Stargazing in Oklahoma? Look for Vega, Altair, and Deneb — the Summer Triangle
Look at the star chart and notice the three bright stars, Vega, Altair, and Deneb that sit in the center of the sky. Together, these three stars make up the Summer Triangle. You really can’t miss them. Vega is the third brightest star visible from Oklahoma. Altair is the ninth brightest we can see, and Deneb is the 15th.
Two factors determine the brightness of a star in our sky: How much light it emits, the star’s luminosity, and the star’s distance. We rate luminosity compared to our sun’s light output. Altair is 17 light-years away and is 10.6 times brighter than our sun. By comparison, the closest star to us beyond the sun is 4.2 light-years away. Vega sits 25 light-years distant and puts out 50 times more light than our sun. Deneb is one of the most distant stars visible to the naked eye at 1467 light-years and shines an incredible 196,000 times brighter than our sun. If Deneb were as close to us as Vega, it would far outshine anything in our sky other than the full moon and the sun!
Vega and Altair are the main characters in the Japanese Star Festival known as Tanabata. Vega and Altair sit on opposite sides of the Milky Way, the great heavenly river in the sky. Vega represents Princess Orihime, a weaver who made beautiful cloth by the sky river. Her father is the God of the Heavens. Because she was so despondent at never finding love, Orihime’s father introduced her to Hikoboshi, a cow herder who lived on the other side of the Milky Way, marked by the star Altair. Their attraction instantly grew great, and they married soon after.
The Sky God soon became frustrated as Orihime stopped weaving her beautiful cloth, and the cows wandered all over the sky because Hikoboshi spent all his time with his beloved wife. To set the heavens right again, Orihime's father forbade the lovers from seeing each other. Orihime begged her father to reconsider. Out of love for his daughter, he allowed the two to spend one day a year together, on the seventh day of the seventh month, when Japanese lovers celebrate Tanabata.
But, the river of the sky proved to be too deep. Orihime cried until a flock of magpies formed a bridge for her to cross. They do this every year unless it rains on that day, in which case Orihime and Hikobosi must wait another year to be together. In Japan, young couples pray for nice weather on Tanabata so Orihime and her husband can unite for that one day. The festival is celebrated on July 7, but the stars are highest in our sky in August.
Views and shorter days
On Sept. 16, a nearly full moon sits below Saturn in the evening sky, and by the 18th, it has moved eastward to sit below Jupiter. Both nights offer interesting astronomical views.
At 1:21 p.m. Sept. 22, the sun shines directly over the equator marking the autumnal equinox. From then until next March, nights will be longer than days.
Planet Visibility Report
All five visible planets Mars, Mercury, Venus, Saturn and Jupiter shine in the sky at sunset throughout September, although Mars will be lost in the evening twilight. By the end of September, Mercury also becomes overpowered by the evening twilight. The new moon occurs on Sept. 6, with the full moon lighting up the night sky on Sept. 20.
Star Map Caption/Credit: The map shows the sky at 11:00 early in the month, 10:00 in the middle of the month, and 9:00 at the end of the month. Map produced using Night Vision star mapping software.
Image Caption/Credit: Detail star map with Milky Way produced with SkyGazer star mapping software.