POSITION OF THE LUNAR TERMINATOR
Though the position of the Lunar Terminator is given for mean midnight throughout the year in that very useful publication the Companion to the Observatory, it is frequently important in examining or comparing former drawings and observations to ascertain its position at the times when they were made. For this purpose the subjoined tables (which first appeared in the Selenographical Journal) will be found useful, as they give for any day between A.D. 1780 and A.D. 1900 the selenographical longitude of the point where the terminator crosses the moon's equator, which it does very nearly at right angles.
[Tables and examples]
LUNAR ELEMENTS
Moon's mean apparent diameter - 31 min. 8 sec.
Moon's maximum apparent diameter - 33 min. 33.20 sec.
Moon's minimum apparent diameter - 29 min. 23.65 sec.
Moon's diameter, in miles - 2163 miles.
Volume (earth's = 1) - 1/49.20 or 0.02033.
Mass (earth's = 1) - 1/81.40 or 0.0128.