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Night Skies - August 2006

TheNightSkies ofAugust, 2006:Planetary dances in August dawn skies

by Leo Enright

In the month of August we always expect shorter days and longer nights than we had in July, and so, stargazers have more time to enjoy the views of the great Summer Milky Way, an active meteor shower, and for this year, very bright planets in both the evening and morning sky. At the beginning of August, sunset in this part of Ontario is at about 8:30 p.m. EDT, and evening astronomical twilight ends at about 10:30 p.m., almost an hour earlier than it did in late June. By the end of August, sunset will be at about 7:45 pm., with twilight ending at about 9:30 p.m..

Letters

Late summer skywatchers, who generally in our rural cottage country, are fortunate enough to enjoy dark skies unmarred by smog and light pollution can truly get to know the Summer Milky Way and the constellations within it. Just let your late-evening gaze sweep from the northeastern to the southern part of the sky. In the northeast, entirely within the Milky Way, you see Cassiopeia, the Queen, in the shape of a very large letter “W”. High in the east you notice Cygnus, the Swan, also called The Northern Cross from the shape of its star pattern, and down in the south in the widest and densest part of the Milky Way is Sagittarius whose star pattern forms the shape of a teapot with the handle to the left and the spout to the right. Each August night as you trace out its broad pathway across the sky, remember that this Summer Milky Way is really one arm of our home galaxy, the Milky Way Galaxy, and remember, too, that our immense solar system (with the Sun, the nine planets, and their many moons) is really just a small dot just one star system among the 200 billion stars that make up this galaxy which is over 250,000 light-years in diameter! During August we also have a chance to see the famous Andromeda Galaxy, the only other entire galaxy that can be easily seen from rural skies with the unaided eye. This “close neighbour” of our galaxy is one of the largest members of the “local group” of over a dozen galaxies, and it is only (!) about 2 million light-years away. To find it, locate the “W” of Cassiopeia well up in the northeastern sky at about 11 p.m. Then trace a line from the right side of the “W” down and to the right toward the eastern horizon. About half way along that line, if your sky is moonless and unpolluted, you should see a “faint fingerprint” on the sky. That is it! Just remember that what you are seeing is another whole spiral galaxy made up of 400 billion stars, and that the light from them has taken over 2 billion years to reach your eyes! Among the five bright planets, all five may be seen in August this year, but only the two brightest are visible for the entire month, and two of the others provide fascinating views of a “dance of the planets”. On all clear evenings this month, Jupiter, the second brightest of the planets, is the first object to appear in a moonless sky. It is well up in the southwest, and as darkness deepens, careful observers will be able to notice two things: (1) that it appears a bit to the right of a background star (the star has the Arabic name Zubenelgenubi and is the brightest star in the constellation Libra), and (2) that, as August progresses, Jupiter seems to move to the left and closer to that star. This is actually Jupiter’s orbital motion around the sun that is being observed. Mars, the red planet, may be seen in the first half of August and for only a short while on clear evenings beginning about 30 minutes after sunset. Be sure to have a very good view of the western sky right down to the horizon, because Mars appears barely above the horizon. Binoculars can certainly help in being sure of seeing it. After mid- to late August probably only a few people will see Mars again until December. Brilliant Venus, the brightest of all the planets, continues, during August, to dominate the eastern morning sky in the hour or more before sunrise, just as it has for several months, but now it is joined by two other planets and there is a real “dance of the planets” display for those who rise early enough to see it. For the first 10 days of the month, the planet Mercury, seen directly below Venus, brightens and moves upward toward the much brighter Venus, until they appear very close (a bit more than the width of a fingernail held at arm’s length), but after August 11th, Mercury drifts downward again though it is still visible for another 10 days. Saturn is the second “dancing partner” for Venus. By the morning of August 20th, observers should start to notice Saturn, which is brighter than Mercury, just below brilliant Venus. Beginning then, Saturn, also, gradually moves upward, morning by morning, until by August 27th it appears extremely close to Venus. This “Venus-Saturn dance”continues until the end of the month. Try not to miss seeing either of these performances!

The moon’s orbit around the earth provides several interesting lunar-planetary conjunctions this month. On the evenings of August 1st, 2nd, and 3rd, we have a good chance to record the daily movement of the moon as it glides past Jupiter in the southwestern sky during evening twilight. (Note that on August 29th, the moon again appears back near Jupiter, not far from where it was observed on August 1st. Is that a hint about how our remote ancestors determined the length of a ‘lunar cycle’ or month?) In the eastern dawn sky on August 21st about a half-hour before sunrise, the waning crescent moon presents a beautiful picture as it appears above Venus, and on August 22nd at the same time, it appears a bit to the left and down from Venus. On both of these mornings, if twilight has become too bright to see Mercury and Saturn below Venus, use binoculars to be sure of seeing them, but be sure to put away the binoculars before the sun rises to avoid the danger of inadvertently looking toward the sun.

The famous Perseid Meteor Shower reaches its peak this year on the nights of August 12thand 13th, an event that often means hundreds of people take some time to observe the “shooting stars of August”. It receives the name “Perseid” because all the meteors from this shower can be traced back along their paths across the sky to a radiant in the constellation Perseus which in August is in the northeastern sky below the “W” of Cassiopeia. This year, with a waning gibbous moon rising in the middle of the night for the peak of the event, only the brightest of the Pereids will be seen at that time, but even under such circumstances, there should still be a good number of fast-moving “shooting stars” to be observed on the above dates. Perseids are often more plentiful after midnight than before. Remember also that the Perseids are among the “longest duration” of all the showers, with its meteors being seen for a month or so before the “peak date” and for many days after the peak. Meteor watching on other nights in August is often surprisingly rewarding.

Those who are interested in more information about observing stars, planets, and meteor showers throughout the year should obtain a copy of the book The Beginner’s Observing Guide which is available at The Valley Book Shop in Perth , at Sharbot Lake Pharmacy, and on the internet at www.rasc.ca/publications.htm . Happy observing under clear, dark, unpolluted skies!

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