'Summer Triangle' can be seen in the sky this week

'Summer Triangle,' the famous star formation, can be found low in the eastern sky as darkness falls this week.

By , SPACE.com Skywatching Columnist

With summer in full swing in North America, the famous star formation known as the "Summer Triangle" can be found low in the eastern sky as darkness falls this week.

This huge triangle is composed of three of the brightest stars in the sky, each the brightest star in its own constellation. The pattern is nearly isosceles, which means it appears as a triangle with two equal-length sides.

The brightest in the bunch is the bluish-white star Vega in the constellation Lyra (The Lyre). Next up is the yellow-white Altair in Aquila, the Eagle. Finally there is the white star Deneb in the constellation Cygnus, or the Swan. The stars appear in that order, as the twilight sky grows dark. (This graphic shows how to identify the Summer Triangle stars.)

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When clear skies allow, the Summer Triangle is one of the favorite parts of the sky for most sky watchers, perhaps because of its sheer simplicity in contrast to overabundance of bright stars found in the wintertime sky.

If you are just getting started in astronomy, and especially as you watch for the first stars to come out after sundown during the coming weeks, you are not very likely to confuse the Summer Triangle with anything else.

Moreover, since this area of the sky is far removed from the zodiac, where the bright planets roam, it does not have any strange "stars" temporarily altering its familiar pattern, as Mars has done to Leo over the past few weeks.

Who named the Summer Triangle?

So who was the first to coin the moniker "Summer Triangle?"

In doing some research, it turns out that this celestial designation appears to be of relatively recent origin. Romanian astronomer Oswald Thomas (1882-1963) described Vega, Altair and Deneb as "Grosses Dreieck" (Great Triangle) in the late 1920s and "Sommerliches Dreieck" (Summerly Triangle) in 1934.

In the classic New Handbook of the Heavens, (McGraw-Hill Book Company, New York, 1941), authors Hubert J. Bernhard, Dorothy A. Bennett and Hugh S. Rice do speak of Vega, Altair and Deneb as a "... brilliant triangle composed of three of the 20 brightest stars in the heavens."

But in a twist, the triangle is designated not as a summer star pattern. Instead, it is described under the chapter "Autumn and Winter Stars," since, as the authors point out, the "big triangle" passes overhead on September evenings.

That is indeed the case, although it is only during the summer months of June and July that the triangle is visible for the entire night, from dusk until dawn.

So just exactly where did the popular "Summer Triangle" name originate?

Mystery solved?

Hans Augusto "H.A." Rey (1898-1977), is probably best known for he and his wife Margret's creation of the mischievous little monkey, "Curious George."

But in 1952, Rey wrote a constellation book titled, The Stars – A New Way to See Them (Houghton-Mifflin, Boston). In it, Rey made reference to the triangle on Chart 13, where he clearly sketched the star formation out, but under his description of Aquila, the Eagle, he wrote:

"Altair, Vega (in the Lyre), and Deneb (in the Swan) form a huge right triangle, known to all navigators."

Still, though, no "Summer Triangle."

The name finally came two years later, in 1954, Rey published another Houghton-Mifflin book, Find the Constellations, which was designed for young children. It is here, that (finally) we find a reference to the Summer Triangle.

In his Sky-View 3 description, Rey wrote: "Vega, Altair. And Deneb form the famous 'Summer triangle,' with a right angle at Vega."

Rey always noted that the Summer Triangle was a "navigator's landmark." One of the most notable books on celestial navigation is the American Practical Navigator by Nathanial Bowditch.

As it turns out, this publication does indeed make reference to the triangle formed by Vega, Deneb and Altair . . . but not as the Summer Triangle.

Back in 2005, I received an e-mail from a gentleman in Missouri who told me:

"One summer evening in 1958 (as I recall) my father pointed out a satellite passing through the Summer Triangle. When I asked him what that was he explained that it was a group of three navigational stars taught to him when he studied as a naval aviator.

"He showed me a three-ring binder, dating from about 1944, that contained star charts provided by the Navy. I remember seeing several charts on which Vega-Deneb-Altair were connected by lines and marked 'Summer Triangle.'"

"Sir Patrick's Triangle?"

In the United Kingdom, many credit the legendary British astronomer, Sir Patrick Moore as the first to coin the term.

In his 1992 book Fireside Astronomy (John Wiley and Sons), Moore writes:

"Many years ago, during a television broadcast, I introduced the nickname of "the Summer Triangle" and everyone now seems to use the term, even though it is completely unofficial and the three stars of the Triangle are not even in the same constellations."

While there is no reference in his book, to an exact date when he made this statement, it couldn't have been any earlier than April 1957. That's when Moore's monthly television program "The Sky at Night" made its debut on BBC television – but this came at least three years after Rey first referred to the Summer Triangle.

Susan Rose, a past President of New York's Amateur Observers' Society (AOS), is a good friend of Moore.

"Patrick had not read Rey's books prior to using the phrase during one of his programs in 1958. When he used it, it caught on. It would seem that they coined it independently of each other but because of his TV presence, it became more widely known and therefore associated with him."

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

IN PICTURES: Where stars form

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