calculate means work out. calculated with respect to is almost a special usage here. the period given is the number of days to takes for the moon to obit the earth. The question is as the earth is rotating how would you figure out or calculate when the moon had rotated the earth? In this case they seem to have drawn a line between the earth and the sun and then used that as a marker to calculate to let them measure how long it took for the moon to orbit the earth. Or that is at least what I think they mean. 2. as of in this context means composed of. Its an uncommon usage to me at least. 3. play is a noun as in a theater piece. What the author means is that it can be much harder to understand something if you only read it instead of experience it in full. e.g. it can be harder to appreciate relative distance intuitively just by looking at number on a page, seeing a graphical or real life representation can make it much easier to understand.

1) The second part: "its 29 days 12 hours 44 minutes calculated with respect to the sun" is a sentence fragment and doesn't make sense. 2) "as" indicates that the following ("dust, smoke, or steam") are examples of the kind of mass a cloud can be made of. 3) Both meanings of "play" are being used here. See a play means watch the performance of a play, with actors etc... Read a play means reading the script for a play.