Pair of brightening comets could make for fine fall viewing

By: Kevin Bunch | C&G Newspapers | Published November 6, 2013

 The Hubble Space Telescope snapped this image of Comet ISON moving sunward on Oct. 9, as its tail begins to take shape for its close encounter with the sun. The comet’s closest approach to the sun is expected Nov. 28, and its closest approach to Earth should be around Dec. 26.

The Hubble Space Telescope snapped this image of Comet ISON moving sunward on Oct. 9, as its tail begins to take shape for its close encounter with the sun. The comet’s closest approach to the sun is expected Nov. 28, and its closest approach to Earth should be around Dec. 26.

Photo courtesy of NASA, ESA and Hubble Heritage Team (STScl/AURA)

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MACOMB COUNTY — Two different comets currently whipping around the inner solar system could prove to be nice sights in the night sky in November and December, if astronomical projections are accurate.

Bob Berta, public outreach officer with the Warren Astronomical Society, said while it is too early to know for sure if one of the comets, ISON, will brighten to the point where a person could see it with binoculars or the naked eye, it should be apparent near the latter half of November. Alternately, the comet could break apart during its current sojourn near the sun.

“Once (observers) start seeing it, they’ll be able to determine if it will be visible,” Berta said. “Comets are kind of nebulous items. You can’t really predict if they’re going to be bright enough to see.”

Case in point, Berta said that over the course of a week in late October, another comet, known as LINEAR — both comets being named after the observation programs that discovered them — brightened on the apparent magnitude scale from a 14, which is the brightness of Pluto, to an 8, which is the brightness of Neptune: visible with a telescope or binoculars. He said at that level of brightness, it can easily be seen with a small telescope or a good pair of binoculars.

Wayne State University astronomer David Cinabro said it’s difficult to predict comet brightness due to comets not being truly solid objects.

“They’re basically big chunks of ice, and the question is how do they melt as they approach the sun, and it’s hard to predict that,” Cinabro said. “If they melt in such a way that they get really big, they get really bright. If they don’t get really big, they don’t get really bright. It’s difficult to predict how they’re going to behave.”

The size of the cometary coma, a cloud made of melting ice and gas surrounding the core, as what gives a comet its brightness, Cinabro said.

ISON currently is located in the constellation Leo, found in the eastern sky, while LINEAR is in the northeast sky in the nearby constellation of Coma Berenices, though Berta said that patch of sky is usually below the horizon until after sunset. Cinabro said both comets would likely be most visible in the early morning skies due to their proximity to the sun, though ISON should be visible earlier in the evening.

ISON should make its closest approach to Earth Dec. 26, and its closest approach to the sun in late November. LINEAR makes its closest approach to the sun around January. Both should be near each other in the mid-December sky.

Berta said that while none of the four astronomy clubs in the area — the Warren Astronomical Society, the Ford Amateur Astronomy Club, the Seven Ponds Astronomy Club, and the Oakland Astronomy Club — currently have anything special planned for the comets, he said the Warren group at the least will be updating its website, if the comets become more visible, on any special activities. Most likely, Berta said, all four groups would have open houses.

Since several members of the Warren Astronomical Society are astrophotographers, he said it also was possible that members may take photos of the comets and post them on the website.

He added that the Warren Astronomical Society has an open viewing scheduled around 7 p.m. on Nov. 9 and Dec. 14, and if the comets are suitably visible, the public is welcome to come and observe them with the club members’ equipment, as well as get help locating it with visitors’ own telescopes. They observe in Ray Township at the Wolcott Mill MetroPark, where the club maintains the Stargate Observatory.

“It’s dark enough there that you could see it there,” Berta said. “If you’re down around Detroit or the more built-up areas, where there’s more residential housing and shopping centers, (it’s harder), but up around our observatory, you should be able to see it well.”

If either comet ends up breaking apart in the face of the sun’s heat, Berta said observers could still get a good, bright show out of it, but he stressed that comets are not easy to predict.

“In the past you hear about comets that would be a great show, and then it burns out,” he said. “Then, other times, there was one — had to be in Australia, and the southern hemisphere — that was just a huge swath across the sky.”

Cinabro said both comets are sun-grazers, meaning they come very close to the sun, and until the grazing actually happens, it is impossible to say if they would simply dissipate when coming close to the sun or if they would break apart and shine a lot of light before melting away.

He said both comets are believed to be coming to the inner solar system for the first time, making it difficult to make predictions — both on their behavior and whether or not they will ever return. A comet’s period, or orbit, is hard to predict if it takes the ball of ice into the furthest depths of the solar system.

“The headache is you don’t really know what happens to them when they are really far away,” Cinabro said. “There’s a lot of unknown stuff out there that gravitationally affects them when they are far from the sun — a lot of very dim, frozen objects out beyond the orbit of Neptune. We really don’t know what that landscape looks like, so it’s very hard to predict when these things will come back in.”

Cinabro said both comets are nonperiodic, so scientists do not know if or when they will return. Furthermore, it is entirely possible both comets are on “ejection trajectories,” which would send them out of the solar system.

Very few scientists continue to seek out comets professionally, Cinabro said,  largely only finding them while searching for asteroids. Comets are still a popular target for amateur astronomers, however, who have discovered most of the more recent ones. Cinabro said comets are both visually and historically appealing.

“They’re incredibly beautiful. I don’t know if you’ve ever seen a bright comet in dark skies, but they are amazingly pretty,” he said. “(The other thing is) their past association, when they were thought of as harbingers of bad things, or at least change. Now, we don’t think that, but there is still that past appeal that they mean something, so there’s still that thought that they are the harbinger of something.”

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