Night_skies_sept1

Jeff Green | Sep 01, 2005

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The Night Skies of September, 2005:Two brilliant planets continue their amazing dance by Leo Enright

To the delight of serious skywatchers, the coming of September means longer nights and generally better chances of enjoying the night sky. Locally, on the first day of September, sunset is at about 7:45 p.m. Eastern Daylight Time, and twilight ends at about 9:30 p.m. The time of sunset will be about 2 minutes earlier each day, until by the end of the month it will be at about 6:45 p.m., with twilight lasting until about 8:30 p.m. Over the month there is also a change of over a half-hour for the times of dawn (the beginning of morning twilight) and sunrise. On September 1, dawn begins at about 4:45 a.m., and sunrise is at about 6:30 a.m.

The beautiful Milky Way still sweeps overhead in the late evening hours. We should still look for Cygnus, the Swan, also called the Northern Cross, “flying” almost directly overhead, as evening twilight ends. This “starry bird” flying southward along the Milky Way may well remind us of the yearly autumn migration of our Canada Geese and many other birds.

Among the five bright planets that may be easily seen with the unaided eye, two of them are much brighter than any star in the whole sky. Their sheer brilliance seems to attract great interest, even from those people who are quite unfamiliar with anything in the night sky. So, it must be something VERY special when these two objects are seen in the same part of the sky, in fact, right beside each other, and that is exactly what happens in early September. The planets Venus and Jupiter, easily seen to be the most brilliant objects in a moonless sky, continue throughout the coming month the “great waltz of the bright planets” that began a month ago in the western evening sky. Throughout August we saw, night by night, Venus and Jupiter get closer to each other at the rate of 1 degree a day. (A degree is the width of little fingernail held at arm’s length.)

Now on September 1, they are only about 1 degree apart! Find a location that allows you a good view of the western horizon every evening this month from 30 minutes after sunset until about 90 minutes after sunset and enjoy the spectacle as the waltz continues. During August as these brilliant luminaries were approaching each other, Jupiter was on the left and Venus was on the right. Now, after September 1, the night when they appear to be almost in contact with each other, they will move apart, and spend the rest of the month waltzing apart at about the same speed that they approached in August, and now Venus will be to the left and Jupiter down and to the right. (Some people may want to photograph these twilight events or make drawings of what they see above their western horizon.) Do not for a minute be deceived into thinking that these two planets are actually and physically close to one another. Jupiter is really 5 times as far away as Venus! They appear close only because of the fact that, in their orbits around the sun, they and our planet Earth, now happen to be almost in a straight line.

Tthere is another object very close to Jupiter and Venus: the star Spica, the brightest star in the constellation Virgo. Later in the evening, after the Jupiter-Venus duo have set in the west, many people will turn their attention to the planet Mars rising in the east. It rises earlier each night; at the beginning of September it can be seen after 10:30 p.m., but by the end of the month it rises about 8:30 p.m. Careful observers will also note that it gets much brighter over the course of the month, and if they observe it in a small telescope, they can see that it is getting considerably larger and perhaps even showing some features, yes, brighter, bigger, and even clearer than it has been at any time in the past two years! The planets Saturn and Mercury are for those who observe the eastern sky in the hour before sunrise. Saturn is well above the horizon during the entire month. Mercury is to be seen low, near the horizon and only during the first week of the month.

This month the moon adds some extra highlights to our views of the planets. The two best of all are the views in the western evening sky about 40 to 60 minutes after sunset on September 6thand 7th. Don’t miss those!! On the 6th, the slim crescent is just below Jupiter and to the right of Venus. On the 7th the crescent is to the left of Venus, with the three brightest objects of the night sky (Moon, Venus, and Jupiter) appearing in a straight line, and in that order!! On Saturday night, the 17th, the Full Moon is the annual Harvest Moon – a reminder that, in the coming week, the 18th to the 25th, the moon will be rising earlier than expected. (For most of the year, moonrise, from one day to the next, is, on average, 50 minutes later; during THIS WEEK, it will be only about 20 minutes later from night to night.) On the night of September 20th, the moon will appear beside Mars and not far from the Pleiades star cluster. At dawn on September 28th, the waning crescent moon will appear not far from Saturn in the eastern sky.

Remember this month also to glance to the north every clear night for the possibility of seeing a display of the Aurora Borealis. More information about stars, planets, and the 88 constellations, is to be found in the book The Beginner’s Observing Guide, now available at Sharbot Lake Pharmacy.