StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

MAY 2018

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

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1133 MAY 6, 2018: Gaby: It was just after midnight on Christmas morning about seven years ago. I was standing with my wife, Susan, lit candle in one hand while balancing the Episcopal hymnal in the other, singing Silent Night. That part of the service is always a very emotional moment in our lives, and often Sue and I feel our eyes well up with tears, grateful for another year of being together and at the same time hopeful that we will not be the ones to burn down the church. I believe I was in my third year of teaching astronomy at Moravian College, and as I sang the words of the hymn, the candle moved back and forth, causing the page to brighten and dim as it was relocated toward or away from the open book. I thought it was interesting that I was reading the page by the illumination of one candle, one candlepower, and at the same time witnessing something called the Inverse Square Law. The rule says that intensity is equal to 1/d2, or one divided by the distance of the energy source multiplied by itself. In this case, “d” equaled the distance of the candle from the page. It applies to all energies that travel at light speed, including magnetism and gravity, and is a fundamental concept of science which I believe is important for students to know. Suddenly, I had an idea for a quick lab so that my pupils could demonstrate the brightness of one candlepower and the Inverse Square Rule for themselves, but I needed candles, and more importantly, those little plastic cups to keep the melted wax from dripping all over the room. The service ended with everyone wishing others a blessed Christmas in a feeling of warmth and camaraderie. As I filed to the back of the church, an elderly woman stood with a basket collecting the candles and their holders. With a smile and a look of good cheer, I asked her if I might take a half-dozen candles and holders to achieve this little experiment at the beginning of the spring term. To my surprise, I got an emphatic “No!” followed by a terse, “They are property of the church. You can’t have any.” Well, “Merry Christmas to you too, lady,” were my initial thoughts. As I deposited my candle and holder into the basket, I felt a hand tug on my arm, and I turned to see Gaby Whittier, the church administrator pulling me from the line. She said, “Follow me.” We went to her tidy office filled with the icons of dozens of saints that she had rendered over many years of attending workshops. Gaby opened a box which contained scores of candles and holders all fresh and brand new. She put several handfuls into a paper bag, many more than I had originally asked for and sent me on my way. I still use them today. Gaby retired as church administrator for Trinity Episcopal on East Market Street in Bethlehem this past January. But before her last day she filled several plastic bags with dozens of long, used candles, candles that would fit perfectly into those now empty plastic cup holders that she had originally given me years before. My wife brought them home as a gift, and as a keepsake that Gaby remembered that distant Christmas morning so long ago. Gaby Whittier died peacefully on April 29 after a short illness, less than four months following her retirement. Her candles will continue to burn brightly in my classroom for many semesters to come as a reminder of her kindness and generosity. Thank you, Gaby, for your gift of light.

1134 MAY 13, 2018: Summer of the Planets: The sun is setting later and later each evening, and shortly after it’s gone, a bright “star” makes an appearance in the western sky. For several month I’ve been watching Venus, the Goddess of Love, following nearly in the same path as the sun, but ahead of Sol, where the sun will be in about one month’s time. I first noticed Venus in mid-March, to the south of west just like the sun in its setting position, but the Earth’s orbital motion and its axial tilt have “driven” Sol and Venus northward to higher and higher altitudes, so that now our daystar and Venus are setting in the WNW. It was fun to watch the change through the skeletal branch of my neighbors’ trees, but now Venus has gotten to the point where its first light each clear evening is above the treetops of a slightly more distant horizon. Throughout late May, Venus will continue to gain altitude, topping out during the first half of June at a height of 27 degrees for latitude 40 degrees north. Venus, running far ahead of the sun, will then start to drift southward, setting earlier each evening, becoming more difficult to catch by late August, and eventually disappearing from the evening sky, low in the southwest by mid-September. For the present, however, and throughout all of June, look for Venus to dominate the western sky after sundown. But there is more. What is that bright “star” rising earlier and earlier each evening in the east? If you checked it out with a small telescope, you would have no problem discerning four of its 67 moons. It’s Jupiter and it’s bright, but not as luminous as Venus in the west. If you are out around 10:15 p.m. this week, Jupiter will be just about as high in the SE as Venus’ altitude in the WNW. By the end of May during late evening twilight, Venus is about 18 degrees above the WNW at 10:15 p.m., while Jupiter has climbed to 30 degrees in altitude in the SE. That is equivalent to three fists, thumb on top, held at arm’s length, stacked one upon the other with the bottom of the first fist extended against the true horizon. As late spring turns into summer, Venus wanes while Jupiter continues to gain prominence, but there will be more planetary actors to grace our summer sky. Mars and Saturn will begin to enter the stage as the curtain of night falls. Saturn returns in the SE by the beginning of July, while Jupiter becomes visible due south in the darkening heavens after sundown. Ruddy Mars makes the same curtain call by early August, shining almost twice as bright as giant Jupiter. By the time that Perseid meteors begin to fly in early August, Venus, Jupiter, Saturn, and Mars will be spread across the southern sky at dusk. Mercury even makes a brief appearance in early July in the WNW. The summer of the planets is commencing right now over your own neighborhood skies!

