Crux facts for kids

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Crux
Constellation
List of stars in Crux
Abbreviation	Cru
Genitive	Crucis
Pronunciation	genitive
Symbolism	Southern Cross
Right ascension	12.5^h
Declination	−60°
Quadrant	SQ3
Area	68 sq. deg. (88th)
Main stars	4
Bayer/Flamsteed stars	19
Stars with planets	2
Stars brighter than 3.00^m	5
Stars within 10.00 pc (32.62 ly)	0
Brightest star	Acrux (α Cru) (0.87^m)
Messier objects	0
Meteor showers	Crucids
Bordering constellations	Centaurus Musca
Visible at latitudes between +20° and −90°. Best visible at 21:00 (9 p.m.) during the month of May.

Imagine looking up at the night sky from the Southern Hemisphere! You might spot a small but very bright group of stars shaped like a cross. This is the Crux constellation, often called the Southern Cross. Its name, "Crux," comes from the Latin word for cross.

Even though Crux is the smallest of all 88 modern constellations, it's one of the easiest to find. Its four main stars are super bright, making it stand out. You can find it at the southern end of the Milky Way, which is our galaxy's visible band of stars. The Southern Cross is a very important symbol for many countries in the Southern Hemisphere.

The brightest star in Crux is α Crucis (Acrux). It's a beautiful blue-white star. The other three main stars of the cross are β Crucis (Mimosa), γ Crucis (Gacrux), and δ Crucis (Imai). They appear in a clockwise direction and get a little dimmer as you go. Another star, ε Crucis (Ginan), is also part of the cross shape. Many of these bright stars belong to a large group called the Scorpius–Centaurus association. These stars are hot, blue-white, and seem to have formed together.

Crux also has four special stars called Cepheid variables. These stars change in brightness and can be seen without a telescope on a clear night. You can also find a bright and colorful group of stars called the Jewel Box (NGC 4755) in Crux. Nearby, there's a huge dark cloud in space called the Coalsack Nebula. It looks like a big dark patch against the bright Milky Way.

History of the Southern Cross

Ancient Views of the Crux Stars

The bright stars of Crux were known to the Ancient Greeks. They thought these stars were part of a larger constellation called Centaurus. Thousands of years ago, these stars were visible even from places as far north as Britain.

However, over time, the Earth's slow wobble (called precession) caused these stars to sink below the horizon for people in Europe. By about 400 CE, the stars of Crux could no longer be seen from most of Europe.

Rediscovery by European Explorers

In the 15th century, European explorers began sailing south. In 1455, the Venetian navigator Alvise Cadamosto likely saw the Southern Cross when he left the Gambia River. He called it the "southern chariot."

Historians often say that João Faras was the first European to draw the constellation correctly. He sketched and described it in a letter from Brazil in May 1500. Explorer Amerigo Vespucci also saw the Southern Cross and the nearby Coalsack Nebula during his journey in 1501–1502.

Another early description came from Andrea Corsali, an Italian navigator. In 1516, he sent a letter to the Portuguese king with a map of the southern sky, showing the Southern Cross.

Mapping Crux as a Separate Constellation

Later, sky mappers like Emery Molyneux and Petrus Plancius started showing Crux as its own constellation in the late 1500s. However, they sometimes placed it in the wrong spot.

Crux was first shown in its correct place on sky globes in 1598 and 1600. The stars of Crux were first listed separately from Centaurus by Frederick de Houtman in 1603.

Characteristics of Crux

Location and Size of the Constellation

The Crux constellation is surrounded on three sides by Centaurus. To its south is the constellation Musca. Crux covers a small area of the night sky, making it the smallest of all 88 constellations.

The International Astronomical Union officially named it "Cru" in 1922. The boundaries of the constellation were set by astronomer Eugène Joseph Delporte in 1930.

When and Where to See Crux

You can see Crux in the sky from April to June in tropical regions. It is directly opposite to Cassiopeia in the sky. This means you can't see both constellations at the same time.

