StarWatch: Moravian University Astronomy

JUNE 2025

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

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1502 JUNE 1, 2025: A Primer on Auroras: It has been a year since I highlighted the evening and morning of May 10/11, 2024 when North America and Europe experienced one of the most spectacular aurora displays in recent decades. The Northern Lights were visible as far south as the Florida Keys and Mexico. My friend, Adam Jones, happened to be traveling near Gillette, Wyoming, on May 10 and witnessed the display from Devils Tower National Monument. Adam noted arcs, bands, curtains, rapid auroral motions, rayed arcs, and coronas in all the colors of the rainbow. Adam's videos, recorded in real-time with an iPhone 13, give testament to the magnificence of the display that lasted from dusk to dawn. In the Lehigh Valley it was cloudy until near dawn when we were finally able to see some of the event. * I was already booked with Pete Detterline to travel to Iceland, where from late September into early October 2024, we finally observed good displays on three clear nights, but nothing like Adam had seen. With the auroral season still in high gear, Pete, a mutual friend, Jesse Leayman, and I will be returning to the land of fire and ice during the fall with the hopes of witnessing and recording other active events. * The northern and southern lights are formed by the solar wind interacting with Earth's magnetic umbrella, the magnetosphere. Charged particles, primarily electrons and protons, escape from the sun's corona, its outermost atmospheric layer, at the location of solar flares that often trigger nearby spectacular Coronal Mass Ejections, CMEs for short. During these outbursts, the sun's magnetic field lines, which typically loop back into Sol, disconnect, allowing charged particles—mostly electrons and protons (plasma) —to escape. When reconnection of opposite polarities occurs, vast amounts of energy are released, propelling the plasma into planetary space along the sun's tangled and twisted magnetic field lines, which simplistically and three-dimensionally, resemble an egg beater. The solar wind travels at an average speed of one million miles per hour, twice that velocity in major outbursts. Sporadically, these CME events are Earth-facing, allowing the plasma to interact with the terrestrial magnetic field (magnetosphere) created by the convective flows of electrons in the Earth's liquid outer core. * The magnetosphere wiggles like Jell-O against the sculpting pressure waves created by the solar wind, flattening near the Earth's sunward side, but dragging into an elongated, teardrop-shaped form called the magnetotail away from Sol. In this area, magnetic lines of opposite polarity can connect, energizing, funneling, and trapping solar plasma into the Earth's magnetosphere. Once ensnared, the plasma works its way back along Earth's magnetic field lines into the inner and outer Van Allen Radiation Belts. In these two densely packed regions, electrons and protons can spiral back and forth from the geomagnetic North Pole to the South Pole at relativistic speeds. * When the Van Allen Belts become overwhelmed with charged particles, the plasma can detach and dip into the Earth's thermosphere, which extends from about 50 to 600 miles (80 to 1000 kilometers) in altitude where auroral activity occurs. The ionosphere represents the lower region of the thermosphere, extending from 50 to 95 miles in altitude. Incoming electrons excite oxygen atoms to produce the reds seen at higher altitudes and the greens witnessed at lower elevations. Ionized nitrogen molecules create minimal color influences. Colors created by nitrogen, the dominant gas in Earth's atmosphere, occur in the ionosphere. Additionally, protons streaming into the thermosphere along the auroral oval, which hovers at high latitudes centered on the north and south magnetic poles, have little color contributions. * As the plasma descends, electrons excite oxygen atoms, transferring their momentum (energy) to the outermost oxygen electrons, causing them to jump to specific higher energy levels. When these excited electrons rapidly transition back to their lowest energy states, they descend in a ladder-like pattern through a variety of specific energy steps or quanta. Many of these transitions produce ultraviolet and infrared radiation which is invisible to the human eye; however, some of these downward transitions generate the flickering, dancing lights that we celebrate as auroras. Let us hope another vibrant display occurs in the near future. Lately, the sun has been very active. More about quantifying auroral activity next week. Ad Astra!

