Because it turns steadily and goes through 360 degrees in 24 hours, so you just have to divide 360 by 24.
The Earth turns 15 degrees in 1 hour.
There is no standard set of "lines", so if you want to compare two "lines", you have to specify which two you're talking about. The Earth turns through 360 degrees of longitude in 24 hours. So every 15 degrees of longitude corresponds to one hour of rotation. If you want the clock to read 12:00 Noon when the sun peaks in the sky everywhere, then you have to change the clocks by one hour for every 15 degrees of longitude.
Every time a planet makes a full rotation that is considered one day on that planet.
15 degrees
2 full turns, if one turn is 360 degrees.
Mercury turns to a liquid at 25 degrees Celsius.
Uranus.
Each of them does.
1 turn = 360 degrees so 3.5 turns = 3.5*360 = 1260 degrees.
The earth rotates on its polar axis once in every day - or 24 hours. So over a 24 hour period it turns through 360 degrees. This every time you go 15 degrees of longitude (= 360/24) the solar time is 1 hour earlier or later. The solar time has been modified so that most countries, which do not stretch very far from East to West use the same time throughout.
1080 degrees
The rotation of the earth describes the spinning action of the earth on its axis. That is what gives us night and day.