South of cities like Cape Town and Buenos Aires, Crux is always visible in the sky. This is because it is a "circumpolar" constellation, meaning it circles around the South Pole without setting.

Avoiding Confusion with Other Star Patterns

Sometimes, people confuse Crux with another star pattern called the False Cross. The False Cross is made of stars from the constellations Carina and Vela. It's bigger and dimmer than Crux, doesn't have a fifth star, and lacks the two bright "Pointer Stars" that help you find Crux.

Visibility and Navigation

Where to Spot the Southern Cross

Crux is very easy to see from the Southern Hemisphere. You can spot it almost any time of year if you are south of the 35th parallel. It's also visible close to the horizon from tropical parts of the northern hemisphere. You can see it for a few hours each night during the northern winter and spring. For example, from Cancun (about 25° N latitude), you can see it around 10 pm in late April.

Using Crux for Navigation

In the Southern Hemisphere, the Southern Cross is often used for navigation. It works much like the North Star (Polaris) does in the Northern Hemisphere.

To find the South Celestial Pole (the point in the sky directly above the South Pole), you can draw an imaginary line. Start from the star Gamma Crucis and go through Alpha Crucis (the bottom of the cross). Extend this line about four and a half times its length. This point will be very close to the South Celestial Pole.

Two other bright stars, Alpha Centauri and Beta Centauri, are often called the "Southern Pointers." They help people easily find the Southern Cross. These stars are at a similar distance from the pole and are about the same width as the cross.

Bright Stars of Crux

Main Stars of the Cross

Within the borders of Crux, there are 49 stars that are bright enough to see without a telescope. The four main stars that form the cross shape are Alpha, Beta, Gamma, and Delta Crucis.

α Crucis (Acrux): This is a triple star system located 321 light-years from Earth. It looks blue and is the brightest star in Crux. Through a small telescope, you can see its two close components.
β Crucis (Mimosa): This is a blue giant star, 353 light-years away. It's a Beta Cephei-type variable star, meaning its brightness changes slightly.
γ Crucis (Gacrux): This is an optical double star. The main star is a red giant, 88 light-years from Earth. It's one of the closest red giants to us. Its companion star is much dimmer.
δ Crucis (Imai): This blue-white star is about 345 light-years from Earth. Like Mimosa, it's a Beta Cepheid variable star.

There's also a fifth star often included with the Southern Cross:

ε Crucis (Ginan): This is an orange giant star, 228 light-years from Earth.

Other Notable Stars in Crux

You can see a few other stars in Crux without a telescope:

Iota Crucis: This is a double star 125 light-years from Earth. The main star is an orange giant.
Mu Crucis (Mu^1,2 Crucis): This is a wide double star, about 370 light-years away. Both stars are blue-white and can be seen separately with binoculars or a small telescope.

Stars in the Scorpius–Centaurus Association

Many of the brightest stars in Crux are blue-white B-type stars. This is unusual! Among the five main bright stars, Delta, and likely Alpha and Beta, are part of the Scorpius–Centaurus association. This is the closest group of massive, hot stars to our Sun. These stars are quite young, only about 10 to 20 million years old. Other members in Crux include Zeta, Lambda, and both components of Mu Crucis.

Variable Stars in Crux

Crux has many stars that change in brightness. It has four Cepheid variables that can all be seen with the naked eye:

BG Crucis
T Crucis
S Crucis
R Crucis

Other variable stars include Lambda Crucis and Theta² Crucis, which are both Beta Cepheid type variable stars. BH Crucis, also known as Welch's Red Variable, is a Mira variable that changes a lot in brightness over about 530 days.

Exoplanets in Crux

Scientists have found a planet orbiting the star HD 106906. This planet, called HD 106906 b, has one of the widest orbits of any known planet outside our solar system!

Deep Sky Objects in Crux

The Coalsack Nebula

The Coalsack Nebula is a huge dark cloud of dust and gas. It blocks the light from stars behind it, making it look like a dark patch in the southern Milky Way. You can easily see it with your naked eye. It's located about 6.5 degrees southeast from the center of Crux. This nebula is about 180 parsecs (587 light-years) away from Earth.

