Edwelda's Universe

Ex terra, ad astra . . .

Comets

    

Comet McNaught

Comet McNaught C/2006 P1 at dusk, January 10, 2007. Photo by Edwin and Imelda.

    

Hairy Denizens of the Solar System

    

Comets, with their long, ghostly tails, have struck fear, awe, and fascination in the hearts of skywatchers since the dawn of history. They were viewed either as signs of God’s handiwork or as evil portents of impending disaster. Centuries of careful scientific observations, along with a modern armada of space probes, have unraveled the mystery surrounding these wondrous visitors from the past and revealed their true nature and origin.

    

Comets evolved in the outermost regions of the solar system, called the Oort Cloud, and their nuclei thus contain pristine, well-preserved materials from the great protosolar nebula that gave birth to the Sun and planets some 4.5 billion years ago. By studying the structure and chemical composition of cometary nuclei, we can learn more about the history and evolution of our own solar system.

    

In 1950, American astronomer Fred Lawrence Whipple published a seminal paper that proposed a “dirty snowball” model for the comet’s nucleus. In this model, the nucleus is thought to be a small, solid body only a few kilometers across that consists of conglomerates of ices (water, ammonia, methane, carbon dioxide, carbon monoxide, etc.) mixed with dust particles.

    

Whipple theorized that, as the comet approaches the Sun, solar heating causes the ices to sublimate (vaporize) rapidly, producing jets of gas on the nucleus’s surface. Such outgassing induces “non-gravitational forces” on the rotating nucleus, altering the comet’s orbital motion significantly by either accelerating or decelerating it. Whipple’s idea was confirmed in 1986, when the European Space Agency’s Giotto spacecraft flew by the heart of Halley’s Comet — arguably the most famous cosmic interloper in history — and recorded several bright jets spewing material from the sunward side of the comet’s nucleus.

    

                  Fred Whipple

    

In 1996, we had the honor of meeting Dr. Whipple, a.k.a. “Dr. Comet,” and his wife, Babette, at an astronomy convention in Rhode Island, where he was the featured speaker. There he autographed our copy of his 1985 book The Mystery of Comets. Even in his 90s, Dr. Whipple used to drive his car — with its famous “COMETS” license plate — to his office at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. (You can see Edwin’s photograph of the license plate in his article on astronomy-themed car plates in the November 2001 issue of Sky & Telescope, page 84.) Dr. Whipple passed away in 2004 at age 97.

    

The Second Coming. On a more personal level, comets have had such a profound impact on our lives. They sparked our interest in astronomy, opened doors of opportunities for us, and greatly influenced our way of thinking and philosophy in life. They have been a part of us from the very beginning.

    

(As a young girl growing up in the Philippines, Imelda’s interest in the night sky was sparked when she heard about the appearance of Comet Kohoutek. Imelda actually had an auspicious start — she was born with a brilliant comet in the sky! The great sungrazer Ikeya-Seki, which was visible in broad daylight, was heading toward perihelion when she came into this world. Edwin, on the other hand, got his inspiration to pursue astronomy in earnest in high school, during the apparition of another great daylight visitor, Comet West, in 1976.)

    

In early 1985, the National Research Council of the Philippines (NRCP) published the book we wrote on Halley’s Comet, which was due to return to the inner solar system by the end of that year. Our book was entitled THE SECOND COMING: 1986 Marks Comet Halley’s Second Return This Century.

    

                 Halley book front cover

    

The idea of writing this book began in early 1983, when we were preparing a feature article about the International Halley Watch (IHW) for the local newspapers in Manila. The IHW was a worldwide network of professional and amateur astronomers and observatories set up to coordinate and archive scientific observations of the comet during its 1985-86 apparition.

    

Originally, we only intended to cover Comet Halley and the role of the IHW, but as we developed the materials for the article, we realized that many of the topics, if expanded and written in plain, non-technical language, would be of great interest to the general public. We then decided to thoroughly cover every aspect of cometary astronomy to give readers a better understanding and appreciation of the scientific and historical significance of Comet Halley’s visit.

    

We spent the next two years researching and organizing the materials, and writing, editing, proofreading, and typing the book’s voluminous manuscript with an Underwood manual typewriter (we didn’t have a desktop PC or word processor at the time). We wanted our work to be the most complete reference on the subject — the first of its kind ever written by Filipino authors.

    

The result was a 335-page volume that covered such topics as the nature and origin of comets; profiles of famous comet hunters; the hazards of comet-Earth collisions; comet myths and superstitions throughout history; a biography of the comet’s namesake, the English astronomer and mathematician Sir Edmond Halley (1656-1742); a chronology of the comet’s previous apparitions; where, when, and how to see Halley’s Comet in 1985-86; the IHW; detailed descriptions of the various space missions sent to the comet; and comet photography. (During the book’s launching at the University of the Philippines in Diliman, members of the NRCP’s Governing Council thought we were the program’s ushers and not the authors because we were so young at the time!)

    

                  Halley book back cover

    

In June 1985, respected newspaper columnist and philanthropist Teodoro (“Doroy”) F. Valencia provided us with funds to attend the 3rd American Workshop on Cometary Astronomy, which was held at the University of Arizona in Tucson. It was our very first trip to the U.S. so it was very exciting and memorable.

    

At the workshop, we exhibited copies of our book and met for the first time many well-known figures in astronomy, including then-Sky & Telescope associate editor Stephen James O’Meara, comet discoverer David Levy, nova discoverer Peter Collins, Stephen Edberg and Charles Morris of NASA’s Jet Propulsion Laboratory, Cliff Holmes and Ashley McDermott of the Riverside Telescope Makers Conference, and eclipse chasers Derald and Denise Nye. Many of them have since become very close friends.

