October 29 – November 11, 2018
Mount Washington — The Summer Triangle, a majestic, nearly isosceles triangle shaped by three of the brightest stars visible at northern latitudes, is prominent in evening skies from June through December. Vega, Altair and Deneb – in descending order of brilliance – are so luminous that we can spot them in the deepening blue of twilight.
On the summer solstice, the great triangle is found suspended above the eastern horizon at dusk, beginning its all-night journey in the heavens. At this time of year, midway between the autumn equinox and winter solstice, the three stars are positioned high in the south at twilight. Find Vega, 0.00 magnitude (m), high in southwest about half an hour after sunset. Altair, 0.75m, appears next, pointing south, about 15 degrees below Vega. As the sky darkens, look up above Altair and to the left of Vega to find Deneb, 1.25m, near zenith. Notice that the smaller the magnitude number the brighter the celestial object.
The Summer Triangle is an asterism* composed of the brightest star from each of three distinct constellations. In Arabic, the meaning of “Deneb” is “tail of the swan.” When the sky darkens, see three stars in a line below Deneb: They sketch the spread wings of Cygnus the Swan. Look beyond the Swan’s wings to a dimmer star, Albireo, 3.03m, that marks the head at the tip of the Swan’s long neck. Find Albireo to the left of Vega. Vega is the brightest star in the constellation Lyra the Lyre and Altair the brightest in Aquila the Eagle.
Follow the imaginary line from Vega to Altair to stumble upon dazzling, reddish Mars. When darkness falls, look beyond Mars to spot cold weather star Fomalhaut 1.15m. Fomalhaut, Arabic for “mouth of the fish,” marks the Southern Fish constellation.
Sunset today is 5:51 p.m. Eastern Daylight Time. On November 11, sunset is at 4:35 p.m., due to the trick of “falling back an hour” to Eastern Standard Time. EST is “real time”, determined by the actual time the sun rises. The time change begins on Sunday, November 4 at 2 a.m. Enjoy the hour gained.
Resources
*Asterism explained – https://theberkshireedge.com/eyes-to-the-sky-pegasus-venus-last-days-autumn-equinox-full-harvest-moon/
The naming of the Summer Triangle – https://www.space.com/1206-doorstep-astronomy-summer-triangle.html