1503

JUNE 8, 2025: Aurora Hunting: Judging Geomagnetic Activity

The wonderful auroral storm that blanketed the cloudy East Coast on the evening and morning of May 10-11, 2024, sparked my interest in these phenomena. Travel plans to visit Iceland in late September of 2024 had already been finalized, and they were very successful in terms of recording activity. Ironically after returning from Iceland, action spiked on the evening of Thursday, October 10, during the time I was in class with my Moravian students. My department chair, Dr. Kelly Krieble, was observing me that evening and the lesson could not have proceeded in a more spontaneous manner. * Aware of the possibility of an auroral outbreak, I started the class with a 15-minute photo essay of my trip and then discussed the possibility of an imminent display that evening, with showing my class why this might be the case. Finally, I promised that we would end the lesson a little early to go upstairs to the SkyDeck to see if any activity was occurring. I had no sooner switched gears to my focus topic, when front-row learner, Gavin Labbadia, waved his cell phone in my direction and excitingly exclaimed, "This is what my mom just texted me." It was a stunning image of red auroral curtains happening at that moment over Northampton County. Gavin's mother lived about four miles from the University. So much for the lesson! We proceeded to the SkyDeck, and even through the star-canceling light pollution of center city Bethlehem, the sky was red with auroral action. Check out (Wildman) Jesse Leayman's photo essay of the October 10 event, imaged from just south of Bethlehem. * Southeastern PA is an improbable location for viewing the northern lights, so what are the indicators that best describe when we might see a display? Begin with a wonderful application, spaceweatherlive, and its web sidekick, https://spaceweatherlive.com, which devotes all of its attention to auroral phenomena. Using the smartphone app., which I recommend over the website, the first parameter to be noted is the Kp index. It is a combined measurement of Earth's horizontal magnetic field over the past three hours. The Kp index is determined by 13 widely spaced magnetic observatories situated at mid-latitudes in both hemispheres. Its range is between 0 and 9. If you are using the application, click on the Kp index forecast to see predicted activity for the next three days. If you are under the auroral oval, where downward-moving solar plasma focuses, indices of 2 to 4 can produce fine displays, but not in SE PA. I become interested when the index reaches 5, but the Kp index should most likely be at 7 or 8, and even that may not create an event. However, on August 13, 2024, Pete Detterline and I observed a local display with a Kp index of only 5. During the May 10-11 mega-storm, the Kp index was 9. Indices from 5 through 9 equal G1-5 magnetic storms. Therefore, a G2 storm translates to a Kp6 event. * Another consideration is the speed of the solar plasma passing Earth. Numbers above 500 km/s, along with particle densities in the 10-20 protons per cubic centimeter, begin to awaken my interests after monitoring SpaceWeatherLive for the past year. * Additional markers are used to predict an auroral display. The polarity (north or south) of the interplanetary magnetic field (Bz number) measured in nanoteslas (nT) assesses the magnetic direction of the incoming plasma. Solar plasma is captured more readily by Earth's magnetosphere when the polarity is southward or negative, which is opposite to Earth's northward-pointing field. Bz numbers of -5 to -10 are crucial. When other indicators indicate a high probability of activity, but the Bz number is positive, the promise of an aurora stays far to the north. For the Kp9 storm of May 10/11, 2024, the Bz was measured at -40.42 nT. The Bt number, also measured in nanoteslas, reports the strength of the interplanetary magnetic field, another indicator of auroral activity. Here, the higher the number, the better the chances of seeing a display. During the May storm, the Bt was measured at 47.21 nT. * On May 17, just after midnight, I noticed the Kp index was at 6.25 with a Bt (interplanetary magnetic field ) of nearly 19 nT and a Bz (magnetic polarity) of -10 nT at the location of Earth. The solar wind was traveling at 466.8 km/s with a proton density of 8 particles per cubic centimeter. I immediately journeyed outside to survey the partly cloudy sky, but I could not detect any activity. The solar wind and proton density were not off the charts, but under the auroral oval in Iceland, if it had been dark, a spectacular display would have unfolded. * Finally, check on the auroral oval near the bottom of the page, where a display is most likely to be happening. If it appears angry (yellows and reds), I typically visit the Experimental Space Auroral Prediction Center in Boulder, Colorado, where a more detailed oval prediction can be observed. * Please note that all times are given in Coordinated Universal Time (UTC). Subtract 4 hours for EDT and 5 hours for EST. Auroras are most active around magnetic midnight, which is 1 a.m. during periods of Daylight Saving Time and midnight at other standard times of the year, but excellent displays have occurred right after dark. Happy aurora hunting. It takes perseverance, to say the least. Ad Astra!

