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On October 20th, 2021,

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dozens of astronomers
gathered near Las Vegas.

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They pointed their telescopes at the sky
and waited for the moment

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that the light from a faraway star
blinked out.

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It was an event so minuscule
it would have been easy to miss.

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Yet the data gathered by scientists
from those few seconds

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helped contribute to the success of NASA's
Lucy mission.

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As the astronomers observed the star,

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it appeared to blink out as asteroid
Eurybates passed in front of it.

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Eurybates is one of seven Trojan asteroids

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Lucy will visit over
the next twelve years.

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The Trojans are clustered in two swarms
that orbit the Sun at the same distance

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as Jupiter, though they're as far away
from Jupiter as they are from the Sun.

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These asteroids are remnants
of the early solar system

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and by analyzing them up
close Scientists can hone the theory

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of how the planets formed
and ended up in their current locations.

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As Eurybates eclipsed the star,

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a phenomenon scientists
call an occultation took place

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whereby a shadow the size of the asteroid
passed over the region.

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The best known example of an occultation
is a solar eclipse, which occurs

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when the moon passes
between the sun and Earth, blocking

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the sun from our view.

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Leading up to the occultation, astronomers
predict the asteroid's shadow's

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path across Earth
and set up dozens of telescopes

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along a line
that's perpendicular to that path.

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Spread out under the asteroid's shadow,
they count the seconds

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the starlight blinks out
as the asteroid passes in front.

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Using the asteroid's known velocity,
it is possible to calculate its width.

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By observing multiple occultations
of the same asteroid, scientists can catch

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different sides of the asteroid
and combine their two dimensional

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silhouette projections
into a three dimensional shape model.

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Observing an occultation
is one of the most reliable tools.,

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scientists have to gather information
about Lucy's target asteroids

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and prepare for flybys of each
of the mission's targets.

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The team will continue to

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observe occultations until Lucy's
last flyby of Patroclus in 2033.