StarWatch: Moravian College Astronomy

SEPTEMBER 2017

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

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lunar phases

1098 SEPTEMBER 3, 2017: Total Eclipse of the Heart: I had waited for this moment at least 50 years and had been teaching about it for a quarter century, and here I was on a high, windy bluff in Guernsey State Park in SE Wyoming under perfectly clear skies. Cars had been streaming into the park all morning and kicked up a continuous stream of dust that blew across the grasslands below us. But now all was quiet and expectant. Laramie Peak, 33 miles distant, was a steel grey and behind it and all around us, the sky was becoming darker like some ominous but gossamer thunderstorm was approaching from the west. It was the moon’s shadow. The landscape around us was surreal, still sun-drenched, but as if a giant rheostat in the heavens was rapidly diminishing the sun’s light. Moment by moment, the landscape dimmed. Shadows on the ground paled against the muted, greying sunlit sky. The moon’s darkness grew nearer. Sol on my camera’s screen was a now a razor thin crescent as I imaged my last sequence before totality. In the background, I heard Moravian graduate, Sarabeth Brockley (2010) and friends cueing Bonnie Tyler’s, “Total Eclipse of the Heart,” one of my all-time favorite songs. I sat by my telescope in anticipation, knowing exactly what was going to happen next, yet still feeling the same flush of wonder that had accompanied my first eclipse in 1970. The sun was still shining, but it was providing no heat. I shivered. The wind quieted in the cooling air. Vibrations of changing light rippled in the sky as shadow bands pulsated across the darkening ground. Removing my filter, I gazed skyward and looked at the sun, a point source of safe luminescence, but still too bright to see the dark disk of the moon and its surrounding crown, the corona. Totality was upon the face of the deep. Returning to my telescope, I witnessed two giant lavender prominences dotting the upper limb of the sun. I carefully went through my series of planned images, set my camera for the egress diamond ring, then simply looked up. The prominences sparkled to the unaided eye, the delicate corona elongated near the lower limb of the sun, with the sky now a dark lapis blue surrounded by a peach-colored horizon. Binoculars revealed both faint Mars to the left of the sun and the extension of subtle coronal streamers sculpted by the sun’s magnetic field. Stunning, magnificent, glorious, and humbling was the view. The upper right limb of the eclipsed sun grew brighter, signaling the nearness of the end of totality. I returned to my camera and began imaging. The pink chromosphere returned; bright Baily’s beads punching through the lunar valleys on the moon’s limb gleamed and amalgamated into a spectacular diamond ring of growing brilliance, with pulsations of light as Sol returned. Totality was over. This was my sixth total solar eclipse and the best one yet. My pictures will be online at astronomy.org in about a week, but here a few for starters.

1099 SEPTEMBER 10, 2017: Backstory of an Eclipse: In general, the weather for the Great American Eclipse of August 21 was very cooperative, and most individuals who had traveled to view the event saw it. Guernsey State Park in SE Wyoming where friends and I were gathered had joyfully, clear skies. Only two close colleagues were clouded over by an afternoon thunderstorm that moved into Charleston, SC covering the sun just minutes before totality. The planning of this event spanned about 14 months and entailed traveling along the eclipse’s centerline from Nebraska to central Idaho over a 5-day period in June 2016. Everyone that we had spoken to knew about the event, and all hotel spaces were virtually booked a year in advance. There seemed to be a sense of bewilderment among many of the administrators that we met regarding how to accommodate safely all the eclipse chasers who were expected to arrive. Guernsey State Park officials, on the other hand, were calm and collected, reaching out to us to be part of the Guernsey eclipse experience. Superintendent Todd Stevenson felt that this would be an excellent opportunity for the public to get to know this region of southeastern Wyoming and the park itself. Peter Detterline (Montgomery County Community College) and I were also given use of two of the park’s four spacious yurts for our group in exchange for public star parties and presentations about the eclipse. According to Todd, our six presentations drew record audiences who gathered to hear about the eclipse and participate in star watch programs at night. It was a wonderful experience, but exhausting and intense, especially as E-day approached, and the weather became less and less certain. Climate is what you expect; weather is what you get! Two weeks out, SE Wyoming was the sweetest spot across the entire US. We figured that would not hold, and it didn’t; but the forecast never deteriorated to the point where we thought we were going to have to make a run for it. According to meteorologist and good friend Adam Jones, on E-day eve we were being squeezed between two frontal boundaries, a fast-moving clipper system approaching Wyoming from the northwest and a much slower moving and weakening system to the south over Colorado. He predicted that we would be in a relatively clear zone on the morning of the eclipse as the two systems literally pivoted around us. On the evening of August 20, clouds from the system to the south moved in, but it was too late to chase. Opening my eyes every hour or so, I nested sleepless outside my yurt. By 1 a.m., the sky was mostly clear, and conditions continued to improve as the hours drifted by. By sunup, we realized that Adam’s forecast was going to be spot on, and the eclipse would be ours to view. Conditions were clear, but very breezy at first contact; but as the moon covered more and more of the sun, even the wind succumbed to the cooling temperatures, and conditions during totality became calm. Exhale...

