by For the third time this year, the bright red star Antares will be eclipsed or obscured the moon on Thursday, May 23.
The first event came on January 8, in which a thin crescent moon was waning in the morning sky and visible mainly across the western U.S. Then, on March 5, a last quarter moon was covered. Antaresagain during the early morning hours, mainly in favor of the southern and southeastern United States
This upcoming stellar eclipse will be different from the first two, in that the moon will be nearly full and Antares will be covered during the more convenient evening hours. As for the visibility zone, anywhere south of a line that runs from near London, Ontario to Avalon, New Jersey will see Antares disappear behind the moon.
Related: Full Moon May 2024: The Flower Moon crosses the Heart of Scorpio
Anywhere north of that line will be look at the moon skim just below the stars – almost grazing the limb of the moon for Philadelphia (at 9:50 pm EDT), a near miss for New York (9:55 pm EDT), and just a close call for New England.
For most of the central and western United States, the event will have already occurred before dark and before the moon rises; when they first appear in these regions, Antares will be located close to the west (right) side of the moon.
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Across the southeastern US, Antares will slip behind the moon’s eastern (left) limb during the evening, but emerge from behind the dark, narrow limb after nightfall. For locations as far west as the Sault St. Marie to San Antonio, the disappearance of Antares occurs before the moonrise, but the reappearance of the star will be available shortly after the moon appears above the east-southeast horizon.
Other places that will see the moon cross paths with Antares include Central America, the northern half of South America and parts of western and central Africa.
In the table below, we provide a list of ten selected cities for when Antares will pass and when Antares will pass again later from behind the moon. If time is left empty, it is because the moon has not yet risen.
For a more comprehensive timetable (in Universal Time) covering 658 locations, including a map of the occult zone, go to:
http://www.lunar-occultations.com/iota/bstar/0524zc2366.htm courtesy of the International Labor Watch Association (IOTA)
A bright moon will be a problem
The moon will officially become full during the late morning hours of Thursday, May 23 and the eclipse is scheduled to occur about 13 hours later. To the casual observer, the moon will still appear to be “full” (100% illuminated), but in reality, there will be a very narrow sliver of darkness – less than half of one percent – along the west side of the moon ( right ) limb.
So, as with the previous two Antares occultations, this upcoming event will see the star emerging from the back of the moon’s dark arm. But unlike the previous two encounters, in which the moon was in a narrow crescent or half phase, our lunar interaction in May Antares will involve a nearly full moon.
So, while you may have been able to easily see Antares “pop” back into view from behind the dark, unlit part of the moon with your eyes alone on the previous two occasions, for this event that to come there will definitely be a telescope or at least a pair of binoculars due to the extreme brightness.
Watch out for the weak companion
With Antares emerging again from behind the moon’s dark arm, that means there’s a chance to catch a glimpse of its little star companion. I Burnham’s Celestial Handbook, Volume 3 (Dover Publications, Inc. 1978), notes: “Usually, when conditions are good, it (the partner of Antares) is clearly visible in a 6-inch telescope as a small spark of glittering emerald, almost drowned out in the red light of the giant Antares.”
At size +5.4, this star (called Antares B) appears about 1/50 as bright as Antares itself and lies 2.7 arcseconds west of Antares. Thus, during occulations when Antares is about to reappear from behind the dark arm of the moon, Antares B emerges firstfive seconds before Antares himself.
The color of Antares B is actually closer to bluish-white or white; the emerald green color is most likely an illusion due to the direct contrast with Antares’ buckwheat color. But without Antares as a comparison, the true color of its companion shows itself trending towards a blue or white color.
The next time?
Occultations of Antares occur in a monthly series that lasts for at least several years. The current series began in August 2023 over North America and will end in August 2028 over central Asia. Unfortunately, the upcoming occultation of Antares will be the last in the current series to occur at night, or in the evening for any part of the US.
All remaining Antares events will occur during daylight hours over North America or primarily for regions south of the equator. After 2028, the next series of occultations of Antares will not begin until March 2042.
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Free natural history magazine,the The Farmers’ Almanac and other publications
