<Tr> <Td> November 2 / 3 </Td> <Td> 24 hours </Td> </Tr> <Tr> <Td> December 22 </Td> <Td> 24 hours + 29.9 seconds </Td> </Tr> <P> These lengths will change slightly in a few years and significantly in thousands of years . </P> <P> Mean solar time is the hour angle of the mean Sun plus 12 hours . Currently (2009) this is realized with the UT1 time scale, constructed mathematically from very long baseline interferometry observations of the diurnal motions of radio sources located in other galaxies, and other observations . The duration of daylight varies during the year but the length of a mean solar day is nearly constant, unlike that of an apparent solar day . An apparent solar day can be 20 seconds shorter or 30 seconds longer than a mean solar day . Long or short days occur in succession, so the difference builds up until mean time is ahead of apparent time by about 14 minutes near February 6 and behind apparent time by about 16 minutes near November 3 . The equation of time is this difference, which is cyclical and does not accumulate from year to year . </P>

Wht is the longest day of the year