Page:Practical astronomy (1902, John Wiley & Sons).djvu/25

BPHEMEEIS. 7 longitude of the moon's node, the longitude of the sun, and the obliquity of the ecliptic. Separate tables are constructed for this correction, in which the arguments for entering them are the obliquity and longitude of the moon's node, and the obliquity and the longitude of the sun; the sum of the two corrections is the value of the equation of the equinoxes in longitude at the corresponding times. The Perturbations in Longitude of the earth arising from the attractions of the planets (especially Venus and Jupiter), are the same for the sun; these are computed by the methods indicated in Physical Astronomy, (see Art. 174, Mechanics,) and then tabulated. The Sun's Aberration is taken to be constant, amounting to 20' '.25 and is included in the table of epochs. Ephemeris of the Sun. The above tables having been computed, we proceed as follows : 1. From the table of epochs take out the mean longitude of the sun's mean place corresponding to the exact instant considered. 2. From the table of longitudes of perigee take the mean longi- tude of perigee; the difference between this and the mean longi- tude of the sun's mean place is the mean anomaly. 3. With the mean anomaly as an argument find the correspond- ing value of the equation of the center from its table, and add it