We know that the visual size of the Sun and Moon from the Earth in our lifetime (!) is nearly equivalent.
Now my question: Is this event is random? Or have a scientific reason?
For example, maybe there is a connection between this and the formation of life on the Earth...
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$\begingroup$ I don't know if the apparent size of the Sun and the Moon have anything to do with this, but this study claimed to have found that total solar eclipses have a positive effect on the microbes studied. $\endgroup$– called2voyage ♦Jul 2, 2015 at 13:19
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$\begingroup$ @called2voyage:Thanks. By Giant impact hypothesis we observe that the density of Moon is about the density of Earth mantel(See here) and by according to the effect of tide on formation of life in this article i guess one can find some relations between distance of Moon from Earth and the radius of Moon... $\endgroup$– Ab_ShJul 2, 2015 at 14:14
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2 Answers
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As the front image on the wikipedia-page already indicates, a total solar eclipse is not always total.
Earth's orbit is slightly elliptic, and so is the Moons orbit around the Earth.
Now take the Moon's slight orbital inclination into account and far from all total eclipses are really total.
Unlike stated usually.
In fact wiki states "On average, the Moon appears to be slightly smaller than the Sun as seen from the Earth, so the majority (about 60%) of central eclipses are annular."
On a sidenote: It's important to understand that if the inclination and eccentricity of the orbit would be zero, then we'd have a perfect total solar eclipse on earth every month! But yeah you can look it up, that this is not the case. There are, after all, not every month news reports from ppl staring into the sun, are there ;)
On other note, we know that the Moon is increasing its distance to earth. This happens because Orbital angular momentum is converted into internal heat for both bodies through tidal forces.
This situation will evolve over time, so yes, it's a coincidence.
And no, I'm not aware of the Moon's distance having any strong implications for life.
Tell me, if this is not clarified enough from the above.
answered Jul 2, 2015 at 17:26
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$\begingroup$ You said: "This happens because Orbital angular momentum is converted into internal heat for both bodies" it's wrong because it causes to decreasing of distance between Moon and Earth! See BillOre answer. $\endgroup$– Ab_ShJul 2, 2015 at 20:59
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$\begingroup$ @2000, as the Moon causes the Earth's tidal bulge, it also causes heating in the Earth. The bulge and tidal torque is what primarily causes the Moon to speed up and recede from the Earth, but the heat generated by this process has to be lost or absorbed somewhere. $\endgroup$– BillDOeJul 2, 2015 at 22:34
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That the Moon and Sun both have about the same angular size is just a coincidence; we (humans) just happen to be around at a time when this is so. Tidal torque is causing the Moon to speed up (which in turn is causing the Earth to slow down and the Moon's distance to increase as it gains orbital velocity), so eventually the Moon's angular size will always be less than the Sun's. Then no eclipses will be total, with the Moon only covering up a portion of the Sun's disk.
The Moon raises tides on the earth, but Earth's more rapid rotation than the Moon's orbit causes the Earth to pull the tidal bulge ahead of the Moon.
There are some hypothesis that life may have begun in tidal pools where the Sun's ultraviolet radiation may have been the energy that caused the chemical reactions that created the precursors to life. Because the Moon was so much closer billions of years ago, the tides would have been much larger than today, so tidal pools would have been undisturbed for weeks at a time. This is, in my opinion, hypothesis, not theory, though it certainly seems plausible.
