Understanding the Night Sky

As our ancestors were looking at stars in the sky, they started visualising certain shapes associated with bright stars creating a pattern in the sky. They named these pattern based on what shapes they saw. They named them after animals, objects, humans, gods and anything else. The name and the shape was dominated by the series of bright stars when joined the dots. They called them markers in the sky. The sky had many such markers and today we know them as asterisms.

Asterisms dominate the name and/or share of the constellation however the scientific community has defined constellation as – “a region or space in the sky which helps in identifying the stars and associate them with a particular group”. Constellations are small sections of the sky in which the the entire sky is divided. There are 88 constellations dividing the entire sky, both northern and southern hemisphere and the entire celestial sphere. This makes every single star or other deep space object part of one constellation or the other. Just like every human being on earth has a nationality, similarly every object in space has a constellation.

The constellation is made up of stars, both bright and faint. The brighter stars are usually the ones which help us find and locate and identify the constellation. They are not just limited to the bright star patterns called as asterisms but beyond that. Every inch of the sky is part of some constellation. There are however a few rare instances where a star is just at the border and is part of two different constellations. The constellation of Auriga and Taurus share a bright star with each other.

Identifying the markers in the sky:

When you look up in the sky, the constellations are an important tool to observe the sky but there are a few other important pointers which are essential for us to remember:

Meridian: Meridian is an imaginary line which connects the North direction with south direction. It divides the sky into two halves. Eastern half and western half. It passes right above the head of the observer.

E-W Divide: It is not a technical term but astronomers and stargazers refer to it as often as they need. The imaginary line is formed by connecting the east and west cardinal points on the horizon. It passes right above the head of the observer.

Zenith: Zenith is the highest point in the sky. Theoretically it is the point exactly above our head where the E-W divide and Meridian appears to intersect. The zenith marks a point where all four directions appear to meet in the sky.

Nadir: Nadir is the lowest point in the sky. It is just opposite to Zenith. Nadir is the point below us.

Ecliptic: Ecliptic is an imaginary line drawn in the sky which marks the band/width of solar system. It should be noted that all the solar system bodies like Sun, Moon, planets and most of asteroids in their definitive orbits will be found in this band. The band is about 10 degree wide.

Celestial Sphere: Celestial sphere is an imaginary sphere which expanded in the sky with Earth at the centre of it and now you can see the entire universe/sky with the motion of Earth. This is called celestial sphere. It should be noted that the star and other objects in the sky appear to be embedded in to the celestial sphere and hence appear to be at the same distance.

Celestial Equator: Celestial equator is the projection of Earth’s equator in the sky on celestial sphere. The celestial equator can also be described as the line dividing the imaginary sphere around the earth.

Zodiac: Zodiac is a series of constellations which we observe during the night and the solar system bodies like sun, moon, planets, asteroid and comets move in the foreground of the same. The constellations are very far in the space and lie along the plan of ecliptic.