10 Interesting Facts about Star Constellations

July 20, 2016

Think you know the constellations? Think again!

You may already know that the 88 constellations we use today were only established in 1922 by the International Astronomical Union, but what you may not know is that some of these constellations have histories dating back to 3000 BC and even earlier. In fact, some cave paintings in Europe that date back about 10,000 years clearly depicts patterns of stars that are recognizable even today. Here are some more facts about the constellations that you may find interesting, astonishing, or worth knowing.

Most constellations are very old

Although the Greek astronomer Ptolemy is credited with cataloguing 48 constellations early in the 2nd century, many of these constellations were “borrowed” from depictions of complete constellations scratched into stone and clay tablets by the ancient Babylonians about 3 000 years ago. Available archaeological evidence suggests that the Babylonians created their constellations in a relatively short period, from about 1 300 BC to around 1 000 BC.

Most constellations consist of unrelated stars

While 87 of the 88 constellations consist of stars that are physically unrelated, Ursa Major is a notable exception to this rule. Most of the stars in this constellation belong to the Ursa Major Moving Group, a relatively large group of stars that share a common origin, velocity, and motion across the sky.

There are actually 89 constellations

While most sources state that there are 88 constellations, there are in fact 89, because Serpens is split into two distinct parts- Serpens Caput (the head of the snake), and Serpens Cauda (the snake’s tail) to the west and east of Ophiuchus respectively.

There are 13 zodiacal constellations

Although only 12 zodiacal constellations are recognized, the constellation Ophiuchus, which according to some sources should be the 13th, also lies partially on the ecliptic, but the Sun spends only 13 days crossing it. This is significantly longer than the Sun spends in some other astrological signs, but to get out of this conundrum, some astrologers claim that astrology is not based on twelve astrological signs or constellations, but the four seasons instead. Thus, 12 signs divided by 4 seasons gives a neat answer, and no pesky 13th sign to account for.

Ophiuchus is a violent constellation

Image credit: NRAO/AUI and Yurii Pidopryhora, NRAO & Ohio University

The image above shows the combined effects of about 100 supernova explosions on the gas and dust within the constellation. This bubble of gas blown high above the plane of the Milky Way galaxy is one of the largest known but being about 30 million years old, its walls are now starting to collapse, causing the vast amount of dust in the bubble to fall back into the Milky Way galaxy. Note that this image is greatly enhanced with false color to make the structure visible in optical light.

Some “constellations” consist of dust clouds

The Great Rift is a series of gas and dust clouds within the Milky Way that is best seen from the southern hemisphere, and which form the basis of “constellations” to some cultures. For instance, some Aboriginal peoples from Australia see an emu in the shape of parts of the Great Rift. Look at the image below and see if you would have recognized an emu if it were not for the line drawing.

Image credit: Museum of Victoria, Scienceworks

The Sun does not belong to any constellation

Because the 88 constellations are contiguous and therefore cover the entire celestial sphere, every visible object in the Universe can be placed within a constellation, with the exception of the Sun, which has not been assigned a “home” constellation.

The constellations live in families

The 88 modern constellations are divided into 8 distinct families, with each family sharing some common characteristic such as proximity to each other in the sky, shared historical origin, or mythological theme. Below are the families and the constellations that belong to them.

  1. The Ursa Major Family
    Ursa Major, Ursa Minor, Draco, Canes Venatici, Boötes, Coma Berenices, Camelopardalis, Lynx, Leo Minor, Corona Borealis.
  2. The Zodiac
    Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer.
  3. The Perseus Family
    Perseus, Cassiopeia, Cepheus, Andromeda, Pegasus, Cetus, Auriga, Lacerta, Triangulum.
  4. The Hercules Family
    Hercules, Sagitta, Aquila, Lyra, Cygnus, Vulpecula, Hydra, Sextans, Crater, Corvus, Ophiuchus, Serpens, Scutum, Centaurus, Lupus, Corona Australis, Ara, Triangulum Australe, Crux.
  5. The Orion Family
    Orion, Canis Major, Canis Minor, Monoceros, Lepus.
  6. The Heavenly Waters
    Delphinus, Equuleus, Eridanus, Pisces Austrinus, Carina, Puppis, Vela, Pyxis, Columba.
  7. The Bayer Group (Constellations named by Johann Bayer)
    Hydrus, Dorado, Volans, Apus, Pavo, Grus, Phoenix, Tucana, Indus, Chamaeleon, Musca.
  8. The Lacaille Family (Constellations named by Nicolas Louis de Lacaille)
    Norma, Circinus, Telescopium, Microscopium, Sculptor, Fornax, Caelum, Horologium, Octans, Mensa Reticulum, Pictor Antlia.

The constellations are not fixed

Since all stars possess proper motion, meaning that they move across the sky as seen from earth, the shapes of the constellations are constantly changing, albeit very slowly. In one case in 1992, the constellation Aquila lost the star Rho Aquilae as it moved across the border from its own constellation into the neighbouring constellation Delphinus.

Sagittarius contains the centre of the Milky Way Galaxy

In 1954, investigators from Australia used a purpose-built radio telescope to search for the exact centre of the galaxy. Their investigations turned up an extremely energetic point radio source in the constellation Sagittarius (later dubbed Sagittarius A) which upon closer examination turned out to be the rotational centre of the galaxy.

Nowadays, you can observe a large part of the constellations by using an over-the-counter telescope or even a good pair of binoculars – there’s some great value kit available out there from brands such as Skywatcher Telescopes who have a range of budget and entry level telescopes and binoculars at affordable prices. So if you fancy taking a look at the constellations above yourself, whether you’re a seasoned stargazing pro or a novice telescope user, there’s always something to see and find up there!

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