StarWatch: Moravian College Astronomy

FEBRUARY 2020

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

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lunar phases

1224 FEBRUARY 2, 2020: Not So Mysterious a Moon: Last Friday evening, friends of mine, Peter Detterline, David Fisherowski, and I returned from Vincenzo's, a wonderful Italian restaurant in Douglassville, PA. It’s one of those places where I have never had a disappointing meal. Over dinner our discussions revolved around a grant that Peter and I were applying for that would help to advance astronomy and research opportunities for the College. Were we all in agreement? Were we all on the same page? How could we get the biggest bang for our buck? At the end of dinner there was consensus on how we were going to proceed. Returning from our meal, the darkened fields surrounding Pete’s home were lit in an eerie blue wispy light, with clouds of mist hovering near to the ground, a surreal “Halloweenish” type of appearance. Pete glanced up at the undefined globe of light that was shining through the clouds and remarked, “There goes Betelgeuse.” It brought a spontaneous burst of laughter against a backdrop of what had been a mostly serious but enjoyable conversation that evening. Pete was right; the diffuse moonlight was about the correct brightness for Betelgeuse going supernova. I used to hate the moon, the bane of my existence for making any type of astronomical observation, until one day it dawned on me that the moon itself could be a fun object to watch with just the unaided eye or through a telescope. Pete has sketched it, and he and Dave have taken a wonderful set of images of its surface. I have been more of a telescopic gawker when it comes to viewing its surface, although wide-field photography has played a part in my lunar observations. Telescopically, I’m always amazed at the sharp, crisp detail of crater walls casting jagged shadows across the barren expanses of a smooth crater floor. It brings out the explorer in me. What would I feel like walking on its surface? The detail is particularly vivid when the air is steady with the telescope focused on the moon’s terminator, the region where night is changing into day, and shadow details are most pronounced. It is something I want my learners to witness. The moon brightens and dims in a regular pattern of shapes or phases as the nearside, which is always pointing in our direction, proceeds through its day and night cycles. To make this happen, sunlight reflects from different parts of its surface in a regular, prescribed fashion during its orbital cycle. Let me repeat that again. The moon moves through its phases because it is revolving—orbiting the Earth, and as we watch these series of events transpire, we are actually witnessing the day and night cycle occurring on the moon, something that takes only 24 hours on Earth, but averages 29.53 days for Luna to complete. It is so simple a concept that college students actually have difficulty grasping its straightforwardness. Third graders, however, don’t, as I witnessed from years of teaching in the ASD Planetarium, “my home away from home” for 38 years before coming to Moravian College. Next week, more about simple concepts regarding the moon which seem hard to grasp.

1225

FEBRUARY 9, 2020: Don’t “Give Yourself to the Dark Side”

“It is the only way you can save your friends. Yes, your thoughts betray you. Your feelings for them are strong, especially for [your] sister. So, you have a twin sister. Your feelings have now betrayed her too. Obi-Wan was wise to hide her from me. Now his failure is complete. If you will not turn to the Dark Side, then perhaps she will” (Star Wars: Episode VI – Return of the Jedi, Lucasfilm, 1983).
No, no, no, Luke, don’t do it. Fight! The Force is strong within you. Feel its power. You know that the moon has no dark side, but many others are weak and need you as an example to lead them.
There are certain terms that astronomers use to describe the hemisphere of the moon that we see and the part of the moon which cannot be seen. The moon keeps its same face pointed towards the Earth, a function of tidal forces that caused Luna to rotate (spin) at a slower rate until the moon completed one rotation in the same amount of time necessary to complete one revolution. That happened 4.5 billion years ago as soon as the moon formed near to the Earth. Tidal synchronization occurs on Mercury, two orbits for every three rotations, the four largest natural Galilean satellites of Jupiter, and scores of other smaller natural satellites orbiting their planets throughout the solar system. All parts of the moon go through a day and night cycle. When the moon is new, in the same direction as the sun, the hemisphere that we never see is in full daylight. When the moon is full and opposite to the sun, and visible all night, the hemisphere that we do not see is in full darkness. As we observe the moon proceeding through its phases during the course of a 29.5-day period, we are simply observing the moon’s day and night cycles. The hemisphere (side) of the moon which we continually observe and is closest to us has been termed the nearside, yet in the many astronomy books about the moon that I own that term cannot be found in any of its indices. However, nearside is recorded in the Facts on File, Dictionary of Astronomy and in the online Webster’s Dictionary and the Oxford English Dictionary, but not in Encarta. That’s not my gripe, however; it is the term given to the hemisphere that we cannot see which most people call the dark side. Thankfully, that term cannot be found in any of my books on the moon nor in the dictionaries cited above. My guess is the term originated from sayings like “darkest Africa,” where human knowledge was lacking about an area that was mysterious. Darkest Africa was also popularized by the explorer, H. M. Stanley, of Stanley and Livingstone fame. Today astronomically, the term dark side of the moon is obsolete, associated with a hemisphere of the moon that never receives sunlight. Nothing could be farther from the truth. So don’t give into the dark side, but embrace the light of the FARSIDE. That is where the truth lies Darth Vader. Luke knew that all along.

