During the first half of July Mercury will slowly return to easy visibility in the eastern pre-dawn sky. It will reach greatest western elongation and peak visibility, 20 degrees from the sun, on July 22, and then will continue to be observable through the end of July and early August. Look for the swiftly-moving planet sitting low in the east-northeastern sky before 5:30 a.m. in your local time zone. Mercury’s position south of the morning ecliptic will make this apparition less than ideal for Northern Hemisphere observers, but a good showing for those located near the Equator, and farther south. Mercury will brighten continuously and dramatically during July, ending the month at magnitude -0.62. When viewed in a telescope, the planet will show a waxing phase that grows to 67%-illuminated by month-end. During the same period, the planet’s apparent disk size will almost halve from 10 arc-seconds to 6.2 arc-seconds. For a short period before dawn on Sunday, July 19 the very slender crescent of the old Moon will sit four finger widths to the left (or 4.8 degrees to the celestial east) of Mercury.
Throughout July, Venus will rise about two hours before the sun and then shine prominently in the eastern sky until sunrise. Between July 3 and 12, Venus’ orbital motion will carry it eastward and directly through the Hyades star cluster, the large, triangular grouping of stars that forms the face of Taurus, the bull. On July 10, Venus will reach its greatest illuminated extent, at magnitude -4.47, for the current morning apparition. On July 12, the planet will pass within a degree to the north of the bright star Aldebaran. For the rest of July, Venus will travel eastward through Taurus – ending the month near the southern horn-tip star Zeta Tauri, and only 0.6 degrees to the celestial north of the pulsating variable called the Ruby Star, 119 Tauri, and CE Tauri. Viewed in a telescope during July, Venus will show a crescent phase that waxes from 19% to 43%-illuminated, and an apparent disk size that shrinks from 43 to 27 arc-seconds. On July 17, the waning crescent Moon will be positioned 2.75 degrees to the celestial northeast of Venus, making a lovely wide field photograph.
Mars will spend the month of July moving rapidly eastward along the Cetus-Pisces border. It will begin the month as a reddish, magnitude -0.5 speck that rises in the east just before 1 a.m. local time. By month’s end, Mars will brighten to magnitude -1.1 and will be rising at 11:30 p.m. local time. As the distance between Earth and Mars decreases over the same period, telescope views of the red planet will show an 85% illuminated disk that grows from 11.48 to 14.6 arc-seconds. On July 11-12, the waning gibbous Moon will hop past Mars, allowing observers at Middle Eastern longitudes to see the Moon pass less than three degrees south of Mars before dawn on Sunday, July 12.
During July, very bright Jupiter will be visible all night long while it moves slowly retrograde through the stars of eastern Sagittarius. On July 14, Jupiter will reach opposition, when it will be located 384.8 million miles, 619.2 million km, or 34.4 light-minutes from Earth, and will shine at its maximum brightness of magnitude -2.75 for 2020. Views of Jupiter through amateur telescopes will reveal a generous 48 arc-second wide disk striped with equatorial bands. The Great Red Spot will also be visible every second or third night. Dimmer Saturn will be following Jupiter across the sky, lagging some 6 to 8 degrees to the east. Jupiter will be rather low in the sky for mid-latitude observers, but southerly observers will have a higher, better view of it. Near opposition, the four large Galilean moons appear bigger and brighter, too. Overnight on July 2-3, observers in the Americas can see Ganymede’s relatively large shadow traverse the planet, accompanied by the Great Red Spot. Starting in late evening on July 16, and again in the wee hours of July 24, Europa’s shadow will cross Jupiter accompanied by the Great Red spot. On July 5, the full Moon will form a neat triangle below (or to the celestial south of) Jupiter and Saturn.
During July, Saturn will be visible all night long as it travels retrograde westward through the stars of eastern Sagittarius. It will also be positioned approximately 6 to 8 degrees to the east of much brighter Jupiter and just 2 degrees north of the globular cluster Messier 75. On July 20, Saturn will reach opposition, when it will be located 836.6 million miles, 1.346 billion km, or 74.9 light-minutes from Earth, and will shine at its maximum brightness of magnitude 0.13 for 2020. In backyard telescopes Saturn will show an apparent disk diameter of 18.5 arc-seconds – and its rings, which will be narrowing every year until they close up in the spring of 2025, will span 43 arc-seconds. A handful of Saturn’s moons are readily observable with backyard telescopes in a dark sky. Saturn will sit rather low in the sky for mid-latitude observers, but southerly observers will have a higher, better view of it. On July 5, the full Moon will form a neat triangle below (or to the celestial south of) Jupiter and Saturn.
Uranus will spend July in the eastern predawn sky, where it will be observable in the second half of the night among the stars of southern Aries. Due to its greater angular separation from the sun every morning, the blue-green, magnitude 5.8 planet will be rising around midnight local time by month’s end. The waning crescent Moon will pass less than a palm’s width to the lower right (or 6 degrees south) of Uranus on July 14.
During early July, Neptune will be observable for several hours before dawn in the southeastern sky as it moves retrograde west among the stars of eastern Aquarius. By month’s end the magnitude 7.9 planet will be rising shortly after 10 p.m. local time. The medium-bright star Phi (φ) Aquarii, which will be positioned 3 degrees to Neptune’s west all month, can help with finding the blue planet.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.