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Celestial Coordinates

Updated on January 17, 2018
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Unvrso is a lover of nature and technology. He has been writing for HubPages since 2009 on various topics.

The Celestial Sphere

Celestial Sphere
Celestial Sphere | Source

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

Celestial Coordinates
Celestial Coordinates | Source

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)

Orion
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

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  • scottcgruber profile image

    scottcgruber 6 years ago from USA

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

  • somethgblue profile image

    somethgblue 6 years ago from Shelbyville, Tennessee

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

  • unvrso profile image
    Author

    Jose Juan Gutierrez 6 years ago from Mexico City

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

  • scottcgruber profile image

    scottcgruber 6 years ago from USA

    I take it you're referring to this paper: http://journals.cambridge.org/action/displayAbstra...

    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 profile image

    somethgblue 6 years ago from Shelbyville, Tennessee

    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 profile image

    scottcgruber 6 years ago from USA

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

  • unvrso profile image
    Author

    Jose Juan Gutierrez 6 years ago from Mexico City

    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 profile image

    scottcgruber 6 years ago from USA

    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?

  • unvrso profile image
    Author

    Jose Juan Gutierrez 6 years ago from Mexico City

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

  • claudiafox profile image

    claudiafox 6 years ago from Sydney, Australia

    Nice factual reports, unverso.

  • sligobay profile image

    sligobay 6 years ago from east of the equator

    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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