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Moon and Jupiter meet in Cancer the Crab on May 23

The moon and planets are always found on or near the ecliptic - the sun's annual pathway in front of the constellations of the Zodiac.

Tonight for May 23, 2015

At present, the planet Venus shines in front of the constellation Gemini and Jupiter beams in front of the constellation Cancer. The bright stars Castor and Pollux identify Gemini, and the star Regulus guides your eye to the constellation Leo. In any year, you can locate the faint constellation Cancer in between Regulus and the two bright Gemini stars.

At present, the planet Venus shines in front of the constellation Gemini and Jupiter beams in front of the constellation Cancer. The bright stars Castor and Pollux identify Gemini, and the star Regulus guides your eye to the constellation Leo.

The ecliptic is the plane of Earth’s orbit around the sun. As Earth moves, we see the sun travel a narrow pathway in front of the stars. The ecliptic defines that pathway, which we most often call the Zodiac.

Tonight’s moon – May 23, 2015 – is meeting up with the brilliant planet Jupiter in front of one of the faintest constellations of the Zodiac, the constellation Cancer the Crab. The Zodiac is the narrow band of stars circling through the heavens, marking the sun’s annual path or moon’s monthly path in front of the backdrop stars. Although Cancer is faint, you can use the moon and Jupiter – the brightest and third-brightest celestial bodies of nighttime, respectively – to locate this hard-to-see constellation this evening.

Venus, the second-brightest celestial object in the evening sky, after the moon, appears in the western sky at nightfall.

Why does the moon pass this constellation so often? The moon orbits nearly on the ecliptic, or plane of Earth’s orbit around the sun. So as the moon makes its monthly rounds – orbiting again and again around Earth – it moves in front of the constellations of the Zodiac, passing the same stars and constellations again and again.

Take a look at the chart below to see the boundaries of Cancer. The sun passes in front of this constellation from about July 20 to August 10 every year. Wait, you say, that doesn’t match astrological dates? That’s because the constellation of Cancer as we see it in the real sky – and the astrological sign of Cancer – are not the same thing.

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View larger. | The constellation Cancer. Image via Wikimedia Commons.

Cancer, though one of the dimmest constellations of the Zodiac, is still very significant. In ancient times, this constellation won much fanfare because the sun shone in front of Cancer during the Northern Hemisphere’s summer solstice. Some 2,800 years ago, the star Asellus Australis actually marked the summer solstice point in the sky. Nowadays, the sun has its annual conjunction with Asellus Australis on or near August 1.

Also in our day, the sun shines in front of the constellation Taurus the Bull on the summer solstice. Because the sun reaches its northernmost point from the Earth’s equator on the summer solstice, you’d think the northernmost extent of the sun’s travels would be called the tropic of Taurus. But no. Look on the globe and you’ll find the sun’s northernmost latitude labeled as the tropic of Cancer, in deference to this faint yet celebrated constellation.

Bottom line: On May 23, 2015, the moon is in front of the faint constellation Cancer. The moon’s glare will make Cancer tough to spot. Good night to use your imagination!

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