OCTOBER  2009

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Current Moon Phase

685    OCTOBER 4, 2009:   By the Light of the Harvest Moon

Sunday, October 4, is the Harvest Moon, the full moon occurring closest to the autumnal equinox, which this year happened on September 22. The Harvest Moon has a definite relationship to farming. In our mechanized world where harvesting crops after sundown can be as simple as flicking a switch to engage the tractor lights, it sometimes is difficult to comprehend why this moon was so important centuries ago. The first step is simply to understand the brightness of a full moon. For that you need to get to a suburban or rural locale and bask in the light of a full or nearly full moon. Let your eyes adjust to the darkness, and as the pupils of your eyes widen over a period of 15 minutes or so, an astonishing amount of detail will become visible all around you. Oftentimes, even muted colors can be seen. My grandfather, Ewald Marcus, who was a cook in the German army fighting on the Russian front in World War I, told me stories of how he used to read newspapers by just the light of the bright moon during cold, snowscaped, winter evenings. It really can be done. What makes the Harvest Moon so special is that the tilt of Luna’s orbital path with respect to the horizon in the evening sky is at its smallest angle at the beginning of fall. The moon trudges along at its regular pace of 13 degrees per day, but that motion doesn’t change its altitude to any great extent with the horizon. For five days or so around full moon, Luna rises within 25-35 minutes of its ascending time the day before. The rising times are even closer together in Europe, sometime as little as 10 to 15 minutes between successive nights. It’s easy to see how a farmer harvesting after sundown could have continued working late into the night as day slowly transitioned, aided by the light of a full moon to help guide his horses along the rows of moist, furrowed ground.

686    OCTOBER 11, 2009:   Measuring Brightness in Astronomy

We are surrounded by astronomical objects of varying brightnesses, both during the day and at night. Daylight sightings of the moon are easy. Even Venus can be seen in the daytime, if the sky is transparent enough and you know exactly where to look. Forty-five minutes after sunset, any of the planets that are visible to the unaided eye can also be viewed, given proper placement and sky conditions. At night, hundreds of stars of different intensities can be observed from suburbia. Measuring the magnitude or brightness of a star all started with the Greeks, who qualitatively noted that the brightest luminaries were of the first magnitude, and the faintest stars were of the sixth magnitude. Strangely with magnitudes, the more positive the number, the fainter the object becomes. Presently, astronomers have quantitatively defined the precise brightness of the stars and planets, but have kept the Greek's more positive-fainter rule. A difference of one magnitude equals an intensity change of 2.51. This other unusual concept is made more comprehensible with the realization that a difference of five magnitudes equals an intensity variation of 100. So with this in mind, the sun’s magnitude is a staggering -26.7, the full moon, -12.6, and Venus about -4.4. The stars of the Big Dipper range from +1.8 for Alioth to +3.3 for Megrez. The stars of the Little Dipper vary even more, from +2.0 for the North Star to +5.0 for Eta Ursae Minoris. The faintest stars visible on the clearest nights from urban centers of 100,000 in population are about +4.5, but in more rural settings, you can most likely reach +6.0 on the same clear evenings. That is an intensity variation of nearly four, and it makes all the difference in what you’ll be able to view in the sky between an urban and rural locale.

687    OCTOBER 18, 2009:   Spotlight on Orionid Meteors

We are into the second half of October, and with the lowering sun, colder weather from the north has begun to seep into the lower 48 changing what were dew-drenched car windows several weeks ago, to translucent coverings of stubborn ice that must be vigorously scraped. Observers must now think about bundling up to protect, especially hands, feet, and heads from “succumbing to the numbing” cold. There is a bright spot in all of these chilling autumn prospects, three wonderful meteor showers that send shooting stars zipping across the celestial vault. The first event, the subject of this week’s article, is the Orionid Meteor Shower, peaking Wednesday morning, October 21. The Orionids radiate or diverge near the feet of the Gemini Twin, Pollux, but just on the Orion side of the boundary between both constellations. By 1:00 a.m. Orion the Hunter has fully risen. As the American poet, Robert Frost, wrote, “You know Orion always comes up sideways. Throwing a leg up over our fence of mountains…” Gemini with its two bright stars, Castor (higher) and Pollux are to Orion’s left. Orionids will be radiating essentially between Orion’s three famous belts stars, Mintaka, Alnilam, and Alnitak, and Gemini’s, Castor and Pollux. These meteors are very fast, and will come at the rate of about 20 per hour from a rural location. What I like best about the Orionids is that when you see one, you are actually glimpsing a piece of dust that was set loose tens of thousands of years ago from the nucleus of Halley’s Comet. So even if you’ll be old and senile by the time that the granddaddy of all comets returns in 2061, you’ll be able to see a piece of it this week. Get that sleeping bag and air mattress out and bring along a warm caffeinated drink. Face east after 1:00 a.m. and south by 4:00 a.m., and enjoy the show.

Orionid Meteors radiate from just east of the elbow of Orion the Hunter. Rates of about 10-20 meteors per hour can be expected after 2 a.m., the time for which this map has been constructed. Gary A. Becker graphics...

688    OCTOBER 25, 2009:   Mars Brightening for Winter Show

Several weeks ago, when I popped outside to retrieve the morning paper, there was Orion shining brightly above my neighbor’s maple tree. I did what any astronomer who enjoys looking at the heavens does when he or she is out for just a minute or for an entire night—I made a quick survey of the sky putting everything into its proper place. However, when I got to Gemini, there was an extra star below Castor and Pollux which took me by surprise. My conclusion after several minutes of reflection and a few passing cars with drivers also staring skyward with me, was that I was greeting Mars. Mars has been in the news almost every summer since 2003 when Earth was a scant 34.65 million miles from the Red Planet, the closest approach in 60,000 years. It seems that someone or some group during each of the intervening years has started an Internet rumor that Mars would once again be coming even closer to the Earth, so near to us that the Red Planet would appear as large as the full moon to the unaided eye. Nonsense! Over time the prank has worn thin with people like me answering the e-mails of countless individuals who really want to make the observation of a lifetime. The real Mars will be brightening during the fall season as Earth catches up to and passes our second nearest planetary neighbor on January 29, 2010. The size of Mars through a telescope will only be 14 seconds of arc, that’s 39/10,000th of a degree. That is big for Mars, but tiny in comparison with the moon which is half a degree in angular size. Keep in mind that there are 360 degrees in a circle. By early January 2009, Mars will rival Sirius, the brightest luminary of the nighttime sky, so it will be definitely worth a look. In fact, on the 29th when Mars is at opposition (opposite) to the Earth, it will only be a scant 6.5 degrees from the nearly full moon. A Mars locator map is online.

Find Mars to the left of the Gemini Twins, high in the south by 5 a.m. during the last week in October. On November 1 and 2 see Mars passing through the Beehive Cluster in Cancer, the Crab. Binoculars will be needed because of bright moonlight. Gary A. Becker graphics...