StarWatch: Moravian College Astronomy

FEBRUARY 2019

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

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lunar phases

1172 FEBRUARY 3, 2019: Earth's Shadow Games: We just had the opportunity of watching the moon sweep through the Earth’s shadow, a night so cold that my voice froze in midair, and no one heard me until the morning’s thaw. The next chance that we have to see a similar event is on May 15/16, 2022. I can already feel the blush of a verdant, vernal evening. There is also a deep, partial lunar eclipse visible from North America on November 19, 2021, if you like being awake at 4:00 a.m. However, no worries about having to wait that long to see the Earth’s shadow projected into space. There is another very simple way to view the umbra without an eclipse, especially from locales with sweeping western vistas and drier air. The southwestern US is an ideal location. Here the planet’s shadow is projected visibly into space almost every clear evening as a rising, elongated, greyish haze, straddling the opposite horizon to where the sun has set. Its upper boundary may be bathed in a pinkish or lavender hue which represents the reddening sunlight as Sol dips below some far distant horizon below the curvature of the Earth. One of my first experiences with observing this phenomenon happened in 1975 while I was hiking and camping in Arches National Park, located in east-central Utah near the town of Moab. The Earth’s shadow was so distinct against the brighter sky above it that I considered disassembling my telescope because I thought a cloud deck was approaching. In reality, it was the harbinger of one the darkest evenings that I had ever experienced until that time. The problems with seeing Earth’s shadow east of the Mississippi are many. More humid conditions and hazier air normally persist. Then there are buildings, hills, and trees that may also get in the way of a good view opposite to sunset. The last time that I saw Earth’s shadow was on Thursday evening traveling to class at Moravian. A photo is online, snapped on the previous evening when the shadow was also seen. It was not very distinct, blending in with the darkening sky, but it was there. Check online to see how Earth’s shadow appears on a really good evening near Hanksville, Utah. Go to astronomy.org and click on “this week’s StarWatch.” Look below those images, and you’ll see smartphone photos of the total lunar eclipse sent to me by two good friends and former Dieruff Huskies, Adam R. Jones and Jesse Leayman. Jones of Denver, now an IT guru for an international company which employs over 100,000 people worldwide, used his grandfather’s home-built reflector that was constructed shortly after WWII. The eyepieces were machined from wood. Adam handheld his phone, positioning the lens directly over the eye lens of the eyepiece, not an easy feat, especially with older oculars. Posted online are the best four of his 200 pictures. Not to be outdone, Jesse Leayman, master outdoorsman (Wildman) who lives right off Moravian’s main campus, used an Astroscan 2001 telescope and a special device that allowed his smartphone to be attached to the telescope’s eyepiece. The monetary value of each setup was in the phones that were employed. I used several thousand dollars of camera gear to achieve what I considered to be “okay” results. You don’t need a huge investment to take good pictures. Thanks, Jesse and Adam, for proving that, and to all of us, “Keep looking skyward for that elusive Earth’s shadow

1173

FEBRUARY 10, 2019: What’s Your Sign?