1135 MAY 20, 2018: The Clustering Effect: Stars and other objects like to cluster. It’s a natural consequence of gravity, which to put it simply, always “sucks.” Gravity pulls; it never pushes. In their largest congregations, millions to trillions of stars form galaxies, but even galaxies cluster into small and large assemblages which creates a universe with the three-dimensional qualities of a sponge, the spongy material composed of the small and large galactic clusters webbing around great bubbles of nearly nothingness. The Milky Way, home to our solar system, is part of a small cluster of 54 galaxies called the Local Group. The two major players, Andromeda and the Milky Way, are starting a galactic collision of their own which will be in full swing 3.45 billion years from now and will eventually lead to the creation of a galaxy with over a trillion stars. Our Local Group lies in the suburbs of the Virgo Cluster, which is part of a much larger assemblage called the Virgo Supercluster; its more than one million component galaxies now appearing in our spring sky. In fact, the moon passes just 15 degrees beneath the center of the Virgo Cluster on May 24. After dark on Thursday, place the bottom of your fist on top of the moon with your thumb pointing straight out. Follow the line of sight using your thumb as a pointer to the Virgo Cluster’s center, a relatively bland region of the heavens to the unaided eye, but packed full of galaxies to large telescopes. To the left and below of the moon will be blue supergiant Spica, the alpha star of Virgo, and below it even more brilliant Jupiter. Within our Milky Way, the second largest galaxy in the Local Group, stars are also assembled into globular clusters and open or galactic clusters. Globulars are large aggregates of between 10,000 to one million stars. They are massive enough to be gravitationally stable, holding onto their members since their creation. Globulars also orbit the galaxy at high inclinations ramming through the denser, star-laden galactic plane, churning up the interstellar medium to create new star clusters. Most globulars are also very old, helping to date the origin of the Milky Way at about 13.5 to 13.6 billion years in age. The universe is only several hundred million years older (13.8 billion years), making the Milky Way one of our universe’s charter members. Open or galactic clusters are the newbies of our galaxy formed from the disruptive effects of globulars, supernovae, and OB associations (grouping of hot, new stars). They pump huge amounts of energy into space pushing interstellar matter to form shock fronts, areas of higher density which collapse to form new open clusters with populations of dozens to several thousand members. Stars do not get born alone, but unlike the globulars, open or galactic clusters do not contain enough mass to be stable for very long. They evaporate, losing members to the tugs and pulls of other objects passing near them; their stars, many of which are double or multiple systems in themselves, become members of the galaxy in their own unique orbits around the Milky Way’s core. Our sun with its entourage of planets, moons, dwarf planets, and other smaller bodies were once part of some unknown open cluster which evaporated billions of years ago. If you want an easy view of a nearby open cluster, just look at the Big Dipper high in the northern heavens after dark. The inner five stars are the core region of an open cluster about 500 million years old that stretches across a good part of the sky and is in the process of evaporating.

1136 MAY 27, 2018: Green Clouds Mean Hail?: On Tuesday, May 15 the National Weather Service predicted severe afternoon storms for southeastern PA. In anticipation I began to watch the weather loops around noon. Outside there was a brisk wind rustling through the trees, a good sign that trouble was brewing. The atmospheric pot was being stirred. Dew points, the temperature to which the atmosphere must be cooled to become fully saturated with moisture, were high, in the low 70s. Then as forecast, the sun made an appearance around noon, warming the ground to create the energy that was necessary to trigger tempestuous, conditions. A line of storms began forming to the northwest in central PA, moving in a southeasterly direction. At 4 p.m. the sun was still shining; by 5 p.m., the west and NW had a greyish appearance. By 5:30 the west was black. As the shelf clouds of the storm approached, the sky darkened even more, and the heavens appeared to be boiling downwards with great snarls of scuddy, black cotton. Was I in Indiana Jones, Raiders of the Lost Ark or maybe The Ten Commandments? I quickly went inside and grabbed my camera. I imaged for about 10 minutes with several wide-angle lenses, taking four or five shots of the same scene at slightly different exposures. A few days later, it dawned on me that because the clouds were moving so rapidly, I might be able to get a false stereo effect of the instability. Two images proved particularly effective and can be found by going to my website, www.astronomy.org/StarWatch/May/index-5-18.html#5-27-18. That wasn’t all of the excitement that made this storm memorable. As the rain and lightning approached with an ominous din of continuous thunder, certain areas of the cloud base appeared greenish. I had only seen this one time before, when friend, Elizabeth Churchill, made me aware of this phenomenon as a large storm approached Chaco Culture National Historical Park near Nageezi, New Mexico. In both instances the storm associated with it produced hail. The greenish color is not due to the hail itself, but rather the conditions that were conducive to producing it, towering roiling clouds like those which are found in a severe thunderstorm and a low sun. The droplets of water which produce the cloud are very small, causing entering sunlight passing through its tall vertical structure to be scattered. Small bodies scatter blue light (shorter wavelengths) more effectively than larger bodies “ricocheting” the blue light around in the cloud, causing the light from the cloud to be biased toward the blue. In addition, the longer wavelengths of visible light, such as oranges or reds, are more readily absorbed by these same small droplets and larger ones enhancing the blue bias. That is why if you are photographing under cloudy conditions, you must change your sensor settings in order to compensate for this excess of blue light, although in most cameras this is achieved automatically. Sunlight traveling through a longer cylinder of air when Sol is low in the sky is so effectively scattered by even smaller air molecules that virtually no blue light is present. If yellow light from the low sun mixes with the blue light being scattered by the clouds, the greenish hues seen in certain parts of the cloud can be produced. See my online photograph of the green clouds associated with this storm. The vertical updrafts and downdrafts associated with these clouds lifts and freezes water around an initial droplet coating it with numerous layers of ice until it is too heavy to be lifted again, and it falls to Earth as hail. Green clouds and hail are not a “done deal” according to meteorological studies, but they do seem to have a better fit with high altitude, convective turbulence which is associated with thunderstorms bathed in the warmer light of a late day sun.

[May Star Map]

[May Moon Phase Calendar]