A bright star will disappear for up to an hour tonight — here's what's happening

If you live in the middle Atlantic or southeast part of the United States, you'll have an opportunity tonight (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. Because 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. …