October is the month of Mars. Like a glowing coal it stands out in the eastern sky during the evening hours, especially during the first half of the month when it will glow brighter and appear bigger at any time until September 2035. Mars will be closest to Earth on the 6th and arrives at opposition to the sun on the 13th when it rises around sunset and moves across the sky all night. Meanwhile, Jupiter (a bit dimmer than Mars for much of this month), and mellow, yellow Saturn sitting off to its left, begin to draw noticeably closer to each other, particularly as October winds down. During the waning hours of the night, Venus dazzles in the east-northeast. Finally, there is Mercury, which is visible with difficulty very low in the west-southwest right after sunset during the first week of October.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10-degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury – reaches greatest elongation, 26° east of the sun on the 1st. But this zero-magnitude planet is also some 12° south of the sun in declination, so from latitude 40° north it sets only ¾ hour after sundown and is nearly impossible to see. From the Gulf Coast states and the Southwest, however, Mercury will be somewhat higher, sets a bit later and should be glimpsed with the unaided eye. On October 25th, Mercury passes inferior conjunction (between the Earth and the sun) and then rapidly enters the morning sky.
Venus – shines as the brilliant Morning Star in the east during dawn. It rises about 3½ hours before the sun as October opens, and 3 hours before the sun at month’s end. On the morning of October 3rd, it is closely paired with first-magnitude Regulus in Leo. Venus will be within 2½° of this 1st-magnitude star from October 1st through 5th, but on the 3rd, they are separated by only ½°, with Venus, burning 150 times brighter, sitting just below it. Throughout this period, some of us may notice an enhancement of their subtle colors because their contrast is more obvious when they’re near each other. The hint of yellow in Venus and touch of blue in Regulus should be exaggerated to the unaided eye. On October 14th, check out the eastern sky at around 5:30 a.m. local daylight time and you’ll see the slender sliver of a waning crescent moon, just 2½ days before new, and hovering 6° to its upper right will be Venus. Despite their rather wide separation, still an eye-catching sight for early risers.
Mars – arrives at its closest approach to Earth on October 6th at 10:18 a.m. EDT, when the distance will be 38,586,816 miles (62,099,460 km); reflected sunlight from the planet will traverse the distance to the Earth in 3 minutes 27 seconds. It will not come this close again until the year 2035. Through a telescope Mars’ apparent diameter measures a bit less than 23 seconds of arc; looking through an eyepiece with a magnification of 80X will cause the planet to appear the size that the moon appears to the unaided eye. Since its south pole is inclined toward the Earth, Mars’ polar cap should be visible in small telescopes. Mars arrives at opposition to the Sun on October 13th, visible from dusk to dawn and shining at a head-turning magnitude of -2.6 . . . three times brighter than Sirius! After reaching this pinnacle, Mars will recede from Earth and gradually become dimmer through the balance of the year. This close approach will be unusually favorable for observers in the United States since the planet will be north of the celestial equator in declination (+5.4°) and at its highest point in the southern sky (56°) at 1 a.m. local daylight time from latitude 40° north. Call October 2nd, “M&M” Night (Moon and Mars). Look due east at 8:30 p.m. local daylight time and you’ll see the moon and shining like a fiery beacon to its upper left will be Mars. As the night wears on, watch how the moon slowly creeps (at its own diameter each hour) eastward to just below Mars by around midnight. By the time dawn is breaking the following morning, you’ll see the moon descending the western sky, with Mars now sitting to the moon’s lower right. Then on October 29th, for the second time this month, the moon again pays Mars a visit, although they’re more widely separated (4° apart) as opposed to their previous encounter. Mars is also 4 million miles farther away and therefore will appear about 28% dimmer, yet still dazzling at magnitude -2.1.
Jupiter – stands watch in the south-southwest at dusk to the upper left of the Teapot of Sagittarius. The big planet is lower and a little more distant than it was in summer, but next to Mars, it’s the brightest star-like object in the evening sky.
Saturn — stands in the south at dusk. The Summer Triangle of Vega, Deneb, and Altair points down at it from on high like an arrowhead, but Saturn shines coolly with a steady yellowish glow, in marked contrast to the stars’ twinkling.
As darkness falls on October 22nd, look toward the south-southwest sky for a broad triangle formed by the moon, Jupiter (magnitude -2.2) and Saturn (magnitude +0.6). Jupiter will be situated 4° to the moon’s upper right, while Saturn will be nearly 5° to the moon’s upper left.
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications in New York’s lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook.