The pools have been unlocked and children are out for summer vacations, however, in an astronomical sense, summer starts on Monday that is formally summer break for the Northern Hemisphere.
The virtual arrangements of sun and Earth think it so.
Earth is inclined on its axis at 23.5 degrees, so it bends one way as it rotates around its axis whilst revolving around the sun. On June 21 this year, some years it's June 20, the North Pole is positioning towards the sun as much as is feasible.
Winter vacation takes place when the top half of the Earth, all north of the equator, moves directly away from the sun, leaving the North Pole in full darkness.
The sun will be seen as high as possible in the sky as it can be at 7:28 a. m. EDT (11:45 UTC) and will remain in the sky for a little bit of a second more than the previous day or the day after.
As Monday marks the sun’s crest, you may speculate why June 21 does not usually stands for summer's apex heat.
According to NASA, the logic has something to do with the slow speed at which seas and oceans boil over and cool down. By mid-June, the oceans of the Northern Hemisphere are found to be still cooler from winter's coldness, postponing the maximum air temperatures by a month and a half.