Today is the longest day of the year as June 21 marks the summer solstice. It’s the day when there are the most hours of sunlight.
The summer solstice occurs when the tilt of a planet's semi-axis, in either the northern or the southern hemisphere, is most inclined toward the star that it orbits. Earth's maximum axial tilt toward the Sun is 23° 26'. This happens twice each year, at which times the Sun reaches its highest position in the sky as seen from the north or the south pole.
As the Earth takes its yearlong trip and spring turns to summer, the North Pole heads more and more toward the sun until a date between June 20 and 22, when it reaches its maximum before starting to point away again.
That maximum is the summer solstice, which this year falls on June 21. Today, the sun will be directly over the Tropic of Cancer, which is at 23.5 degrees North latitude.
A few other things to know about the summer solstice:
- The summer solstice occurs when the sun is directly over the Tropic of Cancer, located at latitude 23.5 degrees North. (It runs through Mexico, the Bahamas, Egypt, Saudi Arabia, India and southern China.) The sun will be directly over the Tropic of Cancer at 11:39 am CDT on June 21, 2015. For every place north of there, the sun is at its highest point in the sky and this is the longest day of the year, according to the National Weather Service.
- The summer solstice in the Northern Hemisphere occurs at the same moment the winter solstice occurs in the Southern Hemisphere. Their days will now begin to get longer, while the days in the Northern Hemisphere begin to get shorter.
- Today may be the longest day of the year, but it likely won't be the hottest. According to the National Weather Service, there is about a six-week lag between the longest day of the year and the warmest average temperatures for most mid- and high-latitude locations.
- Even though the summer solstice marks the start of summer for many, it's actually the midpoint of the season.
- Your shadow at local solar noon will be the shortest of the year.
- At lower latitudes daylight hours are shorter but the sun reaches a higher point in the sky.
- The summer solstice has one of the earliest sunrises of the year (but not necessarily the earliest). For example, Birmingham saw its earliest sunrises on June 8-17, at 5:37 a.m. CDT. Birmingham's sunrise on Sunday will be at 5:38 a.m. (Huntsville's earliest sunrises were at 5:33 a.m. on June 6-20, but the sun will rise at 5:34 a.m. Sunday. Mobile's earliest sunrises were at 5:49 a.m. CDT June 5-17. Sunday's sunrise there will be at 5:51 a.m.)
- Twilight in the Northern Hemisphere is longer on the solstice than at any other time of year.
- The days will slowly grow shorter following the June solstice. The shortest day of the year will be Dec. 21 at 10:49 p.m. CST.
- The summer solstice usually occurs on June 20 or 21, and rarely on June 22. According to TimeandDate.com, the next solstice on June 22 won't be until 2203. The last one was in 1975.
- Yes, you can stand an egg on its end on the summer solstice. But you can do that any day of the year, if you are patient. It is a myth that there is a special gravitational balance on solstice days.
