Once upon a midnight summer’s dream

The Summer Triangle, outlined by Vega, Deneb and Altair is up in the eastern sky around midnight in early May and by 10 p.m. at month’s end. The band of the Milky Way passes directly between the trio. Stellarium

Midnight. Too late for a look at the sky? Not if you hungry for a token of summer. It’s out there alright – the Summer Triangle. It’s unclear who named this giant triangle formed by three of summer’s brightest stars – Vega, Deneb and Altair – but its usage has been around since at least the 1920s. The first person we know of to connect the three stars in a triangle, even though he didn’t give the figure a name, was the German astronomer Johann Bode back in 1816. Bode created some of the most beautiful star atlases ever made.

Star chart created by Johann Bode in 1805 showing Cygnus the Swan (Schwan) with Deneb and Lyra the Harp (Leyer) with Vega.

Sometime in the late 1920s Austrian astronomer and prolific astronomy popularizer Oswald Thomas described these stars as the “Grosses Dreieck” (Great Triangle) and later in 1934 as the “Sommerliches Dreieck” (Summerly Triangle). Another great name in astronomy, England’s Patrick Moore, who passed away last December, described the trio as the Summer Triangle starting in the 1950s in his many books and lectures.

A short time exposure shows the three bright stars of the Summer Triangle (Vega at top) and bright Milky Way. Photo: Bob King

Tonight you’ll see the famed asterism crest the eastern horizon around midnight. Vega, the westernmost of the three and earliest to rise, sparkles in the northeast by 10 p.m. Deneb’s up by 11 and joined by Altair shortly before midnight. Although tipped on its side and slung low in the east in early May, by month’s end, the triangle stands higher and becomes visible at nightfall.

From July through September the Summer Triangle rules the sky, standing upright in the south balanced on its southermost apex Altair. That’s how it got its name of course, since it’s most obvious in the mid to late summer months. Come October and November, the figure scootches over to the west and by December it’s gone – just in time for winter.

Each of the Summer Triangle stars has its own individual character. Altair (17 light years distant) is about twice the diameter of the sun, Vega (25 light years) about three times and Deneb (~2600 light years) is a supergiant star 200 times as big. Altair and Vega rotate rapidly causing them to bulge out at their equators. Illustration: Bob King

The brightest of the three pivotal stars is Vega in the constellation Lyra the Harp. All Lyra’s stars are dim, but Vega more than compensates with a radiance as pure and white as burning magnesium.

To find Deneb, the brightest star in Cygnus the Swan or Northern Cross, reach your balled fist to the sky and look ‘two fists’ to the lower left of Vega. Altair in Aquila the Eagle is way down to the lower right. Three-plus fists will get you there. Vega, Deneb and Altair are all easy to see even from a middle-sized city and suburban areas.

You can use this map to help you find the constellations belonging to each of the Summer Triangle’s stars. Stellarium

An additional treat awaits the eyes of rural observers or those who make a drive to the country. The Summer Triangle frames a bright section of the Milky Way, and with the moon out of the way for the next couple weeks, it’s worth the time to witness this most impressive sight.

I don’t know about you, but winter was too long in the tooth around here, so every time I see those three bright stars and swirly Milky Way I get jazzed for summer nights ahead.

7 thoughts on “Once upon a midnight summer’s dream

  1. Yes Bob it was a long winter also here, and now a spring of very variable weather, so the summer triangle is indeed a welcomed return. Thank you for the interesting article about its story, and Bode’s map – quite remarkable for a man which had trouble with his eyes.

    • Giorgio,
      You’re welcome, thank you. I’m hoping for clear skies again by the weekend to take in a view of Comet Lemmon. Wishing clear skies your way as well.

  2. When I looked into the sky I automatically looked at the summer triangle. I found it really interesting and did some research on it, and now its been almost a year and I am still thinking about it. I even have 3 moles on my shoulder that look just like it lol.

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