BETHLEHEM, Pa. — Brad Klein reviews upcoming astronomical highlights with Bethlehem’s "Backyard Astronomy Guy," Marty McGuire.
During the month of November we will continue the look at comets that began here last week. There are three comets currently passing through the inner solar system: Comets 3I/ATLAS, C/2025 A6 (Lemmon), and C/2025 R2 (SWAN).
Comets are generally named for their date of discovery and for the person or scientific instrument used to find them. ATLAS, for example, is an acronym for Asteroid Terrestrial-impact Last Alert System, the robotic telescope array in Chile that detected that so-called "interstellar comet."
Lemmon was not named for the citrus fruit, but for the Mount Lemmon Observatory outside of Tucson, Arizona. And likewise, SWAN is an instrument onboard the Solar and Heliospheric Observatory (SOHO), a European spacecraft. An amateur astronomer used data from the SOHO mission to discover the comet that now bears its name.
Comets are typically compared to "dirty snowballs" of ice and small bits of sand or gravel. As a comet nears the sun, it heats up and releases gasses that create the familiar and unique tail sometimes dramatically visible in the night sky.
“Comets are like cats: they have tails, and they do precisely what they want,” is a quote attributed to the Canadian writer and amateur astronomer, David H. Levy.
He was co-discoverer of the comet Shoemaker–Levy 9, which collided with the planet Jupiter in 1994. It’s clear that comets have tails, but in what way do they seem to have a mind of their own?
“As a comet melts, it's lifespan decreases,” McGuire said.
“Some comets totally vaporize,” and break apart or change their orbit as they are warmed by the sun. And so their exact behavior can not be predicted. It can only be observed.