1100 SEPTEMBER 17, 2017: In the Shadow of Discovery: Last week, I had the pleasure of being in Los Angeles and attending the 20th International Convention of the Mars Society where Pete Detterline of Montgomery County Community College and I hosted a session about the Mars Desert Research Station’s new robotic observatory currently under construction. Moravian has a 25 percent usage share of telescope time with that facility. The meeting, however, was not the highlight of my weekend in sunny California. Before we flew home, we made it our mission to visit the Mount Wilson Observatory, about 30 miles to the NE of downtown LA. The light pollution from the greater LA basin and the age of the instrumentation, much of it constructed in the first quarter of the 20th century, has rendered the facility obsolete. It is still well maintained; however, its gleaming white solar and celestial observatories were freshly painted from grant money obtained during the Obama administration. The cornerstone of the Mount Wilson success story is the observatory which houses the 100-inch aperture Hooker reflector, the largest in the world from 1917 to 1949. Here discoveries were made that changed forever our perceptions of the universe, like the mid-1990’s when the mind-blowing unveiling of the accelerating universe, dark energy, and dark matter took hold. It was at Mt. Wilson that Harlow Shapley, future director of the Harvard College Observatory, used the precise fluctuations of a new type of variable star, discovered by Harvard calculator, Henrietta Swan Leavitt, to determine the size of the Milky Way Galaxy and the sun’s position in it. Although his estimate of our galaxy’s proportions was three times its actual size, Shapley proved conclusively that we were not in the middle, thus changing our perspective from a heliocentric universe to our sun being just a common member of a huge galactic city. In addition, the same techniques used by Shapley were incorporated by Mt. Wilson astronomer, Edwin Hubble, who discovered the distance to our nearest spiral galaxy in Andromeda. He found that it was one million light years away (today 2.5 million light years), making our Milky Way, not the island universe that many had thought it was, but simply a member of a much larger cosmos filled with countless other galaxies. Hubble went on to discover the red shift, a stretching of light’s wavelengths emitted by receding galaxies. Our universe was expanding, and the more distant the galaxy, the greater the expansion rate. The Hubble Space Telescope was one way that the scientific community paid tribute to these achievements. Two final notes: in the 1930’s, Mt. Wilson’s Fritz Zwicky found the first evidence for dark matter in the universe, and Walter Baade discovered two distinct populations of stars in our galaxy (1940’s). Knowing that Pete and I were astronomy educators, Mike Thacher, our enlightened tour guide, took us to the basement of the 60-inch (Hale) reflector where he showed us the night lockers of some of the greatest astronomers of the early 20th century— Hubble, Zwicky, Babcock, and others. We were literally touching astronomical history.

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SEPTEMBER 24, 2017: Harvest Moon, Shine Down on Me

Have you been watching the moon lately? It was new and invisible last Wednesday, September 20, but instead of passing in front of the sun, as it did on August 21, producing a solar eclipse, it was substantially above the sun, and no eclipse happened. That is because the moon’s orbit is tilted by five degrees to the sun’s path in the sky. One of the interesting aspects of observing the autumnal moon after its new phase is that it remains virtually hidden from view. You may have just noticed its increasing brilliance in the evening sky during the last few days, even though it is no longer a silvery sliver of a crescent, but well along toward its first quarter phase, half on—half off, sunlight on the right half of the moon (Wednesday). The reason for this lunar elusiveness in the late summer and fall seasons results from the moon’s orbit which at this time of the year is slanted at a very shallow angle to the horizon. The moon moves about 13 degrees per day while it revolves around the Earth, but its orbital progress does not greatly change its distance above the horizon. Therefore, the Earth’s rotation (spinning) will set the moon at nearly the same time for several days after its new phase. By the time the moon is full, nearly 15 days later, and is easily visible in the evening sky, the same conditions still apply, and the moon rises at nearly the same time for several nights in a row. The effect is even more pronounced in Europe where the moon’s orbital plane is even less inclined to the horizon and differences in moonrise times can be as little as 10 minutes. Farmers harvesting crops would be able to continue their work uninterrupted as western twilight blended into the brilliance of a full moon rising in the east. Full moons were named, and the one occurring closest to the autumnal equinox which had the minimal changes in rising times was called the Harvest Moon, one of dozens of titles that Luna in her full phase received throughout the passage of a year. Usually the date falls in September, but every third year, it happens in October. Watch this week as the moon continues to wax (grow) in brightness. On October 5, it reaches its full phase, the Harvest Moon for 2017. Next year, it is back to September on the 24th, nearly the best Harvest Moon that can possibly occur. If you think that the full or nearly full moon is not bright enough to harvest crops, take a ride into the country around the time of full moon and bring along a book. Find a location untainted by street lamps but under moonlight. Let your eyes adjust to the lower levels of light and see if you can read the printed word by the illumination of the silvery moon. I’ll bet you can!