StarWatch: Moravian College Astronomy

MAY 2020

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

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lunar phases

1237 MAY 3, 2020: Big Dipper: Pulse of the Seasons: A better weekend for the East Coast could not have been imagined. May is here, the transition month between the colder, damp weather of spring blossoming into the warmer, more extreme conditions that define summer. The Northern Hemisphere has been heating up since late January, but it takes a long time for the Earth to catch up, lagging behind the higher, more direct energy from the sun and the longer days that its movement into the Northern Hemisphere has dictated. Cooling down takes its time too, allowing September and early October to feel quite pleasant. Ocean waters heat up even more slowly, topping out in late August through early September along with the hurricane season. It takes time for the Earth to release all of its absorbed energy before the transition to much colder conditions can occur in November. Spring is also being announced in the heavens. The early evening sky could not agree more with the milder conditions of this past weekend. The seasonal clock just happens to be the Big Dipper, revealing the time of the year at dusk by its position in the sky. Currently, its seven stars are topping out, upside down, the four stars of its cup in the lead, followed by the arc of the three handle stars. It is probably the most recognizable group of stellar VIPs known to Americans and can be seen anywhere in the US, except perhaps from America’s largest cities. The two lead stars, Dubhe (lower) and Merak are famous for being the Pointer Stars, directing the eye downward to Polaris, the luminary about which the sky pivots as the Earth spins. If you begin to understand the Dipper’s location, either by observing it at the same time in the evening or just as it is becoming dark, its relation to the seasons will become obvious. In the mid-Atlantic with buildings and trees cluttering the horizon, the Big Dipper begins to make its appearance in the NE by mid-February rising cup up, handle down in back of my neighbor’s bare-branched trees. Of course, by that time it is becoming apparent that the days are lengthening, but this is also the traditional time of our biggest snowfalls. By March, the Dipper begins to tilt ever so slightly; by April it is tipped at a 45-degree angle; so that during May it will be positioned up-side down, horizontally over the North Star. At the time of the summer solstice, this year occurring on June 20, just shy of 6 p.m., EDT, the imaginary “Ferris wheel” holding the Dipper sky bound has turned downward fully, announcing that nothing lasts forever, and the time of the long shadows have already been set into motion. The first days of school find the Big Dipper sweeping towards the horizon in the NW, and by Thanksgiving, its seven stars have all but disappeared, gliding along the icy northern horizon during winter, gathering their strength and momentum to make a reappearance, announcing the prologue to spring in February’s sky. Check out the Big Dipper at dusk. It’s a seasonal clock worth knowing.

1238

MAY 10, 2020: High Sun—Low Moon and Planets

I honestly have to admire the individuals who can get up at 5 a.m., go for a run, shower, and grab breakfast before heading off to work. Of course, those same individuals may be crashing and burning by 10 p.m. That’s pretty much like my neighborhood, except for the early morning runs. By the time I am getting my second burst of energy for the day—a good time to shovel snow in the winter—it is basically lights out on my block. So you might guess that mornings are not my favorite time unless I stay up all night to greet the dawn. That may happen several times during the next two weeks. The morning sky is brimming with activity including Comet SWAN which has been brightening faster than expected and will be at its best next week, low in the NE just before dawn. Currently, it is naked eye from rural locations in the Southern Hemisphere and just making its debut into northern skies. I’ll write about that in detail next week if it doesn’t fizzle. However, if you are up by 5 a.m. or roughly 50 minutes before sunrise, and live in a location with a good SSE horizon, you may want to have a look. You’ll see three bright stars, two relatively close together and the third glimmering at a wider berth. In order from left to right will be reddish Mars; Saturn, the faintest of the trio; and leading the pack, bright Jupiter. To the NE will be the brightening enflamed horizon announcing a new, hopefully warmer day. The week begins with a fat, waning gibbous moon, approaching the pack of bright planets. By Tuesday Luna sits on Jupiter’s doorstep, passing just three degrees under Jove. Luna is eight degrees below and to the left of Saturn by Wednesday morning. Thursday at dawn finds the last quarter moon, the sun’s light illuminating its left half, west (right) of Mars. Friday, a fat, waning crescent has glided past the God of War and now lies to its east. This whole drama takes place low in the SSE where astronomical objects are approaching their highest altitudes. No orb, however, gets any loftier than 28 degrees above the horizon. From the best location in my backyard, the whole week’s activities will take place near my neighbor’s treetops, and hopefully, above them. It is the fate of most solar system objects visible during late spring through early August to be low in the sky. Think of it this way. The moon travels around the Earth very near to the ecliptic, the plane of the solar system, where the planets and sun are also found. When the moon is full, at opposition and visible all night, it must be OPPOSITE to the sun with the Earth in between them. From about May 1 through August 1, the sun is highest in the heavens, maxing its noontime altitude on the summer solstice on June 20 this year. When the moon is full near the time of the high sun, Luna must be near to the sun’s winter solstice location, and therefore, low in the sky. The planets Jupiter, Saturn, and Mars which are presently near to the sun’s winter house must also be low in the sky. If you want good positioning and viewing for Mars, Jupiter, and Saturn, the best time of the year will be near the winter solstice. It is either low planets seen in temperate conditions or high planets viewed during winter’s chill. You can’t really compromise unless opposition occurs near the time of the autumnal equinox. Opposition for Jupiter occurs on July 14, for Saturn, July 20, and October 13 for Mars, which will have moved to a much higher and better position for viewing by that time.

