February 10, 2002: A Comet for New York

(An abridged version of a story that appears in the Astronomy section of this website; click here for the full story.)




Comet SOHO C/2002 C4 (the modest dot to which the arrow points), which I found
on Feb. 10, 2002 on images taken by the SOHO (Solar and Heliospheric Observatory)
spacecraft. Venus is the bright object at the left edge . To the upper right
is a bit of the occulting disk that blocks the sun, in effect creating an artificial eclipse.
(Images courtesy of the SOHO/LASCO consortium. SOHO is a project
of international cooperation between ESA and NASA.)




By celestial measure it was a tiny thing, a chunk of ice and dirt perhaps the size of a bus, and its lifetime—which extended back to the dawn of our solar system—was fast nearing an end. Locked in an Icarian plunge almost straight towards the sun, it was already within 5 million miles of the solar furnace, and each hour brought it a few hundred thousand miles closer. The comet’s already depleted core—whittled away by successive encounters with our star over millennia—steadily melted, releasing its last reserves of gases, water vapor, sand, and dust. For a few hours after I became the first to detect the comet now designated C/2002 C4 (SOHO), its smudge of light held steady, then it rapidly faded as the last of its material vaporized. Within 12 hours it was gone, though its scattered molecules will continue circling the sun in roughly the same orbit.

Ever since I got started in amateur astronomy in the early 1970s, it had been a dream of mine to discover a new comet, but I never could have imagined in those early years that I would find it on a rainy night, from my New York City apartment. The comet was visible on images taken by the SOHO (Solar and Heliospheric Observatory) spacecraft that are regularly posted to the Web. SOHO, a joint project between NASA and the European Space Agency, was launched in late 1995 to study the sun and its vicinity. Along with the solar phenomena such as flares, prominences, and coronal mass ejections that the probe was designed to study, some of SOHO’s images contain comets—over 700 to date. NASA and ESA professionals found the first SOHO comets; Terry Lovejoy of Australia became the first amateur astronomer to find one, soon after the images were first made available to the public on the Web in late 1999. Soon a trickle of amateur discoveries became a flood, and now almost all SOHO discoveries are found by a far-flung band of enthusiasts who scour the latest images on their home computers.

Although SOHO’s bounty includes the smallest comets ever discovered (it is generous to even count some of them as comets, as they can be as small as 5 meters in diameter), most are fragments of the brightest known comets, a family of objects known as Kreutz sungrazers (after Heinrich Kreutz, who noticed the similarities in their orbits, and theorized that they had all come from the same parent body, a “mega-sungrazer” that is believed to have progressively fragmented into smaller pieces). These comets—which take between 400 and 2000 years to complete an orbit—come within a fraction of a solar diameter of the sun’s surface, and some are believed to even collide with our star (with no apparent harm to the sun)—if they don’t vaporize first. The brightest of them, which include 1965’s Comet Ikeya-Seki and the Great Comets of 1843 and 1882, are easily visible in broad daylight even when very near the sun. Although the largest of the Kreutz comets seen in SOHO images have become about as bright as Sirius—the brightest star in the night sky—their proximity to the sun has rendered them invisible other than in the satellite images, and none have survived the solar passage.

I’ve had a longtime love of comets, and make every effort to get to a relatively dark-sky site when one is in easy binocular range; I’ve observed close to 25 to date. I was drawn to comets because of their surprising nature; their often unexpected arrival out of the depths of space, their tendency to travel in orbits that take them far beyond the bounds of the zodiac, and their dramatic variations in brightness and appearance. As noted comet hunter David Levy has said, “Comets are like cats. They have tails, and they do precisely what they want.” Comet hunting and observing is an area in astronomy in which amateurs have traditionally made significant contributions.

In the summer of 1973, I took an observational astronomy class. One night I showed my teacher a pale streak of light in my telescope, which I hoped was a new comet. He agreed it was a comet, and suggested I call Brian Marsden at the Harvard/Smithsonian Center for Astrophysics the next day to report my “discovery” Dr. Marsden was quite skeptical, but very patient; he even took the trouble to track my number down and call me back when we got disconnected. It turned out that “Hoffman’s Comet” was a reflection from a bright star in the tube of my telescope. I did a small amount of hunting for comets in the years to follow, but never lived in a place that was conducive to it. Moving to New York City in 1980 made it very difficult to observe comets, let alone search for them. Then in late 2000, I read about amateur astronomers finding new comets on photos posted to the Internet, a project that even a citybound cometophile could engage in.

I started my SOHO comet search on June 21, 2001, examining the images from two cameras—the narrow-field C2, which shows the solar vicinity through an orange filter, and the wider-field, blue-filtered C3—posted to the SOHO website
as often as two or three times an hour. I look for specks or teardrops of light that move in a predictable manner, usually in a beeline for the sun from frame to frame. I particularly like C3; the sky is a deeper-than-daytime blue yet it is filled with stars ten times as faint as you can see from a rural night sky. The technology I used at first was simple, a computer with a dial-up connection, a program for measuring the position of objects (Microsoft Paint will do in a pinch), and a web browser. By opening a series of images in different browser windows I could blink between them by hand, looking for objects that moved in a predictable manner over several frames. I have since gotten a faster connection and a higher-end graphics program, but the principle is the same.

