Night_skies_aug_07

Jeff Green | Jul 26, 2007

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The Night Skies of August 2007:TheStars andMeteors ofAugust, and Even a Lunar Eclipse

by Leo Enright

In August we always have noticeably shorter days and longer nights than during July, and so stargazers have more time to enjoy the views of the Great Summer Milky Way, and the “shooting stars” of a well-known annual meteor shower, and this year, we even have the added bonus of a total eclipse of the moon, though the latter event is one that may require a bit of effort. Locally, at the beginning of August, sunset is at about 8:30 p.m. EDT, and evening astronomical twilight ends about 10:30 p.m., almost an hour earlier than it did a month ago. By the end of August, sunset will be at about 7:45 p.m. and twilight will end about 9:30 p.m..

Most summer stargazers in our rural cottage country are able to benefit from its dark skies – unpolluted by smog and excessive street lighting, when compared with most city skies – and continue this month to get to know the Summer Milky and the constellations it contains. In the late evening, as your gaze sweeps from northeast to southwest, you see first the distinctive “W” of Cassiopeia, the Queen of ancient mythology, and then, almost overhead, the great bird, Cygnus the Swan, sometimes called The Northern Cross from the shape of its star pattern, and then down in the southern sky, where the Milky Way is widest and densest, the distinctive shape of Sagittarius with its outline resembling a simple teapot with its handle to the left and spout to the right. Each clear August night as you trace out this broad pathway, remember that it is really one arm of our home galaxy, the Milky Way Galaxy, and remember too, that our solar system is really only one star system – among the 200 billion stars that make up this immense galaxy. Also, during the month of August we have a chance, even with the unaided eye, to look OUTSIDE our home galaxy and see the famous Andromeda Galaxy, which is the only other entire galaxy that can be easily seen with the unaided eye. This “close neighbour” of our Milky Way 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. (Recall that a light-year is the distance light travels in a year, and it travels a million kilometres in about 3 seconds!!) To find the Andromeda Galaxy, locate the “W” of Cassiopeia, well up in the northeastern sky at about 11 p.m., and 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 fairly easily see a “faint fingerprint” on the sky. That is it! Remember to tell your friends that what you are seeing is thousands of times farther away that anything else they can see in the sky and it is actually another whole spiral galaxy made up of 400 billion stars, many of them like our sun, and the light from those billions of suns has taken 2 million years to reach your eyes.

Among the five bright planets that may be seen with the unaided eye, only two will probably be seen by most readers this month. (What a difference from August of last year when all five of them could be seen. Proof indeed that the “cycle of visibility” of each planet is not based on the earth’s year and is different from that of every other planet!) Jupiter is the dominant planet that becomes visible in the southern sky within a half-hour of sunset. It appears just above the distinctive star pattern of the constellation Scorpius and almost directly above that constellation’s brightest star, Antares, a star that was so named by the ancient Greeks because its deep reddish colour reminded them of Mars. (The star’s name means “rival of Mars”.) Owners of small telescopes may be fascinated by the four brightest of Jupiter’s moons, seen changing position from night to night and even hour to hour as they orbit the planet, and our fascination with this spectacle should recall that of Galileo when he discovered those moons 400 years ago. Reddish Mars may be seen rising in the east at about 1:00 a.m. in early August and slightly earlier each night until it may be seen above the eastern horizon at midnight by the end of the month. It is in a very easily recognized area of the sky, and may be easily seen moving over the course of the month – in the region between two great clusters of stars, the Pleiades and the Hyades. The Pleiades are a “cloud of stars” that some people mistakenly call a “Little Dipper” from the shape of the compact star formation, the star formation the Japanese call “Subaru”and represent on a symbol for one of their automobiles. The other cluster of star, the Hyades is the “head of Taurus the Bull” and contains a star, Aldebaran, that is almost as reddish as Antares. Periodically over the month try to notice the movement of Mars downward and away from the Pleiades and toward the star Aldebaran in the Hyades. Careful observers may note that, though Mars and Aldebaran are similar in colour, the planet is changing in brightness. Last month it was about as bright as the “eye of the Bull”; by the end of August it will be twice as bright – an easy indication that the orbits of Mars and Earth are bringing them closer to each other, and a foretaste of their closeness later this year.

The famous annual Perseid Meteor Shower reaches its peak this year on the night of Sunday, August 12th, an event that usually means hundreds of people take some time, perhaps the whole night, to see “the shooting stars of August”. They are named “Perseids” because all the meteors from this group can be traced back along their paths across the sky to a radiant in the constellation Perseus which is just below the “W” of Cassiopeia. This year with New Moon on the date of the shower’s maximum, conditions should be ideal, if the weather cooperates. Remember that the ‘flashing streaks’ of these meteors are caused by bits of dust and tiny pebbles left as a trail in space by a comet that was once called Comet Swift-Tuttle, and they all streak through the atmosphere at an incredible 60 kilometres per second, creating a trail of hot, glowing ionized gas. It is the glowing gas, not the particle that is seen by observers. Use a reclining lawn chair, and though Perseids may “come from the northeast”, you may face in any direction that is away from distracting lights that should be avoided. Record the numbers seen per hour throughout the night, and if the weather is inclement, try again any night in the following week.

Since it is about 5 months since the last lunar eclipse, we have another eclipse season with a Total Lunar Eclipse that happens to be almost exactly the reverse of the one we had on March 3rd. On that night the eclipse was half over when the moon rose in this area, and those who had good weather were able to see only the last half of the event. This time we see only the first half of the event before the moon sets. As always, it is on Full Moon night, that is on the night of Monday-Tuesday August 27th– 28th. At about 4:20 a.m. EDT we should start to notice the darkening of the moon’s disk. As morning twilight begins in the east, the partial eclipse starts at 4:51 a.m., and the total phase starts at 5:52 a.m.. Locally the moon sets 34 minutes later, at 6:26 a. m.. Note these times VERY carefully. Plan to observe from a site with a good western horizon, and, if possible, record carefully the colour of the lunar disk, that is, whether it is rusty red, dark orange, dull grey or some other colour.

Those interested in more information about summer observing should obtain a copy of the non-technical book, The Beginner’s Observing Guide, which is now available at Sharbot Lake Pharmacy . Happy observing under clear unpolluted August skies!