StarWatch: Moravian College Astronomy

JUNE 2017

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

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lunar phases

1085 JUNE 4, 2017: Eclipse Viewing on the Cheap: Preparation for the total solar eclipse that sweeps across our country on Monday, August 21 should be occurring now. In fact, if you are interested in obtaining lodging along the path of totality, where the moon completely covers the sun, accommodations were already difficult to obtain during the summer of 2016. However, enthusiasts all across the continental US will be treated to a partial solar eclipse, where part of the sun will be covered by the moon. Anytime a partial solar eclipse is occurring, or for that matter anytime the sun is visible, presents a dangerous situation for retinal damage if the sun is observed directly without any appropriate filtration. It seems that everyone knows this, but during eclipse mania, the public wants to sneak a peek. The glance may turn into a stare, and that is where significant eye damage can occur. In addition, the extreme brightness of the sun will foil any unfiltered attempts to see the dark moon covering Sol. For younger children, I suggest a projection system which is easy to construct and to use. Obtain a long box, maybe in the range of two to three feet. On one of the long ends of the box, cut a hole several inches in diameter and tape to its surface a piece of aluminum foil perforated with a small pinhole. The optimum ratio of pinhole size to box length is 1 to 400. On the other end, glue or tape several thicknesses of white paper to the back of the box, or paint it white to act as a screen. Then cut a rectangular opening, perhaps three inches long by one inch wide near the screen of the box as a peephole to allow the screen to be visible. The child takes the box and puts it on his shoulder with his back towards the sun, the pinhole aperture facing Sol. On a clear day, the pinhole will project a safe image of the partially eclipsed sun onto the screen. Here are other ways of creating pinhole images of the sun which are even easier. Take a colander and a white bed sheet. Hold the colander in the direction of the sun, and allow its holes to project images of the partially eclipsed sun onto the bedding, or let the motions of leaves on a tree project thousands of solar images onto a white sheet which is placed beneath it. Even the holes in a Ritz cracker will work, if you don’t eat the snack. These are simple, inexpensive, and extremely safe methods to view a partial solar eclipse. Pictures are online at astronomy.org/StarWatch/June/index-6-17.html#6-4-17.

1086 JUNE 11, 2017: Filtered Solar Eclipse Viewing: Last week, I wrote about safe and inexpensive solar projection techniques for viewing the August 21 total solar eclipse. If you are not positioned along the narrow path of totality that stretches across the continental US from Oregon to South Carolina, then all aspects of the eclipse will be partial, and at no time will it be safe to view the sun unless the image of Sol is safely projected or filtered. The eye acts like a lens, focusing light onto the fovea and retinal net. “The mechanism by which retinal tissue damage occurs in solar retinopathy (retinal ‘disorder’ burn) is photomechanical [and chemical] in nature (Ross Bronson Chod, MD),” due to the sun’s brightness. This situation may be thermally enhanced if the retina is heated by infrared radiation from the sun, but it should be noted that staring into any bright light source is bad for the eyes. In addition the retinal net has no pain sensors, making it difficult at the time of observation to realize that any damage is occurring. In most cases, patients with solar retinopathy make partial to full recoveries after about 18 months, but you’d be plain stupid to take any chances. In addition, the overwhelming brightness of the sun hides the moon in a total solar eclipse until about 15 seconds before totality. Filtering the sun’s light is an inexpensive alternative that produces a much sharper image than the simple projection techniques discussed last week, but the solar intensity must be reduced by about 99.99 percent before safe solar viewing can occur. Here are some suggestions. Go to any welding supply store and purchase a No.14 welder’s filter. They come in two different varieties. A less expensive version produces a green representation of the sun, and for a few dollars more, a filter that is “gold” coated which will give the observer a more natural view of Sol. You can also buy goggles, usually red in color, with a filter holder in front and watch the eclipse in a chaise lounge while relaxing and sipping a margarita. My recommendation, however, is to purchase a pair of black, Mylar eclipse glasses which can be worn just so or over regular glasses. None of these filtering techniques are meant to be used at the eyepiece end of a telescope or binoculars. The focused light from the sun will melt the Mylar or crack the welder’s filter. Contact Rainbow Symphony for your Mylar eclipse glasses at https://www.rainbowsymphony.com/eclipse-glasses/ or stop into the Collier Hall of Science office at Moravian College where Lou Ann Vlahovic (610-861-1425) will sell you as many as you would like for just a buck each. Do it now before the big rush in a few weeks.

