StarWatch: Moravian College Astronomy

NOVEMBER 2021

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lunar phases

1316 November 7, 2021: Some Lunar Eclipse Misconceptions: The Americas, but particularly North America including Hawaii, are in for a memorable treat on the morning of November 19 when the moon enters the shadow of the Earth and a nearly total lunar eclipse ensues. The best time to view this eclipse will be at 4 a.m. when 97.42 percent (4:02-53 a.m.) of the moon’s diameter will be occulted. At that time the moon will be due west at a respectable altitude of 30 degrees with the southern hemisphere of the moon bright, and the rest of its surface subdued in yellows, oranges, and brownish reds. Binoculars will enhance these different colors because they focus more light into the eyes. • There are a number of misconceptions that are held by the public surrounding lunar eclipses. One of them is most likely driven by a confusion between the two types of eclipses, solar and lunar, that can occur. • Eclipses are always named after the object that is being hidden. In a solar eclipse the sun (Sol) is being veiled by the moon. At all times when the sun is visible, the event is dangerous to watch unless Sol is viewed with proper filtration or projected via a pinhole or lens system onto a white screen. In a lunar eclipse, the moon hides in the shadow of the Earth and is perfectly safe to view. • Countless parents have forbidden their children from viewing lunar eclipses because of this confusion. If you can look at the full moon with your unprotected eyes, then watching the beauty of a lunar eclipse unfold before you, as the full moon pierces and traverses through the shadow of the Earth, is not going to facilitate any retinal damage. I once had the opportunity of viewing the full moon through a telescope with a 25-inch diameter mirror. It was gathering over 4000 times the amount of light that my eye would normally collect. Yes, the moon was very bright, but it was not detrimental to my viewing eye. • The most common misconception about lunar eclipses is that the monthly phases of the moon result from Luna going in and out of the Earth’s shadow. Here I usually have up to one third of my students who hold this misconception as the truth. Admittedly, there is a sort of phase progression as the moon enters and leaves the shadow of the Earth, but partial and total lunar eclipses represent rather rare phenomena, usually happening only once each year or less for a given locality. The duration from start to finish is more like six hours for a total lunar eclipse, not the 29.5 days it takes the moon to complete its cycle of phases. What causes the lunar phases is simply the moon orbiting the Earth and our watching its nearside, which always faces us, progress through a day and night cycle as different parts of it are illuminated by the sun. • And finally, to the flat Earthers, the shadow of our planet falling onto the moon during a lunar eclipse will always appear round. Since lunar eclipses can occur in all parts of the sky along its orbital path and at all times of the night on Earth, no one has ever observed a line or bar representative of a disk-shaped Earth falling onto the moon. Oh, well, another theory bites the dust. More about lunar eclipses in next week’s StarWatch.

1317

November 14, 2021: Lunar Eclipse on Tap This Week

Finally after nearly two years of waiting, the East Coast and Americas are back in the groove to witness one very deep partial and two total lunar eclipses during the next 12 months. The first one of the series occurs on November 19, the other two on May 16, 2022 and November 8, 2022. Unfortunately, all three eclipses are intended for insomniacs, for their most colorful sequences all occur after midnight. • Eclipses are named for the object that is being hidden. A lunar eclipse arises when the full moon hides within the shadows of the Earth. As the moon orbits the Earth, it always overtakes Earth’s shadow, entering first the penumbra, Earth’s secondary shadow, from left to right. The word penumbra means light shade from the Latin, where an observer on the moon would witness part of the Earth covering part of the sun. As the moon moves deeper into the penumbra, the diminution of light begins to make the moon appear dusky on its leading side. Eventually, if the alignment is precise enough, Luna begins to break into the umbra, Latin for shade. An astronaut on the moon’s surface would see our world completely covering the sun, a total solar eclipse with the sun’s crown, the corona stretching around the Earth, a spectacular sight yet to be witnessed by humans. The limb or circumference of our spherical world would be aglow with all of the possible reddened sunsets visible at the same time. • Watching the sun approach the horizon from the Earth, an observer will notice its colors mellowing into deep yellows, oranges, and sometimes even reds, flooding the landscape with their warm hues. It is the golden hour in cinematography. The denser layers of air that the sunlight must penetrate as it tangentially brushes near to the Earth’s surface, scatters the shorter wavelengths of light, the blues and the greens, acting like a filter, but allowing more of the longer wavelengths of yellows, oranges, and reds to pass through. • At the same time, some of this reddened sunlight is refracted (bent) into the Earth’s shadow as it travels from the emptiness of space through the thicker, denser atmosphere of our planet, caressing the lunar surface with these same spectacular hues that make lunar eclipses such a delight to view. • And speaking of viewing, the human eye will easily detect colors across the lunar backdrop during this eclipse. On the other hand, binoculars, or even that rickety old telescope stored away in your basement, will enhance the colors of the eclipse because they will be drinking in perhaps 20-30 times the light that the eye alone can collect. • The November 19 eclipse starts with the moon entering Earth’s penumbra at 1:02-09 a.m., EST, a contact that is undetectable to the human eye. Subtract an hour for each time zone to the west. It will be somewhere around 1:45 a.m. before observers will begin to notice a dusky appearance near the north lunar pole on the moon’s leading side (upper left). The Earth’s umbra is encountered at 2:18-41 a.m. The greatest eclipse coverage happens at 4:02-53 a.m. when 97.42 percent of the moon’s diameter will be immersed within the umbra, and Luna is perched at a respectable 30 degrees above the western horizon for the East Coast. It is at this time that the colors on the lunar surface should appear most vibrant. The moon exits Earth’s umbra at 5:47-04 a.m., and the penumbra at 7:03-38 a.m., just before it sets and the sun rises. Say a prayer for clear weather on the 19th and have a great eclipse experience. Ad Astra!

