Celestial Coordinates

Imaginary Sphere around the Earth

Celestial Sphere
Celestial Sphere

The Celestial Sphere

The celestial sphere is an imaginary sphere concentric with the Earth. This sphere is used by astronomers to navigate through the night sky. 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 allows to map the position of heavenly bodies in the sky, in the same way that cities or countries are mapped on earth using the geographic coordinate system. The celestial coordinate system helps locate the positions of stars, planets, the moon, and other objects.

Declination and Right Ascension

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.

On the Earth´s map, the lines that run parallel to the equator are used to measure angular distance (latitude) to the north or south of the equator. On the celestial sphere, astronomers use a measure known as declination, in the same way to measure angular distances above or below the celestial equator.


Greenwich England

Prime Meridian
Prime Meridian

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

Orion

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 includes declination and right ascension lines covered until here.

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Comments 11 comments

sligobay profile image

sligobay 4 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.


claudiafox profile image

claudiafox 4 years ago from Sydney, Australia

Nice factual reports, unverso.


unvrso profile image

unvrso 4 years ago from Mexico City Author

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


scottcgruber profile image

scottcgruber 4 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

unvrso 4 years ago from Mexico City Author

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 4 years ago from USA

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


somethgblue profile image

somethgblue 4 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 4 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.


unvrso profile image

unvrso 4 years ago from Mexico City Author

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


somethgblue profile image

somethgblue 4 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 . . .


scottcgruber profile image

scottcgruber 4 years ago from USA

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

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