Summer will officially arrive in the Northern Hemisphere today (June 21), marking the longest day, the shortest night and the beginning of summer.
The June solstice will occur at 11:54 a.m. EDT (1554 GMT), as the sun reaches the point at which it is farthest north of the celestial equator. To be more precise, when the solstice occurs, the sun will appear to shine directly overhead for a viewer stationed on the Tropic of Cancer (latitude 23.5 degrees north) in the western Atlantic Ocean, roughly 600 miles (965 kilometers) to the northwest of San Juan, Puerto Rico.
From midnorthern latitudes, we can never see the sun directly overhead, but the same principle holds. For example, as seen from Philadelphia at 1:02 p.m. EDT on solstice day, the sun will attain its highest point in the sky for this entire year, standing 74 degrees above the southern horizon.
To gauge how high that is, your clenched fist held at arm’s length measures roughly 10 degrees, so from the City of Brotherly Love, the sun will appear to climb more than “seven fists” above the southern horizon. And since the sun will appear to describe such a high arc across the sky, daylight will be at its longest extreme, lasting 15 hours and 1 minute.