Mercury on the Horizon
Credit & Copyright: Juan Carlos Casado
Explanation: Have you ever seen the planet Mercury? Because Mercury orbits so close to the Sun, it never wanders far from the Sun in Earth's sky. If trailing the Sun, Mercury will be visible low on the horizon for only a short while after sunset. If leading the Sun, Mercury will be visible only shortly before sunrise. So at certain times of the year an informed skygazer with a little determination can usually pick Mercury out from a site with an unobscured horizon. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during March of 2000. Each picture was taken from the same location in Spain when the Sun itself was 10 degrees below the horizon and superposed on the single most photogenic sunset. Mercury is currently visible in the western sky after sunset, but will disappear in the Sun's glare after a few days.