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When does summer start and when is the longest day?

Here's when the summer is officially set to begin.

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Published: May 26, 2023 at 5:12 pm

Ahh, the summer. Those blissful months where we spend more time outside than in (read: would if we weren’t stuck behind our desks). If you can’t wait to hit the beach, you’ll want to know precisely when summer starts.

As the clocks have already gone forward, activating British Summer Time, you may think that summer has already started. Not quite.

So when is it? With those in the US and in the UK wanting to know the exact timing of the summer in 2023 so they can finally start feeling The Sun’s warmth and see some butterflies, we’ve provided both meteorological and astronomical dates for you below (yes, they're different).

The summer is also home to the longest day of the year, with the most hours of sunlight. Keep on reading to find out when the longest day will be in the USA and in the UK in 2023.

When does summer start?

In the UK, the first day of summer 2023 is set to land on Wednesday 21 June. That is the astronomical first day of summer this year – the time at which the northern hemisphere is pointing directly towards The Sun.

This date also marks the summer solstice. Summer is set to end on 23 September, according to the astronomical calendar.

The first day of astronomical summerin the US is the same as in the UK, as both nations are in the northern hemisphere.

However, the meteorological first day of summer is Thursday, 1 June 2023.

The meteorological first day of summer is always on the first day of June (with summer ending on 31 August). Splitting the seasons into distinct three-month chunks divides the Gregorian calendar into four equal parts. This makes it simpler for meteorological observing and identifying seasonal trends, according to the Met Office.

When is the longest day?

The longest day of the year is Wednesday, 21 June 2023. This is the same as the astronomical first day of summer and is when we’ll see the most daylight hours in a single day in the northern hemisphere.

Throughout most of the UK and US, at least 16 hours of daylight is expected on this day. The longest day also means the shortest night.

What causes summer?

The seasons are caused by the Earth’s tilting axis as it orbits around the Sun. Summer is caused in the northern hemisphere when the north pole is tilting toward the Sun. Conversely, winter in the northern hemisphere is caused by the south pole tilting toward the Sun.

Essentially, the summer in the northern hemisphere takes place because the Sun’s rays hit that part of the Earth more directly. Of course, it is the other way around for those living in the southern hemisphere, with their summer starting in December.

Strangely enough, we are closest to the Sun (the perihelion) in January and we are furthest from the Sun (the aphelion) in July.

What caused the Earth to tilt?

Gravitational forces from the Sun and Moon, as well as the larger planets in the Solar System, Jupiter and Saturn, exert a pull on the Earth.

In addition to the series of bombardments endured by the Earth in its early days, this has resulted in a tilted axis. The angle of tilt cycles between 21.5 degrees and 24.5 degrees, in an astronomical cycle that occurs over a period of around 41,000 years.

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