Summer’s here officially, since today’s the summer solstice. That’s when the sun reaches its highest point in the sky.
The noontime altitude of the sun in Everett is about 66 degrees above the southern horizon. That’s within 25 degrees from the overhead zenith. Actually the sun doesn’t reach its highest point in the sky at noon this time of year. That happens after 1 p.m. because of daylight savings time and our exact longitude.
This is the longest day of the year with the sun making a big arc across the sky, rising in the northeast and setting in the northwest. The summer solstice is kind of a bummer, because from now until late December daylight hours will get shorter and shorter.
There’s a sure sign of summer in the rising stars in the east-northeast skies. It’s the bright summer triangle, made up of the three brightest stars from three different constellations.
Finding the summer triangle is easy. Just look for the three brightest stars you can see in the northeastern sky and that’s it. Each of the three stars has its own special story.
The highest and brightest star is Vega. Some pronounce it like the old Chevrolet car, Vayga, and some pronounce it Veega. Any way you say it, Vega is a significant and even historic star.
It is the brightest star in the constellation Lyra the Lyre. Vega is the third brightest nighttime star we see during the course of the year.
The main reason it’s so bright is that it’s relatively close. It’s only 25 light-years away, almost 146 trillion miles. That’s relatively close for a star. One light-year equals a little less than six trillion miles and is defined as the distance light can travel in one year’s time in the vacuum of space. Since Vega is 25 light-years away, the light we see from it tonight left that star in 1984 when Ronald Reagan was still our president.
Vega’s diameter is believed to be a little more than 2 million miles across, about 2.5 times our sun’s diameter. It’s also twice the mass of our sun. Astronomers have concluded that Vega is only about a 10th of the sun’s age.
In 1983 the Infrared Astronomical Satellite discovered a ring of dust surrounding Vega. This was thought to be evidence of a developing solar system around Vega and was big news.
Later, in the 1997 movie “Contact” with Jodie Foster, Vega was used as the place that we made contact with aliens. Since then astronomers have detected at least one planet about the size of Jupiter orbiting Vega.
The second brightest star in the summer triangle is Altair, on the lower right hand corner. It’s the brightest star in the constellation Aquila the Eagle. Altair’s even closer to Earth than Vega, just under 17 light-years away. The remarkable thing about Altair is that it’s a real spinner, rotating on its axis once every nine hours. By comparison, it takes our sun about a month to make a complete spin.
Altair is whirling so fast that it’s lopsided. It’s believed that its equatorial diameter is at least 20 percent larger than its polar diameter. Many astronomers believe that if it spun much faster Altair would literally fly apart.
The third and faintest star in the summer triangle is Deneb, on the lower left corner. It’s the brightest star in the constellation Cygnus the Swan. Cygnus also has the nickname “The Northern Cross” because it really looks like a cross. Deneb is positioned at the top of the cross, which is rising on its side above the eastern horizon. Just gaze to the right of Deneb to see the crosspiece and the rest of the cross.
Even though Deneb is the faintest star in the summer triangle, it’s one of the largest and most luminous stars in our part of the Milky Way galaxy. It’s believed to be 200 times the size of our sun and kicking out 60,000 times the light of our home star. If you were to put Deneb in place of our sun, the inner planets Venus and Mercury would be inside Deneb and what’s left of our Earth would be at the outer edge of Deneb.
It’s really difficult for astronomers to determine the distance of Deneb, but it’s believed to be somewhere from 1,300 to more than 1,800 light-years away. At 1,300 light-years, the light we see from Deneb this summer left that star in A.D. 709
Mike Lynch is an amateur astronomer and professional broadcast meteorologist.
He is author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com.
The Everett Astronomical Society welcomes new members at www.everettastro.org/
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