The total lunar eclipse of September 27, 2015 was glimpsed for only about half a minute when clouds parted just at the time that the moon became completely immersed in the Earth’s shadow. I may have been the only person in the Lehigh Valley to have caught totality. Notice the stars surrounding the moon. Image by Gary A. Becker…

1318 November 21, 2021: Playing in the shadows: A fast-moving cold front sweeping across the Midwest and into Pennsylvania threatened to put the kibosh on Friday morning’s deep partial lunar eclipse. The National Weather Service was forecasting rapid clearing after the front’s passage, but when I exited Collier at 9:45 p.m. after teaching my Thursday astronomy class, it was still raining, a real downer because the start of the eclipse was less than four hours away. However, by 11 p.m. the rain had ended. Midnight saw the cloud deck thinning, moonlight flashing between the scudding altocumulus. By the start of the eclipse at 1:04 a.m. the sky had become perfectly clear, the air dry and crisp with a light breeze to keep the dew and frost away from my equipment. It was perfect for this lunar eclipse. • Watching the shadows of the Earth play across the face of the moon represents one of the most colorful sky spectacles that nature can produce. At the start, my backyard was awash in bright moonlight, veiling the stars, allowing the green of my lawn to be distinctly visible, and my telescope to be operated without the use of a headlamp. Then gradually, imperceptibly at first, the luminescence began to fade as the moon settled into Earth’s main shadow, the rounded boundary of the umbra marching across Luna’s surface, swallowing craters in its path, unstoppable, as the sky darkened and the stars became visible, a curtain lifted against the backdrop of the heavens. The blood moon gradually appeared against the velvety backdrop of the winter sky, a beautiful sight that I had not seen in nearly three years. • There are two total lunar eclipses that will take place during the next 12 months, the first on May 16, 2022 and not quite six months later on November 8. If you missed the November 19 eclipse, plan for some quiet time next year to watch the reddened moon playing hide and seek in the shadows of the Earth. You’ll be making some wonderful memories. More photos can be found below. Ad Astra!

1319 November 28, 2021: Dyslexic Forever: I am mildly dyslectic, a condition that I discovered in a high school driver training class when my instructor told me to take a right and I took an immediate left. The rearview mirror reflection of that attractive brunette in the back seat just shaking her head will be indelibly etched in my mind forever. • Fast forward to 1994 when my wife and I vacationed in Scotland. As the red-eye approached Glasgow International Airport, I looked down at the ribbons of roadways beneath me and realized that indeed, they did drive on the left side of the road. Of course, I had realized that before we had departed, but it worried me nevertheless because with my dyslexic tendencies, I would be driving our rental car within a couple of hours headed for our first destination of Stirling in the eastern neck of the country. Would I experience difficulties? • Instructions from the airport rental agency easily got us on the M80 without incident, but within a few miles of driving, something felt terribly wrong. Sue felt the same way. We were going in the wrong direction. I exited, and we made our way through Glasgow jumping a curb now and then as I became adjusted to driving on the left. Eventually, we found our way back to the M and headed in the correct direction. That was until the highway sign read, “Entering Port Glasgow” which was on the far western side of Scotland, and we realized that we had originally been journeying in the correct direction after all. Our Glasgow deviation had set us on the wrong course. Luckily, there was a roundabout (circle) to set us motoring along the correct thoroughfare. We turned effortlessly around and headed eastward through the heavy traffic of Glasgow again, and then onward to Stirling. Despite the tribulations of the first day, that vacation remains one of the best in our memory books. • My dyslexia continues to this day, but it’s nothing compared to the misfortunes that my students experience when they first try to navigate a telescopic image. “I wanted the star to move to the right, but it always goes in the wrong direction—aaaaah!” Telescopes change the image by inverting it and/or reversing right and left. The latter is called a perverted image, an unexpected word that always elicits laughter from my learners. • Watching my students manipulate their hand controllers wanting to move the scope east when it has to go west, or north when it has to move south, has got to make them a little more empathetic to my situation. • Then there are the finders, the smaller telescopes attached to the larger ones. They point in the same direction as the bigger scopes, but their wider fields of view act as a homing device. If both telescope and finder are aligned, centering an object in the lower magnification finder will place it within the field of view of the higher power main scope that is ready for centering. Some finders pervert and invert the image, while others give you a normal view, while others may only interchange right and left. Everyone has dyslexia when first learning the ins and outs of telescopic observing, and some of us with the real deal never get over it. Ad Astra!