StarWatch: Moravian University Astronomy

JUNE 2023

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

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Current Geomagnetic Field:

lunar phases

1398 June 4, 2023: Antarctic Australia: Three cheers for the Australian Bureau of Meteorology! They have their issues just like our own National Weather Service. Meteorologists in Oz can also forecast to an accuracy of 50 percent and still retain their jobs. Try that in education or the medical profession. * Night one was clear at our dark observing site, Franklin River, in the southern part of Western Australia. I collapsed around 3 a.m. The second evening was mostly cloudy except for a few hours after sundown, so I got some needed rest. The third night was supposed to be cloudy as an advancing and deepening low pressure system (cyclone) approached from the south across the Indian Ocean, but it turned out to be mostly clear, especially after midnight. In fact, it was possibly one of the most transparent nights that I have ever witnessed. The sea air had been cleansed for thousands of miles in its journey towards the Australian continent making the stars appear so bright that you felt as if you could reach out and simply touch them. * That would have been nice because what we did not expect was the bitter cold. Yes, it was about the same time of the year Down Under as we experience at Halloween, but the normal nighttime lows should have bottomed in the upper 40's to low 50's, not in the upper 30's. Afterall, Australia is closer to the equator than the States. Yes, Western Australia was having a "cold snap," as some of the locals had pointed out. In addition, our house that we rented for six nights, which was very clean and beautiful, had no central heating. It had a typical corrugated metal roof that is found in rural Australian homes, but so were its walls with definitely no insulation in between them. Our house was equipped with a wooden stove with plenty of wood for a fire, but we did not use it because the smoke and heat emanating from the chimney would have possibly distorted the air through which our images outside were being taken. As a result, we left the house get cold at night. On a sunny day it heated up nicely, into the low 70's, but by 4 a.m. it was just as cold as the outside temperature, minus the wind which had been pretty tame by some Australian standards. * Pete and I had planned to climb 7,812-foot Mt. Kosciuszko in Kosciuszko National Park, about 350 km (217 mi) south of Sydney, so we took with us enough winter gear to be successfully warm in our ascent. That never happened. The day of our climb was the wettest 24 hours of our trip. * What we did not imagine was that we would be wearing all of our winter gear inside our home after sundown. I remember around 2 a.m. looking out at the stars while sitting shivering by large, multiple, heat-releasing window panes in our dining room. Thinking he would warm me up, Pete snuck up behind me throwing a heavy woolen blanket over me. It felt as if it had just arrived from frigid Antarctica making me feel even colder as my body heat retreated to warm the covering (second law of thermodynamics) before its insulating effects started to be noticed. However, then it was outside into the frosty night air again to tend to my camera needs to start a new series of exposures, releasing every calorie of warmth that my body had generated and the blanket had stored. * The clouds did return for good around 4 a.m. but the Bureau of Meteorology blew the forecast again. Instead of getting up to an inch of rain, we just had a few passing sprinkles through the early morning hours. * I took a long, hot shower, and by 5 a.m. I was wearily crawling into a cold, icy bed topped with four woolen blankets, a quilt, and bed sheet that nurtured me into a deep sleep. Okay, the Melatonin didn't hurt either. The next day it poured, followed by a cloudy night, then a mostly clear night, with overcast conditions the subsequent day, as we departed Franklin River and headed back to Perth for our flight to Sydney. See more images here. Ad Astra!