A guy cozies up to an attractive young woman sitting at a bar and asks as his pick-up line, “What’s your sign?” The woman looks him squarely in the eye and with one word, “Exit,” sends him on his way. That always gets a laugh from my students, but the concept of signs and the sky dates back thousands of years to the Babylonians. It was perfected by the Greco-Roman mathematician, astronomer, and geographer, Claudius Ptolemy, who reach his greatest epoch of achievements about AD 140 and died around 168. Ptolemy refined the geocentric universe, where the Earth was in the middle and all other objects revolved about it. Ptolemy did not consider his system as reality; it was meant to be a mathematical and aesthetic predictive model for the future and past positions of the sun, moon, and planets. When the Church later turned Ptolemy’s ideas into dogma, causing all kinds of problems for Galileo and others, the immovable Earth was considered to be the cesspool of corruption for a universe that was pure and unchanging surrounding our planet. Ptolemy was simply happy with his predictive model which allowed him to perfect the pseudoscience of astrology, culminating in the rules of its operation with his Tetrabiblos (four books), which still remains the primary source of astrological information today. The sun, moon, and planets all had traits, which heightened or diminished the influence of each other on the human condition (humors) depending upon where these objects were located in the sky. Although completely bogus by today’s scientific standards, about 13 percent of American still believe that astrology is real (Chapman University, 2014). That is “probably down” from 90 percent of Americans, who in a survey published about 30 years ago, believed that astrology had some influence on their lives. There is good science rooted in astrology because the accurate positions of celestial objects need to be known. However, when those objects are given traits and these qualities are related to one’s life, the science departs like a falling lead weight. I try to support this idea to my students because I was born under the sun sign of Gemini. My traits fit Geminis pretty closely. They are smart, witty, and good articulators, but they can also be quick tempered with split personalities. The “smart” and “witty” statements always elicit smiles. I’m actually pretty average. However, here is the rub. If you mock up the date of my birth on a computer, June 10, 1950, you will find that the sun is squarely in the star pattern of Taurus the Bull and not in the constellation of Gemini. The reason for this change is the 26,000-year wobble of the Earth’s axis which moves the star patterns against the yearly position of the sun. Ptolemy was aware of precession, but who cared at a time when everything was in perfect synchronization? How do astrologers account for this discrepancy today? They claim that the birth sign remains the same and remembers the traits, even though it has nothing to do with the true location of the sun in the sky when you were born. My sign is still Gemini even though the sun was in Taurus when I came into this world. Good science, right? WRONG!!! More about precession, without the astrology, next week.

1174 FEBRUARY 17, 2019: Wobbling Earth and the Tropical Year: Astronomers monitor a plethora of different motions of the Earth and many other effects which change the positions of objects in the sky. Two of these motions are fairly obvious—rotation, the spinning of the Earth on its axis in a 23-hour, 56-minute, 4-second period and the revolution of the Earth around the sun in a 365.26-day interval. These times are referred to as the sidereal periods of rotation and revolution and are related to the 24-hour day and the calendar year that we use. The sidereal day brings a star to the same position in the sky, and the sidereal year brings the sun to the same position in the sky with respect to the stars. Each rotation occurs during an interval of time that allows the Earth to orbit the sun by about one degree. The 365-day calendar year is intimately related to the 360 degrees found in a circle. The orbiting Earth shifts the sun about one degree to the east each day after one rotation. We return the sun back to its original location, due south at noon, by adding four minutes to the sidereal day, and all is well. Our 24-hour clocks keep on ticking in relative congruency with what the sun is doing. Unlike one spin period of the Earth, our calendar year does not return the sun back to its original position with the stars, but rather to the intersection point of Sol’s path with the celestial equator, the projection of Earth’s terrestrial equator into space. When the sun crosses this point in the heavens, we call it the first moment of spring, the vernal equinox. That will happen at 5:58 p.m., Wednesday, March 20; but why a calendar year with 365.24 days rather than one full Earth revolution of 365.26 days? It all has to do with the precession of the equinoxes, the conical wobbling of Earth’s axis in a 25,772-year period and keeping the calendar in step with the seasons. The tipped Earth is like a slowly spinning top with the sun trying to pull the Earth’s slightly bulging equator into alignment with the Earth’s orbital plane. Because the Earth is spinning, the action of the sun’s gravitational force causes the axis to pivot at a right angle to Sol’s downward pull, resulting in the wobble. This causes the point of the vernal equinox to slide westward against the stars by 50.287 seconds of arc per year or about 0.013969 degree. “Who cares?” one might quip, but it’s really important to the calendar! Just like we want to the sun to return to the same due south position in a 24-hour period to repeat the day, we want the sun to revisit the same point in the heavens, the vernal equinox, with respect to the start of the seasons to repeat the year. This is called the tropical year as opposed to the sidereal year, a length of time which is about 20 minutes shorter than the actual orbital period of the Earth around the sun. By using the vernal equinox as the marker, we will insure in perpetuity that Christmas will always happen at the beginning of winter when it is cold and that Independence Day will always happen when it is summer. There will be changes, but it will only be in the position of the sun with respect to the stars. Two thousand years ago, I would have been born with the sun in the constellation of Gemini, about 11 days before the summer solstice. Today, because of precession, the sun is in the constellation of Taurus, but babies born on June 10 are still brought into this world 11 days before the summer solstice. Twelve thousand years from now, Christmas will still be celebrated in winter, but with many of the stars we currently view in the summertime gracing our yuletide sky

