Amidst all the bright constellations, stars and galaxies visible in the night sky, there is a small, tiny constellation identified by a French astronomer Augustin Royer in 1679. It is the constellation Crux. Crux ‘the Cross’ or also referred to as ‘the Southern Cross’ holds an important place in the history of the southern hemisphere. The bright stars in this brilliant cross make it one of the most familiar sights to the southern hemisphere observers. Many southern hemisphere nations including Australia, New Zealand, Brazil, Papua New Guinea and regions of Chile and Argentina have used it as an insignia on their flags and stamps. Crux was a part of the Centaurus constellation. In the year 1679, Augustin Royer, a French astronomer formally separated Crux from Centaurus. Some historians also credit the Dutch astronomer Petrus Plancius for discovering this constellation in the year 1613. The constellation belongs to the Hercules family of constellations and is best visible in the month of May. Let us discuss Crux in detail.
Some notable stars of this constellation are:
- Acrux (Alpha Crucis): Acrux is the brightest star in Crux and is the 12th brightest star in the sky. It has a visual magnitude of about 0.77 and is about 320 light years away. It is basically a multiple star system comprising of Alpha Crucis–1, a B class giant and Alpha–2 Crucis, a B class dwarf. Both of these stars are very hot and their respective brightness is about 25,000 and 16,000 times that of the Sun.
- Mimosa (Beta Crucis): Mimosa is the brightest star in the constellation and is the 20th brightest star in the night sky. It has a visual magnitude of 1.30 and is about 350 light years away from the solar system. The estimated age of Mimosa is believed to be 10 million years. It also represents the State of Rio de Janeiro on the flag of Brazil.
- Gacrux (Gamma Crucis): It is basically a red giant with a visual magnitude of 1.59 and is about 88 light years away from the earth. Gacrux is the third brightest star in this constellation. It is a binary star with a primary component. The companion star is about 400 light years away from the earth.
- δ Crucis (Delta Crucis): Delta Crucis is a sub giant in this constellation with a visual magnitude of 2.775 and is about 360 light years away.
- Z Crucis (Zeta Crucis): It is a double star composed of a blue–white dwarf and a faint companion. Zeta Crucis has a visual magnitude of 4.04 and is about 360 light years away.
- e Crucis (Epsilon Crucis): Epsilon Crucis is an orange giant in this constellation. It has a visual magnitude of about 3.56 and is about 228 light years away from the earth.
- θ Crucis (Theta Crucis): Theta Crucis is a designation shared by two star systems. Theta–1 Crucis is basically a spectroscopic double, with a visual magnitude of 4.30 and is about 230 light years away. Theta–2 Crucis is also a spectroscopic binary star, has a visual magnitude of 4.72 and is about 750 light years away from the solar system.
- λ Crucis (Lambda Crucis): Lambda Crucis is a blue–white dwarf in this constellation. It has a visual magnitude of 4.6 and is about 360 light years away from the solar system. Its brightness varies by 0.02 magnitudes over a period of 0.3951 days.
- i Crucis (Iota Crucis): Iota Crucis is an orange giant in this Constellation, with a visual magnitude of 4.69 and is about 125 light years away. Iota Crucis also has an optical companion; it has a magnitude of 10.8.
- BZ Crucis: BZ Crucis is a B class sub giant portraying emission lines in its spectrum. It has a visual magnitude of 5.316 and is about 1,000 light years away. BZ Crucis lies behind the Coalsack Nebula.
- NGC 4349-127: It is basically a red giant star in this constellation, which is about 20 times as massive as Jupiter. It has a visual magnitude of 7.4 and is about 7,097 light years away. Its companion star is believed to be a brown dwarf; it was initially discovered in the year 2007.
The deep sky objects of Crux include:
- Coalsack Nebula (Caldwell 99): It is basically a famous dark nebula, which is seen as a large dark patch in the southern region of the Milky Way. It stretches across nearly 7°x 5° of the sky. Crossing its neighbouring constellations Musca and Centaurus, Coalsack Nebula is about 600 light years away from the earth.
- The Jewel Box (NGC 4755, Caldwell 94): The Jewel Box is an open cluster in Crux. It is one of the youngest clusters ever discovered. The estimated age of the cluster is believed to be only 14 million years old. The Jewel Box has a visual magnitude of 4.2 and is about 6,449 light years away from the solar system. The cluster comprises of about hundred stars and can only be observed from the southern hemisphere. In this cluster, the dominant star is Kappa Crucis (HD 111973), a red supergiant and has a visual magnitude of about 5.98.
Crux lies in the third quadrant of the southern hemisphere and can be seen at latitudes between +20° and -90°.
Crux occupies an area of only 68 square degrees and is the smallest of all the 88 constellations.
There are no Roman or Greek myths associated with Crux as it is not visible from most latitudes in the northern hemisphere. It was merely used by the explorers of the southern hemisphere to point south since and is not marked by any bright star.
Crux is surrounded by constellations like Centaurus and Musca.
