Elusive little Mercury is commencing a fine apparition as an evening star following its superior conjunction behind the Sun on 2008 APR 16. The springtime celestial geometry favors northern hemisphere observers. From Chicagoland at 30 minutes after sunset Mercury will achieve its greatest altitude of 13.7° on MAY 12. The next day it will reach its greatest eastern elongation of 21.8° before tumbling toward inferior conjunction between Earth and Sun on JUN 07. In a telescope Mercury will appear 50% illuminated like a Half Moon on MAY 08. Before that date it will be gibbous and afterward a crescent. Mercury is currently at magnitude -1.7 (brighter than Sirius) but will dim to magnitude +3.6 by June.
I’ve created a panoramic graphic demonstrating Mercury’s position in the west-northwestern sky as viewed from Chicagoland 30 minutes after sunset from now through JUN 01. Although it should well serve most northern hemisphere observers. To see it, click: http://www.curtrenz.com/astronomical.html
A slender crescent Moon aged about a day and a half will appear to pass near Mercury on MAY 06. That may present a fine photo opportunity. Below is a photo I took from Arlington Heights, Illinois of a similar conjunction during the evening of 2007 MAY 17.