The astronomical beginning of summer in the Northern Hemisphere is marked by the June solstice. Depending on the year, the day that marks the offical start of summer can be June 20 or June 21. The following is a list of exact dates and times for upcoming summer solstices:
- June 20, 2008 at 7:59 pm EDT
- June 21, 2009 at 1:45 am EDT
- June 21, 2010 at 7:23 am EDT
- June 21, 2011 at 1:16 pm EDT
- June 20, 2012 at 7:09 pm EDT
- June 21, 2013 at 1:04 am EDT
- June 21, 2014 at 6:51 am EDT
The First Day of Summer is Earlier in Western North America
For the years 2009 and 2013, people in the Mountain and Pacific time zones and farther west greet the first day of summer a day earlier, on June 20. So when people ask what the first day of summer is, it not only depends on the year but on where you live.
The moment of the summer solstice in the Northern Hemisphere is determined by when Earth's North Pole axis is tilted most directly toward the sun. When this is occuring in the Northern Hemisphere, the Earth's South Pole axis is tilted most directly away from the sun, which marks the first day of winter in the Southern Hemisphere.
Watching the Effects of the Summer Solstice
If you have been watching the sun each day leading up to the summer solstice, you will see that it climbs higher in the sky each day. On the day of the solstice, which marks the first official day of summer, the sun appears to stand still. It has reached as far north as it will get. The word "solstice" means the sun stands still. This is also true for the winter solstice, when the sun gets as far south in the sky before coming to a stop.
Is the First Day of Summer the Longest Day of the Year?
The first day of summer is often said to be the longest day of the year. This is because people believe that there is more sunlight on this day than on any other. It is true that the days have been getting longer and the nights shorter. The sun is higher in the sky and takes a longer path across our sky, giving us more daylight. That, combined with the more direct rays of sunshine, give us the warm summer season.
The longest day of the year depends on location. In some places it will be on the solstice, but for others it may occur a day or so before or after (or both). Earth's atmosphere bends the sun's light so that the sun actually appears above the horizon before it truly is. In addition, the sun is so large that the moment of its rising and setting is not instantaneous.
Here are some examples from 2008 of how the longest day of the year can differ by location. Miami, Florida, experiences its longest day of the year two days after the solstice. Chicago, Illinois, experiences not one but two longest days, with sunrise and sunset occurring at the same times on the two days following the solstice. San Francisco, California, has four longest days, from June 19-22, occuring before, during, and after the solstice, with the same minutes of daylight.
