StarWatch for the greater Lehigh Valley

AUGUST  2015


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[Moon Phases]

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989    AUGUST 2, 2015:   Perseid Meteors Flying Now!
As we enter August, the moon is waning and will be at last quarter late on Thursday evening. This is great if you are an aficionado of viewing shooting stars, because August touts one of the most reliable annual meteor showers, the Perseids. The US is in the sweet spot this year, with the East Coast especially favored. The highest rates are forecast for 2 a.m. on the morning of Thursday, August 13, but after last quarter moon, most of the meteors seen will be Perseids. Meteor activity picks up after midnight and is usually highest near dawn because the Earth rotates into the dross released by Perseid precursor, Comet Swift-Tuttle, from its numerous passages around the sun. It is similar to the front windshield of a moving vehicle picking up more raindrops than the rear window. When a piece of cometary dust, smaller than a grain of sand, rams the Earth’s atmosphere around 70 miles up, a cylinder of air about a half mile wide is made to fluoresce (glow), causing the meteor phenomenon. Brighter meteors may descend to an altitude of 50 miles or lower before they are completely ablated. Perseid meteors will not be hard to spot. These shooting stars are fast, often leaving a trail of glowing atmosphere behind them called a wake or a train which may persist for several seconds. Perseids will look as if they are diverging from a location near the head of the constellation of Perseus the Hero, a phenomenon attributed to perspective. Straight sections of road or railroad tracks will appear to have a vanishing point in the distance, even though the sides of the roadway and tracks are parallel to each other. Likewise, the meteoroids in space are traveling parallel to each other in their individual orbits around the sun, and as they approach an observer, they will appear to diverge or radiate away from a vanishing point. All of these attributes will make it easy to identify Perseids against the background of other meteor activity. More next week…

[2015 Perseid Radiant Map]
Perseid meteors will be flying through August 20. Peak time for the East Coast will fall around 2 a.m., August 13. This map is set for about 3 a.m. Software Bisque graphics by Gary A. Becker...

990    AUGUST 9, 2015:   Fire in the Sky!
When John Denver wrote in his iconic song, Rocky Mountain High, “I’ve seen it raining fire in the sky,” he was referring to the annual Perseid Meteor Shower which is now active. Highest rates are predicted for the morning of Thursday, August 13. Temperatures will be tolerable; it’s vacation time, and unlike last year when faint meteors were hidden by a bright gibbous moon that bleached the inky sky, Luna is not even a consideration in 2015. An extremely thin crescent moon rises near daybreak, not in any way affecting observations. Watching a major meteor show is certainly like witnessing fire in the sky. Unexpected streaks of light caused by the dross left behind by Comet Swift-Tuttle’s many orbital passages around the sun will dash across the sky, with an occasional brilliant fireball burning its impression onto your retina as well as your senses. An evening with the Perseids is always time well spent; but don’t forget to dress warmly or at least have extra clothing on hand as the night progresses. I’ve always found it most comfortable to snuggle within the confines of a light sleeping bag on an air mattress with plastic ground tarps under and over my sleeping gear to protect it from the dew. You’ll find a pillow handy and also a thermos containing a warm, caffeinated beverage. Start observing around or after midnight. Face towards the northeast but view overhead, usually the darkest part of the sky. Perseids will appear to fan away from this area of the sky near the border between Perseus and Cassiopeia. Many Perseids leave residual wakes and trains of glowing air after the initial meteor phenomenon subsides. The farther away you are from city lights, the more meteors you will see, but one meteor every minute or two is a reasonable expectation from a rural locale—half of that from the suburbs. If you can’t observe on the morning of the 13th, a few days earlier is better than later because Perseid rates decline rapidly after maximum night. Much success!

[2015 Perseid Radiant Map]
Perseid meteors will be flying through August 20. Peak time for the East Coast will fall around 2 a.m., August 13. This map is set for about 3 a.m. Software Bisque graphics by Gary A. Becker...