The Jewel Box Star Cluster

The Jewel Box (NGC 4755) is a small but very bright open cluster of stars. It looks like a fuzzy star to the naked eye and is very close to the eastern edge of Crux. It's about 1.95 kiloparsecs (6,360 light-years) from Earth.

The famous astronomer John Herschel gave it its name because of the many different colors of stars he saw through his telescope. It's one of the youngest open clusters in the Milky Way, only about seven million years old. The Jewel Box has more than 100 stars, including many bright blue supergiant stars and at least one red supergiant.

Cultural Significance of the Southern Cross

The Southern Cross is a very important star pattern, especially in the cultures of the Southern Hemisphere. It holds great meaning in countries like Australia, Brazil, Chile, and New Zealand.

Flags and National Symbols

Many southern countries and organizations use Crux as a national symbol. The four or five brightest stars of Crux appear on the flags of:

It also appears on flags of Australian states and territories, and some regions in Chile and Argentina. The flag of the Mercosur trading zone also shows the four brightest stars. You can see Crux on the Brazilian coat of arms and on the cover of Brazilian passports.

The five stars are part of the logo for the Brazilian football team Cruzeiro Esporte Clube. The cross also gave its name to the Brazilian currency, the cruzeiro, for many years. All coins of the current Brazilian real currency (since 1998) show the constellation.

In Songs and Literature

The Southern Cross is mentioned in many songs and books.

The Argentine epic poem Martín Fierro talks about it.
Argentinian singer Charly García says he is "from the Southern Cross" in his song "No voy en tren."
The Brazilian National Anthem (1909) includes the line: "The image of the Cross shines."
The Australian National Anthem says: "Beneath our radiant Southern Cross we'll toil with hearts and hands."
The Samoan National Anthem also mentions the Southern Cross.
"Southern Cross" is a popular song by Crosby, Stills and Nash from 1981.
"The Sign of the Southern Cross" is a song by the band Black Sabbath from 1981.

Other Cultural Mentions

The Order of the Southern Cross is a special award in Brazil given to people who have done great service for the nation.
A stylized version of Crux is on the Australian Eureka Flag.
The constellation was used on patches worn by U.S. Army and Marine divisions that fought in the Southern Hemisphere during World War II.
Southern Cross railway station is a major train station in Melbourne, Australia.
The Knights of the Southern Cross (KSC) is a Catholic group in Australia.

Various Cultural Interpretations

Different cultures around the world have seen various shapes and stories in the Crux constellation:

In Chinese, it's called Shí Zì Jià, meaning "Cross."
Australian Aboriginal cultures see Crux and the Coalsack Nebula as the head of the 'Emu in the Sky.' Other groups see it as a possum, a stingray, or an eagle.
Many people in the East Indies and Brazil saw the four main stars as the body of a ray. In Indonesia and Malaysia, it's called Bintang Pari or Buruj Pari ("ray stars").
The Javanese people of Indonesia called it Gubug pèncèng ("raking hut") or lumbung ("the granary").
Bugis sailors used the Southern Cross for navigation, calling it bintoéng bola képpang ("incomplete house star").
The Māori name for the Southern Cross is Māhutonga. They see it as the anchor of Tama-rereti's waka (canoe), which is the Milky Way.
In Tonga, it's known as Toloa ("duck").
In Mapudungun, the language of Patagonian Mapuches, the name is Melipal, meaning "four stars."
In Quechua, the language of the Inca civilization, Crux is known as "Chakana", which means "stair."
The Bororo people of Brazil saw the Great Rhea, a large bird, with Crux as its body.
The Kalapalo people of Brazil saw the stars of Crux as Aganagi, angry bees coming from the Coalsack (which they saw as a beehive).
The Tswana people of Botswana saw the constellation as Dithutlwa, two giraffes.