by As the moon makes its monthly circuit around the sky, it often passes in front of the stars, blotting them out for an hour or so.
Such an event is called Occult (derived from the Latin word hidden, which means “to hide.”), and it can be a scary spectacle, especially if it happens that the star is bright. The star seems to swing up to the moon’s limb, hang on the edge for a minute or two, and then, without warning, suddenly strike out. Later he comes back in such a sudden appearance on the other side of the moon. One of the first proofs that the moon has no atmosphere was the suddenness with which it occurs. If our natural satellite were covered by an atmosphere, a star would appear to be gradually approaching its limb, just as a position would be seen beyond the western horizon from here on earth.
If you live in the Pacific or Mountain Time Zone, be sure to set your alarm clock before sunrise on Monday, January 8, because early that morning a waning crescent moon, 11% illuminated, will occupied the 1st red giant. star Antares, one of the brightest stars in the sky. It would be well worth getting yourself out of bed at the crack of dawn to see if you live in one of the far western states.
Unfortunately for those living further east, across the central and eastern states, this stellar eclipse occurs after sunrise in a clear daytime sky. From these regions, Antares will appear very close to the left side of the moon as it slowly ascends in the east-southeast sky before sunrise. But gradually drawing closer to them, the bright, ever-brightening sky will finally overtake Antares before the moon has a chance to hide it.
Related: The night sky, January 2024: What you see tonight
Region of visibility
For westerners, the action begins when Antares disappears behind the bright arm of the moon. For those living in the Northwest States the moon will barely be above the horizon, so poor visibility will compound the problem. From Seattle, for example, the cancellation of Antares comes just after moonrise.
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Further south, the moment of cancellation will appear higher. From San Francisco the pair will be 6 degrees high and from Los Angeles they will be 11 degrees above the horizon. (A clenched fist at arm’s length is about 10 degrees wide.) Moon and star will make a spectacular sight as the latter sets near the southern edge of the crescent moon.
Since Antares will pass behind the bright arm of the Moon, binoculars or a telescope will likely be required to view this event.
However, the same Northwestern states, as well as northern California, will be in an excellent position to see the reappearance of the star, which will be spectacular wherever the moon is high in the dark sky; an event that is easier to detect, because the moon will be higher above the sky and the star will not be washed out by the blinding brightness of the crescent. For most of Washington, Oregon, the northwest corner of Nevada and the northern third of California, dawn will have already begun, but the sky will still be quite dark when Antares comes back into view from behind darkness. the moon. It should come up suddenly with the unaided eye if you have good vision. Binoculars will pull in the star well, and a small telescope will give a great view.
Those who live as far east as a line that runs from southernmost California to southeastern Montana will see Antares emerging during the morning glow; the further east you go, the brighter the sky gets. For those who live east of a line that runs from about southeast Arizona to northwest South Dakota, Antares will unfortunately reappear after sunrise. However, the moon should still be visible and provided it is not too hazy, a good telescope should bring out Antares as a tiny speck against the blue sky.
“Delightful companion”
Adding even more interest to this event for those watching under a dark sky is Antares’ 5th magnitude companion star, discovered by Professor Johann Tobias Bürg of Vienna, Austria during the Antares occultation on 13 April 1819. a faint secondary star 2.7 arcseconds directly west of Antares, it will always reappear five seconds before Antares itself. (To appreciate how small 2.7 arc seconds is, the moon’s apparent width is 1,800 arc seconds in diameter. Thus, Antares and its companion are separated by 1/667 of a lunar diameter, or 0.00075-degrees! ). The American astronomer, Mary Proctor (1862-1957) referred to it as “the wily companion of Antares.”
The companion star has been described as appearing emerald green or “verdant in color” compared to the glow of Antares. But the coming interrogation will provide a rare opportunity, albeit a brief one, to measure the true color of the companion free from any illusion of contrast. Back in February 1991, I had the chance to see the faint companion emerging from behind the Earth-encircled edge of a waning crescent moon and I thought it was a pale blue-white color. . What color will you see on January 8?
The departure of the companion will be invisible, because it occurs between the glare of Antares and the bright arm of the moon.
What to expect
In the table below, we provide viewing conditions for seven selected cities, giving times when Antares disappears behind the moon’s bright edge (“i”) and when it pops back into view from behind the dark edge the moons that light the Earth (“out”). Sunrise time is also provided. Note that from Phoenix, Denver and Winnipeg, Antares will emerge after sunrise.
Also available is a chart showing the path of Antares as it passes behind the moon. The star disappears behind the bright crescent, and will reappear behind the dark edge of the Earth. For those in the Far West looking for the early appearance of Antares’ companion star, focus on that part of the moon’s disk where the companion and, five seconds later, the much brighter Antares will be visible.
The next time?
If inclement weather prevents you from seeing the “Antares eclipse,” there are two more chances to see another one in the coming months, but in both cases, the viewing zone will be limited mainly to the Piedmont and Southeast regions the Coast. , as well as Florida and parts of the Gulf Coast. The first scenario involves a last quarter (“half”) moon on March 3 and, like our upcoming event this week, will again occur during the early morning hours. The other case will occur during the more convenient late evening hours of May 23, but the moon will be almost full.
Occultations of Antares occur in a series, which began on August 23, 2023 over much of North America, and will continue each month over different parts of the globe until the current series ends on August 27, 2028 over Central of Asia.
If you’re hoping to catch a glimpse of Antares, the protuberance of the moon or any other view of the night sky, our guides to the best telescopes and binoculars are a great place to start.
And if you’re looking to photograph the occultation of the moon in Antares or the night sky in general, check out our guide to photographing the moon, as well as our best cameras for astrophotography and the best lenses for astrophotography.
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.
