First Day Of Summer

First Day Of Summer, Hot enough for you? With a fearsome heat wave moving from the Midwest to the Eastern Seaboard, we hardly need a reminder that summer is upon us. But we have one anyhow. The summer solstice — the astronomical beginning of summer in the Northern Hemisphere — takes place at 7:09 p.m. ET on June 20. That makes this the longest day of the year north of the equator. From now until December, the days gradually get shorter, though not immediately cooler.

We are already told the U.S. has had the warmest spring since record-keeping began in the 19th century. Today there are heat warnings for 13 states, with highs in the upper 90s in New York, Boston and Washington, D.C., and heat indexes higher than 100 for cities that include Philadelphia and Raleigh.

“You’re talking about almost 15 degrees above normal,” said Kristin Kline, a National Weather Service meteorologist in Mount Holly, N.J.

It is mere coincidence that this is happening on the day of the solstice. Generally, the sun’s heat, trapped by the atmosphere, has a lagging effect, which is why August in the U.S. is usually hotter than April, even though the days are the same length.

A quick reminder of what’s happening: Earth, turning on its axis as it circles the sun, is tilted at an angle of 23.5 degrees relative to its orbit. Whatever the season, the axis points the same way, with Polaris, the North Star, hovering over the North Pole. (ABC News)