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Monday, August 31, 2015

Earthsky Tonight, January 31, 2010: Watch for Leo the Lion, harbinger of spring

Courtesy of EarthSky
A Clear Voice for Science

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The moon, planets and stars – like the sun – rise in the east and set in the west. Tonight, the waning gibbous moon will rise an hour or so after nightfall. However, the constellation Leo the Lion won’t be totally above the horizon until about 2 hours after darkness falls. Like the sun, the stars swing full circle across the sky once a day. Unlike the sun, however, the stars return to the same place in the sky in 23 hours and 56 minutes – not 24 hours. This 4-minute difference between the return of the stars (sidereal day) and the sun (solar day) may seem insignificant, but this discrepancy adds up over time. If the stars returned to the same place in the sky every 24 hours, we’d never have seasonal constellations. One and one half months from now – in middle March – the stars of Leo the Lion will rise some 3 hours earlier than they do tonight. However, the sun will set nearly one hour later (at mid-northern latitudes) than it does today. Adding all that up, that means Leo will appear above the horizon as darkness falls in March. Leo’s presence over the easten horizon at nightfall is a sure sign that springtime is about to return to the northern hemisphere. Related: Find the asteroid Vesta in Leo during February 2010! Written by Bruce McClure Other Links:

Sky and Telescope

National Geographic

Space Com

Amazing Space

The York County Astronomical Society

Scope City

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