## Main Question or Discussion Point

If I was looking at a self-luminous object, and all of a sudden a great pass appeared directly between me and the object, in the line of sight between me and it, I could potentially see an Einstein ring.

Q: If that mass then started moving radially towards me (distance to self-luminous source behind it remains the same), what would happen to the Einstein ring?

My intuition says that the ring with grow in angular diameter as the intermittent mass approaches me - (I think this due to taking the time derivative of the angle of lensing, and assuming the lens is approachign me at a certain constant speed). Does this seem right?

Related Science Fiction and Fantasy Media News on Phys.org
phinds
Gold Member
2019 Award
If I was looking at a self-luminous object, and all of a sudden a great pass appeared directly between me and the object, in the line of sight between me and it, I could potentially see an Einstein ring.

Q: If that mass then started moving radially towards me (distance to self-luminous source behind it remains the same), what would happen to the Einstein ring?

My intuition says that the ring with grow in angular diameter as the intermittent mass approaches me - (I think this due to taking the time derivative of the angle of lensing, and assuming the lens is approachign me at a certain constant speed). Does this seem right?
Given the size of objects that are massive enough to create Einstein Rings, it's not likely to move towards you at a speed (or even a recession velocity) that would show much change during your lifetime, but yes there would be a (probably too small to measure) increase in the size of the ring.

Awesome, thank you! I needed it more as a hypothetical for a short story I'm writing so it's OK if it doesn't happen on single human lifescales :)

Ibix