The mysterious fireball that streaked across the night sky yesterday — visible from Massachusetts to Maine and beyond — was likely a meteor about the size of a golf ball passing overhead at between 10 and 30 miles per second before burning up in the atmosphere, an astronomer told the Herald.

The unannounced celestial wonder left commuters and nighttime strollers awestruck and dumbfounded just before 6 p.m. last night, as they described on Twitter a “ball of light” that was “fiery” with “a greenish glow.” Others saw a “blue flash of light” that was “very bright.”

Kenneth Janes, an astronomy professor emeritus at Boston University, said he doesn’t believe it was part of a meteor shower, the remains of broken up comets falling to Earth. The last one was about 10 days ago and the next one isn’t until January, he said.

This meteor likely burned up before hitting the ground and was probably very small — otherwise it would have triggered a “tremendous explosion” upon impact, Janes said.

It was also likely between 10 and 25 miles up in the air, keeping it out of range of aircraft. A Massport spokeswoman said Boston Logan International Airport operations reported no impact.

“The ones that would do really serious damage are rare, but not impossible,” Janes said. “These are simply bits of rock in orbit around the sun. These occur every day somewhere on the earth.”

Even in the era of the cellphone camera, few witnesses were able to take photos of the spectacle.

But the white trail of light was captured on the webcam operated by the Mount Agamenticus Conservation Program in York, Maine — an image that was quickly retweeted on Twitter.

It’s hardly the first time that their ’round-the-clock lens caught a natural marvel.

“Sometimes it’ll capture an aurora,” said Robin Kerr, the conservation coordinator. “It’s rare. About five or six years ago, it caught a snowy owl up on a viewing platform. We can see when there’s a meteor shower.”

When it comes to objects that are actually dangerous, Janes said NASA believes it has identified all the bits of space rock that are a half-kilometer or larger in size. In October an asteroid the size of a bus passed between Earth and the moon — “a near-miss,” in astronomical terms, said Janes.

A 10-ton meteorite exploded over Russia with the power of an atomic bomb in 2013, injuring 1,100 people.

Something worse in the future can’t be ruled out, he warned.

“There’s always a possibility,” said Janes. “But keep in mind the last really catastrophic one was 65 million years ago. That’s the one that killed the dinosaurs.”