You don’t need a thermometer hovering around 90 degrees to know it’s summertime…just look up at the night sky!
The three bright stars of the sky “asterism” called the Summer Triangle are beginning to dominate the night when darkness settles in around 10 pm. An asterism is a pattern of stars that are part of a constellation of several combined. Look north these nights and you’ll see the most famous asterism, the Big Dipper, hindquarters of Ursa Major.
When it gets dark, before 10 pm, face north and look up toward the east. The corners of a celestial triangle will be marked out by three bright stars, each in a different constellation. Watch in the twilight as they pop out from the azure blue.
The northern most star is Deneb (Da-NEB) in Cygnus the Swan. The brightest member of the triangle, Vega (Vee-GA or Vay-GA) is in Lyra the Harp. And the southern point is marked by Altair (All-TARE) in Aquila the Eagle.
Each star is unique in size, distance and energy output, and the asterism, star-pattern they make straddles the Milky Way. The Summer Triangle is easily seen from just about any skies, including light polluted parking lots and neighborhoods.
Like all stars, these celebrated three are unique suns that just happen to be around our stellar neighborhood of the Milky Way in a line of sight that makes
And like all the several dozen brightest stars of the night skies, the starlight of Vega, Deneb and Altair have been recorded by the eyes of humans since antiquity. They have been given different names by the ancient stargazers of Mesopotamia, Asia and Egypt, filled with tributes to mythological heroes.
Vega is a brilliant, bluish-white star and one of the closest to Earth, just 26 Light Years away. That means the light we see hitting our retina tonight left Vega in 1992. A Light Year is the distance light travels in a year at 186,000 miles per second, or about 6 trillion miles. Vega was the first star photographed through a telescope in 1850 at Harvard University.
As our Sun swings around inside one of the four spiral arms of our Milky Way, we are heading toward Vega at 40,000 miles per hour. At 156 trillion miles away, and just under one million miles a day closer, the Sun will take more than 500 thousand years to reach Vega.
Vega was also the North Pole star some 12,000 years ago, and as Earth’s axis wobbles around every 26,000 years, it will be the pole star again in 14,018 A.D. Vega is a powerful, young star, less than one-fourth the age, but emitting 50 times the energy output of our only slightly smaller, 5 billion-year-old Sun. At 0.03 magnitude, it is the 5th brightest of all the stars in the sky, just a fraction brighter than 0.04 mag. Arcturus of the constellation Boötes, setting in the west around midnight.
Astronomers are looking for a planetary system around Vega, as it has a cloud of dense matter circling it like an early version of our Solar System. They suspect at least one planet the size of our giant Neptune is orbiting Vega!
The northern most star of the Summer Triangle, Deneb, is one of the most powerful stars in the sky. A magnitude fainter than Vega, Deneb has an incredible energy output that is 70,000 more powerful than our Sun. But the supergiant Deneb is very far away at 1,800 Light Years distant. It is so huge that if placed where our Sun is, Deneb would swallow up the orbit of Venus in our Solar System. Imagine Deneb being as close as our close neighbor Vega and we’d have a star easily visible in the daytime and casting a shadow at night.
Deneb is an Arabic name meaning “tail,” and that is where it is in the giant star-pattern Cygnus the Swan that flies down the Milky Way. This is also the top star of another asterism for Cygnus, the “Northern Cross.”
The southern star of the Summer Triangle is Altair in Aquila the Eagle, among the top 50 closest stars to our Sun, that’s why it appears so bright. At just 17 Light Years away, we bathe in its starlight as it appeared in 2001. Altair is the 12th brightest star in the sky at 0.77 mag. and looks white. The constellation Aquila is a miniature version of the Northern Cross asterism of Cygnus, looking like a small bird, or eagle, to the ancient stargazers. Indeed, the Arabic word Altair means eagle.
Altair is slightly larger than our Sun. But where our 800,000-mile-wide Sun rotates around once every 25 days, Altair spins on its axis every 6.5 hours! That makes the star have a huge bulge at its equator, it is twice as wide as it is tall! The shape of Altair will be defined in images for the first time by the powerful Webb Space Telescope when it is launched in 2020.
These brilliant stars and their constellations are the subject of folklore and myths of ancient civilizations. Cygnus is said to be the god Zeus in disguise to help him seduce Leda of Sparta. Aquila was a pet bird of the Greek god Zeus. And Lyra was the musical lyre given to Orpheus by Apollo.
The Summer Triangle is with us the rest of Summer until late fall, and the pattern is fun to watch wheel over head as the warm, late night hours of the Summer of 2018 bring unexpected pleasures to the inquisitive mind staring at the cosmos.
When looking at starlight, remember photon packets of light act like wavelengths (its color) and a particle (reflecting off objects). So, a photon of starlight enters the eye and we see its color while as a piece of that star enters our body. Think about that while under the spell of the Summer Triangle.