StarWatch: Moravian College Astronomy

APRIL 2019

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

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lunar phases

1181 APRIL 7, 2019: Follow the Moon to Easter: Judaism and Islam both follow the lunar cycle to date their yearly religious celebrations and so do Christians when it comes to Easter. Whereas Moslems and Jews are concerned with the first sightings of the moon after its new phase, as an ultrathin waxing crescent, Christians celebrate Easter with the nearly full moon having an importance in the dating process. In all situations, the dates of religious occurrences, based on the lunar phase cycle of 29.53 days, vary from year to year because this interval of time does not divide integrally into the number of days in a year. There are approximately 12.36 phase cycles in a year’s time causing the religious observances of Islam and Judaism to sequence over time through the entire calendar year. Easter, however, has its limits from as early as March 22 to as late as April 25. The general rule for the occurrence of Easter goes like this—the first Sunday after the first full moon after the vernal equinox. That will establish correctly about 80 percent of Easter dates, but it will not work this year, even though the full moon occurred after the vernal equinox. The first moment of spring happened on March 20, at 6:01 p.m., EDT just hours before the full moon at 9:46 p.m., EDT. The discrepancy lies in the Church’s definition of the vernal equinox and the ecclesiastical full moon which differs from their astronomical meanings. The ecclesiastical formula for Easter proceeds like this. It is the first Sunday following the first ecclesiastical full moon (the 14th day of a tabular lunation starting with the new moon) that occurs on or after the day of the vernal equinox. According to the Church, the vernal equinox always happens on the 21st of March. The true vernal equinox, when the sun is at an ecliptic longitude of zero and overhead on the Earth’s equator, usually happens on either the 19th or the 20th of March, but it can occur on the 21st. The phase period or synodic cycle of the moon is 29.53 days. After a synodic month begins, the full moon will essentially happen halfway through that period, or at 14.77 days, not 14 days after the new moon. So this year, the 14th day of the moon occurred before the Church’s definition of the vernal equinox, March 21, and the date of Easter moved forward to the next ecclesiastical full moon in April, Thursday the 18th, about three-quarters of a day before the true full moon on Good Friday, causing Easter to be celebrated on Sunday, April 21. Easter also occurs specific to one’s time zone, whereas the sun crossing the vernal equinox happens at a specific instant and is different for each time zone throughout the world. As an example, while a person on the East Coast may be having Easter brunch in the early afternoon on April 21, it is already Monday in places like Australia and much of Asia. This week, you can watch the Easter moon start to blossom almost as soon as Luna begins to move west of the sun. On Sunday, a razor thin, 7 percent lit crescent moon, looking like a thin-lipped smile, is positioned 15 degrees above the western horizon 45 minutes after sundown. The following evening the “smiley moon” with a more vibrant grin is approaching Mars (above and to the moon’s right) with the bright star Aldebaran and the Hyades, a V-shaped cluster of stars above and to the left of Luna. Observe an hour after sundown and use binoculars for the best views. By Tuesday, Luna, with a Halloween pumpkin laugh is directly above Aldebaran with Mars below and to the right. On Wednesday and Thursday, the moon passes Orion the Hunter, now in its sideways, setting position towards the southwest. By Friday, in the evening sky, the first quarter moon is only seven degrees to the left of Pollux, in the constellation of the Gemini Twins, just six days from the ecclesiastical full moon and 9 days before Easter.

