Stars form triangle in summertime sky
We're just about all done with spring and even though we're already living the summer life with kids out of schools and vacations under way, summer has still not officially arrived, at least astronomically. That happens Monday at 6:34 p.m.
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 more than 72 degrees above the southern horizon. That's around 18 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., mainly because of Daylight Saving 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.
What's ironic about the astronomical start of summer is that it's the beginning of our slide toward winter, because from now until late December daylight hours get shorter and shorter. So make the most of these longer summer days.
While the sun reaches its high point during the day, there's also summer showing up in the night sky. The summer constellations are really showing themselves on the eastern celestial stage.
When it's finally dark enough for stargazing, and that's after 10 p.m. this time of year, there's another sure sign of summer. It's the bright summer triangle in the eastern sky, 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 eastern 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 and some stargazing snobs insist on pronouncing it Veega. Any way you say it, Vega is a significant and even historic star.
It is the brightest star in the small constellation Lyra the Lyre, which is supposed to be an old fashioned harp. It sure doesn't look like one though.
Vega is the third brightest nighttime star that 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 1991 when George H. Bush was still the U.S. president.Vega's diameter is believed to be a little over 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 tenth of the sun's age.In the early 1980s astronomers had evidence of a developing solar system. Since then, astronomers have detected at least one planet about the size of Jupiter orbiting Vega.Also since that time hundreds of other solar systems have been confirmed in just our local neighborhood of the Milky Way, but at the time that was the first sign of what we now refer to as extra solar planets.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, a constellation I'll tell you more about next week in Starwatch.Altair's 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. Altair is whirling so fast that it's lopsided. Altair's equatorial diameter is believed to be at least 20 percent larger than its polar diameter.Many astronomers believe that if it spun much faster the star would literally fly apart. There's no way you can see how lopsided Altair is, though, even through the largest of backyard telescopes.The second highest but faintest star on the lower left corner of the summer triangle is Deneb.It's also 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, don't be fooled. 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.The only reason Deneb is the least brilliant star in the summer triangle is that it's a heck of a lot farther away than the other two.It's really difficult for astronomers to determine the distance of Deneb, but it's believed to be somewhere from 1,600 to maybe more than 3,000 light years away.Even at the lesser distance, of the light we see from Deneb this summer left that star in around 400 A.D. That was right about the time of the fall of the Roman Empire.Enjoy the Summer Triangle in our night sky not only through the summer, but right through autumn.Remember tomorrow at 6:34 p.m. to raise a glass of lemonade or the beverage of your choice to the official start of summer.<i>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</a>
