Tuesday, June 21, is the first day of summer. The actual moment of what astronomer’s call the summer solstice occurs at 10:16 a.m. This the longest of the year and the shortest night of year.
The sun takes its longest path across the sky, rising is the northeast and setting in the northwest, and in between reaching its highest point in the sky at midday. Around Everett that means a little more than 65 degrees above the southern horizon.
As soon as it finally gets dark enough you can easily see what’s call the “Summer Triangle” in the eastern sky. It’s not one of the 65 to 70 official constellations we can see around here, but rather what astronomers dub an asterism: an easily seen pattern or picture in the stars that’s not one of the official constellations.
Most asterisms are made up of bright stars of several constellations. That’s certainly the case with the Summer Triangle. It’s easy to see even if you’re stargazing from a lit up urban area. Just look for the three brightest stars you can see in the low- to mid-eastern sky and that’s it. Each of those bright shiners is the brightest star in three respective summer constellations and each of them is very special in its own way.
The brightest and highest of them is Vega, the brightest star in a small constellation called Lyra the Lyre, which is an old-fashioned harp. Vega is a star that’s more than 25 light-years away, with just one light-year equaling nearly 6 trillion miles. The light we see from Vega this week left that star when Ronald Reagan was president.
Vega’s also bigger and hotter than our sun. It’s about 2 million miles in diameter, more than three times the girth of the sun and 17,000 degrees at its surface, 7,000 degrees hotter than our sun. In fact you can tell Vega’s one of the hotter stars in the sky by its faint blue tinge.
The second brightest star in the Summer Triangle is Altair in the lower right corner, fairly low in the eastern heavens. Altair is the brightest star in the constellation Aquila the Eagle. Altair is the closest star in the triangle, just over 16 light-years away.
Even with the best of backyard telescopes there’s nothing all that special to see. However astronomers know from spectroscopic analysis that Altair really has a spin to it, literally. It rotates on its axis every 10 hours.
My favorite star in the Summer Triangle is the faintest member on the lefthand corner, Deneb. It’s the brightest star in the constellation Cygnus the Swan, also known as the Northern Cross, and is one fanatically large and luminous star.
According to the latest data, this star at the tail of the heavenly swan is more than 1,500 light-years away. As well as we see this star you have to figure that it’s one humongous star. In fact it may be more than 250 million miles in diameter and kicking out over 39,000 times more light than our sun.
If you could magically pull Deneb in from its 1,500 light-year distance to the proximity of Vega, about 25 light-years away, about the only thing brighter in the sky would be the moon. Deneb is virtually the biggest single thing you can see with the naked eye in the early summer skies.
Mike Lynch is an astronomer and professional broadcast meteorologist, and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.
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