Celestia Forums

Good day to everyone!
Unfortunately, I forgot how the coordinates for such objects as nebulae and galaxies are computed. This is very important for me now, since I am preparing for the implementation of a VERY interesting addon . More precisely, the collection. I need to finish it as soon as possible ..

Do not tell me what formula you need to apply to make the correct calculations ?

Are you asking how to convert between angular measurements based on Degrees and those based on Hours?

Degrees = Hours*15.0
Hours = Degrees/15.0

DSC catalogs require RA values to be specified in fractional Hours, using Hour values from 0 to 24. 1 hour = 60 minutes = 3600 seconds.

STC catalogs require RA values to be specified in fractional Degrees, from 0 to 360. 1 degree = 60 minutes = 3600 seconds (but they are not the same size as the minutes and seconds of Hours.)

In more detail:

Values of Right Ascension (RA) are measured starting with 0 at the apparent position of the Sun at the time of the vernal equinox.

To convert from Degree values to Hour values, divide the number of fractional Degrees by 15.
To convert from Degree values to Hour values, multiply the number of fractional Degrees by 15.

For example:

M31 (the Andromeda Galaxy) is located at RA 0h 42m 44s | Dec +41° 16′ 9″
(by convention, alphabetics are used to specify minutes and seconds when hours are involved, while symbols are used for minutes and seconds when degrees are involved.)

Fractional Hours = hours + minutes/60 + seconds/3600
Fractional Degrees = degrees + minutes/60 + seconds/3600
Degrees = Hours*15.0
Hours = Degrees/15.0

So an RA of 0h 42m 44s = 0 + 42/60 + 44/3600 = 0 + 0.7 + 0.0122222 = 0.7122222 hours. 0.7122222 * 15 = 10.683333 degrees (but degrees aren't used in DSC catalogs.)

Both DSC and STC catalogs require Declination (Dec) values to be specified in fractional degrees measured from from +90 at the North pole to -90 at the South pole, with 0 at the equator..

Dec = 41+ 16/60 + 9/3600 = 41 + 0.26666666 + 0.0025 = 41.26916666