    

On October 11, 1985, fellow Philippine Astronomical Society (PAS) member John Nassr became the first amateur astronomer in the Philippines to recover Comet Halley photographically. John recorded the object’s diffuse, 10th-magnitude glow in Orion, near the nebula NGC 2174-5, from his Stardust Observatory in Baguio City, north of Manila. He was using at the time an 8-inch f/1.5 Celestron Schmidt camera loaded with hydrogen-hypersensitized Kodak Technical Pan 2415 film.

    

Meanwhile, our search efforts at the Manila Observatory in Loyola Heights, Quezon City, were hampered by persistent clouds and monsoon rains. We didn’t spot the comet visually until early November. From then on, we began our nightly vigils on the observatory’s roof deck, collecting photographic and visual data for the International Halley Watch together with members of the Halley Watch Committee of the Philippines (HWCP), which we had organized earlier. We also conducted a lot of public outreach programs, giving lectures and interviews, and showing the famous celestial visitor to the hundreds of people who gathered every night at the observatory.

    

Even through the light-polluted skies over Marikina, the comet put on a decent naked-eye show, attaining about 3rd magnitude in brightness and displaying a 5°-long dust tail around mid-March 1986.

    

Halley’s Comet is one of a handful of visitors whose return could be reliably and accurately predicted. Like clockwork, it appeared in the sky roughly every three-quarters of a century, and astronomers were able to find records of its sightings dating as far back as 240 B.C. But it was Sir Edmond Halley who first recognized the periodic nature of this comet, which now bears his name and had been given the permanent designation “1P/Halley.”

    

Comet Halley stamps and cover

    

To celebrate Comet Halley’s historic 1985-86 visit, we proposed to the Philippine Postal Services Office for the issuance of a commemorative stamp. The Postal Services Office did mark the occasion by issuing a set of Comet Halley stamps (in 2.40 and 0.60 peso denominations) as well as first-day covers. The stamps’ design was adapted from the artwork we had submitted to the Postmaster General and was based on our book’s cover. (Later on, the Postal Services Office presented us with a souvenir frame of the Halley stamps and first-day covers.)

    

We also suggested to Father Victor Badillo, S.J., then PAS president and director of the Manila Observatory, the idea of burying a Comet Halley time capsule on the observatory’s grounds. On the evening of February 9, 1986, at the exact moment of the comet’s perihelion passage, we lowered the capsule into the ground. On hand to witness the event were Father Badillo, members of the HWCP and the Manila Observatory staff, and several guests.

    

The capsule, which contains memorabilia from that time period —personal letters, notes, poems, postcards, pictures, books, 1986 calendars, copies of that day’s newspapers and magazines, a Holy Bible, maps of Metro-Manila, paper money, coins, stamps, unused T-shirts and toothbrush, and a bottle of local red wine (Sangria) — was then sealed in concrete. A simple marble plaque marks the site.

    

    

                  Halley time capsule

    

The capsule is meant to be opened upon Comet Halley’s next return, in A.D. 2061. We hope it will survive intact until that time. Who knows what the world will be like, and how much science and technology will have progressed by then. Unfortunately, many of us will not be around to find out!

    

In 1987, the Asia Foundation (through the late Miss Edith Coliver) and Mrs. Patricia Gonzalez (formerly of Mondragon Industries International) funded our second trip to the U.S. to participate in the 4th American Workshop on Cometary Astronomy, held at NASA’s Jet Propulsion Laboratory in Pasadena, California.

    

(In addition to the workshop, our weeklong mission for the Asia Foundation was to observe firsthand the various formal and non-formal youth science development programs and curriculums in the San Francisco Bay Area, and make suggestions on how these programs could be applied to the Philippine educational system. As part of this important mission, we held a series of meetings with officials at the Foundation’s San Francisco headquarters, as well as with staff members at the Lawrence Hall of Science, the Tilden Nature Area, the Exploratorium, the Monterey Bay Aquarium, the California Academy of Sciences, and the John Swett Alternative School. Upon our return to Manila, we presented our report and recommendations to the Asia Foundation.)

    

After Comet Halley’s apparition, there was a decade-long drought for bright, naked-eye comets in the sky. This dry spell was finally broken with the memorable, back-to-back appearances of Comet Hyakutake in 1996 and Comet Hale-Bopp in 1997. The cycle continues to this day, with the spectacular apparitions of Comets McNaught and Holmes in 2008. Who will discover the next great comets of the coming decade? It’s anyone’s guess.

    

            Comet Holmes

    

This sequence of images taken by Imelda and Edwin on October 28, November 2, and November 6, 2007, shows the dramatic expansion of Comet 17P/Holmes in just nine days. The images were also featured in Spaceweather.com on November 8, 2007.

    

During the course of our nearly three decades of comet studies and observations, we have had the privilege of getting to know some of the world’s foremost experts in the field, including Fred Whipple, Brian Marsden, Daniel Green, Donald Yeomans, Charles Morris, Ray Newburn, Michael A’Hearn, Susan Wyckoff, and John Bortle, to name a few.

    

We also had the great honor of meeting (and making friends) with such legendary comet discoverers as David Levy, Carolyn Shoemaker, Don Machholz, Alan Hale, and Thomas Bopp, as well as corresponding with Kaoru Ikeya, Tsutomu Seki, William Bradfield, the late George Alcock, and the late Father Leo Boethin, who found a comet visually from Abra, Philippines, in 1975.

    

Finally, in 1996 we had the pleasure of meeting European Southern Observatory astronomer Richard West when he visited Sky & Telescope’s offices in Cambridge, Massachusetts. (As we had mentioned earlier, it was the comet Dr. West had discovered that sparked Edwin’s passion for astronomy two decades earlier. So it was a dream come true for Edwin!)

    

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All photos, unless otherwise noted, are copyright 2008 by E. