If you are up late on this last Friday night (Oct. 25) in October — or during the predawn hours of Saturday (Oct. 26) — two objects will likely immediately catch your eye if the sky is clear: a waning gibbous moon and Jupiter.
The waning gibbous phase, which is 56 percent illuminated, will emerge from above the east-northeast horizon around 11:20 p.m. local daylight time. And shining brightly, roughly 7 degrees above it, will be the largest planet in our solar system, Jupiter.
Your clenched fist measures about 10 degrees across at arm’s length, so the moon and Jupiter will be separated by roughly three-quarters of a fist. It is, of course, an illusion of perspective: the moon is only 248,000 miles (399,300 kilometers) from Earth. Meanwhile, Jupiter is 451 million miles (726 million km) away — over 1,800 times farther out in space compared with our natural satellite. [Best Stargazing Events of October 2013 (Sky Map Gallery)]
Best views early in the morning
Next to dazzling Venus, Jupiter is the best observer's planet during the fall and early winter. But Venus will quickly exit the evening sky early in January, leaving Jupiter unchallenged in the evening sky for the rest of the winter and on into early spring.
Look for Jupiter currently glimmering balefully above the east-northeast horizon by 11 p.m. local daylight time. But the gas giant will not reach an altitude of 30 degrees above the horizon — one-third of the way up in the sky — until 1:30 a.m. For some, that's considered to be the dividing line between objects that are "low" versus objects that are considered to be "well placed." Sharp telescopic views are seldom possible until an object reaches an altitude of 30 degrees, given the typical turbulent state of Earth's atmosphere.
Right now, Jupiter is in the constellation of Gemini, the Twins, near the star that marks the waist of the twin brother Pollux. Gemini is also where the ecliptic — the pathway of the sun, moon and planets — comes farthest north. This gives northern observers a decided advantage, for the farther north a planet is, the more time it spends above the horizon and the higher up over the southern part of the sky it will appear.
When Jupiter reaches its highest point in the southern sky, just after the first light of dawn twilight begins breaking over the eastern horizon, it will stand about 55 degrees high for Portland, Ore., and Minneapolis/St. Paul; 60 degrees for Salt Lake City and Philadelphia; 70 degrees for Houston and New Orleans and 75 degrees for Brownsville, Texas, and the Florida Keys.
Two eclipses for the price of one
Through a telescope, Jupiter is always a fascinating sight. Light and dark cloud belts in the giant planet's atmosphere appear to parallel the equator and slowly change, while the famous Great Red spot, some 30,000 mile (nearly 50,000 km) long, now appears rather pale and has been described with hues ranging from very pale beige to salmon pink.
The other attractions are the four Galilean moons. During the overnight hours of late Friday night into Saturday morning, binoculars or a telescope will readily show all four of these big moons. Three will be on one side of Jupiter — Callisto (IV), Io (I) and Europa (II), with Ganymede (III) sitting by itself on the other side.
Interestingly, Io and Europa will appear relatively close to each other, and both will end up being eclipsed by Jupiter's shadow. Io will go first at 4:18 a.m. ET (1:18 a.m. PT). Nineteen minutes later, it will be Europa's turn. If you look at Jupiter anytime after that, you'll only see two of the remaining satellites, Callisto on one side, Ganymede on the other.
Editor's note: If you snap an amazing photo of the moon and Jupiter, or any night sky view, that you'd like to share for a possible story or image gallery, please contact managing editor Tariq Malik at email@example.com.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.