APOD and General Astronomy Discussion Forum
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Still, kind of special, as most moons are much smaller compared to their parent-planet. If our moon was much smaller, as is ‘normal’ in our solar system, there may have been no era in which the Moon had a same anger size as the Sun (31 arcmin).rstevenson wrote:But it is not a coincidence that at some point in the evolution of the Moon's orbit, it happens to look close to the same size as the Sun when viewed from the surface of the Earth. That was inevitable.
It may turn out that fairly large tides are vital in some way for the development of life, and therefore a large moon may be necessary. But I doubt that near total eclipses would be necessary to the devlopment of intelligence, as eclipses in general will be seen anyway -- occasionally, at least -- and will therefore prompt the curious mind to work out what they are.geckzilla wrote:I'd say coincidence. But hey, maybe if it was possible to look at all technological civilizations that ever existed in the Universe, we'd find that they all have to have a satellite that closely matches their parent star in size to allow for fancy eclipses. Throw that in your Drake Equation and see how rare technological civilizations are.
Surely it's a coincidence that they are nearly the same size at this time:geckzilla wrote:
I'd say coincidence. But hey, maybe if it was possible to look at all technological civilizations that ever existed in the Universe, we'd find that they all have to have a satellite that closely matches their parent star in size to allow for fancy eclipses. Throw that in your Drake Equation and see how rare technological civilizations are.
This is a very interesting theory. But this is probably possible in a few hundred or thousand years. It is a pity that we will not catch this phenomenon. By the way, have you ever thought that by that time humanity might no longer exist? We do not know which asteroid can, for example, collide with the Earth or something else. Inspired by the movie "Armageddon".John Done wrote: ↑Tue Sep 01, 2020 1:35 pm I am not quite confident, but this is the result of an amazing coincidence. Indeed, the size of the Sun exceeds the size of the Moon by about 400 times - and it is about the same distance from us. As a result, the apparent dimensions of both are almost exactly the same. This situation is unique for 8 planets of the solar system and over 160 known satellites. But every year the Moon moves away from the Earth by 4 centimeters and our descendants will probably see another view.
It isn't a "theory" in any scientific sense of the word. It's an observation. But it's an observation that we can explain using well supported theory.KayBur wrote: ↑Fri Oct 23, 2020 3:20 pmThis is a very interesting theory. But this is probably possible in a few hundred or thousand years. It is a pity that we will not catch this phenomenon. By the way, have you ever thought that by that time humanity might no longer exist? We do not know which asteroid can, for example, collide with the Earth or something else. Inspired by the movie "Armageddon".John Done wrote: ↑Tue Sep 01, 2020 1:35 pm I am not quite confident, but this is the result of an amazing coincidence. Indeed, the size of the Sun exceeds the size of the Moon by about 400 times - and it is about the same distance from us. As a result, the apparent dimensions of both are almost exactly the same. This situation is unique for 8 planets of the solar system and over 160 known satellites. But every year the Moon moves away from the Earth by 4 centimeters and our descendants will probably see another view.
https://en.wikipedia.org/wiki/Axial_tilt#Earth wrote:<<Earth's axial tilt is known to astronomers as the obliquity of the ecliptic, being the angle between the ecliptic and the celestial equator on the celestial sphere. For the past 5 million years, Earth's obliquity has varied between 22° 2′ 33″ and 24° 30′ 16″, with a mean period of 41,040 years. This cycle is a combination of precession and the largest term in the motion of the ecliptic. For the next 1 million years, the cycle will carry the obliquity between 22° 13′ 44″ and 24° 20′ 50″. The Moon has a stabilizing effect on Earth's obliquity. Recent numerical simulations made in 2011 indicated that in the absence of the Moon, Earth's obliquity might vary by about 20–25°. The Moon's stabilizing effect will continue for less than 2 billion years. As the Moon continues to recede from Earth due to tidal acceleration, resonances may occur which will cause large oscillations of the obliquity.>>Click to play embedded YouTube video.
While those are all true, it doesn't answer the question. There is a much, much greater range of possibilities where the two differ significantly in apparent size. And that great range doesn't alter the role of the Moon in stabilizing the Earth's axial tilt or in providing tides.neufer wrote: ↑Fri Oct 23, 2020 4:48 pm
- Liquid water on Earth requires our (long lived & stable) G type star to cover about half a degree in the sky.
The evolution of tidal basin life has clearly benefited from the semi-regular tides of a Moon that covers about half a degree in the sky.
(The influence of such tides on the human female menstrual cycle and other sorts of human development may also be significant.)
And such a large apparent moon has had a stabilizing effect on the Earth's obliquity over millions of years:
I'll bet you think it's a coincidence that