When is the first day of summer? It depends on whether you are referring to the astronomical or meteorological summer.
Usually when we talk about the first day of summer we are referring to the astronomical summer which is defined by the Earth's axis and orbit around the sun. However, at the Met Office we also mark the beginning of a 'meteorological summer'.
The meteorological summer begins on 01 June 2017 and ends on 31 August 2017.
The meteorological seasons consists of splitting the seasons into four periods made up of three months each. These seasons are split to coincide with our Gregorian calendar making it easier for meteorological observing and forecasting to compare seasonal and monthly statistics. By the meteorological calendar, spring starts on 1 March.
The seasons are defined as Spring (March, April, May), Summer (June, July, August), Autumn (September, October, November) and Winter (December, January, February).
This year the astronomical summer begins on 21 June 2017 and ends on 22 September 2017.
The astronomical calendar determines the seasons due to the 23.5° tilt of the Earth's rotational axis in relation to its orbit around the sun. Both equinoxes and solstices are related to the Earth's orbit around the sun.
Solstices and equinoxes are considered to be the astronomical transition points between the seasons and mark key stages in the astronomical cycle of the earth. In a year there are two equinoxes (spring and autumn) and two solstices (summer and winter). The dates of the equinoxes and solstices aren't fixed due to the Earth's elliptical orbit of the sun. The Earth's orbit around the sun means that in early January, the sun is closest (known as perihelion) and in early July it is most distant (aphelion).
What is the weather usually like in summer?
The graphic below shows what the weather can be like during summertime showing the wettest, warmest, sunniest, driest and coldest summers on record.