StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

NOVEMBER 2011

NOVEMBER STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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794 NOVEMBER 6, 2011: White Halloween: I don’t think I have ever seen a day quite like today. There will be no stars shining in Coopersburg this evening, just the silent beat of star-shaped snowflakes falling among semi-skeletal trees and some fully leafed ones. After a hot and humid summer where rainfall amounts broke all records, here we are at the end of October with Mother Nature dropping a blanket of white across a landscape deeply enmeshed in autumn. Our garden, albeit struggling yesterday, but still pretty in the delicately warm afternoon air, collapsed this morning under the increasing weight of a torrent of wet snowflakes. But that is not all that is collapsing. Walking outside about an hour ago to take some pictures, I could hear branches snapping all around me. Our street is blocked by fallen debris about 200 feet north of our property, and every neighbor has suffered downed tree limbs except us. That will change shortly, I am sure. Needless to say, power outages are everywhere. The conflict that is raging outside my window this afternoon is one that occurs every year as the sun moves farther south, and we receive less and less of its bountiful energy. The mid-latitudes become a weather battle zone as colder, denser Arctic air builds in the north, spills southward, and clashes with warmer more tropical air from the south. The highs and lows that form as part of this energy exchange, rotate in directions which on the East Coast can drive warmer, moist ocean air inland (low pressure) forcing it up and over a wedge of Arctic air reinforced from the north by a high pressure. Usually this results in a chilled rain in October, but today, the cold air was more entrenched and it snowed, the earliest nor’easter of any fall season that I can remember. It certainly took our neighborhood jack-o-lanterns by surprise, their gaped-tooth smiles and oval eyes now buried by winter’s (fall’s) first snowfall. Trick or Treat!

795 NOVEMBER 13, 2011: Empty Magnification: Last week, I wanted to continue a dialogue on telescopes, since the holidays are fast approaching and scopes have an affinity to find themselves under Christmas trees; but a freak Halloween snowstorm which blanketed the East Coast stole the show. Clean up still continues, but the snow is gone and almost everybody has had their electricity restored. I wanted to say a few words about magnification since it is considered so important to people purchasing their first scopes. It should never be the prime consideration for owning any telescope, but it does have its place in using a telescope properly. Mathematically, magnification equals the focal length of the telescope divided by the focal length of the eyepiece. The focal length is simply the distance that light takes to come to a precise focus. Both the telescope and the eyepiece play a role in how powerful a telescope’s magnification can become. Because of the nature of light, images are brought to a focus as a series of dots or diffraction disks similar to a newspaper photograph. Larger aperture scopes produce smaller diffraction disks and can tolerate higher powers. The observer looking at an image in the eyepiece is totally oblivious to this fact, but the analogy is an accurate one. Every time the magnification is doubled, the field of view and the brightness of the image become one quarter of their original value which is a function of inherently larger diffraction disks. If a person looks more closely at a newspaper photo, there comes a point where no new information can be gleaned, and at even closer distances, less detail is perceived. Likewise, simply “jacking up the power” in telescopes produces “empty magnification” where no new detail can be revealed. The upper limits of magnification are about 50-60 power per inch of light gathering aperture. Beyond this point the magnification becomes empty, in other words, useless.

796 NOVEMBER 20, 2011: Magnitude: It's all Greek to Me: Look up into the clear night sky, and you’ll notice dozens to thousands of stars depending upon your location. Some stars are brighter, and others are fainter. How do astronomers identify stars with respect to brightness? It all started with the Greeks, and to the uninitiated, the system may still sound like Greek. To Greek philosophers of antiquity, the heavenly luminaries were divided into six categories called magnitudes. It was strictly arbitrary with the brightest stars of the night classified as first magnitude and the faintest as six magnitude. If two astronomers with different visual acuities looked at the night sky, the number of stars in each of the various magnitude categories would undoubtedly be different. But there was another catch. Normally, we associate bigger, more positive numbers with greater values. As an example five apples represent a larger quantity than two apples. However, in the Greek system, the more positive the number becomes, the fainter the star. To astronomers of all ages, a fifth magnitude star has always been less bright than a second magnitude star. In addition to this confusion, when the magnitude system was finally formalized in 1856 by the English astronomer, Norman Pogson, a first magnitude star wasn’t just twice as bright as a second magnitude star; it was 2.512 times brighter. A difference of five magnitudes represented an intensity change of 100. Brighter objects were even recognized to have negative magnitudes. Confused? You can image how my college students react to this system and to what could have been a much simpler way of quantifying stellar brightnesses. Science sometimes does itself a disservice when it isolates concepts from better public understanding. Astronomy remains popular, but with many misconceptions and poor community awareness of concepts like stellar brightness.

797 NOVEMBER 27, 2011: Catch Venus in the Southwest: A few nights ago it was clear, and when I went to a local pizzeria to pick up my dinner, there was a brilliant “star” low in the SW that unexpectedly caught my attention. Maybe you’ve seen it too. At mid-twilight it is less than a fist held at arm’s length above the horizon, scintillating in the amber glow of dusk. I knew it was Venus, but still I gave pause because this apparition of the goddess of Love has been more of a hide-and-seek affair than its usual brilliant evening displays in the west. Venus was at superior conjunction with the sun—in line with the Earth and the sun, but on the sun’s far side on August 16. After that date it moved into the evening sky. If this would have occurred in the spring instead of August, Venus would have rapidly risen into the heavens becoming visible in three weeks. However, this time the sun was headed south as Venus pulled away, and because of Venus’s orbital path which nearly mimics the sun’s path, Venus drew away from the sun in a direction that kept it nearly parallel to the horizon. That meant that when the sun set, so did Venus. Now, after three months of separating from Sol, Venus has gained enough altitude to become noticeable after sundown, and it will only get better in the New Year. Early next year, Venus reaches its angle of greatest eastern elongation, meaning that it will have pulled away from the sun to its greatest extent. Venus then begins to slide back towards the sun reaching inferior conjunction (Earth-Venus-sun) on June 5, 2012. On that date, Venus will pass between the Earth and the sun so precisely that observers equipped with proper solar filters will view Venus as a black dot against the sun’s disk. That last happened on June 8, 2004. The next transit of Venus occurs on December 11, 2117, and that is no typo. Even though Venus’s performance this year has been more than lackluster, “Love” will triumph in the end.

[Noveber Star Map]

[November Moon Phase Calendar]