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Understanding Physics Topics is essential for solving complex problems in many fields, including engineering and medicine.
Constellation – Definition, Origin, History, & Facts
We see thousands of stars on a clear, moonless night. Some of these stars are arranged in groups or patterns. These groups of stars appear to form some recognizable shapes and patterns. For example, one group of stars suggests the outline of a big bear (great bear), another group of stars reminds us of a hunter, and so on. The group of stars which appears to form some recognisable shape or pattern is known as a constellation.
All the stars of a constellation always remain together. Due to this the shape of a constellation always remains the same. Our ancestors named these ‘star groups’ or constellations’ after the objects which they seemed to resemble. About 88 constellations are known at present. Each constellation has been given a name signifying an animal, a human being or some other object which it appears to resemble. All the constellations appear to move in the sky from east to west. This is because the Earth (from where we view them), rotates on its axis from west to east. Some of the important constellations are:
- Ursa Major
- Orion
- Cassiopeia
- Leo Major
All these constellations can be easily recognised (or identified) in the night sky. A constellation does not have a small number of stars. A constellation consists of a group of a large number of stars, some of which are bright and can be seen easily with the naked eye whereas others are dim and seen with difficulty. While describing the various constellations we will give the arrangement of only bright stars in them which can be recognised easily in the night sky. All the stars which make a constellation are not at the same distance from us. They are just in the same line of sight in the sky. We will now describe the four common constellations, Ursa Major, Orion, Cassiopeia and Leo Major in somewhat detail. Let us start with Ursa Major.
1. Ursa Major Constellation
Ursa Major constellation is one of the most famous constellation which we can see in the night sky. Ursa Major constellation is also known as ‘Great Bear’, ‘Big Bear’, ‘Big Dipper’ or ‘Plough’. The Indian name of Ursa Major constellation is ‘Saptarishi’. Though Ursa Major constellation is a group of many stars but seven of its stars are quite bright and can be seen easily. The arrangement of main stars in the Ursa Major constellation is shown in Figure. The Ursa Major constellation consists of seven bright stars which are arranged in a pattern resembling somewhat a big bear (see Figure). The stars marked 1, 2, 3, and 4 are supposed to form the body of the big bear whereas the stars marked 5, 6 and 7 form the tail of the big bear. The head and paws of this bear are formed from some other faint stars which are not shown in Figure.
It is clear that a lot of fertile imagination is required to make out some recognizable shape from a group of stars. The ‘Ursa Major’ is called ‘Great Bear’ because its stars are arranged in such a way that they seem to form the outline of the body of a ‘Great Bear’ (or Big Bear) (see Figure).
The Ursa Major is also called Big Dipper because it resembles a dipper (a bowl with a handle), which was used to drink water in olden days. The stars marked 1, 2, 3 and 4 (in Figure) appear to form the bowl of the dipper whereas the stars marked 5, 6 and 7 seem to form its handle. Please note that Ursa Major constellation also resembles a ‘big kite with a tail’, a ‘big laddle’(a big spoon with a cup-shaped bowl), or a ‘big question mark’ in the night sky. The Ursa Major constellation is visible during the summer season in the early part of the night. It can be seen clearly in the month of April in the northern part of sky at night. The stars marked 1 and 2 in Ursa Major constellation are called pointer stars because the line joining them points to the direction of Pole Star.
We can locate the position of Pole Star in the night sky with the help of Ursa Major constellation. This can be done as follows : Look towards the northern part of the sky on a clear, moonless night during summer (at about 9 pm) and identify the Ursa Major constellation in the sky. Now look at the two pointer stars at the end of the Ursa Major constellation (see Figure). Imagine a straight line drawn through the two pointer stars of the Ursa Major constellation. Extend this imaginary line towards the north direction in the sky. This line will lead to a star which is not very bright (see Figure). This star is the Pole Star.
If we observe the Ursa Major constellation at different times in the night, we will find that it appears to move from east to west. Since the Pole Star remains fixed in the night sky, therefore, the Ursa Major constellation appears to revolve around the Pole Star in the night sky (see Figure). Please note that some of the northern constellations like Ursa Major are not visible from some points in the southern hemisphere of the Earth.
2. Orion Constellation
Orion is one of the well known and most impressive constellations in the night sky. Orion is also known as ‘Hunter’. The Indian name of Orion is ‘Mriga’. There is a greater number of bright stars in Orion than any other constellation. The Orion constellation consists of seven or eight bright stars (and several faint stars). Thus, the Orion constellation can be drawn either with seven stars or with eight stars. The Orion constellation drawn with eight main stars is shown in Figure. The arrangement of stars in Orion constellation is supposed to resemble a ‘hunter’ in the kneeling position. The star marked 1 in Figure represents the head of the hunter. The stars marked 2 and 3 in Figure are supposed to form the shoulders of the hunter whereas the stars marked 7 and 8 are imagined to form the feet of the hunter.
The three stars in the middle marked 4, 5 and 6 in Figure represent the belt of the hunter. The arms and weapons of the hunter are formed from some other faint stars which are not shown in Figure. Again , a lot of fertile imagination is needed to make out the shape of a hunter from a group of stars in the night sky (When the Orion constellation is drawn with seven main stars, then the star marked 1 at the top in Figure is not shown and the stars marked 2 and 3 are joined by a dotted line). The Orion constellation is visible in the sky during the winter season in the late evenings.
The brightest star in the night sky is ‘Sirius’. The brightest star called ‘Sirius’ is located close to the Orion constellation. We can locate the position of Sirius Star in the night sky with the help of Orion constellation. This can be done as follows : In order to locate Sirius, imagine a straight line passing through the three middle stars of Orion constellation in the night sky. Look along this line towards the east direction in the sky. This imaginary line will lead us to a very bright star (see Figure 8). This very bright star is ‘Sirius’.
3. Cassiopeia Constellation
Cassiopeia is another prominent constellation in the northern sky. Cassiopeia constellation consists of 5 main stars. The 5 main stars of Cassiopeia constellation are arranged to form the shape of distorted letter W or M (depending on the position of Cassiopeia constellation in the sky). Thus, Cassiopeia constellation looks like a distorted letter W or M (see Figure). The Cassiopeia constellation is thought to represent an ancient Queen named Cassiopeia seated on a chair. Cassiopeia constellation is visible during winter in the early part of the night.
4. Leo Major Constellation
Leo Major constellation is a yet another constellation in the northern sky. Leo Major constellation usually consists of 9 main stars. Leo means lion. So, the arrangement of stars in the Leo Major constellation is thought to form the outline of a big lion (see Figure). Leo Major constellation is visible during summer in the early part of the night. Leo Major constellation is sometimes called just Leo constellation.