Understanding the Night Sky

The sky has certain coordinate system to measure the distances and position of celestial objects in the sky. These coordinate systems are very useful and handy when it comes to communication of certain object and event with your friends/colleagues. Also these coordinate system comes in handy during record keeping. There are two different systems used as coordinate system.

Local coordinate system: Local coordinate system is the measure of altitude and azimuth of an object in the sky at a specific time and hence you keep a record of the same. It is a local system and usually works with in a small group of participants/observers observing from the same location at the same time.

The altitude is the angular measurement of the object vertically above the horizon. The measurements starts from horizon and ends at zenith while it changes the azimuth when moving on the other side.

The azimuth is the angular measurement of the object horizontally away from the north direction while moving eastward. North is 0, East is 90, south is 180 and west is 270.

The altitude and azimuth of an object always change with respect to time as the Earth continues to rotate and hence the objects appears to move. The coordinates are relative to time and the location dependent hence it changes with time and if the observer changes it location.

Universal Coordinate System: The universal coordinate system is the system of coordinates which are used by professional astronomers around the world as it is a standard system accepted globally. The universal coordinate system uses a more complex but universal positioning system which helps in locating and record keeping the sky better. The universal coordinate system uses Right Accession and Declination method which are universal and accepted globally.

Right Accession is the measurement of position of the object placed along the celestial equator. It is measured in hours, minutes and seconds. The celestial equator is circle with 360 degrees.  As the earth rotates in 24 hours, the sky appears to come back in exactly 24 hours. So by the maths below:

24 hours = 360 degrees

1 hour = 360/24 degrees

60 min = 15 degrees

1 degree = 60/15 min

= 4 min

So each 15 degree in the sky is equivalent to an hour each degree is 4 mins and so on.

Right accession is measures counterclockwise direction starting with the point of contact between the ecliptic and the celestial equator in the constellation of Aries.

Declination is the measure of separation of object from the celestial equator towards Polaris. Celestial equator marks the 0 degree where as the pole star measures the +90 degree in the northern hemisphere. From the celestial equator moving in the south direction, the declination of star increases but with a negative sign. Similarly from Polaris towards the horizon on north the declination will be reducing however positive.