Last week, a sort of “bright spiral” appeared in the sky over Hawaii. Curiously (or not), the shape appeared on the same day that SpaceX launched a satellite of the North American Space Force. For some experts, the spiral arose from propellant ejected by the rocket during the launch of the mission.
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The phenomenon was captured by the Subaru-Asahi Star Camera of the National Astronomical Observatory of Japan and the Japanese newspaper Asahi Shimbun. It is installed on the Subaru telescope, located in Hawaii, and recorded a luminous shape that seems to move across the sky, then disappear.
In a Twitter post, the telescope team suggested that the bluish spiral appeared to be related to the SpaceX launch. Scott Tilley, a citizen scientist, agreed, noting that the spiral appeared in a position that matched where the second stage of the Falcon 9 rocket should have been after launch.
This is not the first time SpaceX launches have generated luminous phenomena in the sky and made the news. Last year, for example, residents of the coast of Florida, in the United States, observed a luminous structure with a shape that resembled that of a jellyfish, which appeared with the interaction of the Falcon 9 rocket with the atmosphere. This phenomenon usually occurs when a rocket takes off in the early hours of the day or a few hours before dusk.
What Caused the “Spiral” in the Hawaiian Sky?
To understand the probable cause behind the appearance in the Hawaiian sky, it helps to understand how Falcon 9 rocket launches happen.
When the first stage (the one that propels the launch vehicle) separates from the second (the one that stores payloads), it begins its return to Earth. After separation, the second stage starts its engine to move to the necessary position to release the satellites into orbit. Afterwards, the remaining fuel is ejected before the stage re-enters the atmosphere. With that, it starts rotating, until it leaves Earth’s orbit and descends to land in the ocean.
As a result, a cloud of frozen fuel crystals appears in a spiral shape that, when illuminated by the Sun, stand out in the sky. Spirals are most often seen over the Pacific Ocean as this is where most Falcon 9 rocket stages descend to be rescued, restored and reused.
Source: Space Weather; Via: Space.com, Chris Combs