StarWatch: Moravian University Astronomy

JULY 2024

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

lunar phases

1455 JULY 7, 2024: Running with the Moon/Spectacular Spica Occultation: The moon, a fascinating object to track, not only changes its brightness each night as it progresses through its monthly (29.5-day) phase cycle, but Luna also moves swiftly against the backdrop of stars. This rapid movement allows it to aid in the identification of the celestial objects it passes. The moon's journey has been a periodic theme in StarWatch articles. Witness its celestial dance in July from its new phase to its full phase. The times mentioned are specific to the Lehigh Valley, PA.
Friday, July 5: The moon enters its new phase at 6:58 p.m., when it is completely invisible to the naked eye as it aligns between the Earth and the sun. New moons, such as this one, are a rare sight, only becoming visible during a solar eclipse. It's worth noting that Earth is at its farthest point from the sun, known as aphelion, at 1:06 a.m. EDT on the same day. Earth's orbital speed is slowest at aphelion.
Sunday, July 7: This is the perfect opportunity to spot Mercury. A slender, five percent sunlit, moon hovers directly above Mercury in the dusk, WNW sky. Their separation is a mere three degrees. To make the most of this observation, start your sky watching 30 minutes after sundown in a location with a clear western horizon. Both Mercury and the moon will be six and nine degrees above the horizon, respectively. Binoculars are highly recommended to enhance your viewing experience.
Tuesday, July 9: Identify Regulus. An hour after sunset, observe the 16 percent lit, waxing crescent moon above and to the left of Regulus, the brightest star of Leo the Lion. Regulus and the moon are positioned 12 and 16 degrees above the western horizon. Binoculars will help to make Regulus easier to view.
Saturday, July 13: Moon Occults Spica. The moon is at first quarter at 6:49 p.m., half lit and half in its own shadow. Its terminator where the sun is rising appears as a straight line. Observe the moon with binoculars at 10 p.m., and you will see the blue supergiant, Spica, just off to the moon's left. By 11 p.m., the leading dark limb of the moon has moved to within 10 minutes of arc or 1/6th degree from Spica. The moon is 1/2-degree in angular diameter. Between 11:26 and 11:27 p.m. (11:26-25), according to my computer program, the moon occults the blue supergiant. This observation needs to be made with a telescope or binoculars because the nearly 27,000-time brightness difference between the moon and first magnitude Spica will overwhelm the eye, making Spica impossible to observe without optical aid. At the time of the occultation, the moon will only be nine degrees above the WSW horizon, adding another challenge for a successful observation. Luna sets before Spica emerges against its sunlit limb.
Wednesday, July 17: Moon near Antares. About an hour after sundown due south, check on the bright waxing gibbous moon. Luna will only be three degrees to the left of the first magnitude, red supergiant star, Antares. Like Spica a few days before, you will need binoculars to witness easily the rival of Ares in the sky. Ares is Greek for Mars. Make sure that trees are not blocking your view because the moon will only be only 21 degrees above the horizon, about as low as Luna can go for its highest altitude, which for the Lehigh Valley always occurs when a celestial object is due south.
Sunday, July 21: The moon is full at 6:19 a.m. It sets in the SW at 5:36 a.m., just as the sun rises. This is exactly what full moons do because they are opposite to the sun.
Ad Astra!

