Summer Triangle: Vega, Deneb, Altair

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1 Summer Triangle: Vega, Deneb, Altair During the summer months, the Summer Triangle star formation lights the sky from dusk until dawn. It consists of three bright stars: Vega in the constellation Lyra, Deneb in the constellation Cygnus, and Altair in the constellation Aquila.

2 Summer Triangle While this asterism dominates the summer sky at our latitude it can be seen at least in part all year.

3 Vega The dominate star of the Summer Triangle asterism is Vega in the constellation Lyra. Vega is the brightest star in Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. Vega is a relatively close star at only 25 lightyears from Earth. Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun.

4 Vega Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun. Vega was the northern pole star around 12,000 BCE and will be so again around the year 13,727 when the declination will be '. Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded. It was one of the first stars whose distance was estimated through parallax measurements. Vega has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV* photometric system. * a wide band photometric system for classifying stars according to their colors

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6 Altair Look to the lower right of Vega to locate the Summer Triangle s second brightest star Altair. Altair (Alpha Aquilae) is the brightest star in the constellation Aquila the Eagle.

7 Altair is an A-type main sequence star just 16.7 light-years from Earth, making it one of the closest naked-eye stars visible in the sky. It is the 12th brightest star in the night sky with an apparent magnitude of Altair

8 Altair Georgia State University's Center for High Angular Resolution Astronomy (CHARA) The star is also rotating so rapidly at nearly 185 miles (300 kilometers) a second at the equator that it is at about 90 percent of the speed it would take to rotate fast enough to blow apart. One rotation takes about 9 to 10 hours. In 2006, astronomers were able to resolve flattening at the poles using long-baseline interferometry or networking several telescopes together to collectively obtain an image of the star

9 Altair Georgia State University's Center for High Angular Resolution Astronomy (CHARA) Altair is one of the few stars for which a direct image has been obtained. In 2006 and 2007, J. D. Monnier and his coworkers produced an image of Altair's surface from 2006 infrared observations made with the MIRC (Michigan Infrared Combiner) instrument on the CHAR array interferometer. This was the first time the surface of any main-sequence star, apart from the Sun, had been imaged

10 Altair resides in the G- Cloud (or G-Cloud complex). This is an interstellar cloud located next to the Local Interstellar Cloud. The Sun is currently moving towards it. It is currently unknown whether the Sun is embedded in the Local Interstellar Cloud, or in the region where the two clouds are interacting. Besides Altair the G-Cloud also contains the stars Alpha Centauri, Proxima Centauri and possibly others. Altair

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12 Deneb or Alpha Cygni is the brightest naked eye star in the constellation Cygnus. Deneb is the 19th brightest star in the entire sky. Its absolute magnitude is Deneb has a spectral type of A2Ia, a surface temperature of 8525 Kelvin and a luminosity 54,000 times the Sun. It has a mass of 20 solar masses and a diameter 110 times the Sun. Hertzsprung Russell diagram:

13 One of the truly great stars of our Galaxy, Deneb is among the most intrinsically bright stars and one of the largest white stars known. One 2008 study from the Hipparcos Data puts the most likely distance at 1,550 light-years, with an uncertainty of approximately 10%. Deneb's high mass (20 solar masses) and temperature (8, 525 Kelvin) mean that the star will have a short lifespan.

14 Vega, Altair and Deneb, these three white class A stars have roughly similar surface temperatures, Vega at 9500 Kelvin, Altair at 7550, Deneb in the middle, radiating at ~ Though Vega and Altair are really quite luminous, they are first magnitude primarily because they are close to us, averaging only 25 light years away. Deneb, on the other hand, comes in at an amazing 1,550 light years If placed at the distance of Vega, Deneb would shine at magnitude - 7.8, 15 times more brightly than Venus at her best, Deneb would be as bright as a well-developed crescent Moon, cast shadows on the ground, and easily be visible in broad daylight. Deneb is a true supergiant, its diameter, calculated from its temperature and luminosity, is 108 times that of the Sun, half the size of Earth's orbit.

15 With a rotation velocity of at least 30 kilometers per second, Deneb might take as long as half a year to make a full rotation. The star is evolving and has stopped fusing hydrogen in its core. It might be expanding and cooling with a dead helium core and on its way to becoming a red supergiant, or it might have advanced to the state of core helium fusion. Its fate is almost certainly to explode sometime astronomically soon as a grand supernova. The star is constant in its light, but its spectrum is slightly variable. Blowing from its surface is a wind that causes the star to lose mass at a rate a millionth of a solar mass per year, 40 million times the flow rate from the Sun. Deneb was a halfway decent pole 18,000 years ago, and will be again around the year 9800.

16 Summer Triangle: Vega, Deneb, Altair The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere s celestial sphere, with its defining vertices at Altair, Deneb, and Vega, the brightest stars in the three constellations of Aquila, Cygnus, and Lyra, respectively.

17 Summer Triangle The term was popularized by American author H.A. Rey and British astronomer Sir Patrick Moore in the 1950s. The name can be found in constellation guidebooks as far back as The Austrian astronomer Oswald Thomas described these stars as "Grosses Dreieck" (Great Triangle) in the late 1920s and "Sommerliches Dreieck" (Summerly Triangle) in The asterism was remarked upon by J. J. Littrow, who described it as the "conspicuous triangle" in the text of his atlas (1866), and Bode connected the stars in a map in a book in 1816, although without label.

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