The Crux con­stel­la­tion is the small­est out of all the 88 mod­ern con­stel­la­tions. It’s name comes from the latin trans­la­tion of “Cross”, which is reflect­ed in it’s cross shaped aster­ism com­mon­ly known as the South­ern Cross. The Crux became a con­stel­la­tion in it’s own right in 1679.

The five main stars of Crux that com­prise the South­ern Cross aster­ism are Acrux, Mimosa, Gacrux, Imai and Ginan, and there are cur­rent­ly only two stars in Crux that have been dis­cov­ered to host plan­ets. There are no Messier objects in the con­stel­la­tion of Crux, how­ev­er there are many inter­est­ing stars and oth­er deep-sky objects such as Coal­sack Neb­u­la or the Jew­el Box Clus­ter.

The Crux con­stel­la­tion is asso­ci­at­ed with many sto­ries and makes an appear­ance in many mytholo­gies in the south­ern hemi­sphere. It is par­tic­u­lar­ly impor­tant in Aus­tralia and New Zealand, because it is cir­cum­po­lar and can be seen through­out the year.

History And Mythology Of The Crux Constellation

The ancient Greeks con­sid­ered Crux to be part of the con­stel­la­tion of Cen­tau­rus. How­ev­er, the French astronomer, Augustin Roy­er, sep­a­rat­ed Crux from Cen­tau­rus. That being said, some his­to­ri­ans and astronomers cred­it Dutch astronomer Petrus Plan­cius for cre­at­ing the con­stel­la­tion in 1613, as it was pub­lished by Jakob Bartsch in 1624.

The ancient Greeks saw Crux before it’s stars dropped below the hori­zon for Europe and most of the north­ern hemi­sphere. Chris­tians saw the sig­nif­i­cance in this and linked the dis­ap­pear­ance of the cross from the sky with the cru­ci­fix­ion of Christ.

Location Of The Crux Constellation

As we men­tioned above, the Crux con­stel­la­tion is the small­est out of all the 88 mod­ern con­stel­la­tions. It spreads out for around 68 square degrees in the sky.

It is vis­i­ble between +20° and ‑90° in the south­ern hemi­sphere and it is cir­cum­po­lar south of 34°S, this means that it nev­er sets below the hori­zon. The Crux con­stel­la­tion is best seen a 9pm, dur­ing May. It’s right ascen­sion is 12.6h and it’s dec­li­na­tion is ‑60°.

The neigh­bor­ing con­stel­la­tions around Crux are Cen­tau­rus and Mus­ca and it belongs to the Her­cules fam­i­ly of con­stel­la­tions.

Notable Stars

The South­ern Cross aster­ism stars — Acrux, Mimosa, Gacrux, Imai and Ginan — are the bright­est stars in the Crux con­stel­la­tion.

Acrux

Acrux, also known as Alpha Cru­cis, is the bright­est star in the con­stel­la­tion of Crux, and the 13th bright­est star in the night sky. How­ev­er, it can also be the 12th bright­est star in the night sky, due to its vari­abil­i­ty in bright­ness.

Acrux is a mul­ti­ple star sys­tem. The pri­ma­ry star is a blue-white sub­giant star locat­ed at around 321 light-years away from the Sun, and the sec­ondary star is a blue dwarf.

The pri­ma­ry star, Acrux A, is around 25,000 times brighter than our Sun and has 1780% of our Sun’s mass. Acrux B the sec­ondary star, is 16,000 times brighter than our Sun and has 552% of our Sun’s mass.

Acrux A is also big­ger than our Sun, hav­ing 780% of our Sun’s radius. The sec­ondary star Acrux B has 540% of our Sun’s radius. Both stars are hot­ter than the Sun, too, with Acrux A hav­ing a sur­face tem­per­a­ture of 24,000 K and Acrux B hav­ing a sur­face tem­per­a­ture of 28,000 K.

Gacrux

Gacrux, also known as Gam­ma Cru­cis, is the third bright­est star in the con­stel­la­tion of Crux, and the 25th bright­est star in the night sky. It is locat­ed around 88.6 light-years away from the Sun, yet is the near­est M‑class giant star to it.

