StarWatch: Moravian University Astronomy

JULY 2025

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

lunar phases

1507 JULY 6, 2025: Summer's Low Full Moons: Weather-wise, it has been so miserable lately that I needed to focus on something bright enough to be detected even on a hazy, partly cloudy summer night. The moon immediately came to mind as a possible target. It is full on the tenth, so even if the sky becomes exceptionally transparent this week, Luna's brightness will have a significant effect on the objects that individuals can view. * To keep this blog on the positive side, summer full moons are less conspicuous than the winter full moons. Even at its highest, summer full moons are horizon huggers, particularly near to the solstice. They stay well hidden in my neighbors' treed backyards during this time of the year. Luna rises well to the south of east and sets well to the south of west, just like the sun during winter. * The explanation is relatively simple and starts with the axial tilt of our planet, 23.5 degrees from the perpendicular to Earth's orbital plane known as the ecliptic. The axial tilt of Earth causes the sun to vary in altitude by twice that amount, 47 degrees, over the course of a year. * During the summer months, the sun shines down from its perch high in the sky, reaching a noontime altitude at summer solstice for the Lehigh Valley of 73 degrees. At winter solstice, the sun hangs low in the south, reaching a maximum altitude of only 26 degrees. * Since the moon's path around the Earth is very close to Earth's orbital plane, it stands to reason that a high summer sun must necessitate a low summer full moon because the two bodies must be opposite to one another. * However, that is not the complete explanation for low summer moons. If the moon's orbit were precisely in the plane of the ecliptic, we would have a total solar and total lunar eclipse happening at least once each month, and these spectacular astronomical apparitions might become ho-hum. However, the moon's orbit is tilted to the plane of the ecliptic by five degrees, causing Luna's highest and lowest positions to be even greater than the sun's annual variations. * In addition, the sun's gravitational pull wants to right the Earth's tilted axis, as well as pull the moon's orbit into the plane of the ecliptic, Earth's orbital plane. This force causes the Earth's axis to wobble, completing one oscillation in approximately 26,000 years, a phenomenon known as precession. The same gravitational force causes the moon's ascending and descending nodes, crossing points on the ecliptic, to slide completely around the sky in an 18.61-year interval. During this time, one midnight full moon will be positioned five degrees above the summer solstice position of the sun (78 degrees at midnight) and five degrees below the winter solstice sun (21 degrees at midnight) for the latitude of Moravian University (approximately 40.5 degrees north). The July full moon will be very close to this maximum low altitude, known technically as a major standstill. The moon will be just 21 degrees above the southern horizon at 12:35 a.m. on July 10. How low can the moon go? Check it out this Thursday or several days before or after this month's lowest Luna. Ad Astra!

1508

JULY 13, 2025: Moon Plays Pac-Man

Mark the morning of Sunday, July 20, 2025, on your calendars. Luna will be playing Pac-Man with the brightest and most well-known open star cluster in the heavens, the Pleiades, also referred to as The Seven Sisters. * Open clusters are aggregates of young stars numbering in the dozens to several thousand and represent the general manner in which star formation occurs at present. Stars are not born alone, but rather in large, denser regions of interstellar gas and dust found in the arms of spiral and irregular galaxies. Once formed, the cluster lacks sufficient total mass to generate a strong enough gravitational force to hold itself together. Over hundreds of millions of years, outer members of the cluster are pulled away by the gravitational attraction of stars passing nearby, to begin orbiting the galaxy as orphans like our sun. This reduction in mass causes the cluster as a whole to expand, repeating the process until the cluster has completely evaporated. * The Pleiades, marking the shoulder of the star pattern of Taurus the Bull, are between 75-150 million years old, 440 light years distant, and contain over 1000 members, of which 57 percent are multiple star systems. * Look east at 4 a.m. EDT on the morning of July 20! The moon begins entering the Pleiades around this time, but does not occult its first bright star, 3.7 magnitude Electra (17 Tauri), until approximately 4:34 a.m., just before the beginning of Nautical Twilight. Because the moon has no atmosphere and the stars are points of light, Electra and the other luminaries will wink out when the occultation happens. Caleano (16 Tauri) at 5.4 mag. disappears at approximately 4:42 a.m., 3.9 mag. Maia (20 Tauri) 5:09 a.m., and 4.3 mag. Teygeta (19 Tauri) at 5:15 a.m. Binoculars should be sufficient for Electra's disappearance, but I believe more light-gathering power and higher magnifications only found in a telescope will be necessary for the other three. Sunrise is at 5:48 a.m., making this observation a fight against twilight. Central Time and Mountain Time zones will be in a better position to view this event, but it is worth a try in the East. A successful observation to all! Ad Astra!

