Summer arrived astronomically in Marshall at 5:51 a.m. today, the moment of the annual summer solstice. That's when the sun, in its path among the celestial sphere, reaches its highest point in our sky. The noontime altitude of the sun around here is just more than 68 degrees above the southern horizon. That's just a little more than 20 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 a little after 1:15 p.m. because of daylight- saving time and our exact longitude.
While we have 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. That's because from now until late December, daylight hours will get shorter and shorter. The kind reality, though, is that the best of summer weather is still ahead of uswell let's just hope!
When it's finally dark enough for stargazing this time of year and that's after 10 p.m. for decent stargazing, there's a sure sign of summer among 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, each of the stars being the brightest in their respective 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 unreliable Chevrolet car from the 1970s, and some pronounce it Veega. Any way you pronounce it, Vega is a significant and even historic star. It is the brightest star in the tiny constellation Lyra the Lyre, which is supposed to be an old-fashioned harp. 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, which equates to just less than 146 trillion miles. Trust me, that's relatively close for a star. One light year equals just less than 6 trillion miles and is defined as the distance light can travel in one year's time in the vacuum of space. So, since Vega is 25 light years away, the light we see from it tonight left that star in 1989 when very folks had a cell phone and email was virtually unknown. The price of gas was about a $1.12 a gallon!
Vega's diameter is believed to be a little more than two 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 and that's part of the historical aspect of this young star. 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 is even closer to Earth than Vega at 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. It's whirling so fast that Altair is 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. Now there's no way you can see Altair as a lopsided star through even the largest of backyard telescopes, so you don't have to worry about getting dizzy gazing at it.
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 and you'll 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 around 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 living inside Deneb and what's left of our Earth would be at the outer edge of the great shiner.
The only thing that makes Deneb less brilliant in our sky than Vega and Altair is that it's a heck of a lot farther away. It's really difficult for astronomers to determine the distance of Deneb, but it's believed to be around 1,500 light years away. The light we see from Deneb this summer left that star in 709 A.D. No one was twittering back or taking selfies with their smart phones back then.
Well that's it, the Summer Triangle that we'll get to enjoy not only this summer but into this autumn as it gradually migrates to the west from night to night. Don't waste the summer of 2014!
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/Paul and is author of the book, "Stars, a Month by Month Tour of the Constellations" published by Adventure Publications available at bookstores at www.adventurepublications.net
MAKE THE STARS YOUR OLD FRIENDS!
If you have any astronomical questions or want me to write about something you're seeing the night sky drop me a line at firstname.lastname@example.org
Astronomical Happenings around the Greater Marshall Area
Planetarium show at Southwest University. For more information call 507-537-6178 or www.smsu.edu/CampusLife/Attractions/Planetarium/Index.htm