A constellation is the name given to a group of stars in the sky that make up a certain pattern. Sometimes this pattern is imaginary. When the sky is clear these stars can be seen from Earth without the use of a telescope. There are 88 named constellations and they take many forms, including mythological creatures, animals, people and objects. The name is usually given based on the shape made by the brightest stars within the constellation. Some of these shapes appear much more obvious than others. Sometimes there is a smaller shape distinguishable within the constellation that is also given a name, this is known as an asterism.
People have gazed up at the stars for many thousands of years and 48 of the 88 constellations recognised today were named in Ancient Greece. Constellation is a latin word meaning “set with stars”. Before the compass was invented people used the stars to navigate, particularly when sailing across the ocean. They used a constellation called the Ursa Minor to identify the location of Polaris, also known as the North star. This allowed them to calculate their latitude and work out which direction they were travelling in. This map of the sky was also used as a rough calendar. Although the layout of the stars remain the same, the exact location of some constellations will change throughout the year and people used this to understand that the season was changing. Of course it isn’t the stars moving through the sky, it is the Earth moving through space and changing our viewpoint. There is a star chart called a planisphere, this has moveable wheels around the edge of it. The wheels can be adjusted to the time of year and location on Earth and will show an accurate map of the sky and the constellations that should be visible to you.
Some constellations are better known than others. Here are a few you may have heard of and some interesting information on each one.
The Ursa Major and the Ursa Minor
These constellations are located in the Northern Hemisphere and rotate in the sky throughout the seasons. The Ursa Major is otherwise known and the “Big Bear” and the Ursa Minor as the “Little Bear”. Ancient myths tell a story of the Greek God Zeus becoming jealous of a woman and her son. In his jealous anger he turned them both into bears and cast them into the sky. The Big Bear represents the mother and the Little Bear represents the son. The Ursa Major is well known due to its asterism made up of seven bright stars. This asterism has several names given to it by different parts of the world but is most commonly known as the big dipper or the plough. It visually looks like a large ladle with a long handle. At the very end of the bowl portion of the ladle are two bright stars. These are often called pointer stars as they point directly to polaris. This is the star commonly used for navigation purposes.
The Zodiac Constellations
These are the groups of constellations that the Planets, the Moon and the Sun pass through as they travel through the solar system. There are twelve in total and they are known as the signs of the Zodiac. Their names are Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius and Ophiuchus. These constellations are well known because of their use in astrology. All but one, Ophiuchus, corresponds to a “birth sign” or “star sign”. As the Sun travels through the sky it spends roughly one month in each constellation per year. A person’s star sign is represented by which segment of the sky the Sun was in when they were born. For example if you were born between May the 21st and June the 20th, the Sun would have been in the Gemini segment of the sky and therefore you would be “a gemini”. It is important to note that unlike astronomy, astrology is not scientifically based.
Orion is a very well known constellation. Its location on the celestial equator allowed it to be seen from any point on Earth. Orion is named after a Greek mythical hunter. The easiest way to spot this constellation is to look for three bright stars in a line. These three stars are Orions belt. The Ancient Greeks told many tales of Orion the Hunter. The most popular version is that Orion was killed by a Scorpions sting and cast into the stars.
Cassiopeia is named after a beautiful queen. The Queen often boasted about her beauty, comparing herself to the sea nymphs. This angered the God of the Sea, Poseidon, and she was turned to stone and set amongst the stars eternally as her punishment. The main brightest stars within the constellation spell out an “M” or “W” in the sky and are often easy to spot.
There are many more beautiful constellations with interesting back stories. See if you can find some of them in the sky yourself. You can also go to a place called a planetarium, where the map or the stars is cast brightly onto a dome for you to view.
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