I wasn't sure whether this was the right place to post this since it isn't really coursework, but it seems like it could be.(adsbygoogle = window.adsbygoogle || []).push({});

My problem is with the deflection angle of light for several point masses.

The deflection for a point mass can be described as:

[itex]\frac{4GM}{c^{2}\xi}[/itex]

where [itex]\xi[/itex] is the minimum distance between the light and the lens.

For a thin lens approximation of several point masses, the equation for the deflection angle is:

[itex]\sum[/itex][itex]\frac{4Gm_{i}}{c^{2}}[/itex][itex]\frac{\xi-\xi_{i}}{|\xi-\xi_{i}|^{2}}[/itex]

where [itex]\xi[/itex] is the position of the light ray in the lens plane and [itex]\xi_{i}[/itex] is the position of the mass [itex]m_{i}[/itex]. (they are vectors)

It seems to me to be a direct extension of the point mass equation, but I don't understand where the [itex]\frac{\xi-\xi_{i}}{|\xi-\xi_{i}|^{2}}[/itex] comes from. It seems to me that it would just be [itex]\frac{1}{\xi-\xi_{i}}[/itex]. Can anyone explain it?

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# Homework Help: Gravitational Lensing deflection angle question

Can you offer guidance or do you also need help?

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