Gacrux is around 820 times brighter than our Sun, and has 150% of its mass and 840% of its radius. It has an appar­ent mag­ni­tude of +1.64. It is also the near­est red giant to the solar sys­tem.

Imai

Imai is the fourth bright­est star in the con­stel­la­tion of Crux. Des­ig­nat­ed as Delta Cru­cis, it is a blue-white sub­giant star with an appar­ent mag­ni­tude of 2.79.

Imai is around 10,000 times brighter than our Sun, and has 890% of its mass and 800% of its radius. It has a tem­per­a­ture of around 22,570 K. It is also a fast-spin­ning star with a rota­tion­al veloc­i­ty of around 210 km/130.4 miles per sec­ond.

Mimosa

Des­ig­nat­ed Beta Cru­cis, Mimosa is the sec­ond bright­est star in the con­stel­la­tion of Crux and the 20th bright­est star in the night sky. It has an appar­ent mag­ni­tude of 1.25 and is locat­ed around 280 light-years away from Earth.

Mimosa is around 34,000 times brighter than our Sun. It has 1600% of its mass and 840% of its radius. It is also quite a young star in com­par­i­son to oth­ers, hav­ing an esti­mat­ed age between 8 to 11 mil­lion years.

Ginan

Ginan, also known as Epsilon Cru­cis, is locat­ed around 230 light-years away from Earth. It is the fifth bright­est star in the con­stel­la­tion of Crux and has an appar­ent mag­ni­tude of 3.58. It is an orange-hued star that is 302 times brighter than our Sun.

Ginan has 152% of the Sun’s mass and around 2841% of its radius. It is evolv­ing away from the main sequence and thus it will con­tin­u­ous­ly expand.

Other Stars

There are also many oth­er stars in the Crux con­stel­la­tion. Four of them can be seen with the naked-eye.

Zeta Crucis

Zeta Cru­cis is a bina­ry star sys­tem that is locat­ed around 360 light-years away from us. It is vis­i­ble to the naked-eye and has an an appar­ent mag­ni­tude of 4.04.

The pri­ma­ry star is a B‑type main sequence star. It is 737 times brighter than our Sun and has 640% of its mass. It is also cool­er than our Sun.

Theta Crucis

Theta Cru­cis is locat­ed around 850 light-years away from us. It has an appar­ent mag­ni­tude of 4.7. Theta Cru­cis is a spec­tro­scop­ic bina­ry star and it’s pri­ma­ry star is 809 times brighter than our Sun. It also has sys­tem con­sist­ing of a B‑type main-sequence blueish-white star, as well as a Cephei vari­able star.

Lambda Crucis

Lamb­da Cru­cis is locat­ed around 384 light-years away from us and has an appar­ent mag­ni­tude of 4.62. It is near the con­stel­la­tion bor­der with Cen­tau­rus and is a sus­pect­ed Beta-Cephei vari­able star.

It is 790 times brighter than our Sun and has 300% of its radius and around 500% of its mass.

Iota Crucis

Iota Cru­cis is locat­ed at around 125 light-years away from Earth as has an appar­ent mag­ni­tude of 4.69. It is a wide dou­ble star that appears with an orange hue.

It is around 24 times brighter than our Sun and has 726% of its radius. Iota Cru­cis is also an age­ing star with a sur­face tem­per­a­ture of around 4,824 K.

BZ Crucis

BZ Cru­cis is a Be star clas­si­fied as a B1IVe class star, a B class sub­giant show­ing emis­sion lines in its spec­trum. It has an appar­ent mag­ni­tude of 5.316 and is approx­i­mate­ly 1,000 light years away from us.

BZ Cru­cis is an X‑ray source and aa Gam­ma Cas­siopeiae type vari­able star, which means it is a shell star that has a cir­cum­stel­lar gas disk around the equa­tor.

