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MARCH 1, 2020: Leap Year: More Complicated Than You Think
When Julius Caesar was wooing Cleopatra in Egypt, he was introduced to the astronomer, Sosigenes of Alexandria, who may or may not have accompanied the couple back to Rome. The best that can be said historically is that Sosigenes consulted with Caesar to create a solar calendar, which Julius proposed in 46 BC to replace the much-abused Roman lunar calendar, recalibrating the new Julian calendar with the sun and the seasons. The Julian calendar was adopted by Rome on January 1, 45 BC. The concept was that the sun would pass a particular point in the sky called the vernal equinox, marking the first moment of spring in a period of 365.25 days. Since calendars needed to be created with a whole number of days, the Earth would fall behind by one quarter day each year until a full day was accumulated after a four-year interval. An additional day was then added to the calendar to bring the sun back into position with the vernal equinox. February was chosen as the leap year month because it was the shortest and least favorite Roman month of the year. With the Julian calendar, every year that was divisible by four without a remainder was a leap year. There were two issues with Sosigenes’ 365.25-day tropical year. The tropical year was actually not the time it took Earth to orbit the sun because the vernal equinox was not a stationary target but moved westward each year due to the 25,772-year precessionary cycle or wobble of the Earth’s axis. The actual revolution of the Earth around the sun, known as the sidereal year, was 20 minutes, 24.5 seconds longer than the current tropical year, yet this was actually a good idea because in the beginning it kept all holidays with fixed dates happening at the same time of the year with respect to the seasons. The other factor about a 365.25-day tropical year, caused serious issues because it really took 365.24219 days between the sun’s two passages of the vernal equinox. The Julian tropical year was just over 11 minutes too long. What this 1/128th day of extra time created was a backward slide of the dates of vernal equinox against the calendar and the earlier occurrences of Easter which were slowly moving toward the fixed date of Christmas. The Church saw the problem. If given enough time, the season of Advent would be overlapping the season of Lent, and things might get a little confusing in the Church’s liturgy. The solution was the introduction of the Gregorian calendar under the leadership of Pope Gregory XIII in October of 1582, reducing the tropical year to 365.24250 days and bringing the calendar to an accuracy of one day in 3236 years. The actual tropical year is 365.24219 days, a difference of about 27 seconds. The ingenious manner in which this was accomplished was to make century years leap years only if they were divisible by 400 without a remainder. Thus, the year 1600 was a leap year, but 1700, 1800, and 1900 were not. The year 2000 was a leap year. To correct for the backward 10-day drift of the vernal equinox that already had occurred, the date was advanced so that October 4, 1582 was followed by October 15, 1582. The Gregorian calendar ensures that holidays like Christmas which have a fixed date will remain fixed with the seasons and that Easter and Christmas will never “collide.” What will not remained fixed are the constellations which will gradually shift backwards against the dates of the year due to the westward drift of the vernal equinox. So eventually we will still be celebrating the 4th of July in the summertime, but with the current winter constellations in the sky. Not to worry, that’s about 12,000 years into the future when global warming and nationalism will be things of the past and topical discussions among historians about the early wisdom of humanity and how we learned from our mistakes.
Moravian College astronomer, Gary Becker, explains the importance of leap year to the morning newscast. Photo courtesy WFMZ News...
MARCH 8, 2020: Saving Daylight
We passed the winter solstice on December 21, 2019, passed the latest sunrise on January 5, heard about an early spring from Punxsutawney Phil on February 2, left in the dust the meteorological winter on March 1, and now we are springing ahead into daylight saving time. The next stop on the express train towards summer is the vernal equinox, March 20, and finally the pinnacle of all hills on the seasonal climb, the summer solstice or “sun still” where Sol will have reached its highest position north of the equator for the year over the Tropic of Cancer. That happens on June 20 in 2020. That is still a long way to go from where we are now, but the beauty of the heavens is that they are relentless in their forward stride. Now is that time of the year when we all begin the myth of saving daylight by shifting our clocks ahead by 60 minutes. There was no 2-3 a.m. on Sunday, March 8, which was great if you were working an eight-hour shift during that period, but the piper will be paid when we fall back an hour on the first Sunday in November. Many people believe that when we go on daylight saving time, yes, there is no “s” in “saving,” the sun goes down an hour later and comes up at the same time or an hour earlier. That would have to be called “Miracle Extending Time.” What we accomplish by “springing” our clocks forward by 60 minutes is to shift our daylight hours more in step with our waking hours. The sun goes down an hour later, about 7 p.m. starting March 8, but it also rises an hour later, around 7:25 a.m. on the same day. Note that we are still not at the time of equal days and equal nights which befalls the characteristic of the vernal equinox (equal nights). What we have essentially done is switched our time zone to Atlantic Standard Time, one hour east of us where the time is one hour later. We have sprung forward. Daylight saving time was first adopted in Germany in 1916 as a means of saving energy to promote higher production efficiency during WWI. England followed suit in 1917, and in the US, the Daylight-Saving Act of 1917 went into effect in 1918 from the last Sunday in April to the last Sunday in September. Currently, the time parameters are from the second Sunday in March to the first Sunday in November. After the war, states were allowed to adhere to or ignore the policy, but it became official again in WWII under the synonym of “War Time.” England went one step farther and incorporated a “Double Summer-Time,” the sun setting two hours later than its normal measure to boost war production even further. After WWII, states’ rights mostly won over again allowing the moving of the clocks forward as a state convention and not as a federal law. Hawaii and Arizona do not observe daylight saving time, but other states, such as Texas, Oklahoma, and Kansas are considering its abolishment. US territories that remain on standard time include American Samoa, Guam, Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. On the other hand, Alabama, Arkansas, Florida, Nevada, Oregon, Tennessee, and Washington have passed legislation that would make daylight saving time year-round if Congress approves their request. I would easily support that measure here in Pennsylvania. Does daylight saving time really reduce energy, and therefore, cut costs? The answer is probably not because the extra hour of sunlight that is gained at the end of the day with later sunsets is stolen from the morning hours, when most people are also awake. Still, I really like the idea of extending the daylight hours at the expense of morning light because, selfishly, I am normally asleep during that time anyway. Happy daylight saving time starting now! Another milestone reached and passed on our way to summer.
