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.

2000 March 20
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

Mercury on the Horizon
Credit: Juan Carlos Casado

Explanation: Have you ever seen the planet Mercury? Because Mercury orbits so close to the Sun, it is never seen far from the Sun, and so is only visible near sunrise or sunset. If trailing the Sun, Mercury will be visible for several minutes before it follows the Sun behind the Earth. If leading the Sun, Mercury will be visible for only several minutes before the Sun rises and hides it with increasing glare. An informed skygazer can usually pick Mercury out of a dark horizon glow with little more than determination. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during the middle of last month. Each picture was taken from the same location in Spain when the Sun was 10 degrees below the horizon and superposed on the single most photogenic sunset.

Tomorrow's picture: Star Jet

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U.