At 11:50 p.m. Eastern on Thursday night, skywatchers in the eastern half of the nation gazed toward the heavens, hoping to catch a predicted “outburst” of Alpha Monocerotid meteors.
But ... they didn’t.
Sure, a few lucky folks spotted a handful. In Georgia, one observer witnessed about two dozen “faint meteors,” according to Spaceweather.com; another stargazer in Germany saw 15, while in North Carolina the lucky number was 10. Those numbers are a far cry from the several meteor-per-minute rates advertised leading up to the event. So what happened?
“The deal is that we don’t know the parent comet [that sparks] the Alpha Monocerotids,” explained Bill Cooke, a scientist with NASA’s Meteoroid Environment Office.
Cooke believes that assumptions made about the instigating body’s orbit may have contributed to the botched predictions. Among these was assuming that Earth passed through the heart of the comet’s remnant debris stream in 1925 and 1935, when some astronomers reported a bona fide outburst of meteors was seen.
But Cooke argued this may not have been the case. “I could find no meteor rate numbers for the 1925 outburst” he wrote in a blog post Tuesday. “Just that it was short, with a fair number of meteors.”
In 1995, another sputtering of meteors was observed. Astronomers assumed that the 1995 show represented Earth being sideswiped by the edge of the debris stream. They used that, and a presumption that 1925 and 1935 were more direct hits, to model a possible orbit for the unknown comet.
“They came up with a comet orbit on this assumption that wasn’t correct,” Cooke said.
On Tuesday, he expressed skepticism on his blog, given exactly these concerns, writing, “I now think there is a pretty good chance there may be no outburst at all.”
There was, however, a small increase in the number of visible meteors. And Cooke mentioned that the pair of scientists who predicted the outburst got the timing spot-on.
“Someone in Georgia saw about 20 of them,” Cooke said. “In the Canary Islands, same. And, radar up in Canada, they got a handful of [meteors.]"
The meteors that people saw weren’t that spectacular, either: “Typically they were faint. So kind of interesting.” But he noted that there were “very few fireballs unlike Perseids or Geminids or Leonids."
But it’s not just an erroneous prediction that disappointed hopes of catching something out of this world. Cooke also points to problems with how the media communicates the intensity of a meteor shower.
“What the forecasters gave were zenithal hourly rates, which is the idealized thing that never occurs in reality” Cooke said.
Zenithal hourly rates, or ZHR, are the number of meteors an observer would see in a given hour under ideal viewing conditions. That means no moon, crystal-clear air, no light pollution, and the radiant point of the meteor shower positioned directly overhead. Not to mention that they would have to be able to scan the entire sky at once. That just doesn’t happen.
“When you talk to the general public, they want to know how many meteors they’re going to see. They don’t want idealized numbers,” Cooke said.
When Cooke was making his predictions for the meteor shower, he looked to past eyewitness accounts.
“I just took the actual observations and worked from them rather than this idealized rate,” he said. “That’s why I was trying to tamp down people’s expectations. My thinking was you’d see just a few tens of these moderately bright meteors."
He remembers thinking, “That’s not going to go over well with people.”
Cooke did mention that this meteor shower, even if it had delivered in its entirety, would have been nothing, compared with the epic “meteor storms” of the Leonids or Draconids.
The Leonids produced a prolific meteor storm in 1833 and again in 1966. During those episodes, rates briefly topped 20 to 40 meteors per second.
Unfortunately, meteor storms like that are unlikely during our lifetimes.