Mountain Skies: Planets Disappear One By One This Fall
Last updated 9/3/2018 at 2:30pm
The Summertime Milky Way is now high overhead just at sunset. While this beautiful veil in the sky may have been obvious to the casual observer in years gone by, nowadays it takes some planning and effort to enjoy it. However, all one really needs is a dark night with a clear view of the sky; some of the overlooks on the Blue Ridge Parkway and the campus at PARI provide gorgeous views not only of the mountains during the day, but also the stars at night. Start by looking a little to the west of due south and you will find our old friends Scorpius and Sagittarius. The center of the Milky Way is in the direction of Sagittarius and, for this reason, this area of the sky is rich in the nebulae and star clusters so popular with astronomers. If you have a pair of binoculars handy, lean back in your lawn chair and enjoy this rich area of the sky.
Now follow the band of the Milky Way upward until you are looking straight overhead. Notice a pattern of six stars that looks like a large cross in the sky. While some people call this pattern The Northern Cross, it is officially the constellation of Cygnus, the swan. In Greek mythology, Cygnus was the friend of Phaeton, the son of Helios, god of the sun. Helios had the job of driving the sun chariot, pulled by four spirited horses, across the sky each day. One day, Phaeton “borrowed” his father’s chariot and tried to drive it himself. But he could not control the horses and, with a little help from a thunderbolt thrown by Jupiter, soon fell out of the chariot landing in the river Eridanus. Cygnus saw this and dove into the river until he had recovered the mortal remains of his friend. Jupiter rewarded this act of friendship and loyalty by turning Cygnus into a beautiful swan and placing him in the sky. We find Cygnus with his tail and long neck stretching along the Milky Way, which represents the river Eridanus. By the way, it is in a small select section of this area of the sky that the Kepler spacecraft carried on its initial search for extrasolar (not in our solar system) planets. As of Aug. 25, Kepler had discovered 2,737 planet candidates and 2,652 confirmed extrasolar planets. We know of 30 planets less than twice the size of the earth that lie in the “Goldilocks zone,” i.e., the habitable zone, of their central stars. (Visit NASA’s site http://www.nasa.gov/kepler/dis coveries for the latest numbers.)
How many planets in our solar system lie in the Goldilocks zone of our sun? In other words, how many of the planets in our solar system could have, now or in the past, been able to support life as we know it? Normally, the answer given by astrobiologists, the scientists investigating this issue, is two: Earth and possibly Mars. However, in the cover story of the September issue of Sky and Telescope (p.17), author Shannon Hall, a freelance science journalist, suggests Venus might have been included and states “If scientists could pinpoint the factors the tipped Venus away from becoming a habitable world and toward a noxious one, then they would also be able to pinpoint the factors that kept Earth on the other course.”
Venus, no matter its role in harboring possible life forms, is quickly disappearing on us for a couple of months. This, the brightest object in the nighttime sky after the moon, has been our “Evening Star” since March but passes by the sun in inferior conjunction on Oct. 26 to re-emerge in the morning sky in early November. But, never fear! Jupiter, the second brightest planet, will remain as our “evening star.” But, exactly one month later, on Nov. 26, Jupiter passes behind the sun in superior conjunction to pop out in the morning sky about a month after Venus. Another month passes and Saturn follows suit. So, the only visible planet well up after dark throughout the fall is the red planet Mars; but, as we pull away from it in our journey around our central star, its brilliance fades (to about half as bright by the end of September). Mercury does make an evening appearance in October and early November but is very low in the evening twilight.
Sept. 9, 2:01 p.m. EDT - New moon.
Sept. 16, 7:15 p.m. EDT - First quarter moon.
Sept. 16 -The sun, in its apparent path around the sky, moves from Leo, the lion, into Virgo, the maiden. Virgo personifies Ceres, the ancient goddess of the harvest, and we derive our English word “cereal” from her ancient name.
(About the Learning Center at PARI: The Learning Center at PARI is a public not-for-profit 501 (c) (3) organization established in 1998. Located in the Pisgah National Forest, the Learning Center provides STEM educational programs at all levels, from K-12 through post-graduate research. For more information about the Learning Center at PARI and its programs, visit http://www.pari. edu.)