The Moon, Regulus And An Opportunity

Regulus and the moon as viewed through binoculars Tuesday night, May 21 when they’ll be just ½° apart. From the East Coast, the moon will be slightly farther to the right, and from the West Coast, a little to the left of the position shown here. Stellarium

Can you see stars in daylight? The sun of course, but there are others if you know just where to look. I cheat by using the moon for assistance, a method I’ll share with you in a moment.

Sirius, the brightest nighttime star, has been seen without optical aid before sunset as have the bright planets Venus and Jupiter. When Mars glows as brightly as Jupiter later this summer, keen-eyed skywatchers may spot it after sunrise or just before sunset. Most daytime stargazers use binoculars to find their target first and then line it up with a familiar landmark like a tree or building to make it easier to nab with the naked eye.

Tomorrow night, the half-moon will perch just one moon-diameter above the bright star Regulus in the constellation Leo the Lion. Regulus is a good deal fainter than Jupiter or Venus, so we shouldn’t expect to see it before sunset without optical aid. But it does make for a fun challenge to look for it in binoculars shortly before or after sundown.

First, click here to find out when the sun sets for your city and have your binoculars ready to go 10 minutes before that time. Point them at the moon, focus until the edge of the moon looks as sharp as a knife. Then, look for a pinprick of light in the blue almost exactly one moon diameter below and a little left of the moon as shown in the diagram. If you come up Regulus-less, try again at sunset and just after. If you still can’t see the star, give it a little more time. The two should make a sweet naked eye sight from late twilight till setting time.

The moon shows off the charming crater trio of Theophilus, Cyrillus and Catharina near the terminator tonight. Bob King

Anything happening tonight (May 20)? I’m glad you asked. The moon will be just shy of half and shine about a fist to the right of Regulus. Through a small 3-4 inch telescope, you’ll see a celebrated triplet of craters near the terminator or day-night line on the moon: Theophilus, Cyrillus and Catharina.

The terminator is the sunrise line on the waxing moon so anything near it will cast dramatic shadows just as trees and houses do at sunrise here on Earth. The contrast between light and shadow should be strong enough for you to see the crater Theophilus and perhaps the entire trio in 10x binoculars. Give it a try. All are easy targets in a scope.

Theophilus is named after an ancient Greek geographer and measures 68 miles across. It fairly fresh as lunar craters go, with a sharp-edged rim and a couple of distinctive central mountain peaks. Theophilus overlaps much older Cyrillus, 61 miles across and named for a 4th century theologian. Scientists determine relative crater ages by looking at which craters overlap others (the ones on top are younger) and noting how eroded their rims are. Cyrillus’s rim is clearly lacks the crispness of Theophilus which means the asteroid that carved it out, hit before the one dug out Theophilus. Catherina, named for St. Catherine, a Greek theologian and philosopher, is 62 miles across and even more beaten down than Cyrillus is the eldest of the trio.

Happy skygazing on these shirtsleeve evenings!