Originally posted by ndmmxiaomayi:
[b]Question 17
Why is a solar day about 4 minutes longer than a sidereal day
?
This is too obvious. Use google will find out answers.[/b]
There are 366.2422 sidereal days in a tropical year, but
365.2422 solar days, resulting in a sidereal day of 86,164.091
seconds (or 23 hours, 56 minutes, 4.091 seconds). The reason there
is one more sidereal day than "normal" days in a year is that the
Earth's orbit around the Sun offsets one sidereal day, giving
observers on Earth 365 1/4 days, even though the planet itself
rotated 366 1/4 times. 
