Coordinates - Equatorial

The Sky Chart shows lines of right ascension and declination.

Right Ascension

The geometry of the right ascension (RA) lines on the celestial sphere is identical to the longitude lines on Earth. Longitude lines on Earth divide one rotation into 360 degrees, but RA lines on the celestial sphere divide one rotation into 24 hours. Therefore one hour equals 15 degrees (360 divided by 24).

Zero degrees longitude passes through Greenwich, England and is the designated reference line for longitude. What then is the reference line for zero hours right ascension? Astronomers use the vernal equinox, the location where the Sun crosses the celestial equator during its apparent annual motion against the background stars, as a "starting point" for right ascension.

The term right ascension comes from the fact that when viewed from the equator, all stars rise (or ascend) at right angles to the horizon, so their times of rising are called their times of right ascension.

Declination

The Declination lines on the celestial sphere are similar to the latitude lines on Earth, ranging in value from -90 degrees to +90 degrees. The "declination" of an object is the angle measured from the celestial equator (0 degrees declination) along a meridian line through the object. Polaris, the North Star has a declination of 89.26 degrees so it is very close to the North Celestial Pole. Mintaka, the western-most star in Orion's belt has a declination of about 0 degrees 17 minutes south so it is very near the celestial equator.

Objects with a declination below the latitude of the observer less 90 degrees will never rise at that latitude. For example, if you live at 40 degrees North latitude, objects with a declination below minus 50 degrees (40 minus 90) will never rise. If you are located at 90 degrees latitude (the North Pole), you will never see any objects with a negative declination.

Equatorial Coordinate System

In the equatorial coordinate system, the coordinates of all celestial objects remain fixed* from hour-to-hour, day-to-day and so on. An object's equatorial coordinates remain the same regardless of from where on Earth the object is viewed. This allows us to create star maps that apply to any place on Earth, or publish the anticipated position of an upcoming comet so that astronomers everywhere know where it is located among the stars.

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Entertainment

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• Equatorial

[TIMMEHHURTS]

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[WorldwideWakeupCall]

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[caramelkissesaywat]

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[sixdaysfool]

yea the voice was a bit trippy.. o.O

[badymojoy]

Nah, this video is was just fine for me. Not everybody has a beautiful speaking voice, and I'd rather hear a robot than some humans.

[nmssis]

Do over, do over!