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.
Summer Triangle
While this asterism dominates the summer
sky at our latitude it can be seen at least in
part all year.
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.
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 +86°14'.
• 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
• Look to the lower
Altair 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.
• 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 0.77.
Altair
• 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
Georgia State University's Center for telescopes together to
High Angular Resolution Astronomy
collectively obtain an image of
(CHARA)
the star
Altair
• 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
Georgia State University's Center for star, apart from the Sun, had
High Angular Resolution Astronomy
been imaged
Altair
(CHARA)
• Altair resides in the GCloud (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
• 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 -8.73.
• 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:
• 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.
•
•
•
•
•
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 ~ 8500.
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.
• 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.
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.
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 1913.
• The Austrian astronomer Oswald Thomas described these
stars as "Grosses Dreieck" (Great Triangle) in the late
1920s and "Sommerliches Dreieck" (Summerly Triangle) in
1934.
• 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.
Summer Triangle