StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

OCTOBER 2001

OCTOBER STAR MAP | INDEX | MOON PHASES

267 OCTOBER 7, 2001: City Lights, Starlight: We live in curious times. While many of us desire a return to nature, we reside in urban environments, which flood our senses with concrete, macadam, mechanical noises, and if you are interested in astronomy, light polluted skies. But there are those temperate days, especially during the fall and spring, when the sky is a saturated blue right down to the horizon, and the sun sets still radiant and yellow, without many of the reddening effects that polluted air produce. On these days, an hour after sunset or before sunrise often produces a type of competition between city lights and the dimming or brightening sky that is uniquely beautiful and uniquely urban. As night falls, pavements and building facades start to become tinted with the reflections of yellow or green street lamps, braking cars splash red, and advertising lights switch on, but the sky still remains an untainted fresh navy blue with perhaps a bright crescent moon bowing in the west. Of course, the city lights will win eventually, but for about five to ten minutes there is a kind of magical balance between sky and concrete, moon and street lights that can be truly aesthetic. This week during evening time, if the weather cooperates, look overhead about 7:30 p.m. for the three bright stars of the Great Summer Triangle. Low to the horizon in the south will be Mars, still dominating the evening sky, but reduced in brightness by nearly sevenfold since mid-June. The brightening morning sky around 6:00 a.m. still has most of the drama. Orion and Taurus are south with Saturn in Taurus, left and above the Bull's eye, and dazzling Jupiter, above and to Orion's left. The bright waning moon is near Saturn on Monday and close to Jupiter on Tuesday and Wednesday. Clear skies!
VENUS AT DUSK: This image of Venus was recorded with a 24mm lens on Fujifilm 800 Press around mid-January of this year. Note how the glow of a nearby sodium vapor streetlight adds an orangey cast to the snow covered ground. Gary A. Becker photo...
268 OCTOBER 14, 2001: Orion's Meteors: Mid-October begins what I like to call the fall meteor season. There are three great showers of shooting stars to anticipate: the October Orionids, the November Leonids, and the December Geminids, all related to cometary debris which collides with Earth during the course of its annual circuit around the sun. In many ways these showers are as interesting as the Perseids of August, but since conditions are colder, they require just a little more in the way of preparation. Orionid meteors result from the Earth's passage through the orbital debris left behind by Comet Halley. Even though it has been over 15 years since the don of all comets was visible, its meteors witnessed in our skies, annually reminds us of Halley's lingering presence. The moon will be a nonentity for this event, setting about 9 p.m. on the 20th. So the morning of peak activity, Sunday, October 21st, will be perfect if weather conditions permit. Useful observations can commence after 11 p.m. on the 20th, but activity won't pick up to any great extent until Orion has climbed higher into the sky. You'll find a star map showing the October 21st sky looking ESE at 2 a.m. Orionids will appear to be radiating away from the base of the Hunter's club. At 2:00 a.m. this location will be from the area to the left of Orion's bright reddish shoulder star, Betelgeuse. October nights can be chilly, so dress appropriately, making sure you're wearing head protection, a scarf, and gloves. Consider also wrapping yourself in a sleeping bag or several blankets for extra warmth. Face southeast and focus near the zenith where the meteor trails will appear longer. Orionid meteors are swift, and many leave persistent trains after they streak, eliciting "ooohs" and "aaahs" from viewers.

269 OCTOBER 21, 2001: Seeing Mercury: Mercury is the most elusive of the five planets observed by the ancients. For mid-latitudes, Mercury's close proximity to the sun allows it to be seen only during twilight and near the horizon. Buildings and trees complicate matters. Viewing Mercury through a long path of murky atmosphere can dim the planet into invisibility, and a lack of celestial reference objects can make it difficult to locate even with binoculars. Over the next several weeks Mercury will be lurking near the eastern horizon in the dawn sky. Although there will be the usual set of problems associated with viewing Mercury, there will be a major perk, and that is an 11-day period when Mercury will be within one degree of brilliant Venus. Finding Venus as a target object should be easy if you are high enough with a good eastern horizon. Since the sky will already be brightening, there will be no special advantage to being in a dark rural location. In fact, city dwellers living in high-rise apartment buildings with windows or porches facing east may actually have the advantage. Crystal clear skies are a must, but this is precisely the type of weather that we associate with this time of year. The use of binoculars will vastly improve the chances of seeing fainter Mercury. Observations can begin as early as October 22 when Mercury will be less than one binocular field below Venus at 6:30 a.m. Venus will be about 10 degrees off the eastern horizon, or the equivalent of one clenched fist held at arm's length with the thumb on top. Each successive morning, Mercury and Venus will appear closer, but the pair will also be located slightly lower in the sky. Between October 28 and November 7, Venus and Mercury will be positioned within one degree of each other. Remember that on Sunday morning, October 28, we fall back an hour to Standard Time, so that means getting up at 5:30 a.m. to recreate the same sky conditions. Mercury's closest approach to Venus occurs on the morning of October 30 when the two planets will be slightly over one half degree apart or separated by an angle just a little greater than the diameter of the full moon. Good viewing!

270 OCTOBER 28, 2001: Seeing Earth Rotate: I made a curious little observation this past summer when I was volunteering for the National Park Service at Chaco Culture, near Nageezi, NM. Standing by our automatic telescope at 4:30 a.m., on July 5th, I saw the Earth rotating. Over a period of several seconds I viewed the planet Venus emerge from behind North Mesa to become fully visible in the dawn sky. The Earth's rotation is responsible for the daily paths that the sun, moon, planets, and stars take across the sky. It is possible to observe our planet rotating by lining up a bright star with the wall of a more distant building. Depending upon the location of the star in the sky, it might be approaching the wall or moving away from it. You'll have to decide how to position your head to perform the experiment, but the trick is to bring the star very close to the obstacle. Hold your head very still and watch the star blink out as the spinning Earth carries it behind the wall; or if the star is about to emerge, barely hide the star behind the wall, and watch it suddenly pop into visibility. You are witnessing the moment-by-moment rotation of the Earth. It's even more fun to attempt this observation, like I witnessed it, with a planet. Rather than a point of light, the planet presents a tiny bright disk. If your head is held very still, the planet will appear to emerge or disappear, becoming brighter or dimmer over a period of several seconds. Positioning the star or planet near a telephone wire will produce a brief occultation of the object as it passes behind the wire, only to emerge rapidly from the other side. So now you know what sleepy astronomers do for entertainment in the wee morning hours at Chaco Culture National Historical Park. We watch the Earth rotate and dream of a deep sleep to come.