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Waning moon, Saturn and Libra stars on morning of February 21

2014-february-20-moon-saturn-zubenelgenubi-night-sky-chart

Tonight for February 20, 2014

The moon and the planet Saturn in front of the constellation Libra the Scales

The moon and the planet Saturn in front of the constellation Libra the Scales.

A larger view of the predawn sky on Friday, February 21.

A larger view of the predawn sky on Friday, February 21.

Saturn as viewed from the Cassini spacecraft. Image Credit: NASA

Saturn as viewed from the Cassini spacecraft. Image Credit: NASA

Unless you’re a night owl, you might want to wake up before dawn on Friday, February 21, 2014 to see the moon and planet Saturn in front of the constellation Libra the Scales. At southerly latitudes, the moon and Saturn rise at an earlier hour, perhaps before your bedtime.

As seen from North America, the dark side of the waning gibbous moon will point right at Zubenelgenubi, Libra’s alpha star. Binoculars reveal that Zubenelgenubi (alpha Librae) is actually a double star. Zubenelgenubi is an Arabic phrase meaning “Southern Claw of the Scorpion.”

Zubenelgenubi is Libra’s alpha star

Ancient sky watchers noted that Saturn took more time to travel through the constellations of the Zodiac than any other planet known at the time. It takes nearly 30 years for this world to go full circle in front of the background stars. Given that Saturn was the slowest-moving planet, the ancients correctly ascertained that Saturn was also the most distant planet.

Saturn’s distance from the sun varies from about 9 to 10 astronomical units. (One astronomical unit = the sun/Earth distance = 150 million kilometers = 93 million miles.)

However, when the astronomer Hershel discovered the planet Uranus in 1781, the radius of the known solar system doubled. Then with the discovery of the planet Neptune in 1846, the outer reaches of the planetary system tripled in distance. To date, there are no known solar system planets beyond the orbit of Neptune, at least as the word planet is presently defined by the International Astronomical Union.

Bottom line: On the morning of February 21, 2014, let the moon be your guide to the planet Saturn and the constellation Libra the Scales. Saturn is the most distant world that you can easily see with the unaided eye.

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