The planets Mercury and Jupiter appear quite close together on the sky’s dome during the last several days of October 2018. Far and away, though, the Southern Hemisphere has the advantage over the Northern Hemisphere for witnessing this celestial attraction in the deepening glow of evening twilight. But even from southerly latitudes, Mercury and Jupiter sit rather low in the sky at sunset, and then follow the sun beneath the horizon around nightfall.
Our feature sky chart at top is for around 35 degrees south latitude to accommodate our friends in the Southern Hemisphere. We figure that all places north of the tropic of Cancer will have difficulty catching Mercury and Jupiter (especially Mercury) after sunset, although EarthSky watchers have surprised us before and may well surprise us again.
Given an unobstructed horizon at 35 degrees north latitude, Mercury struggles to stay out as long as one hour after the sun, whereas Jupiter stays out for about one hour and 10 minutes after sunset. In the days ahead, Mercury will set a little later and Jupiter a little earlier.
Given a level horizon at 35 degrees south latitude, Mercury and Jupiter stay out for a whopping 1 3/4 hours after the sun. In the days ahead – just as in the Northern Hemisphere – Mercury will set a little later and Jupiter a little earlier.
Jupiter is the brighter of these two worlds, shining some 4 times more brilliantly than Mercury. Even so, Mercury is actually brighter than a 1st-magnitude star, and, given favorable seeing conditions, can be seen with the eye alone. However, Mercury’s luster is often tarnished by the glare of evening twilight.
Do you have binoculars? If you see Jupiter but not Mercury, aim your binoculars at Jupiter and you might be able to view Mercury in the same binocular field with Jupiter. These two worlds should fit inside a single binocular field for several days to come.
To increase your chances of spotting Mercury and Jupiter, find an unobstructed horizon in the direction of sunset. Better yet, stand atop a balcony or hilltop to see a little more sky. If you live at northerly latitudes, bring binoculars.
Best of luck on your search for Mercury and Jupiter!