One of the most interesting events in visual astronomy, and certainly the fastest, occurs when the Moon occults a star. The edge of the Moon approaches the star, almost seems to press against it for a few seconds, and then suddenly the star disappears! It reappears just as abruptly on the other side of the Moon, an hour or more later.
On Saturday (July 13), anyone with a telescope and clear skies should focus on the evening Moon, just after first quarter (52 percent illuminated). That’s when the Moon will pass in front of the magnitude 1 star Spica, as seen from North America.
As the Moon waxes, its dark side faces forward as it moves eastward against the starry background. Spica will disappear against the dark edge of the Moon, dimly lit by Earth, a spectacular sight. In a dark sky, Spica will suddenly appear to “go out,” a stunning demonstration of the Moon’s orbital motion and the star’s small angular size. Binoculars or perhaps just your eyes will be all you need.
Spica’s reappearance, on the other hand, will occur on the bright edge of the Moon, and even such a bright blue diamond will be partially obscured by the dazzling lunar surface for a few seconds after its reappearance. How well you observe the reappearance will depend on the size and quality of your telescope and the stability of local atmospheric visibility.
If you’re looking for binoculars or a telescope to get a close-up look at lunar occultations like these, or anything else in the night sky, be sure to check out our guides to the best binoculars and best telescopes.
And if you want to take pictures of these kinds of events, don’t miss our guide on how to photograph the moon . We also have recommendations on the best cameras for astrophotography and the best lenses for astrophotography .
What to expect
Along and near the Atlantic coast, Spica’s disappearance will be visible, though quite low—for the mid-Atlantic and northeastern states, typically 10 degrees or less above the west-southwest horizon. Keep in mind that your closed fist, held at arm’s length, is about 10 degrees wide. So for many locations, Spica will disappear behind the moon less than a “fist’s width” above the horizon. Over the southeastern states, Spica and the moon will appear several degrees higher in altitude.
For locations to the right of a line extending roughly from Toronto, Ontario to Miami, Florida, Spica’s reappearance does not occur until after moonset.
The best region to observe this event is probably the central part of the country, where the entire occultation, from start to finish, usually occurs in a dark sky.
Further west, the disappearance will occur closer to sunset. East of the Rockies, the disappearance will occur at dusk, while the reappearance will occur in a dark sky.
West of the Rockies, Spica will disappear before sunset and reappear during bright twilight. Over the Pacific Northwest, complete occultation will unfortunately occur before sunset in a daytime sky; by nightfall, Spica will be visible just to the right of the Moon.
When to watch
In the table below, we provide local viewing times for 15 selected cities. “Daytime” indicates that the event takes place before sunset. Times are marked with an asterisk
indicates that the event occurs at dusk. “Below the horizon” indicates that the moon and Spica have set and are therefore not visible. For Atlanta, Georgia, Spica reappears after midnight on the calendar date, July 14. For a more concise list of times that includes over 700 locations in Canada, the United States, Mexico, and Central America, as well as a map showing the visibility area, visit the International Occultation Timing Association (IOTA)page for this particular occultation
| Lunar Occultation of Spica on July 13, 2024 | Location | Disappears |
|---|---|---|
| Reappears | San Francisco | Day |
| 8:44 p.m. | Denver | 8:49 p.m.* |
| 10:10 p.m. | Winnipeg | 9:44 p.m.* |
| 10:58 p.m.* | Helen | Day |
| 9:49 p.m.* | Kansas City | 10:05 p.m. |
| 11:22 p.m. | Chicago | 10:10 p.m. |
| 11:22 p.m. | Austin | 10:18 p.m. |
| 11:36 p.m. | New Orleans | 10:29 p.m. |
| 11:43 p.m. | Toronto | 11:15 p.m. |
| Below the horizon | Montreal | 11:16 p.m. |
| Below the horizon | Boston | 11:24 p.m. |
| Below the horizon | new York | 11:25 p.m. |
| Below the horizon | Washington | 11:26 p.m. |
| Below the horizon | Atlanta | 11:29 p.m. |
| 00:40 (July 14) | Miami | 11:48 p.m. |
Below the horizon
Where to watch
(Photo credit: Joe Rao)
Facts about Spica
Spica is the brightest star in the constellation Virgo. Virgo is the only female figure among the signs of the zodiac and has been considered to represent a large number of deities since the beginning of history. Virgo is usually depicted holding an ear of wheat or carrying the scales of the adjacent constellation.
Spica is almost exactly first magnitude, although it has some slight variations; it is actually two stars whose components orbit each other every four days. They are so close together that they cannot be distinguished as two stars through a telescope, and their respective shapes are mutually distorted so as to resemble ellipsoids. The name Spica is derived from Latin the tip of the virgin“the virgin’s ear of wheat”. It has also been anglicized to “virgin’s ear”.
“The primary star is more than seven times larger, more than 11 times more massive and more than 20,000 times more luminous than our Sun.
Our current best estimates put Spica at a distance of 250 light-years (give or take 10 years). That said, perhaps by 2026 we could be referring to Spica as “America’s Star,” because during this summer, the light we see from this star will likely have begun its journey to Earth in 1776, the year America declared its independence.
(Photo credit: Getty Images/Stocktrek Images/Luis Argerich)
The next time
If clouds or unstable weather prevent you from observing Saturday’s stellar eclipse, you’ll have another opportunity early Wednesday morning, November 27, when another Spica occultation will occur over North America. In the east, the occultation will occur near sunrise, while in the west, the moon will interact with Spica in a dark sky, but rather low on the east-southeast horizon. Joe Rao is an instructor and guest speaker in New YorkHayden Planetarium He writes about astronomy forNatural History Review THE Farmers’ Almanac and other publications.