Right Ascension Calculations

Study the diagram below which shows the northern half of the major celestial meridians. At midnight on March 21st, the Vernal Equinox, the prime meridian is as shown below. (If you lived in Greenwich).

Notice the following: Star A will culminate in 1h 45mins, at 01:45. Star B will culminate 2h and 29mins later, at 02:29.   If you look at this "clock" at midnight on every day after March 21st this clock will have moved anti-clockwise by 4 minutes. e.g. on March 27th it will be 6 x 4 = 24 minutes further on so star A will culminate at 01:21.

Your longitude, how far East or West of Greenwich you are, will also affect the time at which stars culminate.

The further East you are the sooner they will culminate, by 4 minutes for every degree East.

The further West you are the later they will culminate, by 4 minutes for every degree West.

E.g. If star A culminates at 01:21 in Greenwich the in Middlesbrough (1.13 W) it will culminate 1.13 x 4 = 4.4 minutes later.

Remember that the Sun rises in the East so if you lived more Easterly than you do now the sun would rise sooner.