Mercury Achieves Greatest Elongation

Mercury, always a challenge to observe because of the planet's close proximity to the sun, achieved its greatest western elongation Sunday morning, January 9, 2011. This nine-second exposure at f/6.3 of a clear southeastern sky captured Mercury (left center between power lines and horizon) just 2 1/2 hours before its greatest elongation (maximum angle between the sun and an inferior planet as seen from Earth). Mercury's apparent magnitude was -0.22. The bright star between the power lines at right center is the red giant Antares, in the constellation Scorpius. The brightest object at upper right is the planet Venus, which achieved its own greatest western (morning) elongation the previous day. This image was shot around 6:30 AM, January 9 along Boyson Road near Timber Oak Place in Marion, Iowa. The artificial lights along the horizon at right belong to the city of Marion. Air temperature at this time was -1 degree F.