Crescent Moon Meets The ‘Little King’ Tonight

Face west at dusk this evening (June 27) and you’ll the crescent moon right under the star Regulus in Leo the Lion. Regulus means “Little King,” after the king of the beasts. It’s also called Cor Leonis (Heart of the Lion). The lion’s tail goes by Denebola, Arabic for Deneb Alased or “tail of the lion.” Created with Stellarium

We may not see many total eclipses in our lifetime, but nature provides plenty of smaller celestial alignments we can enjoy almost anytime. Awareness of the simplest of things, the moon’s night-to-night track across the sky for instance, guarantees we’ll see it pair up in pretty conjunctions with bright stars and planets every month. And none of these pairings are alike for reasons explored in this earlier blog.

Regulus and the moon in binoculars tonight as seen from the U.S. Midwest. Along the East Coast, they’ll be slightly closer; out west a little further apart. Created with Stellarium

Take tonight. A banana-shaped crescent moon will shine very close to Leo’s brightest star, Regulus. Leo’s a mythological lion, known as the king of the beasts since antiquity. Back then, people called it Rex, the Latin word for king.  But it was Copernicus, the 16th century Polish astronomer who cooked up the crazy idea that Earth goes around the sun and not the other way around, who renamed the star Regulus, Latin for “little king.” Why he diminished its status isn’t clear though perhaps he considered the entire constellation a “Rex,” making its brightest star a little rex or Regulus.

The crescent — lit by the sun — and the remainder, lit by light reflecting off Earth. Credit: Bob King

Tonight’s conjunction should appear striking because the moon will appear only about ½° or one moon diameter south of the star. They’ll be close together seen without optical aid, but don’t miss the chance to view them in binoculars. Beside the pairing itself, there will be many craters visible along the inner arc of the crescent visible at a magnification of 7x or higher. You’ll also get a great view of the dusky, earth-lit portion of the moon.

Sunlight reflecting off the blue ocean, the brown and green land,  snow and even someone’s shiny new car reflects into space. The moon intercepts a portion and reflects it back to lucky earthlings who happen to be looking. The twice-reflected light is much fainter than the direct sunlight that illuminated the bright crescent.

Between the white dotted lines, skywatchers will see the moon occult Regulus tonight. The event occurs around moonset in the pale blue oval and during twilight between the dark blue lines. The red dotted lines are where it takes place in daylight. Credit: Occult 4.2

Skywatchers on the Galapagos Islands and west coast of South America will be getting more bang for their buck this evening. For them, the earth-lit edge of the moon will cover up or block Regulus from view for a time. For a table of locations and times where you might see the star disappear and then reappear, click here.

This should be a nice conjunction, so I hope you’ll have good skies. If you have a camera and tripod, try for a photo of the close pair (and earthshine!) from mid to late twilight.  A short telephoto lens (to capture both the even and the scene) and a half-second time exposure at ISO 800 at f/3.5 or 4.5 might be a good starting point.