Bob Moler's Ephemeris Blog

This is Ephemeris for Thursday, April 23rd. Today the Sun will be up for 13 hours and 52 minutes, setting at 8:37, and it will rise tomorrow at 6:43. The Moon, at first quarter today, will set at 3:42 tomorrow morning.

When one gazes upon the moon tonight the thought of where the moon came from might come to mind. Did it form with the Earth? Was it captured by the Earth? The latest thinking on the origin of the moon centers around a grazing collision with the Earth of a Mars sized body that has been given the name Theia, the mother of Selene, the goddess of the Moon, shortly after the Earth was formed. This is based on Apollo mission discoveries that the composition of the rocks on the moon are approximately the same as those of Earth’s crust. It’s been known for a while that there are two dense masses within the Earth about halfway to the center. One geologist has put forth that these masses could have been the core of Theia that sank into the Earth.

The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.

Addendum