Comment Re:Cant wait (Score 1) 170
It's not that a day (in any sense) varies between 58.7 and 176 (Earth days), it's that those numbers are measurements for different definitions of day.
Mercury's sidereal day, the time it takes Mercury to make a complete rotation (with respect to the background stars), is 58.7 days. The length of Mars' solar day, the time it takes to for the sun to cross the same meridian on Mercury (or the time it takes to reach the same place in the sky from the perspective of someone standing at a fixed point on Mercury) is 176 days. This notion is a little strange when you first hear about it, because the distinction is much narrower here on Earth: Our solar day is (very close to) the usual 24 hours, but our sidereal day is about four minutes shorter. (The difference on Mercury is so much larger than it is here because Earth's orbital period -- how long it takes to complete one trip around the sun -- is more than two orders of magnitude larger than its sidereal day. By contrast, on Mercury those quantities are comparable.)