sign 10/24–11/22
Solar sign 11/23–11/29

Simianus is a caelregio located in the third quadrant of the southern hemisphere at its midpoint, but it extends into the second and fourth quadrants. Simianus is the third smallest caelregio after Selachimorphus and Malus with an area of 2963 square degrees, covering about 72‰ of the sky. Simianus is divided into eleven constellations (listed in the infobox), including three famous constellations: Centaurus, Crux, and Scorpius.

Simianus contains the nearest star system Alpha Centauri to Earth as well as the Southern Cross, which is the most recognizable asterism in the southern sky. This caelregio also contains few recognizable doubles and multiples, as well as a couple of famous globular clusters.

Name and symbolism[]

Simianus is named after the Latin word for monkey. Simianus contains component constellations with symbolisms of animals occupying same habitat as monkeys, such as wolves (Lupus), chamaleons (Chamaeleon), scorpions (Scorpius), and flies (Musca).

Former name[]

Vexilius the flag was the former name for Simianus until December 2010.

Notable stars[]

Bright stars[]

A G-type main sequence Alpha Centauri A is the Simianus' brightest star and is also the fourth brightest overall at a magnitude of −0.01.

Antares is the brightest star in Scorpius at a magnitude of 1.09. It is a red supergiant containing a companion star. Antares is one of the four brightest stars within 5° of the ecliptic, the others are Spica in Noctua, Regulus in Felis, and Aldebaran in Araneus.

Sargas is an F-type bright giant located in Scorpius. Its magnitude is 1.86.

Atria is a K-type giant located in Triangulum Australe. Its magnitude is 1.93.

The Southern Cross[]

Acrux is a B-type main sequence 25,000 times more luminous than our Sun. Acrux is the Crux's brightest star and is the twelfth brightest star in the night sky at a magnitude of 0.77. Also Acrux is the southernmost first magnitude star of the sky. Acrux is the leading pointer to the south pole.

Becrux is a B-type subgiant. Its magnitude is 1.30, the second brightest star in Crux and 19th brightest star in the night sky.

Gacrux is the nearest red giant star at a distance of 89 light-years. Its magnitude is 1.63, the third brightest star in Crux. Gacrux is 30% more massive than our Sun but it is 84 times larger than our Sun. It is 1500 times more luminous than our Sun and is enriched with barium.

Decrux is a B-type subgiant 10,000 times more luminous than our Sun. It is the faintest member of the Southern Cross at a magnitude of 2.78.

Variable stars[]

In Scorpius, the variable star V907 Scorpii is an unique eclipsing binary star that it turns on and off caused by inclination changes by the gravity of a tertiary star. Antares is a type LC slow irregular variable star varying between 0.88 and 1.16 in magnitude.

Multiple stars[]

Alpha Centauri is a tertiary star system. It comprises of G-type, K-type, and M-type stars. The M-type star Proxima Centauri is the nearest star to the Sun at a distance of 4.24 light-years (1.30 parsecs). The separation between components A and B ranges from 11.2 AU to 35.6 AU with an orbital period of 79.91 years. Proxima Centauri orbits the binary at a distance of 13,000 AU with a period between 100,000 to 500,000 years. Despite that closest approach in binary system, the habitable zones (region around the star where liquid water is stable on the planet's surface) around both stars should be stable.

Another notable star system is Acrux, which is a binary system comprising of α1 and α2 Crucis. One of the pair α1 is a spectroscopic binary with a period of 76 days at a separation of about 1 AU. The binary period is at least 1500 years at a minimum distance of 430 AU, and may be much longer. Another nearby companion α3 Crucis at 90 arcseconds away from the binary pair may be just an optical closeness but not gravitationally bound. The proper motion suggest that α3 is moving further away from the main binary pair. α3 may be twice as distant as the main binary pair.

Double stars[]

Zeta Scorpii, a beautiful double star

Scorpius has a beautiful double star: Zeta Scorpii. ζ1 is a blue supergiant while ζ2 is an orange giant and is the brighter of the pair, thus ζ1 is 19.5 times more distant than ζ2, 2573 vs. 132 light-years. ζ1 is a member of the open cluster NGC 6231.