MARCH 15, 2020: A COVID-19 Spring
Last semester, I remember complimenting my classes on their good attendance which was nearly perfect at the time. The following week, the first student was diagnosed with the mumps. There were less than a dozen cases confirmed on Moravian’s campus, but two of them came from my classes. As the new semester began in January, I jokingly remarked to my students that I had never taught a spring term when evening classes were not cancelled for some type of a weather-related event—NEVER. As the warm winter continued, my daylilies sprang into life, and my hopes of a snow day melted. I was for once almost in step with my syllabus. I thought we had dodged the bullet. Enter COVID-19, and the disruptions that it has caused. Moravian may not be down, but we are certainly out. All of these changes occurring all at once remind me of one of the reasons why I like astronomy so much. Yes, Betelgeuse may have just gone through a record fading cycle, a dazzling fireball could drop a meteorite at any time, or new bright comet could unexpectedly come on the scene; but there is a relentless consistency about astronomy which is reassuring against the uncertainties of the world. It may be too hot, too cold, too dry, too wet, but I know for sure that on Thursday, March 19, six minutes before midnight, EDT the sun will be crossing the vernal equinox, the intersection of Sol’s path with the celestial equator. The sun will be at its ascending node (crossing point). That will signal the first moment of spring and the beginning of my favorite time of the year. While the world may be in turmoil, the sky and its various objects keep marching to the rhythm of their ancient celestial beats. The sun will race momentarily past the equator, shining directly overhead at that location, and then continue its rapid ascent into the Northern Hemisphere. It is possible to see where Sol is headed by viewing Venus, that really bright starlike object high in the west as it is becoming dark. Once you know exactly where the goddess of beauty is positioned, let’s say 40 minutes after sundown, go back to the same location to find her on the next clear evening about five to ten minutes after sunset, and look essentially in the same location. Venus should be easily visible under transparent skies. On an amazingly clear summer afternoon about 25 years ago, I was able to catch Venus in broad daylight, about 4 p.m., by standing in an area of my yard shaded by my house. You may want to try this feat just before sundown. Just make sure that you return to the same position when you made your dusk observations and note beforehand the location of a few terrestrial objects, like a tall tree or building that may be in Venus’ vicinity. Venus will reach its angle of greatest eastern elongation from the sun on Tuesday, March 24, about 6 p.m. EDT, and then begin its slow slide back towards Sol as it moves to its inferior conjunction, passing between the Earth and the sun on June 4. Not to worry, we still have two good months of Venus viewing ahead of us. Stay safe, and keep looking up.
