Tonight – March 17, 2016 – the waxing gibbous moon shines in front of the constellation Gemini the twins. If you look carefully, you might be able to see the Gemini stars Castor and Pollux, despite the moonlit glare. Another bright star, Procyon, is also nearby.
Look eastward at nightfall, rather close to the horizon, and you can’t miss the planet Jupiter, the brightest star-like object in the evening sky. Draw an imaginary line from the moon to Jupiter to spot the Regulus, the brightest star in the constellation Leo the Lion, between these two beacons.
The dark side of the waxing moon always points in its direction of travel – eastward – in front of the backdrop stars. As Earth spins beneath the sky, the stars, planets and moon go westward throughout the night. Even so, the moon actually travels eastward through the constellations of the Zodiac. That eastward motion of the moon is a reflection of the moon’s true motion in orbit around Earth.
As a result of the moon’s eastward (orbital) motion, the moon will move away from Castor, Pollux and Procyon and edge closer to Regulus at the same time tomorrow, on March 18. Then it’ll shift closer to the star Regulus on March 19. And it’ll meet up with Jupiter on March 21. See the chart below.
As seen from the Southern Hemisphere, the moon passes between the Gemini stars and Procyon once a month, as well. People living south of the equator will see the moon, Gemini stars, Procyon and Jupiter in their northern evening sky. We in the Northern Hemisphere will see all of these objects more south to overhead. From either hemisphere, the other hemisphere see things “upside down.” From the Southern Hemisphere, Procyon shines above the moon on March 17, and Castor and Pollux below the moon.
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 toward the North Star), and Procyon lies south of the moon (in the direction away from the North Star). Meanwhile, Jupiter is east of the moon – in the direction of sunrise – as darkness falls on March 17.
Bottom line: Tonight – March 17, 2016 – you’ll find the moon, the Gemini stars, the star Procyon in the same part of the sky. See the chart at the top of this post, and, if you’re in the Southern Hemisphere, turn this chart upside-down!