Another double star is Xi Centauri. This can be resolved using just the unaided eye with the separation of 0.66°, a bit more separated than the apparent diameter of the full moon. ξ2 is twice as distant as ξ1, 467 vs. 221 light-years.

Solar twin[]

The most Sun-like star known is 18 Scorpii. 18 Scorpii is similar to the Sun in terms of mass, radius, temperature, luminosity, metallicity, age, rotation period, and spectral type. The prospects for extraterrestrial life are very good. I spectulate that 18 Scorpii has 11 planets, three more than our Sun, including a forest planet located in its habitable zone.

Planetary systems[]

As of 2015, there are about 80 exoplanets known around nearly 60 stars in Simianus. The first example is PSR B1620-26 (P1 Sim) in Scorpius, which hosts the third oldest known planet at 12.7 billion years old that survived the supernova explosion. This planet, named Methuselah (PSR B1620-26 b, P11), orbits at a distance of 23 AU, placing between the orbits of Uranus and Neptune in our own solar system.

Another notable planetary system is Mu Arae (P4 Sim), which has four planets with the innermost is a midplanet and the outer three are mid-Jupiters. In Centaurus, 2M1207 (P11 Sim) is the first brown dwarf known to have a planet (named Lerna (2M1207b, P115)) which has mass 4.22 MJ and orbits at a distance of 41 AU.

In Scorpius, Gliese 667 C (P35 Sim) contains two planets, including the habitable planet Cresphontes (Gliese 667 Cc, P677). In Ara, Gliese 676 A (P36 Sim) contains four planets, the inner two are rocky or watery while the outer two are gaseous. 47 Lupi (P46 Sim) contains three confirmed planets, one super-Earth and two midplanets, all orbiting within 0.5 AU from the star. It is speculated that 47 Lupi contains 14 planets, six more planets than our solar system with the outermost planet orbiting at 50 AU, beyond the orbit of Pluto.

Alpha Centauri B (P49 Sim) contains the nearest known exoplanet, Ixionidae (Alpha Centauri Bb, P832). The planet masses 1.28 M, making it the lowest-mass planet yet discovered with the wobble method. The planet induces stellar wobble at just 51 cm/s, the lowest value ever measured with HARPS. Ixionidae takes just 3.236 days to orbit the star at an average distance of 6.261 gigameters. Although right now the planet is unconfirmed.

Notable deep sky objects[]

Simianus contains two famous globular clusters: Ptolemy Cluster (M7) in Scorpius and Omega Centauri (NGC 5139, C80) in Centaurus. Crux contains the Jewel Box Cluster (NGC 4755), which is an open cluster.

In Scorpius, there is the less famous globular cluster M4. This was the first globular cluster to have its stars resolved and is competing with NGC 6397 in Ara for the nearest globular clusters to the Solar System.

In Ara, there is the open cluster Westerlund 1 (also known as the Ara Cluster) visible to a large telescope. This cluster contains a lot of massive, blue stars including some 24 Wolf-Rayet stars. In fact, it is the most compact young star cluster not just in the Milky Way but the entire Local Group of galaxies. In Norma, there is the S Normae Cluster (NGC 6087, C89), which is a naked-eye open cluster with the variable star S Normae being the brightest member.

Scorpius contains the bipolar planetary nebula: the Butterfly Nebula (NGC 6302, C69); and it also contains the War and Peace Nebula (NGC 6357), which is a diffuse nebula, which contains the open cluster Pismis 24 which is home to several massive stars.

Centaurus contains the Boomerang Nebula (also known as the Bow Tie Nebula), which is a protoplanetary nebula. In this nebula, the temperature is only one kelvin above absolute zero, which is the coldest known place in the universe. Also in this constellation, there is the planetary nebula NGC 3918. In Norma, there is the bipolar nebula NGC 6164–5. This nebula glows red caused by the ultraviolet radiation from the massive central star HD 148937 ionizing hydrogen gas. This nebula is shaped by the star's magnetic field and fast rotation.