MARCH 22, 2020: The Ursas: The Bears’ “Tail”
We are at that time of the year when the Great Bear, Ursa Major, is rising prominently in the northeast right after nightfall. My high school students at the Allentown School District Planetarium thought her to be unbearable because she was so difficult to see as a complete entity. For suburbanites in more light polluted locales, consider the Big Dipper which is really the heart of the bear, the handle substituting for the tail, and the bowl for the body of sexy Callisto who was turned into a bear by Hera, Zeus’s wife, after one of his many encounters with her. Zeus, king of the gods, had a very low tolerance for beautiful women. Currently, the Big Dipper is handle down, cup up in the early evening, one way that the heavens are declaring that spring is in the sky, even if temperatures may not be always cooperating. The story of Zeus and Callisto is one of pure lust, and another notch in the belt of the famed god of the Olympians who had a penchant for wooing mortal earthly maidens. The affair caused Callisto to bear a son who she named Arcus, and Hera to seek revenge against Zeus’ lover by changing her into a mangy looking bear. Off into the woods Callisto trampled, a seemingly fitting end to the story, but Hera’s deeds were not complete. Arcus grew up to be a handsome, stalwart teen who had a passion for hunting. One day while in the woods, he spotted a bear, unaware that it was his own mother. As he drew his arrow back taking careful aim, Zeus, who knew all things, immediately intervened. Hera, consumed with rage, entered the scene, and the couple began to quarrel. Zeus, having the weaker position, simply wanted Callisto to remain alive. The compromise was to have Zeus change Arcus into a smaller bear, perhaps as punishment for not having killed his mother, and Zeus to swing the mother and the son forcefully into the heavens where they would fall among the northern stars and became luminaries themselves. In the process of the Herculean deployment, both bears’ tails were stretched well beyond the normal length of earthly bears. The brightest star of Arcus, the Little Bear (Ursa Minor) or the Little Dipper, is our current North Star, Polaris. It can be found by taking the pointer stars of the Big Dipper, Dubhe and Merak, now positioned at the top of the Big Dipper’s bowl and following them to the left until a fairly bright star is encountered. Keep in mind that the North Star is not famous for being bright but rather the luminary closest to the pivot point of Earth’s axis, the north celestial pole. Allowing a few hours to pass and returning to view the Big Dipper will easily reveal its motion around Polaris as the Earth rotates. Although Polaris was not a very good pole star several thousand years ago, Ursa Minor, the Little Bear, was the closest star pattern to this pivot point. Consider that the Arctic and Antarctic are derived from Arcus, the Arctic where Arcus would appear nearly overhead and the Antarctic, with the prefix “ant” (against), represented “opposite to the north.” It’s a tale of all tails and visible in the heavens tonight for anyone to see if the skies are clear.
MARCH 29, 2020: All Eyes on Comet Atlas
“Comets are like cats: they have tails, and they do precisely what they want.” That quote from famed comet discoverer, David Levy pretty much sums up my experiences with these hairy stars. You win some; you lose some, but still a bright comet gracing our warmer, northern spring skies brings a burst of excitement to my checkered comet soul. Why checkered, you ask? Because comets are like cats, independent. Astronomers still don’t have a very good handle on how comets brighten as they approach the sun, so some comets that were expected to be spectacular fizzle while others that were thought to be nonevents actually become memorable and outperform. Comets are composed of a mixture of different frozen compounds (ices) and dust, their ratios varying from one comet to another, and this influences how bright they will become. Dusty comets that produce long curved tails are apt to become more vivid than icy ones because the dust reflects (actually scatters) more sunlight back towards the observer. A comet’s tail composed mostly of ices is actually glowing, producing light as a result of the interaction of the sun’s ultraviolet energy acting on its component gases. These comets appear generally fainter in the sky. The amount of materials released to form the tail can often be related to the structural soundness of the comet’s interior. A friable nucleus releases more materials to become a brighter object. The latest interloper to bring a sense of expectation to the astronomical community is Comet Atlas (C/2019 Y4), discovered on December 28, 2019, with one of the two NASA-funded, robotic, 16-inch reflectors of the Asteroid Terrestrial-impact Last Alert System (ATLAS), one telescope located on Mauna Loa, (Big Island) and the other on Haleakala on Maui in Hawaii. This all sky search program for small asteroids that could impact Earth weeks to only several days before collision was instituted in 2017 with a southern hemispheric twin installation that will be operational very soon. When first discovered, Comet Atlas was over a quarter million times fainter than the average human eye could detect. Calculations showed Atlas’ orbit would approach the sun to a mere 23.5 million miles, a very respectful distance for a showy event. What the comet has done since that time, and particularly since early February, is outperformed, increasing its brightness by nearly 4000 times. If this brightening is extrapolated forward to its closest approach to Sol, perihelion, on May 31, Atlas would be visible in broad daylight near the sun, one of only a handful of comets to have ever achieved this distinction. However, here is the rub. The last highly speculated barn burner, Comet ISON (C/2012 S1) which passed deep within the sun’s corona on November 28, 2013, disintegrated, never to be seen again. Could this happen to Atlas? Absolutely! Part of that conjecture has arisen simply because of its extraordinary brightening and the fact that astronomers have been unable to determine the size of its nucleus. If Atlas’ over performance is resulting from a small loosely packed snowball, then the chances are much better for an event that will end in a puff, with complete disintegration or a breakup of the main body. If the comet’s nucleus is larger, and more tightly packaged, then it has a much better chance of surviving its passage around the sun, producing a memorable naked eye event during late April thru mid-May, a bright spot in our isolated, dismal, spring, and perfectly adapted for social distancing. Stay tuned to more information about this developing story, particularly if Atlas becomes a naked eye event.