This week is the swan song for spring 2013 while summer astronomically and officially kicks off early Friday morning. At 1:04 a.m., the sun reaches its most northern position and that means the sun takes the longest, highest arc across our sky providing us with a maximum 15 hours and 36 minutes of official daylight. The sun will achieve a midday altitude of 72.5 above the southern horizon. Because of that, you can cast you're shortest shadow of the year at 1:08 p.m. Friday. It doesn't occur in the noon hour because of daylight savings time.
With the long day that means short night and that results in stargazers taking a real beating this time of year. It's a late night affair that's also aggravated with longer evening and morning twilight in our northern latitude. With less than an hour of twilight either side of sunset and sunrise, we're down to about six and half hours of quality stargazing. Okay, I'm done whining here. The bad or good news here, depending on your perspective, is that after tomorrow we start gradually losing daylight and gaining stargazing time.
Once it finally gets dark, what's left of the spring constellations are hanging in the western sky. Unfortunately, the spring constellations are not exactly celestial barnburners. Constellations like Cancer the Crab, Corvis the Crow and Coma Berenices the Cut Hair don't exactly make the highlight film for backyard astronomers. Leo the Lion is a little better. That's the constellation that looks like a rightward leaning, (nothing to do with its politics), backward question mark in the western sky after evening twilight. The moderately bright star at the bottom of the leaning question mark depicts the lion's heart. The rest of the cycle outlines the head of the beast. In about another month, we'll lose Leo in the twilight while Earth turns away from that part of space in its orbit around the sun.
Over in the eastern sky right now, the stars and constellations of summer are on the rise, and from night to night and week-to-week, they'll start out the evening higher in the sky as darkness sets in. Among them are the three bright stars that make up what's known as the "Summer Triangle" that's very easy to find. Simply look in the northeastern quarter of the sky for the three brightest stars you can see and that's it.
This triad of stars is one of the best tools for getting around the summer sky because each of the stars is the brightest member in it's respective constellation. The highest and brightest is Vega in the constellation Lyra the Harp. The second brightest star is Altair on the lower right side of the triangle that is also the brightest luminary in Aquila the Eagle. The third brightest on the lower left corner of the triangle is Deneb, brightest star in Cygnus the Swan, also known by its nickname the Northern Cross.
Deneb is the dimmest of the summer triangle as we see it, it's the biggest and most powerful of the three stars. Its diameter is a little more than two hundred times that of our sun, which would give it a girth of 150 to 200 million miles. Now, that's one big fusion powered nuclear furnace. Deneb is the faintest stellar member of the summer triangle because of its immense distance. It emanates from more than 1,500 light years away.
Just one light year, the distance that light travel in year's time, equals just under six trillion miles. In miles, that would make Deneb 8,700 trillion miles away. If you can get your arms around how far away that is, more power to you. Also, since Deneb is 1,500 light years away, then by definition, the light we see from it tonight left that star right around the year 500 AD.
As far away as Deneb is, it's still a fairly nearby star in our home Milky Way Galaxy, which stretches more than 100,000 light years in diameter. Don't ever forget the vastness of what you're peering into when you spend a summer night under the stars.
Celestial hugging
On Tuesday and Wednesday evening the football shaped waxing crescent moon will pass by Saturn and the bright star Spica in the evening southern sky.
(Lynch is an amateur astronomer and author of the book, "Stars, a Month by Month Tour of the Constellations." Contact him at mikewlynch@comcast.net and https://www.facebook.com/mike.lynch.12327.)