1399

June 11, 2023: Shadow Games

If you read most of the blogs that I have written, then you know that I am an advocate of shadows, particularly when they relate to eclipses. However, did you know that you don't have to wait for one of these rare celestial events to witness the Earth's shadow being projected into the sky? * If you have ever watched the International Space Station or any other satellite disappear as it glides silently across the heavens, then you have witnessed Earth's invisible shadow against the dark sky blanketing the sun's reflected light as the spacecraft passes into nighttime. * The Earth's shadow can also be readily seen at dusk or dawn when the sky is exceptionally transparent if you have good horizons opposite to the locations of the rising and setting sun. This may happen on 30 occasions each year if you live on the East Coast, but out West where the humidity is much lower and the air is less congested with particulate pollution, almost every clear night produces this beautiful phenomenon. * I first experienced this spectacle and realized what it was while camping in Utah's Arches National Park with my friend, Allen Seltzer, back in the mid-70's. The day had been radiantly clear, and during twilight as I set up my small telescope, I became aware of a greyish haze beginning to rise in the northeast. It was topped with a diffuse, peach-colored light. I remember saying to Allen, "How could it possibly get cloudy after a day like this?" As it got darker, the "cloud" moved higher into the sky and finally with my sigh of relief, it disappeared against the deepening greying sky. The night became very transparent with the sky peppered with so many stars that some of the fainter constellations were hard to recognize. * What I had witnessed was the shadow of the Earth being projected and rising against the darkening sky. It is a phenomenon that I have shown my students many times on Collier's Sky Deck, where our horizons are nearly perfect, as we get our telescopes ready for observing. * However, I had another interesting experience witnessing the Earth's shadow while flying from Perth to Sydney, Australia just last month. I always try to get a window seat when taking a flight during the daytime because watching the geography of a continent pass under me is more interesting than taking in a Wi-Fi movie. We were headed eastward, leaving Perth around 4 p.m. which meant that the day would become accelerated because of the two time zones through which we would be passing. Time gets later as you head east. Also keep in mind that in Australia the seasons are reversed from ours. We were in late fall with sundown occurring around 5:15 p.m. * We rapidly headed into the sunset and darkness. At high altitude, in this case 24,000 feet, any sundown is beautiful with the clouds mellowing into yellows and oranges against an ultra-saturated, lapis blue sky. As the plane moved along at nearly eight miles per minute, it became very evident that I was rapidly approaching the Earth's terminator, where sunset was occurring. When seen on the moon, it is that line of demarcation where night is changing into day or day into night, creating the lunar phases. Not only were the clouds yellowed and reddened, but that same grey fuzzy shadow could be seen projecting itself into space with the peach-colored sky above it. That color is created by the thick cylinder of air that the sun's light is passing through, filtering out the blues and greens, but allowing the warmer (longer) wavelengths of light to pass through it. In that location Sol's light is highly reddened. Unfortunately, the sun was behind the plane and not visible, but the Earth's shadow projecting from the terminator was vivid enough to be easily recorded photographically. Take a look below at the similarities between my window view from the aircraft and a 2012 shadow rising at the Mars Desert Research Station located near Hanksville, Utah. It was my first experience witnessing the Earth's shadow rising from the vantage point of a plane. Ad Astra!

The Earth's shadow rises on a particularly clear day at the Mars Desert Research Station near Hanksville, Utah. Note the similarities of colors as witnessed from the air on a flight from Perth to Sydney, Australia on April 28, 2023. Gary A. Becker images...

1400 June 18, 2023: It's Summertime!: Hooray! The calendar has finally arrived at one of my favorite days of the year, the moment when the sun reaches its highest point in the sky, the summer solstice. This occurs on Wednesday, June 21, at 11:01 a.m., EDT. The word solstice means sun still, when Sol stands motionless in altitude, and then ever so slowly begins its descent towards the first moment of winter which this year happens at 10:28 p.m. on December 21. I have always enjoyed the term used by the Brits, midsummer, which goes back centuries as evidenced in Shakespeare's comedy, A Midsummer Night's Dream. * Although the length of time that the sun is visible is at its maximum at summer solstice, it is not the earliest time of sunrise nor the latest time of sunset. The earliest sunrise, 5:31 a.m., happened on June 14 while the latest sunset will transpire on June 28 at 8:33 p.m. This gives the impression that summertime conditions linger because most of us are still awake and coherent at 8:33 p.m., but less so at 5:31 in the morning. * What causes this imbalance is the ever changing eastward motion of the sun in the sky as we orbit our daystar. On a globe it is often shown graphically as that crazy eight-like figure called the analemma which depicts something known as the equation of time. It results from two factors. The Earth's orbital speed around Sol varies throughout the year because we revolve around the sun in an elliptical (oval-shaped) path. Also, the daily change in the altitude of the sun varies because our planet's axis of rotation (spin) is tilted. * When we are closest to the sun, at perihelion in early January, Earth is moving fastest in its orbital track. When we are farthest from Sol in early July at aphelion, the speed of Earth's orbital motion is the slowest. This change is reflected in the sun's daily motion against the heavens, faster in winter, slower in summer. * The second consideration is how the seasonal changes in the altitude of the sun, resulting from the Earth's axial tilt, affects the sun's daily eastward motion. At the time of this year's equinoxes, March 20 and September 23, Sol is moving up and down respectively at its greatest angle, 23.5 degrees to its orbital plane. This up or down vector slows the eastward motion of the sun against the stars. When the sun approaches its solstice locations, the up and down motion is nearly zero, causing Sol to move almost purely eastward. * The observational ramifications of these two factors affect when the sun crosses the meridian, its highest point in the sky for the day. Our clocks beat to a precise rhythm of 24 hours that keeps the sun near the meridian at noontime (1 p.m. when on EDT). However, sometimes the real sun can lead the clock by as much as 17 minutes prior to the clock striking 12 noon. Therefore, sunsets must occur earlier in the evening. For parts of the year, the real sun lags behind the time that our clocks are keeping, by as much as 14 minutes allowing sunsets to happen later than if the sun followed in step with the cadence of our 24-hour time system. * Do not forget about the lag of the seasons either. For the East Coast the hottest time of the year does not coincide with the time of the summer solstice, but rather about one month later around the third week in July. That is because our region of the Earth is still absorbing more energy in the daytime than it is releasing at night. By late July when these two conditions balance, the mean daily temperature reaches its maximum. * Hey, it's summertime, summertime, sun-sun, summertime, (Hear the song by the Jamies), and that is all that matters. Ad Astra!

