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Thursday, July 25, 2024

Earthsky Tonight—May 20, First quarter moon – or ‘half moon’ – near Regulus and Mars

Courtesy of EarthSky
A Clear Voice for Science

In the west-southwest this evening, the first-quarter moon hangs below the “Sickle” of the constellation Leo the Lion, and its brightest star, Regulus. Note that the “Sickle” looks like a backward question mark. If you hold your outstretched fist to the right of the moon, it will span the distance to a ruddy “star” – but that’s no star, it’s the planet Mars.

Ever since the end of January – when Mars and Earth were closest to each other – our planet has been pulling away from the Red Planet in our planet’s faster orbit around the Sun. Curiously, if you were a skywatcher on Mars tonight and you turned a small telescope back toward our Blue Planet, you’d see Earth at a half-lit phase like the moon. Back on Earth, however, Mars appears as a tiny gibbous (90% illuminated) through a telescope. As seen from Earth, Mars always exhibits a full or nearly-full phase.

Make note of this location in the sky. Night to night Mars and the constellation Leo will edge nearer to the horizon while the moon will move east of Leo, becoming a gibbous of its own on its way to becoming full next week. Continue to watch Mars as it closes in on Regulus. They’ll pair up in two weeks, just a pinkie-width apart.

Written by Stuart Goldman

Astronomy Picture of the Day from NASA/JPL

CHANDRA Photo Album

U.S. Naval Observator Astronomical Information center

StarDate Online

Sky and Telescope

National Geographic

Space Com

Amazing Space

The York County Astronomical Society

Scope City

James S McDonnell Planetarium

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