Later this month, skywatchers in Africa can watch a star disappear from view thanks to a quirk of celestial arrangements.
The mission of the European Space Agency (ESA) Gaia, which was launched in 2013, has been a powerhouse of observational astronomy, having a huge impact on the way scientists study the sky. Of map the galaxy in stunning detail for find a star cluster which was hidden by glare in other telescopes, the spacecraft’s ultra-sensitive instruments proved invaluable in studying the Milky Way.
But Gaia doesn’t just help us understand distant stars; it also shapes our view of our neighboring worlds and their moons. In 2017, scientists used data from Gaia to predict for the first time what scientists call a star’s occultation in Jupiterthe moon Europe.
Pictures: Europa, Jupiter’s mysterious icy moon
Occultation occurs when one object is covered by another seen from Earth. For example, a total solar eclipse is a kind of occultation of the sun by the moon, but an occultation that is very obvious to those in the right place to see it.
Conversely, an occultation of a distant star by an extraterrestrial satellite would go unnoticed by almost everyone.
Such occultations can only be seen from a narrow path across part of the Earth’s surface, making them a rare sky-watching treat. But for astronomers, occultations can be even more special because these events provide rare opportunities to refine the orbit and shape of a distant world.
And scientists now say that such an occultation will occur on June 19 (June 18 in the US, where the event will not be visible), because Europa is once again about to occult a star as expected at using data from Gaia. This event will be even more remarkable than the previous one, in particular for the astronomers of the Paris Observatory, who are helping ESA scientists to prepare a mission to study Europa and the neighboring moons.
“What makes the upcoming Europa occultation special is that this moon will be in Jupiter’s shadow at that time,” agency officials wrote in a statement. statement. “Because Jupiter will block this sunlight during the occultation, observers won’t know Europa is there until it temporarily causes the star to disappear.”
Immersed in the shadow of Jupiter itself, the pitch-black disc of Europa will eclipse the star like the new moon passing in front of the sun, making the distant star appear to die out and then re-ignite shortly thereafter. For a brief moment, observers on the ground will be able to stand in the shadow of Europa, cast by the faint light of a star several light years away. By precisely timing the passage of this shadow, ESA astronomers will be able to learn more about Europa’s orbit.
ESA plans to launch Jupiter Icy Moons Explorer, or JUICE mission next year, beginning a long journey to Jupiter where the spacecraft will perform an in-depth survey of both Europa and its larger sister moon, Ganymede.
In tandem with NASA’s Europa Clipper mission, JUICE will reveal one of the most fascinating worlds in the solar system in stunning detail. Some scientists think that Europa might be habitable, but to figure out whether or not that’s the case, they have to look beneath its icy surface. To achieve the best results, Europa’s orbit must be tightly constrained, which is why observing this occultation is so important to ESA.
“It will help spacecraft operators navigate between these icy worlds more precisely, and it will help scientists draw conclusions from flyby data,” ESA officials wrote in the statement. “For example, knowing the spacecraft’s exact altitude above a moon’s surface will make calculations about the moon’s interior more accurate.”
If you’re in the right place, you could observe this event yourself with just a modest telescope. The occultation will carve a path across southern Africa, with the midline passing through Namibia, Botswana and Zimbabwe. Farther east, the invading sunrise will make the sky too bright to see the occultation.
In the early morning hours before dawn on June 19, skywatchers across southern Africa will see Jupiter rising in the eastern sky, following Saturn and the moon with Mars not far behind.
Looking at Jupiter at 5:00 a.m. local time in Namibia, Botswana and Zimbabwe (03:00 GMT or 23:00 EDT on June 18), it will appear as if the four galilean moons (Europe, Ganymede, Callisto and Io) are visible. But by then Europa will actually be completely in Jupiter’s shadow, and the fourth visible light will actually be a 10th magnitude star in the constellation Pisces.
Europa should pass in front of this star at precisely 03:05:57 UTC, but local times will vary by longitude, so be sure to be at the telescope earlier to be safe. It’s only during occultation that you really see all four moons (one in silhouette) as the star disappears, leaving only three points of light flanking Jupiter. As Europa eclipses again, the star will reappear in your telescope.
If you want to take your observations to the next level, be sure to precisely time the start and end of the transit and send this data with your observation location to the Paris Observatory (email@example.com). With your help, astronomers will be able to calibrate their own observations and help ESA get the most out of the JUICE mission!
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