Each year, one year and one month after the previous year, the giant planet Jupiter comes into what we call opposition.
It rises into the eastern sky while the sun sets opposite Jupiter in the western sky. This is when Jupiter and Earth are closest to each other, and when Jupiter is at maximum size and brightness as seen from Earth.
Jupiter’s opposition will happen this year on May 8, just the way it does every 399 days, because of the different orbital speeds of Earth and Jupiter. While Earth orbits the sun every year; Jupiter takes 12 years to do the same.
By 9:30 p.m. Jupiter will be up above the eastern horizon enough to be unmistakable, at magnitude -2.5.
For skywatchers with telescopes, Jupiter reveals many details of its surface, including two dark equatorial belts straddling the brighter zone at the planet’s equator.
Alternating series of zones and belts may be seen from time to time between the equator and the poles, as Earth’s atmosphere steadies, or when looking through larger telescopes.
Small telescopes and even binoculars will show Jupiter’s four bright moons. On May 8, Io, Europa and Callisto all line up on the east (left) side of Jupiter; while Ganymede will be by itself on Jupiter’s right side.
Jupiter will command attention all month because it does not set until dawn and because it is so bright. But Saturn also comes up in the eastern sky around midnight on May 1, and around 10 p.m. on May 30.
Saturn does not come close to the brightness of Jupiter, but it outshines all the nearby stars of Sagittarius around it, brightening from +0.3 to +0.2 through May. Saturn will reach opposition itself in late June, and it will brighten even more to 0.0.
Saturn is always magnificent through telescopes; even smaller scopes show the Cassini division, a dark gap between the outer A ring and the brighter B ring in Saturn’s ring system.
Meanwhile, Mars’s appearance changes a lot during May, as it approaches its opposition in late July. This opposition will bring Mars closer to Earth than it has been in 15 years.
Mars will double in brightness during the month of May, going from -0.4 to -1.2 in magnitude. This will make it nearly as bright as Sirius, the brightest star.
Mars rises about 1:30 a.m. among the stars of Sagittarius, but moves eastward in its orbit into Capricornus during the month, where it will remain until August.
The moon makes its appearance close to several planets at various times during the month of May. Because the moon is so easily spotted in our skies, it will help point to particular planets we will be looking to find.
A waning gibbous moon will be seen just above Mars in the pre-dawn morning of May 6 and a slim crescent moon will be below Venus in the western sky at dusk on May 17. Venus will actually be easier to spot that night because it is shining at magnitude -3.9.
And a nearly full moon (full moon is May 29) appears above Jupiter around 2 a.m. on May 27 and above Saturn on May 31.