This map shows the location of the moon and Pleiades at 4 a.m., EDT, July 20, looking east. Please note that the stars of the Pleiades will look like points of light. The dust cloud moving in front of the open cluster and creating the blue haze around the brighter stars of the Pleiades will not be visible. Gary A. Becker map using Stellarium...

1509 JULY 20, 2025: In the Shadow of Mr. Eclipse: I was saddened by the news of the passing of Fred Espenak, 71, known worldwide as Mr. Eclipse. He died on June 1. Before retirement, Espenak was an astrophysicist working for over 30 years at NASA's Goddard Space Flight Center in Greenbelt, Maryland, specializing in infrared spectroscopy of planetary atmospheres. His real passion, however, was witnessing and chasing after solar eclipses, as well as authoring and co-authoring over 30 books on the subject. He produced a 5,000-year canon of solar eclipses and a 5,000-year canon of lunar eclipses, all of which are available in the public domain via the Internet. I think that is what made him special. Countless eclipses, both lunar and solar, that I have dreamed of seeing and have published in this column had an origin in Fred Espenak's calculations. * As I searched for more information about his life, I was struck by the similarities between his existence and mine. I am not trying to elevate myself. I heard Dr. Espenak speak about his eclipse experiences while in Australia in 2023, and I briefly spoke with him after his presentation. That's it. He was not a friend nor an acquaintance, but he was someone I deeply respected and admired for his public outreach in the field of eclipse astronomy. * We were both baby boomers. His interest in astronomy bourgeoned at age seven or eight. I was eight. We both cut our teeth on the original Golden Book of Astronomy, dissecting it until the pages became tattered from use. His first solar eclipse was witnessed at the age of 11 as a partial event in southern New York State at the home of his grandparents. It was a total eclipse across central Maine. * At 13, I was stuck in Europe with my grandparents, but I was fully aware of the event and wanted desperately to be at home. I knew that my father would have taken me to see it. Please understand that my experiences in Europe, Germany in particular, were a game-changer for how I wanted to experience life and for my enjoyment of travel. Still, July 20, 1963 was a difficult day as I mentally imagined what I might have seen just 12 road hours from my Pennsylvania home. * I was in college at 19 when I traveled to Lumberton, North Carolina, to witness my first total solar eclipse on March 7, 1970. Fred Espenak was 18 and saw it from Windsor, NC. We both spent most of our precious three minutes within the moon's umbral shadow, trying to image the event rather than gazing at it. That has been a problem for both of us: trying to capture the perfect picture rather than just marveling at the beauty of the eclipsed sun and surrounding corona. We were lucky; conditions were overcast to the south. * Clouds did steal the show for the July 10, 1970 TSE that I witnessed with my family from Cap-Chat on the Gaspe Peninsula. Espenak was also clouded out. Satellite images revealed a very narrow band of overcast conditions near totality, so we could not have been that far apart. We both witnessed the long duration June 30, 1973, TSE from Africa; Espenak was in the Sahara Desert, and I was at sea off the coast of Mauritania. * We both spent our lives immersed in the science that we loved, marrying later in life than our peers, most likely because of our astronomical pursuits. Espenak met his wife Patricia; you guessed it, on a trip to see a total solar eclipse in India. I met my Susan at a presentation on the moon that I gave at the Lehigh Valley Amateur Astronomical Society in 1978. * Fred Espenak had his 2006 TSE composite image, taken from Jalu, Libya, immortalized on the first US Postal Service stamp to use thermochromic ink. Heat changed the eclipsed moon covering the sun into a full moon. My image of Comet Hale-Bopp graces several popular award medals currently sponsored by the American Astronomical Society. I also spearheaded and designed a science award medal for Moravian University. Images are here. We both constructed backyard astronomical observatories after retirement; mine is in the final stages of completion. I am confident that had Fred been living on my block when we were kids, we would have become the best of friends. * However, I can honestly say that I'm still happy to be alive, looking forward to the next total solar eclipse in 2026, off the coast of Spain. Thank you, Mr. Eclipse, Fred Espenak, for freely sharing to all who would listen, your love and enthusiasm for eclipse chasing-a life well-lived. Ad Astra!

