Acrux. The Brightest Star in the Southern Cross – Everything You Need to Know

Acrux, also known as Alpha Crucis, is the brightest star in the constellation Crux and the 13th brightest star in the night sky. This blue subgiant star is fascinating for astronomers and stargazers.

However, because it is located in the Southern Hemisphere, it is not visible from most of North America. In this article, we will discuss the physical characteristics of Acrux, its location, its significance in history and culture, and the future of this star system.

What is Acrux?

Acrux is a multiple system located in the constellation of the Crux. Although it looks like a single bright star to the naked eye, it is at least three stars that are gravitationally connected.

Interesting facts about Acrux

• Other names: Alpha Crucis, Alf01 Cru, HD 108248
• Spectral type: B0.5IV + B1V
• Distance from the Earth: 321 light years
• Temperature: 28,840 K and 28,000 K
• Brightness: 30,303 times brighter than the Sun
• Radius: 7.3 times larger than the Sun (the second is 5.3 times larger than the Sun)
• Mass: 17.8 times larger than the Sun (the second is 15.5 times larger than the Sun)
• Apparent stellar magnitude: 0,77
• Absolute stellar magnitude: -3,77
• Constellations: Crux

Acrux in the constellation of the Crux

Crux is one of the most famous constellations in the Southern Hemisphere. It is best seen from locations south of 27° north latitude, i.e., in Australia, New Zealand, South America, South Asia, and sub-Saharan Africa.

Acrux is located at the base of the Crux, making it the southernmost bright star in this constellation.

How to find Acrux in the night sky

If you are in the Southern Hemisphere, Acrux is easy to find. Follow these steps:

1. Look for the Crux: It is a small, bright, cross-shaped constellation.
2. Look at the brightest star at the bottom: this is Acrux.
3. Use the “Southern Signposts”: draw an imaginary line from Alpha Centauri through Beta Centauri and continue along it to find the Crux.

For observers in the Northern Hemisphere, Acrux is only visible from locations in southern Florida, Texas, or Hawaii. It never rises high above the horizon and is best seen in March and April.

Acrux – an amazing double star system

Although Acrux looks like a single star, it consists of at least two gravitationally bound stars.

• Acrux A (Alpha-1 Crusis): a blue subgiant with a mass of 14 solar masses.
• Acrux B (Alpha-2 Crusis): a blue subgiant, slightly dimmer than Acrux A.

The distance between the stars is 430 AU, and they revolve around each other every 1500 years.

In addition, another star, Acrux C, is located nearby, but astronomers assume that it is an accidental background object.

Scientific significance of Acrux

Acrux is a pair of blue subgiant stars that have already passed the main phase of their life cycle.

• Temperature: 10,000-25,000 K, which is significantly hotter than the Sun (5778 K).
• Estimated age: 7.48 million years, which is much younger than the Sun (5 billion years).
• The future: most likely, Akruks will explode as a supernova and leave behind a neutron star or a black hole.

Historical and cultural significance

While most stars have names of Arabic or Greek origin, “Acrux” comes from the combination of the letter “A” (alpha) and the name of the constellation Crux.

Nevertheless, the Crux and Acrux are of great cultural significance:

• Navigation. Sailors used the Crux as a landmark in the Southern Hemisphere, as it points to the South Pole.
• State symbols. The Crux is depicted on the flags of Australia, New Zealand, Papua New Guinea, and Brazil.
• Literature and music. This star is mentioned in the song Southern Cross by Crosby, Stills & Nash.

Even Mark Twain, when he saw the Crux for the first time, described it in his book, although he was not particularly impressed.

Conclusion

Acrux is a unique, bright, and culturally significant star in the constellation of the Crux. It is easy to find in the Southern Hemisphere and is a key star for navigation and astronomical observations.

Frequently Asked Questions (FAQ)

1. What is Acrux?
   • This is a double star system.
2. Is it possible to see Acrux from the Northern Hemisphere?
   • Only from places south of Florida, Texas, or Hawaii.
3. Will Acrux explode like a supernova?
   • Thus, in the future, one of the components of the star will turn into a neutron star or a black hole.
4. What is the distance from Earth to Acrux?
   • Acrux is located approximately 321 light years from Earth.
5. Is Acrux part of a multiple-star system?
   • Thus, the Acrux consists of at least two stars that revolve around each other.
6. Why is Acrux important for navigation?
   • Since it is the southernmost bright star of the Crux, sailors used it as a guide to determine the direction to the south.
7. Is it possible to see Acrux with the naked eye?
   • Yes, Acrux is one of the brightest stars in the night sky, so it can be seen without a telescope or binoculars.
8. What role does Acrux play in culture and national symbols?
   • The Acrux and the Crux are depicted on the flags of Australia, New Zealand, Brazil, Papua New Guinea, and other countries.
9. What will happen to Acrux in the future?
   • In millions of years, Acrux is likely to explode as a supernova, leaving behind a neutron star or black hole.

Acrux is not just one of the brightest stars in the night sky but also an important navigational landmark, an object of scientific research, and a symbol of the Southern Hemisphere.

It is so hot and massive that its life cycle is much shorter than the sun’s, but even after it disappears, it will leave a mark in the universe in the form of a black hole or a neutron star.

For the people of Australia, South America, and Africa, the Acrux is part of their culture and history. It is easy to find in the night sky, and it continues to amaze astronomers and casual observers alike.

If you are lucky enough to live in the Southern Hemisphere, do not forget to find the Crux and admire this cosmic gem!