1456

JULY 14, 2024: Spica Occultation Season is Here

This StarWatch is being sent early to remind everyone about the occultation of Spica and the moon on Saturday, July 13, occurring around 11:26 p.m. EDT for the Lehigh Valley. The moon will be at first quarter, its leading half illuminated by the sun and its trailing half still in its shadow. It will be the unlit portion of the moon that will first encounter Spica. * A first quarter moon is about 8 percent as bright as a full moon, so it is conceivable that this may be an event that can be witnessed by a person with very sharp vision. However, it should be an easy observation with binoculars, and even more enjoyable with a wide field telescope. * We are in the Spica Occultation Season, when the moon's orbital path comes close enough to this star to eclipse it. This period will extend into 2025, but the Lehigh Valley will only get one more opportunity to witness the moon hiding Spica. That will happen in the southeastern sky on Wednesday, November 27, at 5:38 a.m. The relatively thin, waning crescent moon will be about 20 degrees above the horizon. It will then be another 18.61 years before the cycle repeats itself in the same way. What are the parameters that create occultations of Spica? * As shown below, imagine the plane of the Earth's orbit as a line segment and the moon's orbit as a sine curve. The moon's orbit is tilted by five degrees to the Earth's orbit, known as the ecliptic. This inclination gives Luna a swath of 10 degrees that it can reach, five degrees above and five degrees below the ecliptic. The moon can occult all of the stars within this region because the orbit of Luna slides westward, swiveling around the entire sky in 18.61 years. This movement is the reaction of the moon to the Earth's gravitational field attempting to pull Luna's orbital plane into the plane of the ecliptic. This series of occultations with Spica occurs after the moon has passed its descending node (crossing) and it will reoccur in 18.61 years. However, we will not have to wait that long for another series of Spica occultations because we will catch a new sequence around 2032 as the moon approaches its ascending node. * As the unlit portion of the moon approaches Spica, stay vigilant because the star is a point source, and the moon has no atmosphere to dim Spica as a warning sign. The star will wink out and be gone. * Much success in viewing this fun observation. A computer simulation of Spica and the moon can be found below. Ad Astra!

This computer simulation will give potential observers an idea of how the occultation of Spica by the moon will look on July 13. The approximate time is 11:26 p.m., EDT. Spica will look like a point source not an extended object as shown in the drawing. Keep in mind that the moon will only be nine degrees off the WSW horizon when the occultation takes place. Gary A. Becker graphics using Stellarium...

Gary A. Becker graphics...

1457 JULY 21, 2024: Waning Moon Mingles with the Planets: While the Internet media made great efforts to hype the June 3 planetary alignment, it was a bad move. The truth was that only two of the six planets involved in the dawn parade, Mars and Saturn, were easily visible in a dark sky. When the sun was only six degrees from rising, Jupiter and Mercury were on the horizon, making them impossible to observe because of sky brightness. In addition, Uranus and Neptune needed optical aids, such as binoculars or a telescope, to be viewed. Fifty days later, only Mercury and Venus are in the evening sky while the other five wanderers have tracked much farther from the sun so that they can now be viewed without interference from dawn around 4 a.m. Follow the moon as she wanders through the planetary lineup and other exciting sights during the upcoming 13 days. Most observations are at 4 a.m. or early dawn EDT for the Lehigh Valley, PA.
Sunday, July 21: Moon Near Pluto. The moon is full at 6:19 a.m. It sets in the SW at 5:36 a.m., just as the sun rises. This is precisely what full moons do because they are opposite to the sun. At 4 a.m., Luna is only 11 degrees above the SW horizon. The dwarf planet Pluto sits four and one-half degrees above the moon. Only a good star chart and a large telescope will reveal its presence.
Wednesday/Thursday, July 24/25: Moon Near Saturn. The moon travels across the triangular-shaped Sea Goat, Capricornus, and into Aquarius, the Water Bearer, to be close to Saturn on both mornings. This proximity, coupled with the absence of stars brighter than Saturn in these constellations, makes observing this event easy. On the 24th, the moon is positioned below and to the right of Saturn; the following morning, it is above and to the left of the ringed world. Only 20 degrees above the horizon under the moon is Saturn's only rival in brightness, lonely Fomalhaut of the star pattern, Piscis Austrinus the Southern Fish. Except for Fomalhaut, that constellation is also awash in faint stars and too near the horizon for easy observation.
Thursday, July 25: Moon Near Neptune. Four degrees (eight lunar diameters) to the moon's left lies the Roman god of the oceans, Neptune. Ten x 50 binoculars should reveal it, but shift Luna from the field of view. Neptune has a bluish hue in larger telescopes that will not be revealed through binoculars.
Monday, July 29: Moon Occults Star is near Uranus/Pleiades. HIP 15110, (Hipparcos Star Catalog), a 4.9 magnitude luminary, is hidden on the sunlit side of the fat, waning crescent moon at 2:33 a.m. The star emerges from the shadowed portion of the moon 54 minutes later at 3:27 a.m. The moon is 5.5 degrees above Uranus and eight degrees from the Pleiades near the Taurus-Aries border. Binoculars will be needed.
Tuesday, July 30: Moon Near Pleiades/Mars/Jupiter. The 26 percent lit, waning crescent moon is below the Pleiades. Four degrees below and to the right of the moon lies Mars, the ruddy god of war, shining at first magnitude (0.9). Six degrees below Mars will be first magnitude Aldebaran (0.9 mag.), the amber eye of Taurus the Bull. Six degrees to Aldebaran's left will be brilliant Jupiter, reflecting the sun's light at magnitude -2.2. Remember that the brighter the celestial object, the more negative its magnitude. Binoculars are always a help, but even the Pleiades should be visible with just the unaided eye.
Wednesday, July 31: Moon left of Jupiter. The 18 percent sunlit moon is positioned 7.5 degrees to the left of Jupiter and three degrees from 1.7 magnitude Elnath, the tip of the lower horn of a rising Taurus the Bull. Luna is 21 degrees above the ENE horizon at 4 a.m.
Thursday/Friday, August 1 and 2: Waning Moon. Luna is 32 degrees above the ENE horizon on the 1st and 12 degrees on the 2nd. Make both observations at 5:00 a.m. The sun rises at 6:00 a.m., making the observation time critical to success.
Sunday, August 4: The New Moon occurs at 7:13 a.m. and will remain difficult to observe until the 6th.
Ad Astra!