1182

APRIL 14, 2019: Black Hole Lurks in Spring Sky

Greening grass, warming temperatures, and a crack of thunder have all pointed to the winding down of winter and the flowering of spring. The sky has had the same attitude with darkness on the wane and the late Easter moon waxing to full on Good Friday. My students are starting to use the Sky Deck which has a spectacular view of the Lehigh Valley, but brighter stars still cannot hide on a clear, crisp vernal evening. There is a treat in this week’s sky if you are willing to follow the arc of the Big Dipper’s handle, now high in the northeast after the last glow of twilight has passed. The three, curved handle stars appropriately point towards a bright, aging orangey giant star, Arcturus, the “bear watcher,” the fourth brightest luminary of the nighttime sky and the brightest star north of the celestial equator. It’s 37 light years distant. By continuing southeastward along the same path of the curve that revealed Arcturus, blue supergiant Spica will be “spiked.” Spica is actually a double star about 260 light years from the sun, and it is only one of two first magnitude blue supergiants visible in the heavens. The other is Orion’s Rigel, now fading low in the west after twilight. Spica is in Virgo the Virgin, and it is here where the huge elliptical galaxy, M87, can be found. At its center lies the black hole that was just imaged successfully in a two-year effort from data collected simultaneously by radio telescopes throughout the world, effectively making the Earth one giant receiving dish. Here is how you can locate M87. On Wednesday, April 17 at 10 p.m., the nearly full moon will be positioned about 15 degrees above and slightly to the right of Spica in the southeast. By taking your hand and making it into a fist, thumb up, and holding it at arm’s length against the nearly full moon, the tip of your thumb will be pointing essentially towards M87. It’s not an object that can be seen with the unaided eye or even easily with small telescopes, but the system is huge, with about one trillion stars and a black hole at its center which is now estimated, at 6.5 billion solar masses. The imaging of the first black hole in the center of M87 will probably be remembered as one of the great technological achievements of the early 21st century. The resolving power of this giant multiple radio telescope system, named the Event Horizon Telescope (EHT), was enhanced to microseconds of arc. Keep in mind that is breaking a circle into 1,296,000,000,000 (1.296 trillion) parts. With these linked telescopes we could resolve the structure of an object that was 53 million light years distant, and only recently a theory. The five petabytes (one thousand million, million bytes) of data were collected in 2017, but it took nearly two years of computer crunching to assemble the picture of the doughnut-shaped object that was released to the media last week. And this is just one of several projects that is pushing technology to the edge of the impossible to reveal secrets of the universe that decades ago we thought impossible to achieve. These dazzling scientific achievements are also providing opportunities for small colleges like Moravian to put their mark on the map. A $20,000 investment from public donations bought the College a 25 percent timeshare in the Mars Desert Research Station Robotic Observatory near Hanksville, Utah, one of the darkest locations in the continental United States. For only $2000 Moravian could participate in the American Meteor Society’s fully automated global fireball network with all-sky cameras monitoring the heavens above the Christmas City from Collier’s Sky Deck on Main Campus. For $5000 more the College could have an automated, dedicated camera system to hunt for exoplanets from center city Bethlehem, also mounted on the Sky Deck. I saw the exoplanet detection unit at the North East Astronomical Forum at Rockland Community College in Suffern, New York on April 7. Just a few years ago, a similar system cost hundreds of thousands of dollars to become operational. Now the possibilities seem endless and the costs for doing real science on a shoestring budget are becoming more and more feasible.

1183 APRIL 21, 2019: Evil Precession: I was born on June 10, 1950, a fact that my students find more and more curious. I’m not from their world, yet I’m still not quite an alien either. Maybe it is because I might still have some interesting stories to share or I genuinely agree with this generation’s more egalitarian viewpoints; but regardless, my classes and I still communicate well with each other despite the increasingly large generational gap. I retired from public education and came to Moravian at age 60, and shortly will be celebrating my 69th orbit around the sun. Yet the real truth is that I’m not that old at all, because when I was born in 1950, the sun was squarely in the constellation of Taurus the Bull, yet astrologically, my sign was unequivocally a Gemini. This discrepancy between reality and astrology should be enough to convince anyone that this pseudoscience, which purports to decipher future happenings from the positions of the sun, moon, and planets, should be given a wide berth. Nearly 2000 years ago, the Greek astronomer and geographer, Claudius Ptolemy (100-170 AD), assembled the bible of astrology, the Tetrabiblos, or “four-part book” which outlines what philosophers firmly believed was a predictive science to future happenings. The problem was that the Earth wobbles—precesses—like a top, changing the location of background stars against the positions of the sun, moon, and planets, completing one cycle in approximately 25,772 years. Precession is a slow go, but its effects are relentless. Discovered by the Greek philosopher, Hipparchus (c.?190 – c.?120 BC), Ptolemy knew full well that precession would slowly cause the sun to deviate from Gemini into Taurus during the next several millennia, but it was of little concern to his immediate solution of using these objects and their associated astrological relationships as a predictive methodology. Since the quantification of gravity by Isaac Newton (1642-1727), astronomers have known that precession is gravity based. The sun and moon are attempting to pull the tilted and equatorially bulging Earth back into alignment with the plane of the solar system, the ecliptic, but because the Earth is spinning, the result of the action of these forces is at right angles, in the direction of the rotation of the Earth. In the new definition of general precession, we observe the celestial equator sliding westward along the plane of the ecliptic by just over 50 seconds of arc per year. That shift changes the positions of all objects in the nighttime sky on a daily basis, and if not taken into consideration, it adds up over the course of a decade or so to noticeable change the direction of where a telescope is pointing. We have had a displacement issue with our narrow field camera at the Mars Desert Research Station’s 14-inch robotic telescope to which Moravian College has a 25 percent timeshare. Images were shifted by varying amounts when the telescope was pointed to different parts of the sky. It turns out that precession was the evil offender. The Skynet Robotic Telescope Network maintained by the University of North Carolina at Chapel Hill which provides the operating protocols for the telescope was correctly programed for a precession epoch of 2019 while our telescope was programed for the year 2000. The solution became evident when the telescope was positioned independently of Skynet and intended objects were found to be located precisely where they should be. Josh Haislip of UNC and I independently suggested that precession was the culprit. When Josh remotely programed the telescope mount to epoch 2019, the intended objects photographed were centered perfectly in the photographic field. The displacement error was solved. It may be difficult to teach an old space dog new tricks, but it’s sure nice to have a few secrets still left in the bag.

