The Remains of Halley’s Comet Burn and Linger in the Sky

By Phil Plait

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Posted Tuesday, May 7, 2013, at 8:23 PM

Halley’s Comet (technically, Comet 1P/Halley) orbits the Sun once every 75 years or so. Its orbit is highly elliptical, taking it out as far as Neptune and as close to the Sun as Venus. When it nears the Sun it warms up. The ice making up its solid part turns into a gas, creating the familiar fuzzy head and tail, but it also lets loose countless tons of debris: dust, gravel, and pebbles. This jetsam diffuses away from the comet, orbiting the Sun more or less on the same path, but spreading out over time.

Every year, the Earth plows through this material. When it does, the pieces burn up in our atmosphere, generating the Eta Aquarids meteor shower (so named because perspective makes it look like they emanate from the eponymous star). Unlike most showers, the Eta Aquarids are diffuse, with no sharp peak in the number of shooting stars seen. Instead, it rises to a broad maximum over several weeks, topping out at about one meteor per minute. The geometry favors observers in the southern hemisphere.

And that’s just where photographer Colin Legg was on May 4, 2013. From a spot about 100 kilometers (60 miles) south of Newman, Western Australia, he set up his camera hoping to catch a meteor or two. What he got instead was pretty magical:

A meteor flashes, while the remnants of two others still glow in the Australian night sky. Click to enedmondenate.
Photo by Colin Legg, used by permission

Oh, do I love this shot! First, obviously, in this 20-second exposure he caught a bright meteor on the fly, streaking down to the horizon. But those two wiggly orange glows are actually the leftover burned-out trails (called trains) from previous meteors! It doesn’t happen often, but meteors will sometimes leave behind these persistent trains, glowing eerily for several minutes. They’re typically at heights of nearly 100 kilometers, but even that thin air is subject to wind, slowly shearing the trains into fantastic shapes.

Catching one persistent train is pretty lucky, but two in one shot… and with a bright meteor at the same time? Amazing!

The background is fantastic as well. The Milky Way looms high over the horizon, with the dark dust cloud of the Coalsack seemingly poking a hole in it near the tree line. You can just see Crux, the Southern Cross, below the Coalsack, and the bright star Alpha Centauri directly above the Coalsack, right in the middle of the Milky Way.

On the left, the fuzzy patch is the Small Magellanic Cloud (or SMC), a dwarf satellite companion galaxy to the Milky Way, and one of the farthest objects you can see with the naked eye; it lies roughly 200,000 light years away. There’s also a Large Magellanic Cloud (LMC), but it’s behind the trees and just barely too low to see in this picture.

The star above the SMC is no star: That’s 47 Tucanae, a globular cluster. It’s a ball of hundreds of thousands of stars held together by their own gravity, and one of just a couple you can easily see with the naked eye. The other, Omega Centauri, is actually the bright “star” just to the left of the meteor!

My oh my would I love to get this view. From Boulder, though, the Earth itself is stubbornly in the way. I’ve been to Australia, and was able to soak up the southern skies (and once, just once, a trip-of-a-lifetime to the Galapagos Islands, on the Equator, affording a nice view of that part of the sky as well). I remember, after days of rain, heading up Mt. Stromlo on the first clear night, getting out of the car, and seeing both the Magellanic Clouds for the first (and only) time. I had studied a star that blew up in the LMC for my PhD, and to be able to actually see that wee fuzzy patch with my own eyes, to know that the photons registering on my retina had traveled for nearly two hundred thousand years to reach me… I choked up. It was a very emotional moment, and one I will never forget.

And one I am strongly reminded of because of Legg’s photo. I do so love astronomy, and it’s nice, sometimes, to be reminded why.