Solstice boon: It’s the brightest weekend of the year

(Photo by Dion Ogust)

Friday, the 21st is the Summer Solstice.

Together with the equinoxes and the Harvest Moon, it’s the final Earth/sky connection still widely noticed by the public in developed nations. By contrast, older or more primitive cultures continue to celebrate solstices in a big way. It still doesn’t get the attention that it used to, when the Maya tossed in-laws from pyramids on this date. In our time such exuberance is considered over-the-top, so we simply note that it’s the start of summer.

If you’re a stickler for precision, this odometer click to summer happens 64 minutes after the day’s start, at 1:04 a.m. You’ll probably go to sleep in springtime and just sleep through it. Perhaps you’ll at least have solstitial dreams. (Nobody knows why early dreams tend to relate to recent experiences while, as the night goes on, later ones last longer, and are more mysterious and surreal in content.)

Of course, a lot more is happening than the mere “start of summer.” And since solstitial phenomena change very slowly during the days before and after the actual event, what follows here is true no matter when you read this article.

This weekend is when the Sun sets at its most rightward position. Sunlight enters windows at angles unseen at any other time, striking dusty parts of rooms that normally don’t get illuminated enough to deserve cleaning. During the day, we get the highest possible Sun. This occurs at 1 o’clock each afternoon. People now cast their shortest shadows. (Again, if you like precision, our midday shadows stretch away on the ground precisely one-fifth of our body height: Figure slightly more than one foot.) But from nowhere in the continental US is the Sun ever exactly straight up, so that shadows vanish. Key West comes closest: From there, the Sun misses the exact zenith by a paltry and undetectable one degree.

These are our brightest days, with 15 hours and 17 minutes of direct sunshine in the mid-Hudson Valley, plus the year’s longest twilight. Add sun and twilight together and we experience over 17 daily hours of bright, usable daylight and just seven hours of night: bad for astronomers and vampires.

Since the Sun’s intensity depends on its height, its visible rays and ultraviolet now max out. But paradoxically, the Sun appears unusually small – because it’s much farther away than average. The Solstice happens just ten days before our planet reaches its annual far-point or aphelion, making the Sun look three percent smaller and seven percent less bright than in January. Of course, its high-up position more than compensates for this.

Just 21 years ago, in 1992, the Solstice Sun started floating within the constellation of Taurus instead of Gemini, where it had been since the days of the Roman Empire. Before that, it was in Cancer. It will now remain in the Bull Place for the next 30 centuries. However, out of tradition, the line on Earth connecting all the places where the solstitial Sun hovers directly overhead this weekend is still called the “Tropic of Cancer.”

By rights, the signposts down there should be crossed out and changed. Any volunteers?

Largest, closest Moon of the Year:

On Saturday Night, June 22, we’ll see the largest Moon of 2013. It reaches its absolute near-point the same hour it’s precisely full, at 7:32 AM Sunday morning – a few hours after it’s already set. Tides will thus be extraordinarily high that day and Monday.

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