May 4 – 17, 2015
“It’s really kind of cool — when you’re in a science and something all of a sudden falls into place that you don’t expect. It’s the thrill of the hunt.”
— Donald C. Parker, Planetary Imaging Pioneer
Planet Mercury takes its time to emerge from the peach-colored light above the spot where the sun drops into the skyline on these fine, early May evenings. The little planet closest to the sun climbs to its highest point above the west-northwest horizon and is brightest during the first week or so of May, although it is visible through mid-month. At first appearing to be a bright star about one fist-width (extended at arms length) above the skyline, it is gradually dimming and will begin to lose altitude. Depending on your vantage point, Mercury is visible from twilight until about 9:35 p.m. It actually sets at 9:51 p.m. on the 4th and 9:46 p.m. on the 14th. This is Mercury’s best evening apparition of 2015.
Sundown is around 8 o’clock until mid-May. Planets Venus and Jupiter, perceptible within fifteen minutes of sunset, are our guides to dimmer Mercury. Venus appears in the west about 3 fist-widths above the horizon. A fist-width extended at arm’s length equals approximately 10 degrees. Jupiter, not as bright, appears high above in the southwest. ( Click here for the times of civil, nautical and astronomical twilight in your sky. )
I am eager to locate Mercury as soon as it is physically possible for the eye to see it as daylight fades into twilight. It is said that the Greeks tested their eyesight in this way. For an exercise that is sure to delight, arrive at a location with a clear view to the west-northwest skyline sometime between civil and nautical twilight (See diagram. Click here for the times of civil, nautical and astronomical twilight in your sky.) Civil twilight begins at 8:25 p.m. and nautical twilight at 9:03 p.m. on the 4th; add a minute or 2 every night thereafter.
Trace a diagonal line from Jupiter to Venus and continue down towards the horizon to find dimmer Mercury. If the distinctive, star-like point of light is not there at first, retrace the diagonal up to the brilliant planets and back down. Re-read the first Mercury paragraph, above, and gaze with soft eyes. Listen for spring peepers. Look to the left to see bright Sirius the Dog Star that forms a triangle with Jupiter and Venus. Check the diagonal again. When Mercury’s light reaches our eyes it’s like receiving a gift.
Take note that most astronomy writers suggest looking for Mercury 60 – 80 minutes after sunset when twilight has deepened, a wonderful field of bright stars twinkles in the western sky and it is easy to spot Mercury. It’s nice that way, too, except you’ve missed the thrill of the hunt!
