StarWatch for the greater Lehigh Valley
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AUGUST  2018

AUGUST STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

Print Large Sky Charts For 10 p.m. EDT:   NORTH | EAST | SOUTH | WEST | ZENITH

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1146    AUGUST 5, 2018:   Perseids: The Big Show Begins
From Saturday evening into Monday morning, August 11-13 are the big nights for the 2018 Perseid meteor shower. Many astronomy enthusiasts call the Perseids the best shooting star event of its kind during the year, and that may be true because it combines relatively high meteor rates with warm summer nights which are relatively short. Compare that to the Geminids in December, where the number of meteors each hour could be double the Perseids, but the temperature may very well be in the teens. By dawn if you do not succumb to the cold, all you can think about is a hot shower. No sleeping bag or bags, handwarmers, or hot drinks have ever kept me warm for very long during the Geminids. The best advice for Perseid meteor observing is not to start too early in the evening, although this year may be an exception. The analogy is similar to being in a vehicle moving through a downpour. It is the front window that seems to be getting all of the action as you plow through the deluge. The back window only gets a drop or two because it is shielded by the front of the car. Likewise, in the early evening we are being shielded by the Earth and normally see reduced meteor activity. As local midnight approaches, the Earth slowly makes its rotational turn into the meteoroids, bringing us to the front window, with the resultant increase in activity. If the peak rates of the shower coincide with the post-midnight hours, observers could be treated to even more enhanced action. That could happen for this year’s Perseids, but currently Europe is in the most favored locale. The 2018 peak according to the International Meteor Organization occurs between 4 p.m. August 12 through 2 a.m. August 13, EDT which means that meteor activity could be somewhat enhanced on the evening of the 12th before midnight if maximum activity occurs nearer to the middle of this time interval. As we begin to rotate into the debris dislodged from the many passages around the sun of Comet 109P/Swift-Tuttle, some of the first Perseids witnessed are just skimming the top of the Earth’s atmosphere. They can create long bright trails, sometimes fireballs, as they are ablated more slowly by this thinner region of air. A much earlier peak also means that rates may be enhanced on the previous morning, Saturday into Sunday, August 11-12, but more towards dawn than midnight. This is what the American Meteor Society is predicting. If the highest meteor rates are encountered closer to the predicted end time or even beyond, more enhanced rates can be expected on the morning of August 13. Predicting a meteor shower peak is still not an exact science, but the Perseids have been known to show a certain amount of consistency over recent years. Do not fret, however, if the weather looks like it is going to bomb out for the best nights. This week, leading up to Perseid maximum, will yield many beautiful shooting stars with more fireballs being spotted on pre-maximum evenings than post-maximum nights. Observing the Perseid meteor shower for two nights on the banks of Flathead Lake in northwestern Montana in 2016, Pete Detterline and I saw brighter meteors on maximum night than on the following evening. Rates also dropped to about half of the activity of the previous night. That again is very consistent with normal Perseid encounters. Perseid meteor rates climb steadily the week before the time of greatest activity and drop off rapidly afterwards, so you’ll still have plenty of opportunities to snag meteors in the upcoming days. More information about the Perseids will follow in the next article or read ahead at http://www.astronomy.org/StarWatch/August/index-8-18.html.
 

1147    AUGUST 12, 2018:   Night of the Perseids
This is the weekend (August 11-13) that Perseid meteors “fly,” and they will do so against the backdrop of the summer Milky Way. With the moon being virtually new, the rural dark skies of Cherry Springs State Park near Coudersport, PA or Guernsey State Park in eastern Wyoming will glitter with thousands of stars, as well as bright meteors. Get out the chaise lounge or that folding recliner that you bought from L.L. Bean, a sleeping bag or bedroll, a pillow for comfort, a light tarp in case of dew, and perhaps a caffeinated beverage. Right after dark is not the best time to observe meteors, but it may be the only opportunity available depending upon your schedule. Perseids will still be seen, but rates are suppressed at this time of the evening because our location on Earth physically blocks much of the activity. Although the radiant, the region of the sky from which the meteors seem to originate, is above the horizon, we do not catch any of the activity which is happening below this point because of the obstructions that trees, buildings, and the horizon provide. Face your recliners towards the NE, and observe the area of the sky which is overhead. In any locale where there is light pollution, the zenith usually provides the darkest patch of heavens to watch. Perseids will seem to spray outward from a vanishing point in the NE, close to the horizon during early evening hours and high in the east by dawn. The effect is analogous to standing on a long stretch of railroad tracks. The rails approach and pass you on either side, appearing to diverge from a distant vanishing point, even though you know that they must be parallel to each other in order for a train to navigate them successfully. Likewise Perseid meteoroids, the tiny bits and pieces of silicate dross released by Comet 109P/Swift-Tuttle, are moving parallel to each other as they orbit Sol. Just like the railroad tracks, these meteors will appear to diverge from a vanishing point, called the radiant, as they approach you. The radiant is below the constellation of Cassiopeia the Queen and just above the head of Perseus the Hero. Any shooting star that can be traced back to this region is most likely a Perseid. Both of these constellations may be difficult to spot at 10 p.m., but by 1 a.m. they will be much higher and should be visible even from suburban locations. Cassiopeia will be easier to visualize, partly because of its higher elevation and partly because it has a distinct sideways “W” appearance (90 degrees counterclockwise by morning) in the heavens. Perseus will have a triangularly shaped top (his head) which will spread outward, its lines curling at the end for his winged feet. A map and photograph are online at http://astronomy.org/StarWatch/August/index-8-18.html to help you to visualize their shapes better and access a more precise location of the radiant. By 3 a.m. the top of Perseus will be above mid-sky, and you will be catching the action all around the radiant. Meteor rates will be much higher. Perseids are fast; the dust enters the Earth’s atmosphere at 36 miles/second, causing a column of air about a half mile wide to glow as the particle is ablated, vaporized by the air itself. A Perseid meteor may be visible for only a tenth of a second, a momentary blip on the radar of your eyes. Others will last longer, causing the atmosphere to ionize so completely that the glow of its track will be visible for several seconds after its initial light. Sometimes you’ll see bright meteors blink from the corner of your eye, and at other times, you’ll see an extremely faint event because you are looking directly at it. You might even see a point meteor, a shooting star coming straight at you from the radiant, a “star” that will appear to brighten slowly, then fade precisely at the location where all of the other meteors appear to be converging. I’ve had that experience about a dozen times in my life. But most of all, you will have a memorable experience, and several of the fireballs seen that evening will be etched into your psyche for the rest of your life, instantly available to regale others with the wonderful encounter you had on the night when the Perseids “flew.”
 

1148    AUGUST 19, 2018:   
 

1149    AUGUST 26, 2018:   
 

[August Star Map]

[August Moon Phase Calendar]
 

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