Thursday, August 13, 2015

Seasons by the Stars

Several weeks ago after family members observed the close conjunction of the crescent moon and planet Venus, my 10-year old grandson pleased me by asking if the Summer Triangle was visible. Last summer we had pointed out to him this popular asterism. Our family astronomy tutorials had been on hold since last summer. Sure enough, three bright stars were rising toward our zenith from the eastern sky. These jewels are the standouts of three constellations of which they are members: Vega, brightest of the three, fifth brightest in the sky, a member of constellation Lyra; Altair, twelfth brightest in the the night sky, a member of constellation Aquila; and finally, most distant of the three, giant Deneb, is a member of constellation Cygnus, 19th in apparent brightness of all visible stars.

In preparation for this post, I stepped outdoors last night about 11 PM. The three bright stars of the Summer Triangle were directly overhead. They presided over one of the most beautiful summer evenings one could imagine. Cloudy wisps of light stretching across the heavens passed through the triangle and across the sky, reminding us that we are a part of a giant galaxy of billions of stars—the Milky Way. The “cloudy wisps” are composed of billions of distant stars. With naked eye we see perhaps 2000+ above our horizon on the most ideal nights of the year, far more with a good set of binoculars. As we graduate to more powerful telescopes the number of visible stars increases geometrically.

Why has the Summer Triangle asterism been so named? It shines prominently and majestically in the night skies of our Northern Hemisphere summer months, arcing across the dome of the sky each day from sunset to sunrise. This is caused by the rotation of Earth. Rotation causes the diurnal (daily) movement of the Summer Triangle and many other star groups. Owing to Earth’s rotation, every star in the heavens circles 360º around pole star Polaris every 24 hours. Stars such as Vega, Altair, and Deneb, therefore, rise and set each day. Sometimes stars rise or set during daylight hours. The 360º daily swing of each star in the sky relates to rotation of our planet. Rotation causes night and day. Revolution, a 365-day earth movement, causes Earth’s four seasons to cycle annually.

Summer in the Northern Hemisphere occurs only when the constant tilt of Earth’s axis is oriented toward the sun. This orientation results in warm, summer weather. During the night, the Summer Triangle shines overhead. Sky observers look out at the heavens from the night side of the Earth during these warm summer months. And what do they see? The prominent stars of the Summer Triangle shine like rulers of the night sky! 

Summer Triangle stars during the winter are approximately 180º away from their summer position because Earth is 180º removed in its orbit. Changes in position of stars due to revolution of the Earth are slow—about 1º per day because on each of 365 Earth days we revolve about 1º. On winter nights these stars are below the horizon and by day they are not visible in the bright sky.

We cannot resist highlighting another astronomical seasonal herald. Each December a beautiful constellation begins its ascent in the eastern skies as evening transitions to night. It is the constellation of Orion the Hunter, identified by the stars of Orion’s belt, sword and other bright stars. Famous in the mythology of many ancient cultures and mentioned three times in Scripture—Job 9:9, Job 38:31, and Amos 5:8—Orion is beloved among sky watchers. As winter grips the Northern Hemisphere and progresses during cold months, evening observers watch Orion slowly crawl across the winter skies. (This slow crawl is superimposed on the much more rapid daily trek of stars due to Earth’s rotation.) After the winter months springtime evening skywatchers observe it slowly descending into the western horizon over several weeks as warm weather approaches. By July, August, and September an old player appears once more on the sky stage. It is time for the Summer Triangle to manifest itself in all its glory once more.

The Bible does not dwell on lessons of astronomy such as modern discoveries concerning rotation and revolution. Short of being a modern textbook on science, the Holy Book is rich in insightful spiritual applications based on observation of the natural world. Figurative language is sometimes used to strengthen a particular personal interpretation of Bible statements. This problem was prevalent in Galileo’s day. It is still prevalent today. Today’s scientific discoveries, rather than casting doubt on the truth of Scripture, highlight the order and purpose of God’s created world.