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Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

See Explanation. Clicking on the picture will download the highest resolution version available.

Equinox + 1

Explanation: Twice a year, at the Spring and Fall equinox , the Sun rises due east. In an emphatic demonstration of this celestial alignment , photographer Joe Orman recorded this inspiring image of the Sun rising exactly along the east-west oriented Western Canal, in Tempe , Arizona , USA . But he waited until one day after the northern Spring equinox, in 2001, to photograph the striking view. Why was the rising Sun due east one day after the equinox? At Tempe's latitude the Sun rises at an angle , arcing southward as it climbs above the horizon. Because the distant mountains hide the true horizon, the Sun shifts slightly southward by the time it clears the mountain tops . Waiting 24 hours allowed the Sun to rise just north of east and arc back to an exactly eastern alignment for the photo. Today is another Equinox + 1 day, with the Sun crossing the celestial equator yesterday at about 17:32 Universal Time .

Date March 21, 2010
Credit Credit & Copyright: Joe Orman
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
A service of: ASD at NASA / GSFC,
NASA Science Activation & Michigan Tech. U.