The first few weeks of July 2018 continue to present a good time to spot Mercury, the innermost planet of the solar system. Seek for Mercury beneath Venus, the third-brightest celestial object to light up the sky, after the sun and moon. Look westward, in the general direction of sunset, some 60 to 90 minutes after sundown. If you can’t see Mercury beneath dazzling Venus in the deepening dusk with the eye alone, then try your luck with binoculars.
Given clear skies, almost everyplace worldwide should be able to spot Mercury beneath Venus as dusk gives way to darkness. We except the far-northern regions of the globe, where day pretty much extinguishes nighttime at this time of year.
The Southern Hemisphere has the advantage over the Northern Hemisphere for this particular evening showing of Mercury. At mid-northern latitudes, Mercury sets about 90 minutes after the sun; at the Earth’s equator, Mercury plunges below the horizon around 100 minutes after sundown; and at temperate latitudes in the Southern Hemisphere, Mercury sets nearly two hours after sunset. Click here for a recommended sky almanac to find out the setting times of the sun, Mercury and Venus in your sky.
At temperate latitudes in the Southern Hemisphere, throughout July 2018, Mercury actually stays out after nightfall (or after the end of astronomical twilight). Far and away, this will be Mercury’s best evening appearance of the year for the Southern Hemisphere, but in the Northern hemmisphere, it’ll be a decent evening apparition as well.
Want to know when astronomical twilight ends and true night begins for your part of the world? Click here and remember to scroll down and click on the astronomical twilight box.
Mercury, the closest planet to the sun, and Venus, the second-closest planet, are called inferior planets because they orbit the sun inside of Earth’s orbit. Since Mercury never stays far from the sun in Earth’s sky, the innermost planet is oftentimes lost in the sun’s glare. However, Mercury can be viewed when it’s far enough east of the sun to be glimpsed after sunset, or far enough west of the sun to be glanced upon before sunrise. At present, Mercury is nearing its greatest eastern (evening) elongation of 26 degrees east of the sun. So Mercury is now staying out for a maximum amount of time after sunset.
Mercury is easily as bright as a 1st-magnitude star right now but may be hard to see in the glare of evening twilight, especially from far northerly latitudes. Mercury’s phase is waning in the evening sky, so this world will slowly but surely dim over the course of this month. In other words, catch Mercury while you can.
These next few weeks, find an unobstructed horizon in the direction of sunset, and then seek for Mercury, the innermost planet, beneath dazzling Venus in the western sky some 60 to 75 minutes after sunset.