StarWatch 899 for the week of November 10, 2013By Gary Becker
Although we are moving towards the icy grip of winter, some of the vestiges of the summer sky can still be seen high in the west during the early evening hours.
The Great Summer Triangle (GST) is my favorite pattern of the fall sky, for as much as I enjoy those surprise winter snow events, I mentally try to hang onto the aura of summer as long as possible.
The GST is not really a constellation. It is derived from the brightest luminaries found in three constellations: Vega, the GST’s brightest star of Lyra the harp; Deneb, the faintest of the triad in Cygnus the Swan; and middle of the road, Altair of Aquila the Eagle.
After showing my Moravian astronomers the Great Summer Triangle at Shooting Star Farm several weeks ago, one of my students, Sophia Osbourne, posed the question of brightness vs. nearness.
“Are the three stars of the GST bright because they are near?”
As any good politician might respond, my answer was “yes and no.”
In order to answer that query, astronomers had to be able to calculate stellar distances. That problem was not solved to any high degree of accuracy until the early 1990s with the European Space Agency’s Hipparcos satellite, even though the first parallax (triangulation) measurements of stars occurred in the 1830s.
Now we know that Altair is 17 light years distant, Vega 25 ly, and Deneb, a staggering 1550 ly away.
Astronomers mathematically move stars to a standard distance from the sun to compare their brightnesses.
When we do this for the Great Summer Triangle’s stars, Altair turns out to be the wimp, but still 11 times brighter than our sun, Vega, about 50 times Sol’s luminosity; but Deneb, which is visually the faintest star of the GST, turns out to be the real powerhouse. It is nearly 60,000 times the sun’s brilliance. In fact, Deneb is the brightest star for its distance in the entire sky, proving again that in astronomy, looks can be deceiving.
Although we are moving towards the icy grip of winter, some of the vestiges of the summer sky can still be seen high in the west during the early evening hours.
The Great Summer Triangle (GST) is my favorite pattern of the fall sky, for as much as I enjoy those surprise winter snow events, I mentally try to hang onto the aura of summer as long as possible.
The GST is not really a constellation. It is derived from the brightest luminaries found in three constellations: Vega, the GST’s brightest star of Lyra the harp; Deneb, the faintest of the triad in Cygnus the Swan; and middle of the road, Altair of Aquila the Eagle.
After showing my Moravian astronomers the Great Summer Triangle at Shooting Star Farm several weeks ago, one of my students, Sophia Osbourne, posed the question of brightness vs. nearness.
“Are the three stars of the GST bright because they are near?”
As any good politician might respond, my answer was “yes and no.”
In order to answer that query, astronomers had to be able to calculate stellar distances. That problem was not solved to any high degree of accuracy until the early 1990s with the European Space Agency’s Hipparcos satellite, even though the first parallax (triangulation) measurements of stars occurred in the 1830s.
Now we know that Altair is 17 light years distant, Vega 25 ly, and Deneb, a staggering 1550 ly away.
Astronomers mathematically move stars to a standard distance from the sun to compare their brightnesses.
When we do this for the Great Summer Triangle’s stars, Altair turns out to be the wimp, but still 11 times brighter than our sun, Vega, about 50 times Sol’s luminosity; but Deneb, which is visually the faintest star of the GST, turns out to be the real powerhouse. It is nearly 60,000 times the sun’s brilliance. In fact, Deneb is the brightest star for its distance in the entire sky, proving again that in astronomy, looks can be deceiving.
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