NGC 4349–127

NGC 4349–127 is a red giant star almost 20 times as mas­sive as Jupiter. It is locat­ed around 7,097 light years from Earth and has an appar­ent mag­ni­tude of 7.4 and an absolute mag­ni­tude of ‑4.3. It was first dis­cov­ered in 2007.

Deep Sky Objects

There are two main Deep Sky Objects in Crux Con­stel­la­tion — Coal­sack Neb­u­la and The Jew­el Block Clus­ter.

Coalsack Nebula

The Coal­sack Neb­u­la, also known as the South­ern Coal­sack or Cald­well 99, is a famous dark neb­u­la, eas­i­ly seen as a large dark patch in the south­ern region of the Milky Way. It obscures the stars as they cross their south­ern­most region of the sky, east of Acrux.

It stretch­es near­ly 7° by 5° and cross over into the neigh­bour­ing con­stel­la­tions, Cen­tau­rus and Mus­ca. The neb­u­la is about 600 light years dis­tance from Earth and has a radius of between 30 and 35 light years.

The Jewel Block Cluster

The Jew­el Box Clus­ter, also known as Kap­pa Cru­cis Clus­ter, NGC 4755, or Cald­well 94 is esti­mat­ed to be about 14 mil­lion years old although it is one of the youngest clus­ters ever dis­cov­ered. It was first dis­cov­ered by French astronomer Nico­laus Louis de Lacaille on his trip to South Africa in 1751.

It has around 100 stars and the total inte­grat­ed mag­ni­tude of the clus­ter is 4.2. The clus­ter is locat­ed around 1.0° south­east of the star Mimosa and is around 6,440 light years away from us. It can only be seen by the south­ern hemi­sphere.

Extra Facts

• Acrux, Gacrux and Mimosa are known as the South­ern Point­ers as they are used togeth­er find the South Celes­tial Pole.
• With­in the Crux con­stel­la­tion, there are around 49 stars that are brighter or equal to appar­ent mag­ni­tude 6.5.
• A total of 15 of the 23 bright­est stars in Crux are spec­tral­ly blue-white B‑type stars.
• The South­ern Cross aster­ism is rep­re­sent­ed on the Aus­tralian flag. Its stars are fea­tured on the flag of Brazil.
• The con­stel­la­tion of Crux was invis­i­ble for most of Europe in 400 AD. Euro­peans did not redis­cov­er Crux until the great naval expe­di­tions of the late 15th and ear­ly 16th cen­turies.
• The Coal­sack Neb­u­la rep­re­sent­ed the head of the emu in the sky in Aus­tralian abo­rig­i­nal astron­o­my. Among the War­daman peo­ple, it is said to be the head and shoul­ders of a law-man watch­ing the peo­ple to ensure they do not break tra­di­tion­al law.

Images:

• Crux 1 – http://www.astronomytrek.com/star-constellation-facts-crux/
• Crux 2 – https://in-the-sky.org/data/constellation.php?id=31
• Acrux – https://www.constellation-guide.com/the-southern-cross/
• Gacrux – https://www.star-facts.com/gacrux/
• Imai – https://www.star-facts.com/imai/
• Ginan – https://www.star-facts.com/ginan/
• Theta Cru­cis – https://theskylive.com/sky/stars/theta1-crucis-star
• Lamb­da Cru­cis – https://theskylive.com/sky/stars/lambda-crucis-star
• NGC 4349–127 – https://en.wikipedia.org/wiki/NGC_4349
• Coal­sack Neb­u­la – https://astronomynow.com/2015/10/14/zooming-into-the-coalsack-nebula/
• The Jew­el Block Clus­ter – https://en.wikipedia.org/wiki/Jewel_Box_(star_cluster)
• Some Images cre­at­ed with the NightVi­sion app – https://www.nvastro.com/nvj.html
• Some Images cre­at­ed with the Stelvi­sion Sky Map https://www.stelvision.com/en/sky-map/

<a href=“https://theplanets.org/constellations/crux-constellation/”>Crux Con­stel­la­tion – Facts & Features</a>