No one knew about the Comet NEOWISE until this past March, and why would they? Turns out, it only comes our way once every 6,766 years.
But we’re pretty lucky it’s in our neighborhood now. John Keller, the director of the Fiske Planetarium at the University of Colorado in Boulder, says it’s the most exciting comet to be seen in the Northern Hemisphere in more than 20 years.
“The Comet Hale-Bopp was the last really good Northern Hemisphere comet, back in 1997, and Comet NEOWISE is performing equally well,” Keller said, adding that the sudden appearance of NEOWISE has been “hugely surprising.”
According to NASA, NEOWISE was discovered by (and named after) its Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission, which detected “the icy visitor” on March 27 using its “two infrared channels which are sensitive to the heat signatures given off by the object as the sun started to turn up the heat.”
When it became visible to the naked eye earlier this month, Comet NEOWISE could be seen in the morning sky before sunrise. Starting this week, it’s been visible after sunset.
“If people haven’t seen a naked-eye comet, they can try to look below the Big Dipper right after sunset,” Keller said. “With binoculars or the naked eye, you will see a comet with a fuzzy tail extending away from sun.”
Comet NEOWISE was nearest the sun on July 3 and now is on its way back toward the far reaches of the solar system. Its near passage by the heat of the sun causes the celestial light show.
“Comets are super-small ice balls, five to 10 kilometers, and they really need to have a lot of out-gassing in order to be visible in the way we’re seeing Comet NEOWISE,” Keller said. “The ice in the comet’s nucleus is sublimating — it’s going from a solid to a gas — and it’s releasing both an ion tail and a dust tail because there is dust embedded in the ice. What we’re seeing is the reflected light from that gas and dust that has sublimated off the ice ball.”
In a related astronomical phenomenon, the Perseid meteor shower is about to begin. Keller said it will be a few weeks before it gets good, with the peak occurring the second week in August, but it’s definitely something to watch for.
“I would not tell your audience that going out this weekend is going to show the Perseids,” Keller said. “I would say over the next two weeks, as we move toward the 11th (of August), if you see bright flashes in the sky, those may be part of that Perseid meteor shower stream.”
The Perseid meteor shower is caused when the Earth passes through dust left in the wake of the Comet Swift-Tuttle, which continues to orbit the sun.
“We pass through the dust cloud and get lots of meteors,” Keller said. “The Perseids are kind of an Old Faithful of meteor showers. They always have like 60-80 meteors per hour, so they are a pretty reliable storm. The other good ones are the Geminids (December) and the Leonids (November).”
