During the last several days of October 2018, the planets Mercury and Jupiter appear quite close together on the sky’s dome. Will you see them? Well, maybe. The Southern Hemisphere has a huge advantage over the Northern Hemisphere for witnessing this celestial attraction in the deepening glow of evening twilight. And, even from southerly latitudes, Mercury and Jupiter sit rather low in the sky at sunset. For all of us, they soon follow the sun beneath the horizon.
Our sky chart at top is for around 35 degrees south latitude. All places north of the tropic of Cancer will have difficulty catching Mercury and Jupiter (especially Mercury because it is fainter) after sunset … although the EarthSky community has surprised us before with seeing objects near the sun 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. Want a chart for the Northern Hemisphere? Guy Ottewell posted a great one this week:
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 four times more brilliantly than Mercury. Still, Mercury is bright, too. It’s brighter than a 1st-magnitude star. Given favorable seeing conditions, Mercury can be seen with the eye alone. However, Mercury’s luster is often tarnished by the glare of evening twilight. That’s certainly the case now!
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, binoculars are likely your best shot.
Bottom line: Best of luck on your search for Mercury and Jupiter in late October 2018. The pair will be exceedingly low in the west after sunset.