U.S. and Russian officials declined to discuss what the rocket was used for, but experts outside of the government say it was launched as part of a project to bring materials to a space station. They say they rocket's body likely detached from the craft bringing materials into space and burned up as it started to go out of orbit.
"It's not something people need to worry about," said David Wright, a space-debris expert who is co-director of the Union of Concerned Scientists.
The fireball seen over Arizona, Nevada and California was an SL-4 rocket body booster from Russia that was launched Monday, said U.S. Strategic Command spokeswoman Julie Ziegenhorn.
People who witnessed the burning light across the sky expressed a range of responses on social media.
Some speculated that it was a meteor, while others resorted to humor, punctuating their comments by using a rocket emoji and saying the light across the sky looked Santa's sleigh. Some people also expressed distrust about the U.S. government's comments on the rocket.
"I was kind of freaked out to see something like that blowing up in the air and you don't know what it is," said Gunnar Lindstrom, who saw the streak of light as he exited a car at his Las Vegas apartment complex and initially believed it was an airplane.
Lindstrom, a bartender with a side business as a videographer, said his first instinct was to grab his cellphone camera. "I was upset I couldn't grab my real camera," Lindstrom said.
If you took photos or videos of the mysterious light, tag your photos and videos on Twitter, Instagram, or Facebook with #abc7now.