1175 FEBRUARY 24, 2019: Wildman Orion: Straddling the southern sky as soon as darkness falls is perhaps my favorite constellation, Orion the Hunter. His two broad shoulder stars, Betelgeuse (left) and Bellatrix, the three belt stars with equally spaced diamonds that gird his narrow masculine waist (right to left)—Mintaka, Alnilam, and Alnitak; and finally, his Marlon Brando kneecaps, Rigel (right) and Saiph, round out the body that any guy would be proud to possess. In some respects, he may have had a few attributes of a Hemingway Code Hero (maybe 2000 years ago), “a man who lives correctly, following the ideals of honor, courage and endurance in a world that is sometimes chaotic, often stressful, and always painful (Ernest Hemingway).” Well, read onward and make your own decision. Orion was likely the son of the sea-god Poseidon and Euryale, daughter of Minos, King of Crete which gave him three Christ-like characteristics. Orion could walk on the waves of the sea (some say only wade through great depths of water); and because his mother was mortal, Orion would die. Finally, because of his legendary hunting abilities, Orion was resurrected by Zeus as a constellation after his death for all to see and admire. Orion was a giant of a fellow, some say as tall as 70 feet (21 meters) with a spiked wooden club, a jeweled sword, and a shield made from the impenetrable skin of the Nemean lion, the beast slain by Hercules. All of these components are visible in a dark enough sky. Hooking up with Diana, Goddess of the Hunt, on the Island of Crete, the account goes that they hunted most species of wild animals to extinction. Even the SPCA could not bring him to justice. Orion was hated by Apollo, Diana’s brother, who one day tricked his sister into killing her lover by betting that she could not strike that object far out to sea with one of her arrows. It was really Orion’s head in the sunlight as he was clubbing a few fish for dinner. The arrow flew and a surprised Orion died, his last words being “Oh damn!” Diana collected half a drachma for her efforts. “I like wine,” was one of Orion’s favorite slogans. In fact, in recorded testimony before the Roman Senate, Orion is quoted to have said "I drank wine with my friends. Almost everyone did. Sometimes I had too many mugs… but I did not drink wine to the point of blacking out…” There is some historical evidence to prove that Orion may have forgotten the incident which involved his walking to the island of Chios where he got drunk and attacked Merope, daughter of Oenopion. But those were in his “Greek Life” days, long before the Roman inquiry (source: Pliny the Elder). The Roman Senate gave him a mulligan on that one. The blackout story goes something like this. King Oenopion of Chios liked his solitude, but the noisy disturbances from the wild beasts roaming the island were causing him much psychological distress. Enter Orion, who was hired to silence every animal, giving Chios a great fur export industry for a year or so and to find peace and quiet for the king. Then it was payback time, and Orion wanted the hand of the beautiful Merope for his wife to the king’s great displeasure. Enter wine, and lots of it to get Orion “blindingly” drunk, not because of the wine specifically. Oenopion’s soldiers speared his eyes while he slept. He was sent on his way without Merope, but did eventually regain his sight to hunt again. Get acquainted with “Wildman Orion” in the real sky and know that the versions of the stories that have just been told to you have had some 21st century hyperboles added to their Greco-Roman origins. This StarWatch is dedicated to the late Dr. George F. Reed, an innovative researcher in planetarium education, who invited me to obtain my MA in astronomy and geology from West Chester University as his graduate assistant for the 1982-83 school year. That was a truly wonderful experience.