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Observe Gas Giant Jupiter Occulting the Moon on the Morning of May 17

On May 17, the gas giant Jupiter and its four brilliant Galilean moons will pass behind a very thin crescent moon early in the morning. The moon and Jupiter will put on a stunning show in the early morning skies of tomorrow.

Image credit: Chris Vaughan Starry Night

When will the occultation of gas giant Jupiter and its moons occur?

On Wednesday, May 17, gas giant Jupiter and its four brilliant Galilean moons will pass behind a very thin — only 5% lit — waning crescent moon as seen from North America sometime before or after daybreak (depending on where you are). If you want to view the event the greatest place to view this occultation is from the western third of the United States and Canada, where it occurs in part before sunrise. It might be possible to watch Jupiter disappear without using any optical equipment in areas where it happens in a somewhat dark sky, though binoculars would provide a better view and you’ll need a telescope to track its moons. 

The crescent moon’s leading, light limb will initially pass over gas giant Jupiter, taking a minute or more to slowly move over the face of the big planet. About an hour or more later, Jupiter will gradually emerge from behind the dark edge of the moon.

Which states or regions will have the best views of Jupiter’s retreat behind the moon?

Washington, Oregon, a large portion of Idaho, Nevada, Utah, Arizona, New Mexico, northern and eastern California, and the western half of Texas will have the best views of Jupiter’s retreat behind the moon. Gas Giant Jupiter and the moon will be visible from these locations low on the eastern horizon against a twilight sky that is starting to get brighter. 

Which states or regions will not have the best views of Jupiter’s retreat behind the moon?

Unfortunately, Jupiter will slip behind the moon before the moonrise for parts of western and southern California; by the time the moon first rises above the horizon (for cities like San Francisco, Los Angeles, and San Diego), Gas giant Jupiter will already be behind the moon.

Which regions are most favorable for the reappearance?

The western half of Oregon, Nevada, Arizona, and all of California are the most favorable regions for the reappearance. Near and along the Pacific coast of the Golden State, the sun will be about eight degrees below the horizon, while the moon will be a similar height above the horizon. It may be rather impressive to see gas giant Jupiter emerge from the shadow of the moon’s dark limb in the middle of dusk.

Wherever the sun is at least five degrees below the horizon, the Galilean satellites can be seen; the sky should still be enough black to see them with a telescope. Europa won’t be visible because it will be completely hidden by Jupiter, but Io will be very close to Jupiter’s eastern limb. Callisto and Ganymede will be located to Jupiter’s west. In fact, as seen from California, these two satellites appear 11 and 7 minutes earlier than gas giant Jupiter does. These satellites will “ooze” into view instead of appearing suddenly like a star because their disks have a noticeable angular size. 

Where will the occultation of gas giant Jupiter occur during the day?

Wherever Jupiter is occulted during the day, which will be anyplace east of a line approximately extending from middle Montana to central Louisiana, it will occur against a brilliant blue sky (if the weather cooperates, of course!). But this intriguing event might still be visible through your telescope. 

How can I locate the moon and gas giant Jupiter before dawn?

Locating the moon and Jupiter before dawn and following them throughout the day is probably the simplest approach. Look just north of due east, very close to the horizon, around 30 to 40 minutes before sunrise. You can see the thin crescent of the moon there, with Jupiter just a few degrees to its left. 

Why is it difficult to find the moon and Jupiter after sunrise?

The moon and Jupiter are often higher than the sun and far to their right when the occultation occurs in the early morning. Finding the moon and gas giant Jupiter at all will be difficult if your quest is conducted after sunrise. Give yourself plenty of time to complete this in advance. The transparency of the sky, or the intensity of its blue color, will determine a number of things. Generally to the right and, for most places, around 15 degrees higher, aim your scope at the sun at a distance of about 28 degrees (almost three fist-widths at arm’s length). 

What organization provided the viewing data for the occultation event?

We gratefully acknowledge the International Occultation Timers Association (IOTA) for providing the viewing data from this website, which offers times for 953 various places within the occultation viewing zone. The website displays all times in Universal Time (UT). Along with a map showing the visibility area, IOTA also provides details on the sun and moon’s altitudes. While the moon will occult gas giant Jupiter in the morning for observers in North America, Central America, and the Caribbean, northern European observers will witness the spectacle in the late afternoon. 

What does the asterisk (*) next to the time indicate?

The local disappearance and reappearance timings for 17 particular cities in the United States, Canada, and Mexico are listed in the timetable below. An asterisk (*) next to the time means the event will take place when the sun will be below the horizon where it will be taking place. The moon will be below the horizon for this occasion, according to dashes for information about disappearances in Los Angeles.

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