eslHQ - Do you know ..? vs. Did you know ...?

Yes. The second form of the verb (usually known as the simple past but that's a lousy name which obscures the real meaning) is used in English to express remoteness, or distance from the actual "here and now" situation. This remoteness can be

a) remoteness in time - ie past : I went to the sea this summer.
b) remoteness from reality - ie hypothetical ideas : I wish I knew his address (the real, present situation = I don't know his address)
c) psychological distance - ie an attempt to make something sound tentative rather than direct. Compare eg :Mark, I want to see you for a moment and Oh Mark ... I wanted to see you for a moment. Intonation, the "oh" and the use of the second form all serve to make the sentence less direct, and therefore less threatening. This is what's behind the choice of request forms too, Can /May I see you for a moment vs Could/Might I see you for a moment? or I wonder if you ... vs I wondered/was wondering ... You can also see it a work in What's your name? vs What was the name?

Sometimes the effect is fairly slight as here, but it's the same explanation. Do you know ... sounds more like an interrogation, as if I expect the person should know.Did you know ... distances it and makes it softer, more tentative "Well you might have heard about it before but it doesn't matter because I can tell you now."