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Moon, Gemini stars, Procyon February 18

Tonight’s bright waxing gibbous moon – February 18, 2016 – will be bright enough to erase many stars from the blackboard of night. Even so, three stars should be brilliant enough to withstand tonight’s moonlit glare – the Gemini stars, Castor and Pollux, plus Procyon the Little Dog Star. The moon passes south of Castor and Pollux, and north of Procyon, the brightest star in the constellation Canis Minor the Lesser Dog.

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Look for the moon and these stars to reach their high point for the night somewhere around 9 to 10 p.m. local time (that’s the time on your clock, no matter where you live around the globe).

If you live in the Southern Hemisphere, please keep in mind that you’ll see the sky scene upside-down in your northern sky. In other words, you’ll see Procyon at top and the Gemini stars beneath the moon.

No matter where you live worldwide, however, the moon routinely passes to the south of the Gemini stars, Castor and Pollux, and to the north of Procyon each month. As the moon travels eastward in front of the constellations of the Zodiac, it goes through this stellar passageway in periods of about four weeks.

The dark side of the waxing moon always points eastward or in its direction of travel. Although the moon and stars go westward during the night because of the Earth’s rotation, the moon actually goes eastward relative to the backdrop stars because of the moon’s orbital motion, as illustrated on the sky chart below.

The moon moves eastward in front of the backdrop stars, as shown for the same time on two different dates. The green line depicts the ecliptic - Earth's orbital plane projected onto the great dome of sky.

The moon moves eastward in front of the backdrop stars, as shown for the same time on two different dates. The green line depicts the ecliptic – Earth’s orbital plane projected onto the great dome of sky.

Bottom line: On the night of February 18, 2016, watch the moon pass to the south of the Gemini stars and to the north of Procyon. Then watch over the following nights as the moon edges toward the king planet Jupiter.

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Bruce McClure

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