Mass of the Moon and Gravitational Lensing

[Helena Wells]

During an eclipse the Moon covers the Sun.However this shouldn't be happening due to gravitational lensing we should be able to see some light?

Is the mass of the Moon not big enough or photons do reach us but they are so little our eyes can't detect them?

 

[Vanadium 50]

A. Lensing is negligible.
B. The effect of lensing would be to make the moon's apparent angular diameter smaller all the time, not just during eclipses.
C. You would have total and annular eclipses. Just like we do now.

 

[Ibix]

I just told you the formula for the angular deflection of light in the Elon Musk thread! Plug the numbers in and see how much angular deflection you get.

 

[Dale]

And after plugging in the numbers for the lensing then compare that to the difference in angular size depending on orbital distance to the moon.

 

[Helena Wells]

A high definition computer would be able to understand the difference?

 

[Vanadium 50]

What is a " high definition computer"? And what "difference"? The effect of lensing would be to make the moon's apparent angular diameter smaller all the time, not just during eclipses.

 

[berkeman]

A high definition computer would be able to understand the difference?

Never anthropomorphize high definition computers. They hate it when you do that.

 

[DaveC426913]

The effect of lensing would be to make the moon's apparent angular diameter smaller all the time, not just during eclipses.

I think the point he's hoping to make is that it is only during an eclipse that the small amount would make an obvious difference - because of the sun.

But no. Even if it were a non-negligible amount of lensing, the Moon's elliptical orbit means its apparent size changes noticeably from eclipse to eclipse anyway. So you'd get Vanadium's total and annular eclipses anyway.

 

[Ibix]

A high definition computer would be able to understand the difference?

Why would a computer have anything to do with the angular resolution of a telescope? Unless you've got one of those magic CSI computers that can zoom-and-enhance and read a license plate from a single pixel reflection in somebody's eyeball?

 

[PeterDonis]

Is the mass of the Moon not big enough or photons do reach us but they are so little our eyes can't detect them?

Neither. During a total solar eclipse the angular size of the Moon is enough larger than the angular size of the Sun that the miniscule gravitational lensing effect of the Moon is not enough to bend any of the Sun's light sufficiently for us to see it.

 

[hutchphd]

Back to the question at hand for a second. I need a little help. I know these are small effects

B. The effect of lensing would be to make the moon's apparent angular diameter smaller all the time, not just during eclipses.

It is hard for me to understand that the lensing effect would be the same (or similar) for light from behind being occluded and light being emitted (or reflected).
So the sun (assuming it has a sharp limb) actually looks smaller than its size because of gravity acting on light?

 

[PeterDonis]

B. The effect of lensing would be to make the moon's apparent angular diameter smaller all the time, not just during eclipses.

I don't think this is correct. Gravitational lensing refers to an object bending light coming from objects behind it. The Moon's apparent angular diameter normally is determined by light reflected from the Sun off the Moon (or from the Earth off the Moon, if you are seeing "the old moon in the new moon's arms"), not by light coming from behind the Moon. Only during an eclipse is there a light source right behind the Moon such that lensing by the Moon could affect the Moon's apparent angular diameter.

 

[PeterDonis]

The effect of lensing would be to make the moon's apparent angular diameter smaller

Also, the effect of lensing by object A of light coming from object B, behind object A, is not to make object A's apparent angular diameter smaller; it's to make object B's apparent angular diameter larger.

 

[Vanadium 50]

Maybe I should have said "effective angular diameter". If lensing moves the direction of light from an object behind the moon so that it is no longer obstructed, that means the moon obscures less of it, i.e. the effective angular diameter is less.

 

[PeterDonis]

If lensing moves the direction of light from an object behind the moon so that it is no longer obstructed, that means the moon obscures less of it, i.e. the effective angular diameter is less.

I see what you mean; I think a simpler and more intuitive way to describe it is that it makes the apparent angular diameter of the object behind the moon larger.