991    AUGUST 16, 2015:   September’s Total Lunar Eclipse
Dust off your telescopes, uncap your binoculars, and prepare yourself for a total lunar eclipse that takes place at a time that won’t rob you of the necessary sleep to be functional the next day. Sunday evening, September 27 between 9:07 p.m. EDT and 12:27 a.m. Monday, marks the most convenient time slot since early 2008 for a total lunar eclipse. Mid-eclipse occurs on September 27 at 10:47 p.m. Total lunar eclipses occur when the moon passes through the shadow (umbra) of the Earth. They are not particularly rare since anyone on the nighttime hemisphere of our planet has a grandstand seat to the event. However, not all lunar eclipses are created equally because the amount of sunlight refracted by Earth’s atmosphere into its umbra varies from eclipse to eclipse. Also, the depth to which the moon immerses itself into the shadow changes too. These factors affect how colorful the eclipse will become. As an example, September’s lunar eclipse is fairly shallow, meaning that no part of the moon ever reaches the center of Earth’s umbra. The moon’s southern hemisphere always remains relatively close to the shadow boundary, where more refracted light is found, increasing the chances for a colorful event. The amount of particulate matter in the atmosphere must also be factored into the equation. When Philippines’ volcano, Mt. Pinatubo, erupted in June of 1991, it pumped huge amounts of fine ash into the stratosphere, lowering global temperatures by about one degree F over the next five years. The total lunar eclipse of December 9, 1992 saw the moon disappear during totality. It could not be seen with the unaided eye or by using telescopes. My four-minute photographic exposures revealed only an ashen moon with deep somber colors. Currently, the upper atmosphere is clear, adding to the color potential of September’s eclipse. The only unknown factor is the weather for that evening. I’m praying for clear skies. I hope you are too!

[2015 Perseid Radiant Photo]
Three bright Perseid meteors can be seen diverging from the radiant on the morning of August 13. Peak time for the East Coast fell around 2 a.m. The meteor closest to the upper left was a sporadic, not related to the Perseid shower. Composite images by Gary A. Becker from Shooting Star Farm north of Quakertown, PA...

992    AUGUST 23, 2015:   Methane, It Stinks!
We are all familiar with methane through metabolic processes, and it is certainly not the fragrance of choice on a first date. It can also be produced non-metabolically through chemical processes, but those reactions require liquid water. Methane is also the most feared gas in humanity’s race for self-extinction because, as atmospheric carbon dioxide levels increase via our ravenous consumption of carbon-based fuels, warming temperatures will release huge quantities of methane stored in the Arctic’s melting permafrost layers. Methane is a much more effective greenhouse gas than CO2, and if this occurs, the global warming battle will simply be lost. Now for the happier side of methane... It has been discovered on Mars by the highly successful Curiosity rover which has been sniffing the air and probing the ground inside Gale Crater for the past three years. Why is this find such an important revelation? Any methane discovered on Mars is of very, very recent origin because the weaker gravitational pull of the Red Planet (38 percent of Earth’s attraction) cannot hold it down. It escapes Mars in only 200-300 days, so any methane discovered is a real time sign that either life processes are ongoing near the Martian surface, or that chemical reactions induced by liquid water are occurring; and as all biologists know, where there is liquid water, there is life. What is even more intriguing is that Martian methane levels are not homogeneous. Curiosity has found that puffs of methane are being released from the Martian surface, indicating that methane is being produced near Curiosity’s location. This is not to imply that Curiosity is trekking about in a Jurassic Park-like environment with dinosaurs being imaged in the background. Mars is much drier than any location on Earth, but methane will provide an intriguing component to the anticipated discoveries of the first human explorers when they finally traverse the Red Planet’s surface. The time for “boots on Mars” is now!

993    AUGUST 30, 2015:   On High, the Great Summer Triangle
Riding high in the early evening sky are three luminaries which have been dubbed appropriately as the Great Summer Triangle. I’ll confess that any three stars can form a triangle, but the GST is big, and its stars are all bright (first magnitude), making it easy to spot even on the muggiest of summer nights. This week, just after dark, whether the moon is shining or not, face towards the east, look nearly overhead, and you’ll see the GST’s anchor stars, Vega, Altair, and Deneb. Vega is brightest, followed by Altair, and finally Deneb; but would these stars still be of similar brightnesses if they were brought to equal distances from the sun? I have my students work out the calculations after viewing these stars for themselves, and most of them are simply blown away. It turns out that their distances are 25 light years for Vega, 16 light years for Altair, and 1425 light years (best guess estimate) for Deneb. No, astronomers still don’t know everything. Let’s move these stars, including the sun, to a standard distance that astronomers have designated as 32.6 light years to compare them equally with our daystar. A light year is the distance that light travels in one year about 5.8 trillion miles. Now we see these stars for what they are really worth. Our incredible sun would simply not be visible from most suburban areas without our knowing its exact location. Altair would glow as bright as the stars of the Big Dipper, while blue-white Vega would be just slightly fainter than it appears in the sky. The real kicker, however, would be supergiant, Deneb, which has been crowned the brightest first magnitude star for its distance in the heavens. Placing Deneb at the same location of 32.6 light years from us would boost its brightness to that of a thin crescent moon, but in the form of a starlike object, allowing it to cast weak shadows on the ground during the night and be that other bright light that messed up astronomical observations. Thank goodness, its distance causes Deneb to be just another pretty light in the night.

[August Star Map]

[August Moon Phase Calendar]