1401 June 25, 2023: Arrive Before You Leave?: Have you ever wondered why it takes two full days to fly to Australia or China, but less than one full day to return home? It all has to do with the International Date Line. I recently flew from Philadelphia to Perth, Australia in a westward direction. Each time zone that I crossed subtracted one hour from my destination arrival time. Flying directly to Los Angeles from Philadelphia took about five hours, but during that interval, I passed westward through three time zones, arriving in LA just two clock hours later from my East Coast departure schedule. Flying near the time of sunset as I did, the dwindling light of dusk occurred during the entire flight. You can see photos here. The trip duration from LA to Sydney was about 16 hours, but since I passed through seven time zones moving in a westward direction, my arrival time in Sydney should have been just nine clock hours later. The entire flight duration was 21 hours (5 hours + 16 hours) from Philadelphia to Sydney, negating the airport layover in LA, but the clock had advanced by only a total of 11 hours (2 plus 7) because of my westerly travels. It should become obvious that if I flew fast enough in a westward direction, I could make time go backwards, at least from the standpoint of clock hours. * This is not the secret to a time machine which physicists feel would be impossible to construct, but rather the time and date chaos that would result if there were no location on the planet where this situation wasn't rectified. * Enter the International Date Line which technically is positioned at 180-degrees longitude (no east or west) but wiggles back and forth across the globe to avoid countries and territories from having to deal with the inconvenience of different days splitting their boundaries. The IDL corrects for the problem of losing or gaining time as time zones are traversed westward or eastward, respectively. Moving westward through each zone subtracts an hour, but crossing the IDL adds a full day to correct for this westward deficiency. Rather than the clock moving forward by only 11 hours from LA to Sydney, it advanced by 35 hours. This did not include my airport wait times. * I flew eastward from Sydney to LA on May 5 of this year. The flight departed Sydney at 10 a.m. and it took 14 hours to get to Los Angeles. During that interval I passed through seven time zones, each one adding an hour to my clock time. My arrival should have been 21 hours later. However, during that time I traversed the IDL moving eastward and lost 24 hours. This allowed me to arrive three hours earlier, at 7 a.m., in Los Angeles on the same day as my Sydney departure nearly more than one third of the way around the globe. After a three-hour layover, I flew back to Philadelphia. The flight was five hours gaining an additional three hours because I was travelling eastward through three time zones, increasing by one hour in each zone (Mountain, Central, and Eastern). Eight hours of clock time elapsed added to the three hours of layover time in LA which resulted in a total of 11 hours of time difference. I arrived in Philadelphia at 6 p.m. in plenty of time to catch the sunset on the same day that I witnessed sunrise from my hotel room in Sydney. Wow, if time machines were only real, I would certainly want to hop onboard. Ad Astra!