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Q & A: gravitational lensing of the sun

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Most recent answer: 02/21/2013
Q:
I read that the bending of light around our sun caused stars behind the sun to appear further from the edge of the sun than they actually are. Along the same line, does this mean that the sun also appears slightly larger to us than it really is?
- David Hutton (age 62)
Austin, TX, USA
A:
Yes, you're right. The curvature, however, will be only half as big since the first half of the curving path from another star isn't there.

There is, however, another effect. Maybe by the "real" size you mean the distance across the sun, as measured by some local ruler. (Ok, let's not worry too much about the practicality.) That distance is bigger than you would think from the apparent area or circumference, because of the way gravity warps spacetime inside the sun. This effect on the apparent size is less than from the light curvature by a factor of about R/L, where R is the sun's radius and L is the distance from us to the sun. So it's pretty small compared to the light curvature effect.

Mike W.

(published on 02/21/2013)

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