How did the Moon end up with an orbit the perfect distance to cause total eclipses?


How did the Moon end up with an orbit the perfect distance to cause total eclipses?

In: 1369

It’s not a perfect distance. If it were closer the [eclipse paths]( would be far larger than they are. Further away, they’d be smaller to non-existent.

It’s a complete coincidence that the moon is the right size and distance to appear almost exactly the same size as the sun from our vantage point. The iconic total eclipse with the slight ring of light around its edge is unique among the terrestrial planets in our solar system.

If we ever were to become part of a larger, interstellar community, the Earth solar eclipse might be a tourist destination for aliens who would not have a chance to see something quite like it elsewhere.

The moon is very gradually drifting away from the earth. In the distant future it will be too far to completely cover the sun. In the distant past, meanwhile, it was closer, and the moon was always larger than the sun in our sky.

In other words, it’s the perfect distance *now,* and we only care because our civilization arose during that window. If this weren’t the case, then we wouldn’t have even realized that we were missing out; no one would be sitting around going “boy I wish the moon and the sun were the same size so one could *just* cover the other when they line up.”

It’s also *not* perfect; the moon’s orbit is elliptical, as is the earth’s orbit around the sun, and the moon’s orbit also doesn’t line up with the ecliptic. New moon only aligns with the ecliptic a couple of times each year (from our perspective), and for a total eclipse you still need the orbits to be at the right distance. If they’re not, you only get an annular eclipse (which is what we got last weekend), or a total eclipse that just grazes one side of the earth and no one really gets to see it. Total eclipses affect a relatively tiny part of the earth’s surface and if you live your entire life in one spot then chances are you will never see one. My idea of a “perfect” system would be one where the entire surface of the earth gets to see a total solar eclipse at regular intervals, perhaps once a decade or so, common enough that no one misses out but rare enough that they’re still appreciated.

The moon’s orbit isn’t perfectly circular, sometimes it’s too far away to cause a total eclipse, which is what happened for the most recent eclipse.

Now, because of tidal forces, some of the rotational energy of the Earth is getting transferred to the moon, slowly pushing it to a higher orbit. So eventually it won’t have total eclipses anymore.

It’s pure coincidence and chance. Some religious fruitcakes cite this as evidence of god’s intelligent design of the universe.