It has felt like summer at times for weeks, but now it's official. Kind of.
June 1 marks the first day of meteorological summer in the Northern Hemisphere.
Meteorologists mark the seasons using three-month chunks of time, and summer for them officially begins today.
But most people probably mark the beginning of the season with the summer solstice -- also known as the longest day of the year.
This year the summer solstice will fall on June 20 at 11:24 p.m. CDT.
That means that this year, summer will begin on June 20 for the most of the U.S. -- except for those in the Eastern Time Zone, when it will come on June 21 at 12:24 a.m. EDT.
The summer solstice marks the day with the most hours of sunlight for the entire year.
From now until June 21 the day length will increase by about a minute each day. Both June 20 and 21 will have the most daylight: 14 hours, 22 minutes and 39 seconds, according to Timeanddate.com.
The days will begin to get shorter following the solstice, culminating in the shortest day of the year, the winter solstice on Dec. 21 at 10:27 a.m. CST.
The seasons are marked by two solstices and two equinoxes.
According to NASA, they are determined based on the Earth's tilt on its axis and the sun's alignment over the equator.
Meteorologists use a different method to mark the seasons, basing them on the annual temperature cycle and our calendar.
Meteorological summer is made up of the months of June, July and August. Fall is September, October and November. Winter is December, January and February, and spring is March, April and May.
According to NOAA the meteorological seasons were created for observing and forecasting purposes and are more closely tied to the civil calendar than the astronomical seasons.
Consistency is also a factor. Breaking the seasons into neat, thee-month chunks makes it easier to tabulate data and track trends.