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Night Skies - August 30, 2007

Venus dominates our September morning skies

by Leo Enright

Sunset in this area on the first day of September is at about 7:45 p.m. EDT, and evening astronomical twilight ends at about 9:30 p.m., over an hour earlier than it did a month ago. In September the sunset time will be about two minutes earlier from evening to evening until by the end of the month it is at about 6:45 p.m., with twilight then lasting until about 8:30 p.m. In the mornings there is also a change, of over a half-hour in the times of dawn and sunrise. On September 1, morning astronomical twilight begins at about 4:45 a.m., and sunrise occurs at about 6:30 a.m.


The wonderful Milky Way that we learned to appreciate over the summer months still sweeps overhead in the late evening hours. As in the past two months, whenever we observe, we should look for Cygnus the Swan, also called The Northern Cross, “flying” almost directly overhead as evening twilight ends. This “stellar bird”, “flying southward” in the Milky Way, appears within the three bright stars of the Summer Triangle, and it may remind Canadians of the coming southward migration of our Canada Geese and other birds.

Among the five bright planets that may normally be seen with the unaided eye, four of them may be seen easily throughout the month of September, and the fifth one, though it may be seen on any clear evening during the month, will be a serious challenge for most people, because of where it is to be found in the sky. Begin with the challenging planet, Mercury, the first one that may be seen after sunset. Anyone expecting to see it this month must have a very good view of the western horizon with absolutely no trees or buildings blocking the view, and must use binoculars to search in the glow of twilight just above the horizon, beginning 20 to 30 minutes after sunset. It will be visible for only a short while before setting. Those who see it will notice that during the last half of the month it is close to the star Spica, brightest star in the constellation Virgo, and extremely close to that star on the evenings of September 21 and 22. The first bright planet very easily seen throughout evening twilight is Jupiter, which dominates the southwestern part of the sky and is visible for a little more than three hours before it sets. It appears above the red star Antares, brightest star in the constellation Scorpius, by about five degrees, which is half the width of a fist held at arm’s length. Owners of small telescopes will be fascinated by the changing positions of Jupiter’s four brightest moons – from night to night and sometimes even from hour to hour. Reddish Mars may be seen rising in the east shortly before midnight. It is well below the famous Pleiades star cluster and to the left of the larger cluster called the Hyades which is sometimes called the “Head of the Bull Cluster” because of its position in the constellation Taurus. Careful observers will easily note that Mars is becoming brighter over the month, and is brighter than reddish Aldebaran, the brightest star in the Hyades cluster. By morning twilight Mars appears very high in the sky. By far the brightest planet this month is Venus – 12 times brighter than Jupiter! Venus is seen rising in the east 1 hours before sunrise in early September, but its rising time is noticeably earlier each morning, until by the end of the month, it is seen rising over three hours before the sun rises. As with Mars, careful observers of Venus will notice that it becomes a little brighter each day until it reaches its greatest brilliancy in the third week of the month. By then it is bright enough to be easily seen in the daytime. (Yes, it’s true!) If you have never seen it in daylight, try watching Venus during morning twilight, and continue to follow it carefully right up until the time of sunrise, and after. (DO NOT use binoculars, because of the danger that you may accidentally look at the rising sun with them, and thereby cause eye damage or blindness.) The fifth of the bright planets to appear is Saturn. It rises in the east during morning twilight, well down and to the left from brilliant Venus. Throughout the month Saturn appears close to, and to the left of, the star Regulus, the brightest star in the constellation Leo, but very careful observers will notice that these two objects appear to separate slowly as the month progresses. It will be easy to notice, too, that Saturn rises earlier each morning and appears higher above the eastern horizon and closer to Venus that it did on September 1. In fact, by the end of the month it appears only half as far below, and to the left of, Venus as it did on September 1.

A very interesting lunar occultation will be moon’s passage over some of the stars of the Pleiades on the night of September 2-3. To view this interesting event, which may be best seen with a small telescope or good binoculars, one should begin watching at about 2 a.m. EDT. Also, try to see the interesting arrangements of the old crescent moon and Venus in the dawn skies on the mornings of September 8 and 9. Also, on the morning of September 9, the moon is above Saturn and Regulus, and on the 10th it is below them, but seeing such a thin crescent on that morning will likely require binoculars and a perfect eastern horizon about 45 minutes before sunrise. I would be interested in hearing from readers who are able to see those lunar events.

Remember that the September 26th Full Moon is the annual Harvest Moon with its usual “earlier than expected” moonrises during the following week – the week when our farmers get an “extended period of daylight” to complete the harvest.

September is a wonderful month to turn off any annoying outdoor lighting that can hinder your view and your enjoyment of the night sky, and start to “become a naturalist of the night sky”.

More information about observing stars, planets and constellations can be found in the book, The Beginner’s Observing Guide, which is on sale at Sharbot Lake Pharmacy.

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