StarWatch for the greater Lehigh Valley

JULY  2024


[Moon Phases]


Current Solar X-rays:    

Current Geomagnetic Field:    


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!

[Spica and the Moon]
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...

[Spica and the Moon]
Gary A. Becker graphics...

1457    JULY 21, 2024:   Waning Moon Mingles with the Planets

1458    JULY 28, 2024:   

[July Star Map]

[July Moon Phase Calendar]