1239 MAY 17, 2020: SWAN Lays an Egg: “Comets are like cats; they have tails, and they do precisely what they want.” I know I used that teaser to introduce Comet Atlas (C/2019 Y4) to StarWatch readers about seven weeks ago. Then ATLAS fizzled. I also used it to hype Comet SWAN (C2020 F8) three weeks ago. At that time SWAN was swooning the astronomical community with an outburst of brightness that would bring this interloper into naked eye visibility as it rushed towards its closest passage to the sun on May 27. As SWAN rapidly brightened, astronomers did not see the same characteristics in C2020 F8 as they had observed in Comet ATLAS (an elongated coma—brightest area) which signaled that ATLAS was breaking apart. SWAN just seemed to be flying higher than expected until it wasn’t. The drop in brightness began to be noticed around May 1 and has been ongoing. Ironically, when I put the orbital elements of SWAN into my computer program, the magnitude estimates turned out to be very near to what was originally predicted. Comet SWAN will remain binocular for its entire duration of visibility in the Northern Hemisphere. Its low altitude in the sky is another factor that may keep it from being seen at all. Currently, it barely gets above the horizon before the light of a new day makes it fade into invisibility. Adding insult to injury, SWAN passes very close to the bright star Algol on the mornings of May 20th and 21st which would make its fuzzball appearance easy to find. Here are the essentials if you want to try to see SWAN. You will need a nearly perfect northeastern horizon; you will need to be at your observing location by 4 a.m., and will need to possess binoculars. The comet will be about one binocular field above the northeastern horizon and less than one degree away from Algol, the brightest star visible in that locale. On May 21 at the same time, SWAN will be about two degrees to Algol’s left. Depending upon their design and magnification, most binoculars have fields of view of 5-10 degrees. Another opportunity will present itself on June 1st and 2nd, when SWAN positions itself in the evening sky, low in the northwest about one degree under Capella, the sixth brightest luminary in the heavens. The comet stays within five degrees of Capella from May 29 through June 6. Unless another outburst occurs as the comet passes its closest position to the sun (perihelion) on May 27, it will be fainter than the May 20-21 views, but Capella, because of its brightness, should be easily seen right to the horizon if conditions are cloud free. At the start of this window of opportunity, May 29 at 10 p.m., (90 minutes after sundown), SWAN will be eight degrees above the northwestern horizon and to the right of Capella by five degrees. By the end of the window, June 6, SWAN should be fainter and about seven degrees above the horizon, five degrees to the left of Capella. I wish comets were more like rabbits. My wife and I have three of them as pets. They have tails, love a routine, and are completely, and I mean completely predictable.

1240 MAY 24, 2020: The Moon is a Shapeshifter: As the week begins, a thin waxing crescent moon is making its appearance low in the north, northwestern sky. If your locale has an unobscured western horizon, and the evening is clear, it might be worth taking a look. At 9 p.m., or about 40 minutes after sundown on Sunday, look for Luna to be in the company of Mercury and Venus. Venus will only be about six degrees off the horizon, while Mercury, positioned in between them, will be nearly 10 degrees in altitude. The separation of the moon and Venus will only 11 be degrees, basically the angle subtended by a fist held at arm’s length. It may be the very last time that Venus is caught in the evening sky for the next year. The following evening at 9 p.m., Venus it is only five degrees above the horizon. On Tuesday it is less than four degrees, and by Friday it is on the horizon by 9 p.m. After that, Venus passes between the Earth and the sun, reaching inferior conjunction by June 3 at a distance of only 26.8 million miles from Earth. While the planets are playing near to the western horizon, the moon is steadily gaining prominence in the evening sky, passing from a thin waxing crescent on Sunday to a first quarter moon near midnight on Friday, May 29. As the moon changes its shape, there are six phase words that 15 to 20 percent of my students have difficulty mastering: waxing, waning, crescent, gibbous, full, and new. I don’t know why this problem persists other than the fact that some of the words have slipped from common usage in the lexicon. Waxing means to grow; the light of the moon is on the right. Waning is when the moon is decreasing in brightness, and its illumination is on the left. Crescent means horned, like a croissant, and gibbous with its two “b’s” comes from the Latin, humped; the moon bulges outward on both sides. As we are viewing Luna in a gibbous phase, more than half of its surface is illuminated by the sun. Why these same learners get full and new moons mixed up mystifies me. When the moon is full, the hemisphere facing the Earth is completely full of sunlight; it is opposite to the sun with the Earth in between them. When the moon is new, it is in the same direction as the sun, and the hemisphere facing Earth is in complete darkness. It’s the seventh phase word, quarter moon, that I might have sympathy in understanding the confusion because the moon appears to be half illuminated. At first quarter a waxing moon presents the right half of Luna’s disk in sunlight, and at last or third quarter, it is the left half of the waning moon that is observed. In these phases the moon has proceeded through one quarter and three quarters of its phase cycle. Sometimes this leads students to call the full moon the second quarter, and on it goes. With your phase vocabulary refreshed, watch as Luna progresses from a thin waxing crescent to a first quarter moon by Friday. It will still be only about 10 percent as bright as a full moon. The big change in the moon’s brilliance explodes during the three days following first quarter and culminates in the full moon which will grace our skies on June 5 from dusk to dawn.

1241 MAY 31, 2020: Lunar Librations Lead to Libations