1184 APRIL 28, 2019: Leo Riding High: I had my Monday/Wednesday astronomy class over to Shooting Star Farm, north of Quakertown, this past Wednesday for their dark sky field experience. If you recall, midweek turned out to be an absolutely spectacular spring day with the forecast of a mostly clear evening to follow. Too late to call retreat, clouds rolled in as my astronomy buddies taunted, “Just as you arrived,” creating one of those evenings where we saw the heavens between large breaks in the clouds. Still, my students had the opportunity of viewing Mars, double stars, and numerous deep sky objects that would have been much less spectacular to witness from center city Bethlehem where the Sky Deck on the rooftop of the Collier Hall of Science is located. My students ran the protocols which operated my telescope and instructed it to slew to certain objects in the sky. That was fun to witness, the culmination of several lessons using our own computer-driven scopes in my lab. Unfortunately, for the third spring in a row, clouds and rainy conditions, have thwarted our use of the telescopes on the Sky Deck. Back outside at Shooting Star, I remember having a really good view between the parted clouds of a favorite spring constellation—Leo the Lion. In a more passive way, Leo is like Orion the Hunter of the spring sky. The seven stars which composed the torso of the Hunter are unmistakable; everyone sees him. Likewise, but in a more subtle manner, the nine stars which create the Lion, fashion an appropriate likeness of the King of the Beasts resting under the shade of a tree on the African savanna. Also appropriate would be a likeness of the sphinx because, after all, Leo was originally an Egyptian constellation. This week at 9:30 p.m., Leo resides high in the south. A backwards question mark composed of six stars called the sickle forms the head of Leo and the front part of his body. Where the “dot” of the question mark would go is the brightest star of the constellation, first magnitude Regulus, which comes from the Latin and means “the little king.” Regulus at 78 light years distant is a bluish luminary that would be considerably brighter than the sun if placed in the center of our solar system. Its distance is equivalent to the expanse that light, travelling at the speed of 186,000 miles per second, would journey over the timespan of 78 years. Making your hand into a fist, thumb out, hold it at arm’s length next to Regulus. Two fists to the left of the Little King star will be found three relatively bright luminaries that form a triangle which complete the rump of the Lion. In that general area between Regulus and the triangle and particularly to the upper left of Leo’s rear is galaxy city, home to many smaller galactic assemblages like the Leo cluster, and more importantly, the Coma supercluster to which the Leo cluster is a member. They are all invisible to the unaided eye. One elliptical galaxy of the Leo cluster, NGC 3842, contains a 9.7-billion solar mass black hole, larger than the 6.5 billion solar mass black hole measured recently through its image in M87. To find Leo, first locate the Big Dipper high in the NE right after dark. If you follow the two pointer stars (highest stars and located at the top of the Dipper), Dubhe and Merak, down and towards the left, the North Star, Polaris, will be found. Travel in the opposite direction, and Leo will be bisected. It’s as simple as that. You’ll be viewing one of my favorite constellations of the spring and a herald of the warmer weather of summer which will follow.