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Celestial Coordinates

The author is a lover of nature and technology. He has been an online writer since 2009.

The Celestial Sphere

The Celestial Sphere

The celestial sphere is an imaginary sphere concentric to Earth. The sphere is used by astronomers to navigate through the night sky, permitting to specify the apparent positions of stars, planets and other objects. The coordinates used in the celestial sphere correspond to the geographic coordinate system used on Earth. All objects in the sky can be thought of as projected upward from the Earth´s equator, and the North, and South poles.

The celestial coordinate system assumes that the earth is at the center of the sphere whose radius extends to infinity. Three dimensional coordinates are used to mark the positions of the objects in the sky. In spite of their distances from the earth, all objects; stars, planets, seem to be at a fixed distance within the sphere. The eastward rotation of the earth produces an apparent westward rotation of the map of heavenly bodies.

Celestial Coordinates

In the celestial sphere, the point of the sky directly above the Earth´s North Pole corresponds with the celestial north pole, likewise, the Earth´s South Pole corresponds with the south celestial pole, and the Earth´s equator, with the celestial equator.

Declination is a measure that is comparable to latitude on an earth´s map and it´s used to point locations north or south of the equator. Those north of the equator have positive declination while those south have negative declinations. They are measured in degrees, minutes and seconds.
Anywhere from 0 degrees at the equator to 90° north or south of the equator.

Right ascension is the angular distance used to measure locations eastward the celestial equator starting at the vernal equinox. It uses hours, minutes and seconds. When used along with declination, it is used to indicate the astronomical coordinates of an object in the celestial sphere.

Celestial Coordinates

On the Earth´s globe, the lines that run vertically (line of longitude) from pole to pole are used to denote angular distance east or west of the Prime Meridian (0°) located in Greenwich England. On the celestial sphere, in the same way, right ascention (R. A.) is used to to measure distances east or west of a point of reference (0) which is the position the Sun is in the sky on the Vernal Equinox.

Right ascension is measured in hours minutes, and seconds from west to east in the celestial sphere at a zero point. Every 24 hours the Earth rotates on its axis 360°. 360 divided by 24 is equal to 15. Astronomers divide the celestial sphere in 24 R.A. lines, so that each line corresponds to 15° in the sky.

Celestial Coordinates (Orion)



Locating Orion in the Celestial Sphere

The Orion constellation (The Hunter) is one of the most recognisable in the night sky which can be seen at the Northern latitudes throughout the winter season. It is located at (5h, 30m R.A.), and since it runs on the line of the equator, it is at declination 0.

To practice locating objects in the sky, you can get a star chart analog (planisphere) which is an instrument that helps recognize stars and constelations. It makes use of declination and right ascension lines covered in this hub.

© 2012 Jose Juan Gutierrez


scottcgruber on January 15, 2012:

Glad my articles can be of some use to you. Some of us find fact more interesting than fiction.

somethgblue from Shelbyville, Tennessee on January 14, 2012:

Yes Scott if I need any sleep, I'll just read one of your articles, but thanks for giving us your two cents . . .

Jose Juan Gutierrez (author) from Mexico City on January 14, 2012:

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You´ve got the point. It needs further study.

scottcgruber on January 14, 2012:

I take it you're referring to this paper:

Which discusses a currently unexplained anomaly in the Moon's eccentricity of 3.5 millimeters per year in perigee and apogee that cannot be explained by tidal forces alone.

That's interesting, sure. Certainly something worth studying further, but not worth losing sleep over.

somethgblue from Shelbyville, Tennessee on January 14, 2012:

Have you noticed any changes in the Moon's orbit, or do you spend much time on this subject?

Cornell University came out with an article just recently that proposed that the Moon's orbit has changed and am wondering if you have noticed anything yourself and wish to comment on it?

scottcgruber on January 13, 2012:

Yeah, we've got a little time before we need to start reprinting the star maps...

Jose Juan Gutierrez (author) from Mexico City on January 13, 2012:

The Earth´s axial tilt varies from 22.1° to 24.5° within a 41,000 years period; At present, the tilt is decreasing. The earth´s axial tilt won´t affect us in this era; however, I´m sure the geographers and cartographers will make the necessary adaptations when necessary.

scottcgruber on January 13, 2012:

I realize this won't be a problem for a few thousand years, but Earth's axial tilt changes angle and direction over time. This would change the coordinates of all stars as the sky shifts, wouldn't it? Or will we anchor the coordinates to the sky as it is now and just let the Earth shift relative to them?

Jose Juan Gutierrez (author) from Mexico City on January 12, 2012:

The celestial coordinates are very useful when wanting to locate celestial bodies, including planets, stars, constellations, etc.

claudiafox from Sydney, Australia on January 12, 2012:

Nice factual reports, unverso.

sligobay from east of the equator on January 11, 2012:

Voted interesting and useful for this unique subject matter. I always like looking for constellations but now realize that there is a specific and precise reference system used by astronomers. This is new information for me though I knew it existed generally. Thank you.

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