We’re entering peak Jupiter viewing season for 2021. The giant planet rises in the hour before midnight on July 1 and by the end of twilight at the end of the month. This places it near the meridian in the early morning hours — the best time to view it. Jupiter is moving retrograde in Aquarius near its border with Capricornus and lies about 20° east of Saturn.
It’s a dominant object in this region of the sky, shining at magnitude –2.7 most of the month and reaching –2.8 by the end of July. Telescopic views will show a wide range of cloud features on its 48"-wide disk. These features move quickly with the planet’s rotation period of just under 10 hours. Two dark equatorial belts straddle the equator and carry with them dark and light regions, along with more spots and belts in the temperate regions.
Io, Europa, Ganymede and Callisto — Jupiter’s four major moons — wander to different positions each night. You can track them easily with a small telescope and follow the occasional transits of moons and their shadows. Moons also sometimes hide in or reappear from an eclipse behind Jupiter or its shadow, which extends away to the west of the planet before opposition.
A thrilling series of events occurs July 24/25. The shadow of Europa joins the largest moon, Ganymede, in a transit of Jupiter, while a short time later, Io enters an eclipse. Such simultaneous events are rare and fun to watch as orbital dynamics play out right in front of you. Note that some events are not visible from all locations in the U.S., so check the times for sunrise and the altitude of Jupiter at your location.
Neptune sits 12° due west of the Last Quarter Moon early on the morning of July 1. Binoculars are sufficient to detect the magnitude 7.7 planet. Located in eastern Aquarius, Neptune is moving retrograde, heading toward a September opposition. It rises around midnight and is best placed for viewing from 2 A.M. local time through dawn in early July, and from midnight through dawn late in the month. Neptune lurks 5.8° east of Phi (ϕ) Aquarii and due south of the Circlet in Pisces. It lies very near a slightly brighter field star (HIP 116402, magnitude 7.2) and appears like a double star under low magnification. Neptune’s motion relative to the field star is noticeable from night to night. The planet lies 4.1' due south of this star on July 18 and continues westward, ending the month 14' to its southwest. A gibbous Moon returns to Aquarius the morning of July 27, when Neptune stands 8° to its northeast.
Uranus is best viewed in the hour before dawn, high in the southeast among the faint stars of southern Aries. Binoculars will easily reach the magnitude 5.8 planet, although its exact location is tricky given the sparse star field. On July 1, Uranus is 12' due north of magnitude 5.8 Omicron (ο) Arietis. Find Omicron by picking up 4th-magnitude Mu (μ) Ceti, the northernmost star in the head of Cetus the Whale, then moving due north past 38 Arietis (2° north of Mu) until you reach Omicron, 3° north of 38 Ari.
During July, Uranus treks northeastward and is nearly 1° from Omicron on July 31. It is then 14' due north of a fainter (magnitude 6.7) field star. Through a telescope, Uranus reveals its planetary nature in the form of a 4"-wide blue-green disk. A waning crescent Moon lies in the vicinity the morning of July 4, when Uranus stands 4.5° to its northeast.