Jesse Leayman beautifully captured the auroral activity of October 10, 2024 from just south of Bethlehem. Click on the photo above to see his image essay taken with his Samsung Galaxy S24 Ultra. Jesse writes, "That evening, I was riding my trail bike up, down, and all around the south side of South Mountain and Lehigh University's campus. Once it became too dark to navigate the trails on the mountain, I headed for the fields at Stabler where I could continue riding and not have to worry too much about "face planting" over some rocky terrain. As I was heading across the soccer fields, I noticed what I initially interpreted as some pinkish glow reflecting off some low level clouds, possibly from Hellertown. However, the more I looked, the more I was able to discern that this was not some manmade alpenglow caused by the light polluting inhabitants of Saucon Valley; it was far better!" The photos are set to "Goodbye Milky Way," from Enigma.

1504 JUNE 15, 2025: Hi(gh) Sun: We entered meteorological summer on June 1, but astronomical summer, which is marked by the occurrence of the summer solstice, or as the Brits say, the midsummer sun, is not the same. The word solstice comes from the Latin and means sun still. The solstices occur when the sun reaches its greatest angular distance north or south of the equator and has no easily detectable movement up or down for a few days. Summer solstice begins on Friday, June 20, at 11:40 p.m. EDT, when the sun reaches its greatest angular distance, 23.5 degrees north of the equator. That will be the sun's highest position on or north of the Tropic of Cancer, and that is no coincidence. The Tropic of Cancer is located at the same amount of angular distance that the Earth's axis is tilted from the perpendicular to its orbital plane around the sun. The sun shines on the Northern Hemisphere with its most direct energy for the year and with its most extended duration above the horizon. * Northbound from where we live, the days are even longer until reaching the US-Canadian border at 49 degrees north of the equator. Starting here, the sun does not get far enough below the horizon to call it officially night. The altitude of demarcation between night and astronomical twilight is 18 degrees below the horizon. The sun languishes for a few hours near but not under -18 degrees, keeping areas like very northern sectors of Washington, Idaho, Montana, North Dakota, and parts of Minnesota in a deep, deep twilight that does allow for practical observations of the heavens; however, it is technically not completely dark. * Moving farther north to the Arctic Circle, 23.5 degrees south of the North Pole, Sol scratches the northern horizon at midnight, then resumes its upward motion to create an uninterrupted 24 hours of daylight, the start of the Land of the Midnight Sun. Farther north, the length of continuous sunlight increases. * At the North Pole, toy production reaches its peak level of activity at the summer solstice, now powered exclusively by a large fleet of barges equipped with adjustable solar panels. The flotilla is a necessity. Please read on. * For the North Pole, increased Christmas activity began on the Vernal Equinox when the sun rose above the horizon. That had already been anticipated in early February as the sun broke free of its -18 degree altitude and began to give a dim hint of twilight circling the horizon when the sky was clear, growing brighter as the weeks edged towards sunrise on the Vernal Equinox. At the North Pole, the sun is continuously visible for six months, slowly rising in a corkscrew fashion to a maximum altitude of 23.5 degrees on the summer solstice. Then Sol continues downward in the same manner, technically reaching the horizon on the Autumnal Equinox and finally exhibiting a prolonged twilight for six or seven weeks that dissolves into the land of eternal darkness until the sun rises into its twilight position about 16 weeks later. The only rest and merrymaking the poor elves get is a few weeks after the post-Christmas toy exchange, before the dawn of a new season of work begins. The hours are long, and the work is stressful. * One positive outcome to relieve elf anxiety has come from the warming of the Earth. There is no longer a Polar Express. Trains breaking through the ice have canceled that method of reaching Santa. However, an increasing number of ships are making tourist stops at the North Pole, diverting elf productivity to hospitality vocations. All of this is a result of the incredible benefits of climate change, which have led to increased energy absorption by the dark, open Arctic Ocean waters. Then there are the tariffs-OMG! Doll production has taken the most significant hit at the North Pole. * Yes, summer is upon us, my favorite time of the year. That is minus the increasing heat and humidity levels of July and August, which have amplified the haze and cloudiness that accentuates light pollution, as well as the more destructive hurricanes in the Gulf of America and the Atlantic, that I propose should be called the Great American Ocean. Finally, there is the smoke creating those wonderfully colorful sunsets from the annual wildfires in one of our proposed 51 states, Canada. * What's left, you might ask? Maybe the FALL of civilization. Despite the enhanced negatives, and some hyperboles of the last paragraph, I still enjoy summer. I just wish I could see the stars now and then. Ad Astra!