1226 FEBRUARY 16, 2020: Betelgeuse: Deadline Approaches: Red Betelgeuse, the left shoulder star of Orion the Hunter as we see him in the sky, continues to fade as recently reported by Villanova astronomers, Dr. Edward Guinan and Richard Wasatonic, possibly setting the stage for the greatest astronomical event in recorded history, a nearby supernova that would be almost as bright as a full moon. In addition, observations from the European Southern Observatory’s Very Large Telescope in Chile have shown the star has distinctly changed its shape in the last few months. When asked by my students if I thought that this was a done deal, I had to admit, “No.” The chances that we would be so lucky to witness such an event that has been in the making, perhaps for as long as a million years seems slim, but the probability is not zero. Stepping outside from a brightly lit house on Valentine’s Day to visually look at red Betelgeuse, it was barely visible while the other stars of the Hunter were easy to spot right from the start. As my eyes adjusted during the next few minutes, Betelgeuse became brighter, eventually overshadowing the faintest star of the Hunter’s body, Saiph, which represents the tip of Orion’s sword, a scimitar, but looks more like his left knee as we perceive it. Visually, to me the red giant looked distinctly fainter than Bellatrix, the right shoulder of the Hunter, but Villanova astronomers have estimated Betelgeuse to be just 0.02 magnitude fainter than Bellatrix. My fainter estimates of a red Betelgeuse over the other bluish stars of the Hunter may be attributable to the fact that I had cataract surgery back in 2005, and the removal of my two lenses has allowed my eyes to become more sensitive in the blue part of the visible spectrum, thus causing the other blue stars of Orion to appear brighter in comparison. No question that Villanova’s standardized photometric observations are the more accurate, but it’s still fun to participate. Looking at a graph of Betelgeuse’s light output during the last 10 years shows a regular increase and decrease of brightness with a maximum change in magnitude of 0.8 or about twice an intensity difference. Then in the fall of 2019, Betelgeuse simply started to decrease in brightness, perhaps as the result of dust being released into its bloated atmosphere. The diminution in brightness has continued through the present, a change in magnitude of 1.46 since its brightest light output during the last decade or about 3.8 times fainter in intensity. As a semiregular variable star, Betelgeuse has many different pulsations, ranging in length from about 243 days to as long as 6.06 years, but its strongest beat is a 430-day variation which should reach its minimum brightness on February 21, +/- seven days. It is expected that afterwards, Betelgeuse will slowly begin to brighten, but if it does not, and this star of mysteries continues to fade, astronomers will be in uncharted waters with regards to what will happen next.

1227 FEBRUARY 23, 2020: Dead Serious about Sirius: High school students would come up to me every semester and ask, “Are you serious about that, Mr. Becker?” I’d look the learner right in the eye and say, “No, I’m Procyon.” Needless to say, there was a look of confusion on the students’ faces. I’d just continue onward with the discussion. Finally, the day would happen when under the stars of the Allentown School District Planetarium, now the Learning Dome, when I would be identifying Canis Major the Great Dog, its principal star Sirius, also referred to as the Dog Star, the brightest luminary of the nighttime sky. Then I’d move to Canis Minor the Little Dog, and identify its alpha star, Procyon. I’d pause after saying Procyon. The room was silent, and then a few students would begin to laugh. Both Sirius (pronounced like serious) and Procyon are currently visible right after dark at 7:30 p.m. Sirius is literally due south, and Procyon will be above and to the left of the Dog Star. The word, “Procyon,” comes to us from the Greek and means “before the dog” because in the late autumn, Procyon rises about a half hour before Sirius breaks the horizon. It is often mistaken for the Dog Star, so Procyon too is a barn burner, the eighth brightest star of the nighttime sky. To Sirius’ right and above it can be found what is normally the 10th brightest star of the night, red supergiant Betelgeuse, but currently, as reported in several recent StarWatch articles, Betelgeuse, the left shoulder of Orion as we view him, has taken a nosedive in brightness, standing somewhere around the 26th brightest star this week and about as bright as Bellatrix, the bright bluish shoulder star to the right of Betelgeuse. The three stars form the Great Winter Triangle, but with Betelgeuse dimmed, perhaps clouded in dust, the GWT leaves something to be desired. If I’m correct in my magnitude estimate (Friday, Feb. 22), I believe that Betelgeuse is starting to brighten—no supernova this time, and hopefully as spring dawns, the GWT will begin to look more like itself before it sets right after darkness in mid-April, but what about the major actor of the Great Winter Triangle, Sirius? It is its lowest member in altitude, grazing the tops of my neighbors’ trees, twinkling like a mad dog because of the thicker, more turbulent layers of atmosphere that its light must penetrate. This rapid scintillation (twinkling) sometimes enhances its beauty with a spectrum of flashing colors. Its normal, slightly bluish hue is a condition of its larger mass, twice that of the sun. This creates greater internal compression in its core and higher temperatures which cause its nuclear furnace to produce energy at a faster pace than our white sun. Yes, the sun is actually a white star, not yellow as most people think. Although Sirius’ energy output is equivalent to just over 25 suns, its distance of only 8.6 light years also contributes greatly to its brightness. It will continue to get brighter for the next 60,000 years as it approaches our solar system, but it should remain the brightest star of the night for at least the next 200,000 years. A star like Sirius has enough fuel to sustain its energy output for about one billion years, after which it will evolve into a red giant, eventually shedding its outer layers, revealing its dead core—a white dwarf star. Since Sirius has a white dwarf companion, Sirius B, about the same age as the main star, Sirius A, the white dwarf must have been a more massive and brighter luminary that went through its evolutionary stages faster than the Dog Star, first tapping into its hydrogen supply as Sirius is doing now, and then late in life burning its helium, becoming a much brighter red giant star, creating quite a spectacle for early Homo sapiens who roamed northern Africa and Eurasia about 100,000 years ago.