As Ernest Merrill was driving down Route 113 in West Newbury on Saturday night, he glimpsed what many astronomers refer to as a once-in-a-lifetime sighting - a fireball falling from the sky.

Merrill's friends think he's crazy, but scientists say it's entirely possible. Referred to by astronomers as a "fireball," it is caused by a larger-than-average particle, perhaps from a Leonid meteor shower, shooting through the earth's atmosphere and blazing a fiery trail to the treeline.

The object was like nothing 67-year-old from Salisbury and his wife, Laura, had ever seen before.

"We were riding along, and it was dark," Merrill said. "We were talking about the moon, and all of a sudden this thing came into the Earth's atmosphere and was shooting across the sky with a tail, like fire coming off and going all the way toward Haverhill. We watched it going down, and it finally disappeared by the trees. It came into the Earth's atmosphere and it was burning up as it was coming down."

Shooting stars have been plentiful this month, though the peak opportunity to see one from the 2009 Leonid meteor shower passed on Nov. 17. But some days after Earth passed through the field of comet debris that causes the cascade of stars, stargazing enthusiasts are still reporting mysterious objects streaming across the horizon.

It was approximately 5:30 p.m. when the object appeared out of nowhere, Merrill said, and that's just how sightings occur for lucky Earth dwellers fortunate enough to be looking upward when one of the rare fireballs makes its way to Earth, said Kevin Ackert of the North Shore Amateur Astronomy Club out of Groveland.

"Most people get to see something like that maybe once or twice in a lifetime," said Ackert, who had a similar experience many years ago while driving on Interstate 93 toward Concord.

The object Ackert saw exploded upon impact with Earth's atmosphere, lighting up the night sky with four distinct trails of debris, then disappearing again. But that's not what stargazers typically see during a meteor shower.

That fiery display, similar perhaps to what Merrill saw on Saturday, is a rare occurrence that meteor experts track as "fireball sightings," but have a hard time capturing on film due to their unpredictable nature. It was an unusual sight for Merrill, who's still not sure it could be classified as something from a common meteor shower. And he's not the only one who saw it.

Merrill said he called his daughter, Laurie, in Nashua, New Hampshire, following the sighting, and she said she saw it as well. And when he and his wife reached their destination - Building 19 in Haverhill - on Saturday night they told their story and found another woman in the store had seen the object blaze across the sky, too.

But when Merrill called the police, they claimed to his astonishment that they had received no reports of strange, unidentified flying objects in the area.

"Are we cracking up or something?" Merrill recalls thinking on learning no one had reported the sighting. "This thing was big. If I took a ruler and put it up to the sky, this thing would be 6 inches wide in the sky."

Larger-than-average meteors are often seen in association with known meteor showers, according to NASA's informational data compiled on meteor showers. And Ackert believes it's possible the Merrills saw a larger-than-average fragment from the comet Temple Tuttel, which spurred the debris field known as Leonids as it orbited the sun in 1466. The Earth sidles close to that debris field every 33 years or so and produces spectacular meteor storms every November for the few years surrounding the peak, he said.

"It was most likely from Leonid," said Ackert of the fireball. "The Leonid period this year, you could see from the 16th right through the 20th. It's even possible to see it a little later."

As an amateur astronomer with a day job working for a property management company, Ackert serves as treasurer of the Northshore Amateur Astronomy Club, a nonprofit, 501-3 company that holds star parties in schools across the Merrimack Valley to introduce them to the constellations and to stargazing.

According to the American Meteor Society, the Merrills also could have seen something emanating from another, lesser known meteor shower that hit its peak Saturday night. While the Leonids were present from Nov. 10-21, the Alpha-monocerotids, so named for originating near the Monoceros constellation, peaked on Nov. 21 and was to be detectable in the night sky through last night.

Accompanied by a waxing crescent moon Saturday, the unpredictable shower has been known to become visible every 10 years and presents for a short, spectacular burst of up to 400 meteors an hour.

"The way to tell if it's a Leonid is when you see it, draw an imaginary line back from the direction that it came from," Ackert said. "If it came from the direction of Leo the Lion, it's a Leonid."

An Alpha-monocerotids would originate from the direction of Orion, according to experts.

For those who might have missed the fireball across West Newbury, as well as the popular Leonid shower, take heart. The Geminid meteor shower will peak on Dec. 14, and the moon will again be favorable for good viewing, Ackert said.

Merrill, who keeps a $300 telescope in his basement that he picked up for $15 at a yard sale, has been inspired to dust it off and use it. He's even thinking of investing in one with a better capacity.

"I'm 67 years old, and I've never seen anything like that," he said. "I'd like to find out how many people saw this. One in a million chances, and I saw one."