Mercury is always a difficult object to spot, always clinging closely to the sun’s apron strings. But you might be excused for missing its brief appearance this week in the dawn skies.
After many attempts to observe Mercury, I’ve found that the best time to spot it is about half an hour before sunrise in the morning sky, or half an hour after sunset in the evening sky. It’s always a balancing act between Mercury’s low altitude and the brightness of the background sky. I find 7x50 or 10x50 binoculars helpful in spotting Mercury, though once I’ve located Mercury in binoculars I usually have no trouble seeing it naked eye.
Because of the tilt of the ecliptic, the path the Sun and planets follow across the sky, some apparitions of Mercury are more favorable than others. Usually apparitions which are favorable for observers in the northern hemisphere are unfavorable for observers in the southern hemisphere, and vice versa.
The tilt of the ecliptic would indicate that this apparition favors southern observers, but as you can see from these two views, it really isn’t much different: catching Mercury this week will be a challenge for observers everywhere in the world.
A secondary factor affecting Mercury’s visibility is the tilt and eccentricity of its orbit. At 7 degrees, Mercury’s tilt is greater than any other planet. The eccentricity of its orbit, which measures how far it deviates from a circle, is also the greatest, more than twice as eccentric as Mars’ orbit.
The tilt this week also favors southern observers, as you can see in the charts, where Mercury’s orbit is marked in red and the ecliptic in green, but even this doesn’t help much.
If you are successful in spotting Mercury in the next few days, congratulate yourself, and let us know here!