Why Do We Get an Einstein Cross Instead of a Skewed Ring?

[Unredeemed]

Why do we ever get Einstein crosses? I realize it is because the alignment is not right, but why do we get a cross because of this instead of just a skewed ring?

Thanks,
Jamie

 

[George Jones]

Why do we ever get Einstein crosses? I realize it is because the alignment is not right, but why do we get a cross because of this instead of just a skewed ring?

Thanks,
Jamie

Hartle's book Gravity: An Introduction to Einstein's General Relativity has a nice treatment of this. I can look it up on Monday.

 

[Unredeemed]

Hartle's book Gravity: An Introduction to Einstein's General Relativity has a nice treatment of this. I can look it up on Monday.

That would be great, thank you.