Sunday, 27 January 2013

Bright star near moon on night of January 27 is Regulus

As seen from around the world on the night of January 27, 2013, the bright star Regulus climbs over the eastern horizon by early to mid-evening. This star will appear quite subdued in tonight’s bright moonlight but should still be visible to the unaided eye. From mid-northern latitudes, Regulus comes up about two hours after sunset. From mid-southern latitudes, Regulus comes up about an hour after sunset. After rising, watch for the Regulus to chase the moon westward for the rest of the night. The moon will look plenty full tonight, but technically speaking, it’ll be a waning gibbous moon that lights up the sky after sunset today and before sunrise tomorrow.

The moon and Regulus transit – appear highest up for this night – during the wee hours after midnight tonight. The moon transits first and then Regulus follows. This blue-white star – which is the brightest star in the constellation Leo the Lion – reaches its highest point at roughly 2 a.m. You might want to consult an astronomical almanac because the precise rising/transit times of the heavenly bodies depend on your latitude and longitude.

As the predawn darkness starts to give way to dawn on January 28, you’ll see the moon and Regulus sitting low in the western sky. The moon and Regulus parade westward across tonight’s sky for the same reason that the sun goes westward during the day. The Earth rotates from west-to-east on its axis once a day, making it seem as if the sun, moon, planets and stars move westward while the Earth stands still.

To discern the moon’s true orbital motion, note the moon’s position relative to Regulus at the same time tomorrow (Monday, January 28). The moon will have moved about 13o eastward (toward Regulus). This change of the moon’s position in front of the backdrop stars shows you how far the moon has revolved around our planet Earth in 24 hours. For reference, the moon’s diameter equals about one-half degree and your fist at an arm length spans about 10o of sky.

Bottom line: On the night of January 27, all of us around the world can watch the star Regulus chase the big and bright waning gibbous moon westward across the sky from early evening until dawn.

- EarthSky

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