I set myself the task of finding a comet in 2001, which seemed reasonable considering the number of comets being found and my experience as an observer. I soon discovered that it wasn’t as easy as I had figured, and I missed my goal by a little over a month. ( Hunting for SOHO’s comets has become very competitive, with the vast majority found by a core group of about a dozen highly skilled and experienced observers, many of whom have distinguished themselves through their dedication to finding, observing, and studying comets, online and in many cases in the night sky as well.) Despite spending many hours a week downloading and poring over SOHO images, only about once a month did I find an object whose behavior appeared cometlike enough to report to the clearinghouse for SOHO comet claims . They all turned out to be noise, chance alignments of cosmic ray hits, or artifacts of solar activity. Other observers had already reported all the true comets before I saw them.

In the first year of my search, the vast majority of SOHO comets were found by Europeans; in the 16 months between October 2000 and February 2002, although over 150 SOHO comets were found, only one was first spotted by a U.S. amateur. On a Monday night, six weeks into my own search, I came home to read that David Johnson of Chicago had reported a new SOHO comet. I quickly located it, and as new images arrived, I watched its streak of light sail across the field of view, gradually fading into the greater glare of the sun as it headed towards perihelion at about 5 a.m. the following morning: September 11, 2001.

Once my phone and e-mail were restored after the attack (they were intermittent for about a week), I resumed scouring the SOHO images for comets—it beat watching CNN’s endless replays of planes crashing into buildings and the other horrors of that time, and allowed me to try to focus for a little while on something far removed from our world and its troubles—but my reasons for looking had totally changed. Any personal thrill or glory in finding a comet no longer seemed of much importance. I realized that it wasn’t every day that someone in New York City finds a comet—indeed, that it was quite possible that it had never been done before—and saw that I had a chance to help demonstrate in a small way that new and extraordinary things could still be done here despite the terrible reality we had been thrown into, that the life of the city would go on. Hunting for a comet became even more of a mission than before—though I wasn’t looking just for myself anymore, but for my city as well.

In early February, SOHO experienced a technical problem, the spacecraft went into “safe mode,” and the flow of images stopped. When it resumed on February 10, my comet—already halfway across the C3 field-of-view in route to the sun—was visible; I reported it, and other observers easily confirmed it. It was officially given the utilitarian name Comet C/2002 C4 (SOHO); comets found in data from spacecraft or automated searches (such as LINEAR) are named for the source of the data rather than the person making the find. (As challenging and time-consuming as it is to find a comet in satellite images, it pales in difficulty to telescopic comet hunting in the night sky.)

Still, I was told by John Pazmino, former President of the Amateur Astronomers Association of New York, that mine was the first comet ever found from New York City by any method, a mind-blowing possibility. I’ve done some investigating to try to confirm this. The one other candidate I’ve come across is the Great Comet of 1843, ironically a Kreutz sungrazer that is the closest known major relative to my little fuzzball—though it shone a million times brighter at its best. One of the first reports of the comet of the comet (a sighting on Feb. 5, 1843) ran in a New York City publication, but because of the comet’s 30-degree southern declination it is unlikely that the sighting was actually made in the New York area; the report was perhaps relayed by a sailing ship returning from the Southern Hemisphere, where most comet experts put the discovery. Nonetheless, the finder’s identity and location are lost to history.

Today, the pervasiveness of light pollution (skyglow due to excessive and misdirected lighting) makes finding a comet by telescope from major metropolitan areas unimaginable, but there were still dark skies in New York and in other large cities in the mid-1800s, and at least one observatory in lower Manhattan. The 1850s saw the discovery of two comets by Robert Van Arsdale from across the Hudson River in Newark. After 1879, when Thomas Edison commercialized the carbon-filament light, the days of dark skies in cities were numbered, though even in 1910—when Halley’s Comet came through— the Milky Way was still visible from Manhattan. Today, even if Governor Pataki finally were to agree to sign a light-pollution bill here, it would still not reduce sky glare enough to give urban astronomers any real chance of finding a new comet telescopically, so New York City will probably have to be content with the likes of SOHO comet discoveries. Here, it’s often an adventure simply trying to observe known comets; their fuzzy glow is easily obliterated in a sky that never truly darkens.

Even from dark-sky locations, it is becoming progressively harder for amateurs to discover comets telescopically, especially from the Northern Hemisphere. Computerized sky surveys with acronyms like LINEAR, BATTERS, and NEAT, which use high-resolution CCD imaging to locate asteroids that could conceivably collide with Earth, are also discovering comets in large numbers, many of which (unlike the sungrazers found through SOHO) would likely have been found by amateur astronomers in their telescopes. LINEAR (short for Lincoln Near-Earth Asteroid Research) alone has found well over 100 comets, including several that brightened to naked-eye visibility.

Yet while technology has diminished the odds of visual discovery of comets, it has also provided the means for cyber-savvy observers to find them online by using the “eye” of a spacecraft to monitor the solar vicinity. In homes on at least five continents, SOHO comet hunters search through freshly downloaded images, trying to be the one to first detect the next cosmic iceberg that strays too close to the sun. On June 27, 2002, I found my second sungrazing comet. As if to underscore the fact that SOHO’s images are relayed from a spacecraft far beyond Earth’s atmosphere, I found it—as with my first find—on a night of pouring rain.


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tonyhoffman@earthlink.net