Yet another interesting nebula in Centaurus is the Running Chick Nebula (IC 2948), which is a bright emission nebula where new stars form. Embedded within the nebula made of glowing reddish cloud of hydrogen gas is the energetic young star cluster Collinder 249. Also in this constellation, there is the open cluster and emission nebula Running Chicken Nebula (also called the Lambda Centauri Nebula) (IC 2944, C100) featuring Bok globules called Thackeray's Globules with sites of active star formation.

Crux contains the Coalsack Nebula (C99), which is a dark nebula. Coalsack is the largest dark interstellar cloud in the sky. It masses 3500 Suns and stretches dozens of light-years.

In Scorpius, the Cat's Paw Nebula (NGC 6334), which is a red-colored emission nebula caused by ionized hydrogen, can be seen using a small telescope. Located in Musca, we find planetary nebulae, the Hourglass Nebula (MyCn 18) and the Spiral Planetary Nebula (NGC 5189). The Ant Nebula (Mz 3) is a bipolar planetary nebula located in Norma.

Also in Scorpius, there is the Blue Horsehead Nebula, which is a reflection nebula complex. The blue star marking the eye is the multiple star system Nu Scorpii. This complex includes the prominent blue reflection nebula IC 4592.

In Chamaeleon, there is the Space Tornado (also known as the Tornado Nebula) (HH 49/50), which is an unusually tube-shaped emission nebula. It is about 0.3 light-year or 2 trillion miles long, located about 480 light-years away in the star-formation region Chamaeleon I. Jets of particles emitted from young stars colliding with interstellar clouds in the presence of magnetic fields create this unique tubular spiral shape as seen in the image below. This Herbig-Haro object was discovered on January 12, 2006.

NGC 4622, which is an unique spiral galaxy, and Centaurus A (NGC 5128, C77), which is a radio elliptical or lenticular galaxy with unusual dust lane, can be found in Centaurus. It is the only galaxy with opposite rotations between inner and outer arms relative to the observer.

In Lupus, SN 1006 was a supernova seen from Earth in the year 1006. With a peak magnitude of −7.5, it was the brightest supernova in recorded history. The supernova was approximately 7200 light-years from Earth.


The Butterfly Nebula (NGC 6302, C69)

Omega Centauri (NGC 5139, C80)

The Coalsack Nebula (C99)

The globular cluster M4 (NGC 6121)

Westerlund 1 (also known as the Ara Cluster)

The planetary nebula NGC 3918

The Boomerang Nebula (also known as the Bow Tie Nebula)

The Cat's Paw Nebula (NGC 6334)

The Ant Nebula (Mz 3)

The War and Peace Nebula (NGC 6357)

The Running Chick Nebula (IC 2948)

The Blue Horsehead Nebula

The Hourglass Nebula (MyCn 18)

The bipolar nebula NGC 6164–5

The Running Chicken Nebula (also known as the Lambda Centauri Nebula) (IC 2944, C100)

The spiral galaxy NGC 4622

Centaurus A (NGC 5128, C77)

The Space Tornado (also known as the Tornado Nebula) (HH 49/50)

The Jewel Box Cluster (NGC 4755)

The supernova remnant SN 1006

The Spiral Planetary Nebula (NGC 5189)


In the northern hemisphere, Simianus can be visible from late winter till the dawn of summer. About half of this caelregio can be visible from mid-northern latitudes but all of it can only be visible from very low northern latitudes and in the southern hemisphere. For the Southern Cross (Crux) and the nearest star (α Cen) to be seen, it can only be viewed from south of 35°N, that means that the Southern Cross and α Cen would never be visible from places like Europe, northern and central Asia, and northern half of North America.

The Southern Cross is useful for navigation to southern observers because it points to the south celestial pole especially when the bright south pole star is not present, contrasting the bright north pole star Polaris located in Avis.


The Sun appears to briefly cross Simianus from November 23 till November 29: it crosses the only constellation Scorpius. This zodiacal caelregio is located between Noctua to the west and Tarandus to the east.

Simianus was formerly in the sign of zodiac from October 24 till November 22.