1505 JUNE 22, 2025: Lag of the Seasons: The summer solstice has passed. Currently, the days are shortening by a minuscule amount. Nevertheless, the descent towards winter has already begun. The sun's downward slide will continue to accelerate through July and August until the autumnal equinox on September 22, when the duration of night and day becomes essentially equal, then interchanges as the sun's southward movement begins to decelerate until the winter solstice on December 21. It seems as if summer or more temperate conditions linger for a more extended period than they should, and in reality, they do. * In the morning when I make scrambled eggs for breakfast and turn on the electric burner to melt the butter in which the eggs will be fried, the pan does not become instantly hot. It takes a minute or so for the butter to liquefy, before I can begin the cooking process. Likewise, I would be a fool to put my hand on the glass cover over which I had just cooked the eggs, even five or ten minutes after I turned off the stove because it takes time for the infrared energy (heat) to dissipate on the stovetop. * Instead of thinking that our planet is the heat source, consider the Earth as the frying pan and the sun as the heat source. Yes, the Earth has a molten outer core and an inner core that is hotter than the Sun's photosphere from which light escapes; however, the thick mantle and crust conduct very little of that energy to the surface. On top where we live, the heat source that governs temperature, weather, ocean currents, and ultimately climate is a function of the external energy supplied by the sun. * The Northern Hemisphere just passed the summer solstice, the moment in time when we experienced the maximum insolation (energy input) from the sun, yet our daytime high temperatures are nowhere near what they will become near the end of July when statically they are at a maximum. Up until that time, we receive more energy from the sun than we release during our shorter nights that occur within our daily rotational period under the sun's influence. As the Northern Hemisphere moves into August and the sun's insolation decreases, because of Sol's decreasing altitude and sunshine hours, our radiative output of energy at night begins to exceed our input of energy from the sun during the day. We start to feel at times the refreshing and invigorating blasts of cooler air resulting from the meteorological battleground that is beginning to take shape over us. The northern latitudes of the Northern Hemisphere are cooling more rapidly than the southern latitudes of the Northern Hemisphere, and the Earth is attempting to equalize these differences in its energy (heat) budget through the movement and clashing of air masses of different temperatures. * It still feels more temperate than one would expect, and that is because the Northern Hemisphere is still retaining a great deal of the energy that it had received during the summer months, just like the burner on my stove remains hot well after I have turned it off. This lag of the seasons keeps temperatures mild enough so that the transition between warm and cold does not occur until sometime in November. Likewise, we achieve our lowest temperatures in late January, but for us, the transition period into much warmer conditions does not occur until May. Consider that you can still have an enjoyable day at the beach in late September but would never attempt a trip to the shore in late March. The sun is at the same warming altitude, but the Earth's surface energy reserves are vastly different. Enjoy summer while it lasts because you know what's on the horizon. Ad Astra!

