The Big Dipper, also known as the Plough or the Saptarshi, is a distinct grouping of seven stars. These seven brightest stars are of the constellation Ursa Major. The Big Dipper is most significant because by locating it, the North Star can easily be found. To find a constellation or grouping of stars, many use the equatorial coordinate system or celestial coordinates.
Understanding the Celestial/Equatorial Coordinate System
Developed to assist astronomers in describing the placement of objects in the sky, the Celestial or Equatorial Coordinate System uses a map of the sky known as the Celestial Sphere.
This sphere is imagined as a bubble around the Earth with lines drawn through the Earth's poles, marking the North and South Celestial Poles. The Earth's equator is the Equatorial plane.
Using the Celestial/Equatorial Coordinate System
The term Declination describes movement above or below this imaginary plane up to 90 degrees -- plus degrees indicate above or towards the North and minus degrees refer to below or towards the South.
A vertical line drawn (North to South) around this Celestial Sphere at every 15 degrees marks one hour of Right Ascension - the term for the vertical measurement of the coordinate system. The parts of this hour are described just like time -- in minutes and seconds.
It is important to know where you are in relation to the 0 Hour, where the sun crosses the celestial equator at the vernal equinox in March -- known as the Prime Meridian.
To verbalise a location of a certain star, or group of stars, you must relay the degrees of declination and the number of hours of right ascension. By using this method, astronomers everywhere can find the location.
The Exact Coordinates of the Big Dipper
The constellation Ursa Major, which includes the Big Dipper, is located at Right Ascension 13 hours 23 minutes and 55.5 seconds and Declination +54° 55′ 31″.
Using the Big Dipper as a Guide to Other Stars
By finding the Big Dipper, astronomers can easily locate other stars and constellations from it. Since the Big Dipper is rather easy to find in the sky it is a guidepost for beginner astronomers to lead to other points of interest. Some other stars and constellations found by using the Big Dipper as a reference are: the North Star, Capella, Castor, Arcturus and Spica.
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