Night_skies_oct07

Jeff Green | Sep 28, 2006

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TheNightSkies of October, 2006:Pleiades Occultation and Meteor Shower

by Leo Enright

Locally, at the beginning of October, sunset is at about 6:45 p.m. Eastern Standard Time, and astronomical twilight ends at about 8:30 p.m. - more than an hour earlier than it did just a month ago. By the end of October, sunset will be a few minutes before 6 p.m., with astronomical twilight lasting until a few minutes after 7:30 p.m. However on October 29, the last Sunday of the month, at 2 a.m. we will return our clocks to Standard Time, and so on the last three nights of the month, including Hallowe’en on Tuesday, October 31, sunset will occur just before 5 p.m. and the end of twilight about 6:30 p.m. Standard Time.

These increasing hours of darkness mean that many people, even when returning home at the end of the work-day, can enjoy some of the wonders of the autumn sky which still features the Milky Way passing overhead, in a grand northeast to south-westward sweep in the early night and in the east to westward direction later in the night. This great band of light, which we are so fortunate to be able to see from our rural locations, is actually the combined starlight of the many billions of stars in our home galaxy, with our sun being just one of those billions of stars. Having observed the Milky Way over the past few months, many readers know well by now three of the constellations whose bright stars are found within it: Cassiopeia, in the shape of a large “W”, now high in the northeast, Cygnus, the Swan, also known as the Northern Cross, which is now slightly west of the zenith (the directly-overhead position), and Aquila, the Eagle, which is now in the southwest. Low in the south, where we observed “the Teapot of Sagittarius” over the past two months, we now see the constellation Capricornus, the Sea-Goat or Goat-fish, a bizarre animal from ancient mythology. Modern stargazers tend rather to see in the “V” outlined by its bright stars the shape of a large boat’s hull as viewed from the front. Sagittarius’s Teapot has now moved into the low south-western sky, and it may be seen setting soon after midnight, if one has a good horizon view in that direction. The three very bright stars of the Summer Triangle, Vega, Deneb, and Altair, which were almost overhead in the evening skies of the past two months, are now in the western half of the sky, which they dominate until they begin to set at about 3:00 a.m. Meanwhile, in the late evening, the bright stars of the “Winter Sky” are moving up into the eastern part of the heavens. They are led by the close cluster of stars called “The Pleiades”, or sometimes “The Seven Sisters”, but known in Japan as “Subaru” (an image of stars conveniently used by one of the country’s important car-makers). This “little cloud of stars” can be easily seen in the east any clear evening after 10 p.m. On clear moonless nights, use it to test your eyesight. If your location is not too light-polluted, you should be able to distinguish in the cluster its six brightest stars. Then note whether you are among the few people who can distinguish the “Seventh Sister”. (Sharp visual acuity may allow you to do this, but remember that children and young people tend to do it more easily than adults.) Then taking a pair of ordinary binoculars, marvel at the two dozen or more stars that you can easily see within this cluster. If conditions happen to be very good, you may even catch a glimpse of the slightly bluish nebulosity that is near one of the brightest stars in the cluster. By midnight on October nights, the outline of Orion, the Great Hunter, may be seen starting to rise in the southeast – a hint of the many bright stars of winter that he will bring with him for the following months.

Of the five bright planets that may be seen with the unaided eye, only three may be seen this month. Jupiter is very bright and easily visible low in the south-western sky for almost an hour beginning about a half-hour after sunset, IF one has a good view of the south-western sky right down to the horizon. The planet Mercury may be seen below Jupiter for about two weeks beginning on October 10, but it is not as bright as Jupiter and may require binoculars to be sure of seeing it. Saturn rises in the east at about 1 a.m. and is one of the bright objects in the eastern sky from then until dawn.

Several other highlights are to be noted. On the night of October 9, the moon moves in front of the Pleiades Star Cluster, providing an opportunity to observe what astronomers call occultations of some of the bright stars in that cluster. Watch with binoculars or a small telescope to see these stars suddenly disappear at the left side of the moon, and later in the night and early morning, to see these same stars “pop into view” again at the right side of the moon. In the early morning of Saturday, October 21, the annual Orionid Meteor Shower reaches its peak, with many meteors or “shooting stars”, as they are sometimes called, radiating out of the constellation Orion in the southern sky. The best time for seeing them is from midnight to dawn on October 20-21, but also from midnight to dawn any clear night from October 17 to the 24th. This year is expected to be a very good one since moonlight does not interfere. These meteors are interesting for several reasons. They are caused by the stream of dust particles left in the inner solar system by the famous Halley’s Comet which many of us saw in 1986, and these meteors travel the fastest of all the known meteor showers, zipping across the sky at an amazing 66 kilometres per second! Look generally in the eastern and southern directions, and do not use any optical aid. Be prepared to see something moving faster than you have ever seen before! Record the numbers per hour that you observe. I would be interested in hearing from readers about the numbers they are able to see per hour.

Enjoy the many wonders of the autumn skies! For those who are interested in having star maps and information about observing the sky year round, a book called The Beginner’s Observing Guide is now available at Sharbot Lake Pharmacy.