The moon, by far our closest celestial neighbor


It can be challenging to have a new and, hopefully, sparkling article column week. 

My hat goes off to some of the daily blogs that I receive on my computer every morning like, which concerns itself with extraterrestrial news, astronomy and cosmology, with the occasional down-to-earth articles. I glance through it whenever it arrives to see what interesting tidbits Deborah Byrd has for us today. 

Recently, there was an article, “What would the Earth be like with no moon?” Now, that’s not something you give thought to on a regular basis!

Let us first take an inventory of solar system moons. Neither Mercury nor Venus has one. Earth has one and Mars has two. 

And then things get out of hand. Jupiter has 51 official moons and 18 provisional ones (still awaiting official confirmation), Saturn has 53 official and 8 unofficial, Uranus has 27, Neptune has 13, and Pluto — which may not even be a planet anymore — has five. 

While most moons are named for mythological characters, all of Uranus’ moons are named for Shakespearean characters, except for three named for characters in Alexander Pope’s poem “Rape of the Lock.” 

Our moon does not actually have a personal name. Just as we call it the moon, Luna is just the Latin word for it. And selenology, the study of the moon’s geology, comes from Selene, which is Greek, referring both to the moon itself and the name of the moon goddess.

Just where does our moon come from? The current hypothesis involves collisions with the proto-earth and debris eventually coalescing into our moon as we know it. 

There are several versions of this hypothesis. One of them suggests there was a one-time collision of a body between one to two times Earth’s size. The second hypothesizes a series of smaller impacts by bodies of between 1 and 10 percent the size of the Earth with smaller amounts of ejected material that first formed a disk of orbiting debris. This disk would have formed first individual moonlets that eventually coalesced. 

However, since the mass of the moon is only 1/81st the mass of the Earth, it seems unlikely our planet would be substantially different without the loss of the debris material that became the moon.

There is also difference of opinion as to the age of the moon. A recent article suggests that the moon had solidified by 4.51 billion years ago, meaning only 60 million years after the birth of the solar system. The multiple moonlet hypothesis suggests the process may have taken longer — 150 to 200 million years after the formation of the solar system.

The celestial universe is very dynamic. When the moon was formed, it orbited at a distance of only 13,000 to 19,000 miles from the Earth. It is now 238,855 miles away, and continues to recede at a yearly rate of 3.8 centimeters. And because of the gravitational forces exerted between the moon and Earth (the sun also exerts gravitational forces), the Earth is slowing on its axis, and days are lengthening by 1.7 milliseconds per year. 

This process is also not new. There is evidence from fossil corals and sandstone deposits that 350 million years ago in the Carboniferous, the day was less than 23 hours long. And 620 million years ago, in the Ediacaran, the day was only 21.9 hours. 

The shape of the earth is not static either. The gravitational pull of the sun and the moon cause the earth to bulge at the equator. Melting glaciers allow for the land mass of the continents to rise which cause infinitesimal shortening of the day.

The ancients thought that the planets traveled in perfect circles, but all orbiting bodies actually travel in ellipses. The above distance from Earth is an average. At apogee (when it is farthest from Earth), it is 6 percent further away, while at perigee (when it is closest to Earth), it is 7 percent closer than average. 

A solar day is 24 hours long, and means the time it takes the Earth to spin on its axis and return to the same spot under the sun. A lunar day (the time it takes the Earth to return to the same position in relation to the moon) is 24 hours and 50 minutes, which is why the tidal intervals are 12 hours and 25 minutes. The alignment between the moon, the sun and earth governs the strength of the tides.

Despite the sun’s greater size, its effect on tides is much smaller than the moon’s because of its distance from earth.

In short: No moon, much shorter days and very weak tides!

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Sura Jeselsohn, moon,