One of the essential joys of summer vacation is, without argument, sleeping in. So, what better way to celebrate the end of the school year than to rise with the sun? Remembering back to watching late December dawn begin in the middle of first block, this seems an attainable task. This Saturday, however, marks the earliest sunrise of the year for Ann Arbor and locations of similar latitudes. Even though the longest day of the year won’t come until the summer solstice on June 21, the sun will rise just before 6 a.m. the day after final exams officially conclude.

Ann Arbor’s latest sunset of the year is, less stunningly, around 9:15 p.m. and will come a few days after the solstice.

This bizarre phenomenon occurs because the solar day, or the amount of time elapsed between high noons, is actually about 15 seconds longer than the 24-hour clock day during this time of year. The solar day length varies throughout the year as a result of Earth’s elliptical orbit. This occurs because the Earth rotates at the same speed at all times but moves more quickly through the sky when it is closer to the Sun and therefore the angle between the Earth and Sun changes a larger amount than when the Earth is farther away. And, because the Earth’s axis is tilted with respect to its orbit, this effect of staggering the earliest sunrise before the solstice varies by latitude; the date of the earliest sunrise gets closer to the actual solstice the closer you move toward the north pole. Far enough north, however, the question of sunrise times is irrelevant because the sun remains in the sky from late March until mid-September.