On October 20th, 2021,
dozens of astronomers gathered near Las Vegas.
They pointed their telescopes at the sky and waited for the moment
that the light from a faraway star blinked out.
It was an event so minuscule it would have been easy to miss.
Yet the data gathered by scientists from those few seconds
helped contribute to the success of NASA's Lucy mission.
As the astronomers observed the star,
it appeared to blink out as asteroid Eurybates passed in front of it.
Eurybates is one of seven Trojan asteroids
Lucy will visit over the next twelve years.
The Trojans are clustered in two swarms that orbit the Sun at the same distance
as Jupiter, though they're as far away from Jupiter as they are from the Sun.
These asteroids are remnants of the early solar system
and by analyzing them up close Scientists can hone the theory
of how the planets formed and ended up in their current locations.
As Eurybates eclipsed the star,
a phenomenon scientists call an occultation took place
whereby a shadow the size of the asteroid passed over the region.
The best known example of an occultation is a solar eclipse, which occurs
when the moon passes between the sun and Earth, blocking
the sun from our view.
Leading up to the occultation, astronomers predict the asteroid's shadow's
path across Earth and set up dozens of telescopes
along a line that's perpendicular to that path.
Spread out under the asteroid's shadow, they count the seconds
the starlight blinks out as the asteroid passes in front.
Using the asteroid's known velocity, it is possible to calculate its width.
By observing multiple occultations of the same asteroid, scientists can catch
different sides of the asteroid and combine their two dimensional
silhouette projections into a three dimensional shape model.
Observing an occultation is one of the most reliable tools.,
scientists have to gather information about Lucy's target asteroids
and prepare for flybys of each of the mission's targets.
The team will continue to
observe occultations until Lucy's last flyby of Patroclus in 2033.