Question: Imagine you go out tonight at 9:00pm and see a star rising on the horizon. If you go out tomorrow at the same time, the star will be in a different location. What day would you be able to see the same star rise from the horizon at 10:40pm? My half-answer: The difference between a sidereal and a solar day is that the solar day is ~3.9 min longer. However, I cannot seem to apply this concept to figure out which day the star would rise at 10:40pm. I have formulated my own equation, tn = to - 3.9n Where tn is the final value of time (in this case, 10:40pm), and to is the original value of time (in this case, 9:00pm). n is the number of days (in this case, what we are trying to find). By substituting values into my equation, I get: n = (9:00pm - 10:40pm) / 3.9 min However, I cannot figure out the answer from that. This is a very easy question but I am really stumped. Any help?