Dear stupid: how many times does the earth rotate in a year?

[Aractus]

The correct answer for an orbital year is 366.242. There are two further correct answers that so far no one has picked: 366 times in a calendar year, and 367 times in a leap year. Of course those are not exact, but they are correct if rounded. Below I will give you the exact amounts.

First I'll explain how the orbital year is calculated. The earth rotates in the same direction as its orbit. The moon actually does this as well, and it takes 27 days to complete an orbit of the earth. Thus the length of a day on the moon is 27 Earth days. However if the Moon was a planet and the Earth was a star, then it would have daylight shining permanently on the one half of the planet that faces the Earth-star (the near-side of the moon), and the far side of the moon would experience permanent darkness. If it were to rotate twice per orbit, then it would experience one day per orbit. If it rotated three times, it would have two days, and so on. If it rotated 366.242 times it would have 365.242 days.

Next we can calculate how many times the earth rotates in a calendar year. The answer I've provided is 366, but of course it's not quite 366 because we know the earth has to rotate an extra 1/365.242th to experience each day (3 minutes and 56.555 seconds). The calendar year is 0.242 days short of a full year, meaning the total rotation is 366 minus 0.242 * 1/365.242. So the exact answer is 365.9993374... The final correct answer is the number of times the earth rotates in a leap year. Again, a leap year is defined as 366 days, but it is 0.758 days longer than an orbital year, and therefore the the Earth rotates a total of 367 + 0.758 * 1/365.242 times in a leap year, giving an exact answer of 367.002075...