Mercury at Greatest Western Elongation (before sunrise)

On Monday, April 21, Mercury (orbit shown in red) will reach its greatest angle of 27.4 degrees from the morning sun and maximum visibility for its current morning apparition. With Mercury positioned low in the eastern sky and well below the tilted morning ecliptic (green line), this appearance of the innermost planet will be a poor one for Northern Hemisphere observers, but an excellent one for those viewing Mercury from the tropics and the Southern Hemisphere. The optimal viewing times at mid-northern latitudes will start around 5:45 a.m. local time. Viewed in a telescope (inset) the planet will exhibit a waxing, almost half-illuminated phase.