Driftless Dark Skies

John Heasley

Our planet has its closest approaches to Jupiter and Saturn this month. Both worlds spend July in the constellation Sagittarius the Archer. They rise in the southeast around sunset, are visible all night long as they pass low across the southern sky, and set in the southwest around sunrise. Jupiter is brighter than any star and easy to spot. Saturn will be 6 degrees to its left. That’s the width of three fingers held at arm’s length, kind of like you’re giving the Scout salute. Both planets appear their biggest and brightest at opposition. That’s when Earth passes between them and the sun. For Jupiter, this happens the night of July 13. Opposition for Saturn is a week later on July 20. The brightening of Saturn might be a little more noticeable then due to the “Seeliger Effect” when the icy particles in its rings are reflected directly back at the sun (and us). If you can look through binoculars or a telescope, Jupiter’s moons and Saturn’s ring are wonderful to enjoy.

According to the Rand McNally Universal Map of Outer Space from 1958 that still hangs on my wall, Jupiter has 12 moons and Saturn has 10. A few more have been discovered in the last 62 years. Saturn now leads with 82 moons and Jupiter is close behind with 79 moons. Since that time at the dawn of the Space Age, we have sent robot explorers named for pioneering astronomers to visit both worlds: Galileo to Jupiter (orbited 1995-2003) and Cassini to Saturn (orbited 2004-17). Future missions in the 2020s and 2030s will send an eight-bladed rotorcraft called Dragonfly to soar over the methane seas of Saturn’s moon Titan. Other robots will explore the oceans beneath the ice of Jupiter’s Europa and Saturn’s Enceladus looking for signs of life.

If you’re outside the evening of July 4, don’t miss Saturn, Jupiter and the full moon all in a line. That’s a total of 162 moons! The following night, the almost full moon is below and between Jupiter and Saturn forming a triangle. If it’s cloudy those nights, look again on July 31 and Aug. 1 for similar gatherings. If you need to see even more worlds at one time, head outside the mornings of July 18 and 19 around 4:30 just as the sky is brightening to see all five visible planets. A thin waning crescent  moon is rising in the northeast with Mercury below it on Saturday and to its right on Sunday. Venus is brilliant in the east, Mars is higher and reddish in the southeast, and bright Saturn and Jupiter are setting together in the southwest. Six worlds at once! You would need a telescope to see them, but the ice giants Uranus and Neptune and the dwarf planets Ceres, Eris and Pluto are also in the sky at this time for a total of 11 worlds. Add the one you’re standing on, and that’s an even dozen all while sipping your coffee or tea.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador and with the IAU as a Dark Skies Ambassador. For more information about stargazing in southwestern Wisconsin, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies above.