When you buy through links on our articles, Future and its syndication partners may earn a commission.Regulus, in the constellation Leo. | Credit: Franco Tognarini via Getty ImagesIf you live in the middle Atlantic or southeast part of the United States, you’ll have an opportunity on Saturday evening, April 25, to see a 70% illuminated waxing gibbous moon gradually drift toward and ultimately hide the 1st-magnitude star, Regulus, the brightest star of the constellation Leo the Lion.This event is called an occultation, a word that is derived from the Latin occultāre, which means literally “to conceal.” And if you are fortunate enough to live in the zone of visibility for this event (see below), that’s exactly what you will see on Saturday evening: the moon, appearing to temporarily conceal Regulus from your view.AdvertisementAdvertisementBecause the moon is waxing, its dark unilluminated portion faces forward as it advances eastward against the starry background. Regulus will thus disappear on the moon’s dark limb. That event should easily be visible with binoculars and if your background sky is dark enough and if you have sharp vision, you may even be able to watch the occultation with the naked eye (though you might need to block the glare of the moon’s bright portion behind a nearby wall or tree limb). Regulus will suddenly and dramatically “pop” off, as if a switch were thrown, a stunning demonstration of the moon’s orbital motion and the star’s tiny angular size.The star will reappear from behind the moon’s sunlit edge sometime later. To see the reappearance, you’ll most definitely need a telescope, since the star will be buried in the glare of the moon’s brilliant limb — a tiny blue-white diamond suddenly and dramatically erupting into view on the lunar horizon.Zone of visibilityIf you live anywhere to the south of a line that curves roughly from near De Tour Village, Michigan, across Lake Huron to Mississauga, Ontario, then on southeast across a portion of western New York, northeast Pennsylvania and continuing through western and central New Jersey, you’ll see the moon passing in front of Regulus. If you live north of this line, you’ll see the moon slowly glide below Regulus, resulting in a tantalizing near miss!From New York City, Regulus will appear closest to the moon’s dark upper limb at 9:04 p.m. EDT, missing it by just a scant 30 arc seconds or a mere 1/63 of a lunar diameter! From Boston, the closest approach comes at the same time as New York, but the gap between the two will be somewhat wider, equivalent to 2.9 arc minutes or about 0.05 degrees.AdvertisementAdvertisementStill exceptionally close.And if your town or city happens to lie fortuitously within about two or three miles on either side of the line, you may have an unusual opportunity to see the grazing occultation of a 1st-magnitude star. As Regulus appears to move tangent to the moon, it might just disappear and reappear a few times along the rugged terrain of the moon’s dark limb, just off to the left of its upper cusp. The best place to witness this is New Jersey, where twilight will be rapidly fading and the background sky will be quite dark.Observers along New Jersey’s narrow graze line will see Regulus blink on and off as the moon’s rugged limb passes in front of it. | Credit: Joe Rao (background added in Canva Pro)Dark or bright sky?Another important consideration is whether the occultation occurs against a dark sky, a twilight sky, or a daytime sky.The optimal locations for viewing this event will be central …
