Jupiter Greets Crescent Moon in the Pre-Dawn Sky

On Friday, October 28th, the waning crescent Moon and brilliant Jupiter get together for an early morning conjunction.

vic2016_oct28moThe morning commute has been kind to me lately. Orion, the Hunter, waits outside my back door each day, standing high in the southwest. As I back out of my driveway and swing around to the north, I take just a few moments to pin down Polaris, a not-very-bright but still reliable waymark for the amateur astronomer. During the remainder of my 45-minute commute, I head almost due east, which is a fortunate direction, because dark morning skies plus a clear view to the east add up to something great right now: good looks at Jupiter on my way to work.

You may be accustomed to thinking of Venus as the "Morning Star," but that bright light you saw in the east this morning was Jupiter, shining at magnitude –1.7. Jupiter began peeking its head over the horizon at dawn about two weeks ago. Each morning, it edges a bit higher relative to sunrise: today (October 27, 2016), Jupiter stands about 11° high for observers at latitude 40° north one hour before sunrise; two weeks from now (November 10, 2016), look for it 30° above the horizon in the east-southeast about an hour before Sun comes up.

Moon occulting Jupiter

When things line up along our line of sight just right, the Moon occults (hides) Jupiter from view. Compare this view, taken from Korinthos, Greece, on July 15, 2012, with the scene you'll see on Friday morning (above). The Moon will appear close to Jupiter on Friday, but not quite close enough for an occultation.
Konstantinos Christodoulopoulos

The other joy in my morning commute has come from the waning Moon. Less than a fortnight ago, I cast a long shadow on my back porch as I left the house, thanks to the light of the full Moon, which hadn't quite set in the west. Since then, I've been watching the lit part of the Moon's face grow slimmer, moving toward the new Moon on October 30th. Each morning, thanks to its motion around Earth, the thinning Moon has shifted eastward in the sky. Day by day (morning by morning) the Moon steps eastward, on its way to a having a head-to-head chat with Jupiter.

Tomorrow morning (Friday, October 28th) the Moon and Jupiter will be in conjunction, less than 2° apart, making for a pretty naked-eye pairing for viewers at mid-northern latitudes. If you have a clear view to the eastern horizon, the best observing will be about 90 minutes before sunrise, though Jupiter will be quite low. It rises about 5:20 a.m. local time, so it will be less than 10° high that early in the morning. Still, if you can catch it in the dark sky, binoculars should reveal Jupiter's four Galilean moons as well as Gamma (γ) Virginis (Porrima). As twilight brightens, you'll find it increasingly difficult to tease out Jupiter's satellites and Gamma will fade from your field of view.

In the summertime, I keep a running tally of Vega's appearance: how early in the evening can I find it overhead? When planets have early morning visibility in the winter, I play a similar game: when will I lose the planet in the brightening sky? Jupiter should remain visible to the naked eye, rising subtly higher, until about an hour before sunrise. Look away and then look back  — can you find it again? On this occasion, the crescent Moon should point the way back to the planet. Without the Moon, however, it's much more difficult! Keep an eye on your watch this fall and let us know how long you kept Jupiter in your sights.

2 thoughts on “Jupiter Greets Crescent Moon in the Pre-Dawn Sky

  1. Joe StieberJoe Stieber

    The close grouping of the Crescent Moon, Jupiter and Porrima was a lovely sight this morning! I’ve uploaded a snapshot to the S&T gallery. BTW — note that you have a typo in the story. It says Porrima is Gamma Geminorum, but it should be Gamma Virginis.

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