1506 JUNE 29, 2025: Season of Light: Last week, I spoke about the lag of the seasons and how the Northern Hemisphere heats up during the summer months. This energy reserve influences climate until sometime in November when the change from temperate to cold takes place. There are other reasons why summertime seems to hang on a little longer than we might expect. * The most significant, I believe, is the illusion created when we enter Daylight Saving Time which occurs on the second Sunday in March. We set our clocks ahead by one hour, making them tick to the rhythm of Atlantic Standard Time. The sun rises an hour later, and therefore, sets an hour later. Since most of us are still in bed or not quite coherent when the EDT sun rises, it seems as if we have gained an extra hour of daylight without even considering a later sunrise. This time change aligns our waking hours more accurately with the sun's visibility. I'm an advocate of making Daylight Saving Time our standard time all year long, just on that fact alone. Sadly, EDT will end on Sunday, November 2, with the period repeating from 1 a.m. to 2 a.m., and we will fall back to standard time. The earliest sunset for the Lehigh Valley will occur at approximately 4:34 p.m. on December 7, 2025. Yuk! * You might be a little confused here because the winter solstice and summer solstice represent the shortest and longest sunlit times of the year. Although June 20 was the summer solstice and the longest day of the year, the latest sunset just transpired on Friday, June 27. The reason the solstices are not in synchronization with the earliest sunrise and the latest sunset times is due to the change in the Earth's orbital speed as it revolves around the sun. In addition, the sun's increasing and decreasing noontime altitude resulting from Earth's axial tilt must also be considered. * For the sake of simplicity, consider the Earth's rotational (spin) constant at 23 hours and 56 minutes. We do not have to account for the sun's changing altitude because near the solstices, the sun's distance above the horizon at noon is nearly constant. However at the time of the high sun, Earth is farthest from Sol, moving with its slowest orbital velocity, which slows the sun's daily easterly motion against the stars. The four-minute difference between the Earth's period of rotation and our 24-hour day allows the sun on a yearly average, to return consistently to the meridian (due south) at noon (1 p.m., EDT). However when the Earth's orbital motion is slower, the extra four minutes overcorrect, causing the sun to be east of the meridian (due south), crossing it about six minutes later than our clocks indicate noontime (1 p.m., EDT). This overcorrection causes the sun to set later by about four minutes, adding to the illusion of a longer sunlit period in the summer. It will take until about July 5 before the sunset is one minute earlier. * Finally, there is the changing depth of the sun below the horizon at local midnight. The angle of sunrise and sunset does not change for a particular latitude. It is equal to (90 degrees - the latitude in question). It is 49.5 degrees for Moravian's latitude of 40.5 deg. north; however, the angular distance that the sun descends below the horizon at local midnight does change with the seasons. * For Moravian's campus, the greatest angular distance (depth) the sun can achieve at summer solstice is equivalent to -26.0 degrees. View the formula and calculations here. At the time of the winter solstice, that depth increases to -73.0 degrees. Because the sun gets much farther below the horizon at local midnight, Sol has a longer distance (and time) to travel before its arc turns upward, 7-1/2 hours. The slope of the sun's path will change more gradually after sundown, causing the sun to gain a greater depth below the horizon in a shorter time interval. Twilight will last for a shorter duration. Because the sun reaches a shallower depth below the horizon at summer solstice, its slope of descent changes more rapidly (becomes less steep more quickly), allowing twilight to last 25 minutes longer at the summer solstice than at the winter solstice. Check it out. It is still feebly light at 9:45 p.m. We are truly in the season of light, even if a part of it is an illusion. All is good. Ad Astra!