Key Takeaways:
- U.S. West Coast observers are positioned to view the simultaneous transit of shadows cast by Jupiter's moons Io and Europa on its cloud tops.
- Approximately 40 minutes pre-sunrise, Jupiter will be nearly 80° high in the southern sky, revealing Io's shadow near the disk's center and Europa's shadow commencing its transit near the eastern limb.
- The ingress of Io onto Jupiter's disk is predicted for 6:44 A.M. PDT, occurring shortly before local sunrise.
- Ancillary astronomical data, including sunrise, sunset, moonrise, moonset times, and the Moon's phase (18% waxing crescent), are provided for a specific geographic reference (40° N 90° W).
Looking for a sky event this week? Check out our full Sky This Week column.
October 24: The Moon and Antares
U.S. West Coast observers are in luck this morning, as Io and Europa cast their shadows together on Jupiter’s cloud tops as twilight is brightening the sky — an event that occurs after sunrise for the rest of the U.S.
40 minutes before sunrise, Jupiter is nearly 80° high in the south. Through a telescope, you’ll spot a pair of shadows on the disk — one nearly halfway across its trip from east to west, and the other near the eastern limb. The shadow roughly in the center of the planet is Io’s, cast by its parent moon just off the eastern limb. The dark spot that has just begun crossing and is closer to the limb belongs to Europa, to Io’s east. (Much farther east of this pair is Ganymede, while Callisto lies alone to the planet’s west.)
See how long you can follow the moons and their shadows as the sky brightens. Io begins to transit at 6:44 A.M. PDT, not long before sunrise (note the exact time of sunrise will depend on your location).
Sunrise: 7:22 A.M.
Sunset: 6:06 P.M.
Moonrise: 11:35 A.M.
Moonset: 8:18 P.M.
Moon Phase: Waxing crescent (18%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 10 P.M. local time from the same location.
