On the evenings of February 23, 2021, the waxing gibbous moon is bright enough to erase many stars from the blackboard of night. But you’ll likely still see the two bright Gemini “twins” – the stars Castor and Pollux – in the moon’s glare. Another bright star is nearby; it’s Procyon, brightest star in the constellation Canis Minor the Lesser Dog, also known as the Little Dog Star.
The dark side of a waxing moon always points in its direction of travel around Earth – eastward – in front of the backdrop stars. As Earth spins under the sky, the stars, planets and moon all appear to shift westward throughout the night. Meanwhile, the moon’s orbital motion is carrying it eastward through the constellations of the zodiac … and through Gemini on these two nights.
Look for the moon and constellation Gemini to reach their high point for the night somewhere around 9 to 10 p.m. local time. That’s the approximate time on your clock, no matter where you live around the globe.
Every month, the moon in its journey in front of the constellations of the zodiac always travels to the south of the Gemini stars, Castor and Pollux, and to the north of the Little Dog Star Procyon. In fact, an imaginary line drawn from Procyon and going between Castor and Pollux takes you to Polaris, the North Star, although it’s a mighty long jump from Procyon to Polaris. You have to be in the Northern Hemisphere to see Polaris in your sky, otherwise this star sits beneath your horizon.
Are you in the Southern Hemisphere? The moon passes between the Gemini stars and Procyon once a month for you, as well. Around mid-evening, people at temperate latitudes in the Southern Hemisphere will see the moon, Gemini stars and Procyon in their northern evening sky. At mid-evening, we in the Northern Hemisphere will see all of these objects more south to overhead.
From the vantage point of either hemisphere, the other hemisphere sees things upside down. Up or down is a matter of perspective. To avoid ambiguity, we can say that Castor and Pollux lie north of the moon (in the direction of the North Star), and Procyon lies south of the moon (away from the North Star).
Bottom line: On the night of February 23, 2021, watch the moon pass to the south of the Gemini stars and to the north of Procyon.