Three Summer Stars in the Milky Way

The arrival of the warm and long days of summer also marks the return of the Summer Triangle and three of the brightest stars in the night sky, Deneb, Altair and Vega. I wax poetically about these sparkling gems when I give a star talk during warm summer nights, with each of the three stars bringing us a unique perspective. All three are in or near the band of the Milky Way, so a close up look at these through binoculars reveals the depths of our home galaxy. This week the Astronomy Picture of the Day (APOD) featured detailed descriptions of these stars and an excellent photograph shown here. Their article says it best.

Three Stars of the Summer Triangle

From APOD: "Rising at the start of a northern summer's night, these three bright stars form the familiar asterism known as the Summer Triangle. Altair, Deneb, and Vega are the alpha stars of their respective constellations, Aquila, Cygnus, and Lyra, nestled near the Milky Way. Close in apparent brightness the three do look similar in these telescopic portraits, but all have their own stellar stories. Their similar appearance hides the fact that the Summer Triangle stars actually span a large range in intrinsic luminosity and distance. A main sequence dwarf star, Altair is some 10 times brighter than the Sun and 17 light-years away, while Vega, also a hydrogen-fusing dwarf, is around 30 times brighter than the Sun and lies 25 light-years away. Supergiant Deneb, at about 54,000 times the solar luminosity, lies some 1,400 light-years distant. Of course, with a whitish blue hue, the stars of the Summer Triangle are all hotter than the Sun."

It's easy to spot the majestic asterism of the Summer Triangle rising out of the east after the late sunsets of June. Take a few minutes to appreciate the three stars that make up this distinctive pattern in the night sky.

Image and text courtesy of NASA and Rogelio Bernal Andreo.

Observing Twilight into Dusk

The minutes after sunset are some of the most beautiful, as the last rays of sunlight have disappeared and the sky begins its daily transition from bright blue to dark night. Looking west after sunset in the early days of Fall, you quickly find Arcturus shining due west, at first looking almost like an airplane that is moving very slowly. But soon you realize that this is a star, the third-brightest in the heavens. It is bright enough to shine clearly through the glow of twilight. The colors of the sky are changing rapidly during twilight, and the brightest stars soon emerge. In late September, you can easily find the fifth-brightest star in the heavens, Vega, directly overhead, guiding you to its neighbors Deneb and Altair in the Summer Triangle. And looking back toward the western horizon where Arcturus is shining, you can soon find the red supergiant star Antares shining low to the left (south-west) of Arcturus.

Later this week, the young Moon arrives in the twilight sky and passes near Antares. Find a nice western horizon, get comfortable, and enjoy the evening show that is pleasant, relaxing and beautiful to see.

Image courtesy of Sky & Telescope Magazine.

The Summer Triangle

One of the brightest objects in the nighttime sky each summer is called the Summer Triangle. Rather than being a single constellation, the Summer Triangle is an "asterism," a grouping of stars that make an interesting pattern but are not themselves a single constellation. The Summer Triangle is, as advertised, a very distinctive triangle of three very bright stars that form a 30-60 right triangle. The three bright stars are Vega, Deneb and Altair. With three stars at magnitude 0 or 1, the Summer Triangle shines through even light-polluted city skies.

If you have darker skies, the Summer Triangle is a quick guidepost to locating some of the most interesting objects you can see with binoculars or a telescope in the Milky Way. The image to the right is taken from the website of the Great Smoky Mountain Astronomical Society. I like their web images because they present a very easy-to-follow guide to the most interesting objects in the part of the Milky Way that passes through the Summer Triangle, including double stars, nebulae, star clusters and the patterns of the three constellations that include the three bright stars of the Summer Triangle: Lyra, Aquila and Cygnus. For another description of the same objects, try this page from the Royal Observatory in Greenwich.

Use your binoculars or a telescope - even if you are in a big city - and see how much of these constellations you can identify and how many of the interesting objects you can find lurking in their midst.