Intro to Constellation (5) Crux

Today, let us have a look at Crux (Also known as the Southern Cross), a small yet prominent constellation in the southern celestial hemisphere.

Name: Crux

Abbr: Cru

Chinese Name: 南十字座

Brightest Star: Alpha Crucis (0.87 m)

Visibility: 20 N to 90 S, prime in May

Crux is Latin for cross. There are four main bright stars in the constellation, which form a cross shape. Though Crux is the smallest of all 88 modern constellations, it has a significant influence on the culture of South Hemisphere nations and regions. You can find Crux on the national flags of Australia, New Zealand, and Brazil.

At present, one has to go to the regions south of around 20°N to find Crux. For ancient Greek, the task was much easier. At that time, people in Britain could easily see Crux as well. The stars of Crux have never rose again from the horizons of most European countries since 400 CE. A good news is that by the year 14000, we can see Crux in regions to the south of 45°N.

Notable Stars

The four bright stars that form the southern cross are \(\alpha\) Crucis, \(\beta\) Crucis, \(\gamma\) Crucis, and \(\delta\) Crucis.

\(\alpha\) Crucis or Acrux is a triple-star system. Its Chinese name is 十字架二. In the naked eye, the star appears to have a rich blue color. If you can load the image above, \(\alpha\) Crucis is the one in the bottom right corner.

\(\beta\) Crucis or Mimosa, 十字架三, is a blue-hued giant star. In the image, it is the blue star to the lower left of \(\alpha\) Crucis.

\(\gamma\) Crucis or Gacrux, 十字架一, is an optical double star. The primary star is a red-hued giant star, one of the closest red giants to Earth. In the above image, it is the orange dot on the left side.

\(\delta\) Crucis or Imai, 十字架四, is a blue-white hued star. It is the smaller blue dot to the upper right of \(\gamma\) Crucis.

Thus, the labeling of stars in Crux follows a clockwise order. One may also notice the tiny orange star between \(\delta\) Crucis and \(\alpha\) Crucis. That is the firth star of the cross, \(\epsilon\) Crucis.

Notable Systems And Objects

Within Crux, there is a prominent dark nebula, the Coalsack Nebula. It is easily visible to the naked eye as a dark patch in the southern Milky Way.

Jewel Box or Crucis Cluster (NGC 4755) is a small but bright open cluster. To the naked eyes, it appears to be a fuzzy star. If you observe it with a telescope, you may find it colorful.

Credit

Most of the contents are summarized from Wikipedia. You can click the images to reach the source websites.