07-11-10, 09:01 PM #1
Solar Eclipse by the moon - coincidence?
A solar eclipse has been witnessed on Easter Island 12/07/2010
and as part of the editorial:
The sun is 400 times wider than the moon, but it is also 400 times further away. Because of the symmetry, the lunar umbra that falls on the face of the Earth is exactly wide enough to cover the face of the sun.
Now the probablity nutters can have a go at this because I reckon the probability of this sort of coincidence [acka 400,400] is staggering-ly remote. Give the variables and scale.
care to discuss?
07-11-10, 09:08 PM #2
07-12-10, 12:14 AM #3
1. The moon is slowly moving away from the Earth. At one time it was much larger than the Sun and at some time in the future it will be smaller. It only follows that the two would be close to the same size at some point. We are just lucky to live when they are close to the same size.
2. The ratio is not perfect. The average angular size of the Sun is 32.5'. the average size of the Moon is 31.7', slightly smaller. The only reason we ever see a complete total eclipse is because the Earth-Moon distance varies during a month and the Earth Sun distance varies over a year.
Sometimes during an eclipse, the Moon is close and the Sun is far making the Moon slightly bigger than the Sun. Other times the Moon is far and the Sun is nearer and the Moon is the smaller of the two. During these eclipses, we get an Annular eclipse because the Moon fails to completely cover the Sun and we see a ring, or annulus, caused by the limbs of the Sun shining past the moon.
07-12-10, 01:40 AM #4
Yeah, cool coincidince, but like Janus said, not quite so precise.
The distance to the Moon varies by about 10%, from about 36000km to about 40500km:
The distance to the Sun changes as well, by about 3%.
Taking average sizes and distances, the size ratio is 401, the distance ratio is 389.
Last edited by Pete; 07-12-10 at 01:47 AM.
07-12-10, 05:33 PM #5
And we don't even have to be that lucky to live during a time when "near fit" eclipses can occur. At the rate that the Moon is receding, it will take some 729 million years before it will be too small at perigee to cover the Sun entirely, and if we extrapolate backwards we find that its a bit over 1 billion years back to the time when The Moon at apogee just fit over the Sun when it was its closest. This gives about a 1.8 billion year window. The Earth is about 4 billion years old, and might last another 5 billion, so for about 1/5 of the Earth's lifetime it would be possible to see a near-fit total eclipse.
07-12-10, 06:16 PM #6
Would you think the symmetry involved is born of necessity or just simply a random/chance occurance?
I don't mean the above in a trite sort of way as the question is premised on the belief that in physics everything happens because it literally "has" to.
The Sun, Earth, Moon system has for some "unknown" physical reason evolved the symmetry that it demonstrates.
Presuming the uniqueness of this planets apparent circumstance regarding life, exposed liquid water [oceans of it], rotational rate and orbital rate the remote probability of all these things occuring simultaneously to me, is utterly staggering.
To get liquid water that remains liquid for a full planetary rotation requires specific orbital and rotational [ on axis] circusmtances I would think.
If we assume that this has occurred by a random occurance then we can also assume that the moons position in the Sun, Earth moon system is also a part of the randomly generated uniqueness of this planets ability to sustain liquid water [ life that doesn't freeze at night or vapourise during the day.]
When thinking in terms of probability the remoteness of all this occurring randomly just gets further and further away almost to a point of 1: infinitey
So I would contraversally contend that there must be an unknown physical necessity for this system and the life it habors.
Last edited by Quantum Quack; 07-12-10 at 06:24 PM.
07-12-10, 07:06 PM #7
Figuring the probability of a random planet being capable of supporting life is a popular topic for armchair philosophers, and has had some serious attention as well.
There are two big unknowns in the way:
What specific factors are actually required for life to develop in a solar system?
What is the distribution of those factors in solar systems across the Universe?
The Rare Earth Hypothesis (Ward & Brownlee) suggests that the occurence of life-supporting planets could be very low indeed, low enough that there might not be another one in our galaxy.
Anyway, take a wild overestimating stab in the dark and say that the chance that a random star will harbour a life-supporting zone for a reasonable period at some time during its life is only one in a million million million (10^18).
The obvious next question is... how many stars are there?
Wikipedia says "the observable universe contains about 3 to 7 × 10^22 stars"
So, even at that overestimated improbability, you'd still have 10,000 life-capable systems in the observable universe at any given time.
Bonus question: What's the chances that you happen to be born on one of the one-in-a-zillion planets that support life?
07-12-10, 07:10 PM #8
07-12-10, 07:24 PM #9
Having a look at the "Rare Earth" Hypothesis I notice it fails to focus much attention on the importance of planetary rotational/orbital dynamics.
To sustain liquid "Equatorial" surface water through out the entire rotation of the planet, through out it's entire orbital cycle requires a certain set of circumstances determined by the freezing and boiling point of water [ in particular salty water.]
I would contend [ naively ] that it is the nature of salty waters thermo-dynamics that is a "key" if you like to this system that sustains and evolves complex life [especially humanoid]
Reverse engineering question:
If you were to design a solar system that allowed salt water [typically found at our equatorial regions ] to maintain the temperatures that it is recorded to have, how would you do it? What would be required regarding rotational / orbital dynamics.
The answer wil be no doubt~ what we observe with this planet.
07-13-10, 02:14 AM #10
The 'habitable' zone around a star is a common point of discussion in the search for exoplanets. The region of the solar system within which liquid water on an Earth sized object could form due to heating from the Sun is tens of millions of kilometres thick (in terms of the distance from the Sun). As the Sun heats up (over billions of years) this region moves out and will eventually no longer contain the Earth but will contain Mars.
The Earth isn't in some tiny parameter space region where any small deviation makes life impossible. If it'd been 100 million km from the Sun or 85, rather than 92, it'd still have liquid water.
I can't help but feel that you're trying to make an argument for design, ie a case for a designer, which simply isn't justified. It might help if you knew some basic orbital mechanics too.
07-13-10, 03:41 AM #11
07-13-10, 04:52 AM #12
07-13-10, 05:40 AM #13
And no I don't believe in intellgient design of the kind most often referred to.
However intelligent design can be a part of the natural selection process of sustainable evolution. [ axiomatically sustainablility of evolution would automatically be considered as intelligent IMO]
"The more sustainable an system is whether that be organic of other wise the more intelligent in design it would be deemed to be."
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