Summer to officially begin at 3:34 p.m. Monday

Published 8:08 am Friday, June 17, 2016

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 3:34 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 just over 65 degrees above the southern horizon. That’s just about 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 11 a.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 six 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.W. Bush was the president.

Vega’s diameter is believed to be a little over 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 tenth of the sun’s age. In the early 1980’s 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.

Remember on Monday at 1:34 p.m. to raise a glass of lemonade or the beverage of your choice to the official start of summer.

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Stars, a Month by Month Tour of the Constellations” published by Adventure Publications available at bookstores at http://www.adventurepublications.net