1458 JULY 28, 2024: Meteor Rates on the Upswing/Spica Occultation: The meteor season is here with the year's four best shooting star events lying ahead: the Perseids, Orionids, Leonids, and Geminids. Unfortunately, moonlight plays havoc with the latter three. Gibbous or near full moons plague each one. Fortunately, we still have the post-midnight Perseids to count on when the shower is at its peak during the morning hours of August 12. The waxing crescent moon sets just after 11 p.m., allowing the a.m. time slot of the 12th to be free from moonlight. That is when the greatest number of Perseids fly. * If you are interested in warming up to the best meteor shower of summer, try observing two minor streams this week, the Southern Delta Aquariids and the Alpha-Capricornids. Both showers are scheduled to maximize their activity during the morning hours of July 30 to 31. The moon will be practically nonexistent, rising on the 31st at 2:40 a.m. as a thin, waning crescent in the ENE quadrant of the predawn sky, an attractive sight that will not detract from meteor rates. * The Southern Delta Aquariids are one of the best meteor showers of the Southern Hemisphere, sporting as many as 25 shooting stars per hour under rural conditions, and 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 34 degrees around 1 a.m. Observers will miss most meteors streaming downward from Aquarius. Saturn will be about 10 degrees to the left of the radiant, while observers will find the bright star Fomalhaut, the alpha star of Piscis Austrinus, the Southern Fish, about 15 degrees below it. Meteors from the Southern Delta Aquariids are relatively bright, averaging around the intensity of the stars of the Big Dipper. Shower activity is higher before maximum night than after that time. * The Capricornids radiate from a location to the west (right) of Aquarius the Water Bearer above the western tip of the triangular-shaped constellation of Capricorn the Sea Goat. Maximum night will happen on July 30-31 with a rate of about five meteors per hour. 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. At times, fireball-class shower meteors can be seen. Expect to witness one or two Capricornids per hour. Sporadic meteors, shooting stars not affiliated with any shower, are also abundant at this time of the year. When sporadics are included in the mix, totals of 15-20 meteors can be expected in the hours preceding dawn. Readers will find a map of the Southern Delta Aquariid and Capricornid radiants here.
Spica Occultation A Success: Saturday evening, July 13, was a mostly clear but muggy night. Spica was an easy target through binoculars, but I could not see it without optical aid 90 minutes before the occultation of the 16th brightest star of the night. Through binoculars, the unlit portion of the moon was still illuminated by weak earthshine, the reflected sunlight from Earth reflected back from the moon, making it possible to witness the dark limb of Luna approaching the star. Still, when the star blinked out, I was surprised, requiring about two seconds to realize it was gone, then another two seconds to focus on the atomic time "ticking" away on my smartphone resting on the sidewalk. My estimate of when the occultation occurred was 11:23-50 p.m. EDT, one minute and 36 seconds earlier than my computer prediction. As my wife, Susan, has continually told me, "Never trust technology." Ad Astra!