What planetary events are coming up in the night sky? Read about Venus, Mercury, Mars, Jupiter, Saturn, Uranus and Neptune and what’s going on in our Solar System in Planets at a Glance.
This month, Mercury will begin the month shining at magnitude 1.2 in the eastern pre-dawn sky. The swift planet will increase its angle from the sun until it reaches a maximum elongation of 18 degrees, and peak visibility, on October 8.
The best views of the planet will fall between about 6:00 a.m. and 6:30 a.m. local time. After maximum elongation, Mercury will sink sunward again. The early October apparition will be the best of the year for observers at mid-northern latitudes, but a poor one for those in the southern hemisphere.
The planet will steadily increase in brightness during October. Viewed in a telescope, Mercury will wax in illuminated phase from 18% to 99%, while its apparent disk diameter halves from 8.8 to 4.8 arc-seconds — so turn all optical aids away from the eastern horizon before the sun rises. By the time the old crescent moon appears a thumb’s width above (to the celestial northwest) of Mercury on October 24, the planet will be difficult to see.
During the first few mornings of October, Venus may be spotted — with difficulty — just above the eastern horizon before sunrise. The bright planet will sink sunward each morning, pass the sun at superior conjunction on October 21, and then reappear in the western evening sky towards year-end.
Mars will be well-positioned for viewing starting in the late evening during October. On the first of the month, it will rise just after 10:00 p.m. local time and climb high in the southern sky by sunrise. By month’s end, Mars’ rising time will advance to 8:20 p.m. local time. The red planet will spend October slowing its eastward trek between the horns of Taurus.
On October 3, Mars will cease its motion altogether, only to begin a westerly retrograde loop that will last through a fine opposition in early December and end in mid-January.
Over the month, Earth’s distance from Mars will decrease by 13.67 million miles (22 million km). As a result, Mars will brighten from magnitude -0.59 to -1.22. Its appearance in telescopes will show a nearly fully illuminated disk that swells in apparent diameter from 12 to 15 arc-seconds. Watch for suggestions of the dark markings that will become clearer at opposition.
The red planet will pass only 1.2 degrees to the north of the Crab Nebula supernova remnant from October 14-16, but the bright waning gibbous moon will shine nearby to their north.
Jupiter will be well-placed for observing throughout the night in October — although it will be highest (and look sharpest) in telescopes during the middle hours of the night. The planet will continue its slide westward across the stars of western Pisces and towards Neptune.
The yellowish dot that is Saturn, which will be 24-times less bright, will shine about 40 degrees to Jupiter’s southwest. Still only weeks past its closest opposition in decades, Jupiter will shine a bright magnitude of -2.9.
In amateur telescopes, the planet will exhibit equatorial bands girdling a generous 49 arc-seconds-wide disk. The Great Red Spot will appear every second or third night, and Jupiter’s four large Galilean satellites will frequently eclipse and occult one another, and cast their round, black shadows on the planet — singly and in pairs.
The nearly full moon will hop past Jupiter on October 7-8.
As for the yellowish dot that is Saturn, it will be observable from after dusk until late evening in October — though it will not climb very high when it culminates in the southern sky in mid-evening.
The white dot of 24-times brighter Jupiter will be positioned 40 degrees to Saturn’s left (or celestial east). On October 23, Saturn will cease its westerly retrograde motion and prepare to resume a regular eastward prograde motion. That same night, Saturn will approach to within 0.6 degrees east of the magnitude 4.2 star Iota Capricorni in central Capricornus. Their separation will noticeably widen over the following weeks.
Viewed in a telescope in October, Saturn will show an apparent disk diameter of 17.7 arc-seconds, and its rings will subtend 41 arc-seconds. Saturn’s rings will be tilting more edge-on to us every year until the spring of 2025. This year they are already close enough for Saturn’s southern polar region to extend well beyond them.
The waxing gibbous moon will shine to the southeast of Saturn on October 5.
Blue-green Uranus will be observable between late evening and dawn this month. Rising shortly after 8:00 p.m. local time on October 1, Uranus will climb highest in the southern sky, and look best in telescopes, during the wee hours of the morning. By month’s-end, those timings will advance by two hours.
Over the month, magnitude 5.6 Uranus will travel retrograde westward through the stars of southeastern Aries. Its trajectory will be parallel to — and about 1.5 degrees to the south of — the line joining the brighter stars Botein (Delta Arietis) and Pi Arietis, creating a triangular asterism for anyone searching for Uranus in binoculars. Uranus’ small, 3.8 arc-seconds-wide blue disk will appear markedly different from those stars.
On October 11, the bright, waning gibbous moon will shine 2 degrees to the upper right (or celestial WSW) of Uranus. Hours later, observers with telescopes in Alaska, northwestern continental United States, northern and western Canada, and Greenland will be able to see the moon occult Uranus around 05:00 to 06:00 GMT — the tenth in a series of consecutive lunar occultations of that planet.
The distant blue planet Neptune will be an all-night target this month, sharing the sky with far brighter Jupiter to its east, and the yellowish dot of Saturn shining 35 degrees to the southwest.
The Jupiter-Neptune separation will decrease from 9 to 6.8 degrees over the month. Neptune will shine at magnitude 7.8, which is within reach of good binoculars. The blue planet will be traveling retrograde westward among the stars of northeastern Aquarius, towards the medium-bright star Phi Aquarii.
In a telescope, Neptune’s tiny apparent disk size will span 2.4 arc-seconds. Larger telescopes can show Neptune’s large moon Triton.
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.