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Solid Angle From Our Eyes Toward The Moon And The Sun Is The Same. Any Explanation?


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#1 rhertz

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Posted 29 April 2019 - 10:56 PM

Frequently, the Moon passes between our planet and the Sun causing a total eclipse most of the time,

or an annular eclipse.

 

The solid angle from our eyes toward the Moon (steradians, etc.) is the same as the solid angle

that contains the Sun (from our perspective). This happens most of the time.

 

Source: http://www.thesuntod...d-eclipse-2013/

 

Solar_eclipse_geometry-570x362.jpg

 

Is this an incredible coincidence or something else that I don't understand?

 

What do you think?

 

 



#2 sanctus

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Posted 30 April 2019 - 04:32 AM

You mean the moon being at proper distance and of proper size, then yes it is a coincidence. Incredebile? Not really, read link below we have 600million more years to go till the last ever full eclipse.
https://spaceplace.n...lar-eclipse/en/



#3 ralfcis

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Posted 30 April 2019 - 07:40 AM

Yes but in 600 millions years will the sun have shrunk enough to keep the ratio the same? Man, that would be some crazy hard calculation to figure out.



#4 exchemist

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Posted 30 April 2019 - 07:43 AM

Yes but in 600 millions years will the sun have shrunk enough to keep the ratio the same? Man, that would be some crazy hard calculation to figure out.

As I understand it the sun will stay more or less the same for another 4bn years or so and will then swell, becoming a red giant. 



#5 ralfcis

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Posted 30 April 2019 - 07:56 AM

Now I have another question. If satellite orbits decay when the satellite slows down, does that mean the moon's orbital velocity is accelerating in order for the orbit size to increase? What's causing the acceleration? I could look it up but I'm too lazy.



#6 exchemist

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Posted 30 April 2019 - 08:09 AM

Now I have another question. If satellite orbits decay when the satellite slows down, does that mean the moon's orbital velocity is accelerating in order for the orbit size to increase? What's causing the acceleration? I could look it up but I'm too lazy.

Tidal effects.

 

The moon, through its gravity, distorts the shape of the Earth's oceans, causing the tides, and the bulges of the tides in turn exert drag on the moon through the same gravitational attraction. But, because the Earth is spinning in the same sense as the moon orbits, only faster, the effect of this drag is to speed up the orbital speed of the moon, and decrease the rate of spin of the Earth. (Angular momentum, which like energy is a conserved quantity, is thereby transferred from the Earth to the moon.) As a result, the moon's orbit gradually widens, while the rotation of the Earth slows down a bit.