1087 JUNE 18, 2017: Telescopic Solar Eclipse Viewing: At this point you may be saying, “Not another article about the August 21 solar eclipse, Gary!” As astronomical events go, this sun-moon courtship ranks as one of the biggest occurrences of the early 21st century, except for the April 8, 2024 solar eclipse which will be total in Erie, PA or the serendipitous discovery of a Hale-Bopp-type comet which can be viewed from urban locales. What if you would like to observe the partial phases of this eclipse with binoculars or a telescope? There are two basic and relatively inexpensive methods to attain this goal, but first a warning. Never, never observe the sun directly without proper filtration. If you choose to view the partial phases of the August eclipse with an optical aid, my first suggestion would be to purchase a solar filter(s) to attach onto the front end of your telescope or binoculars. You never filter at the eyepiece end of your scope because telescopes and binoculars are used to gather light, and already the unmagnified sun has tens of thousands of times too much light for the unaided eye to view safely. Remember the old magnifying glass trick where you set a bunch of leaves on fire by concentrating the sun’s energy into a focused area? Binoculars and telescopes do the same thing, but with higher precision. To purchase a front end solar filter(s) for your binoculars or telescope, my suggestion would be to go to the Thousand Oaks website, http://thousandoaksoptical.com/shop/solar-filters/full-aperture-solarlite/ (928-692-8903), but you must act now because the demand is high, and they are a relatively small company located in Kingman, AZ. Locally, Skies Unlimited, 52 Glocker Way, Pottstown, PA 19465 (888-947-2673) has a knowledgeable staff and is well stocked. Using a telescope, you can also project the sun onto a screen. The key here is finding Sol without looking through the telescope. When pointed at the sun, your scope’s tube will make the smallest possible shadow on the ground. Your projection area and or telescope should also be baffled so that direct sunlight does not fall onto the screen. Finder scopes, smaller wide-field instruments attached to the main tube, should either be removed or covered so that no one makes the fatal, eye-suicide mistake of looking through them. Also use a cheap eyepiece because all the heat and the light of the sun will be transmitted through the telescope, sometimes damaging the eyepiece lenses. Most importantly, never let your telescope or binoculars unattended because kids do the craziest things, and practice before the event so that on eclipse day everything goes according to plan. Safe solar viewing to all.

1088

JUNE 25, 2017: Learning to Love the Moon

I used to hate the moon. It was the ultimate star destroyer for deep sky objects like nebulae and galaxies, and especially for meteor observing, causing an ultra-clear night in the country to look more like a sky lit by a large metropolitan area. And then one day, when I was older, probably in my forties, I decided to examine the moon more closely through a telescope. I discovered a wondrous landscape that I’ll spend some time discussing next week. I also enjoy watching its rapid motion across the sky from night to night. Luna travels about 26 of its diameters each day (13 degrees), catching up to and passing bright stars and planets along its celestial path. All this happens during a period of a little less than a month, 27.3 days, the orbital period of Luna around the Earth. This week, the moon treks towards brilliant Jupiter, just to its right by five degrees on Friday and eight degrees to Jupiter’s left on Saturday, July 1. Then slogging eastward, Luna heads towards Saturn during the next three days, approaching the Harvest God by July 5. The following evening, the 96 percent lit moon passes over Saturn by less than three degrees low in the SE. On July 9 just after midnight, the full moon lights up rural landscapes bright enough to perceive colors and hike trails exposed to the sky without flashlights as I have done numerous times during vacations in the Southwest. In national parks like Bryce Canyon, moonlit hiking is encouraged by the Park staff. I volunteered at Bryce for two years and was given the assignment of imaging its hoodoo-laced landscape by moonlight. That was a wonderful experience with Luna following me everywhere that I went as my trail companion. I have also enjoyed observing the moon in a more subdued form when it is a thin crescent and embraced in earthshine, the old moon in the arms of the new. Earthshine is caused by the reflected sunlight of our planet mirroring from the portions of the moon that are not sunlit. You can only catch earthshine when the moon is a thin crescent as the light of the old day fades into deep darkness. Tonight, and Monday evenings, June 25/26 are this month’s opportunities. Binoculars will help reveal more distinctly this ghostly sight. Finally, do not forget the opportunity of seeing a new moon when it hides the sun on August 21. Eclipse glasses are available from Lou Ann Vlahovic (610-861-1425) in Collier for a buck apiece or purchase them from https://www.rainbowsymphony.com/eclipse-glasses/. Clear skies and good observing to all!