Archive
06/06/2017 – Ephemeris – Where did the Moon come from?
Ephemeris for Tuesday, June 6th. Today the Sun will be up for 15 hours and 26 minutes, setting at 9:24, and it will rise tomorrow at 5:57. The Moon, 3 days before full, will set at 5:10 tomorrow morning.
The origin of the Moon is a question that has vexed astronomers for years. Did it break off the molten Earth like a cell dividing? Was it captured by passing too close to the Earth? Neither is satisfactory. Chemical elements have different isotopes depending on the number of neutrons in their nucleus. The rocks brought back by the Apollo astronauts show that the isotopes of the elements in the rocks is that same as for the Earth. We know that Mars and the asteroids have different isotope ratios. The hypothesis that seems most likely is that another planet, the size of Mars collided with the 100 million year old Earth in a glancing blow that gave rise to a disk of material that eventually coalesced into the Moon.
The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The hypothetical collision of a Mars sized body with the young Earth. Credit: Joe Tucciarone via NASA
09/17/2013 – Ephemeris – How did the moon form?
Ephemeris for Tuesday, September 17th. The sun will rise at 7:23. It’ll be up for 12 hours and 24 minutes, setting at 7:48. The moon, 2 days before full, will set at 6:27 tomorrow morning.
The question of how the moon formed has long been a mystery. It was considered impossible that the earth could capture such a large body all by itself. An answer came from the age of the Apollo Moon missions. Though the moon has a 64th the earth’s volume, it has only an eighty-first of the earth’s mass, hence it was made of lighter material overall than the earth. The Moon is made of the same material as the crust of the earth. Even the isotopes of the elements matched, extremely odd if the Moon was the result of a capture or collision with the already formed earth. A new theory posited last year has the earth and moon forming from a collision of two large-sized bodies, whose material was mixed to then form the Earth and Moon.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Collision of Mars sized body with the early Earth. A newer theory posited a more equal sized bodies. Credit: NASA
Bob Moler's Ephemeris Blog 