1510 JULY 27, 2025: Southern Delta Aquariids This Week: If you are interested in tackling two minor meteor showers this week, try observing the Southern Delta Aquariids and the Alpha-Capricornids. The International Meteor Organization forecasts maximum rates for both events during the morning hours of Friday, July 31. Still, several days on either side of maximum night will produce rates that are nearly comparable to the night of greatest activity. The moon will be nonexistent, approaching first quarter and setting on the 31st near midnight. It will be earlier on the two preceding evenings and near midnight on the two days after maximum activity. * The Southern Delta Aquariids, are meteors that diverge from the constellation of Aquarius, the Water Bearer, just west of the star Delta. They are one of the most anticipated meteor events for the Southern Hemisphere, sporting as many as 25 shooting stars per hour under rural conditions, when the radiant, the region of the sky from which the meteors are originating, is near the zenith. That means rates in the Northern Hemisphere will be significantly lower because the radiant only gets to an altitude of 35 degrees around 3 a.m. Observers will miss almost all of the shooting stars streaming downward from Aquarius; however, at times observers could witness fireball-class meteors. * Shooting stars from the Southern Delta Aquariids are relatively bright, averaging around the intensity of the stars of the Big Dipper. They are generally brighter before and on maximum night than after that time. * Here is a suggestion for locating the radiant, the apparent location from which the meteors are appearing to originate. Saturn will be above and to the left of the radiant, while lonely Fomalhaut, the brightest star of the constellation of Piscis Austrinus, the Southern Fish, will be positioned nearly 15 degrees below the location from where the meteors are streaming. If a line segment bisecting Fomalhaut and Saturn is imagined, the radiant for the Southern Delta Aquariids will lie about 10 degrees to the right. A fist made with the thumb exposed, held at arm's length, will be equivalent to this angular distance. * The Capricornids radiate from a location to the west (right) of Aquarius, above the western tip of the triangular-shaped constellation of Capricornus the Sea Goat. Maximum time will coincide with the Southern Delta Aquariids on the morning of July 31, but only with a rate of about five meteors per hour under a pristine sky. These shooting stars enter the Earth's atmosphere at a much slower velocity (23 km/s, 14 mi/s) than the Southern Delta Aquariids (41 km/s, 25 mi/s), making the meteors from the two showers easy to distinguish. Expect to spot one or two Capricornids per hour, so it will take several hours of meteor watching before a radiant can be established. * Anticipate witnessing a few bright early Perseid meteors too. A bright, waning gibbous moon will strongly affect Perseid rates when this shower peaks on the morning of August 12. Sporadic meteors, shooting stars not affiliated with any shower, are also abundant at this time of the year. Observers can expect to see a mix of 15-20 meteors per hour in the several hours preceding dawn when sporadic rates are included. Readers will find a map of the Southern Delta Aquariid and Capricornid radiants below. Ad Astra!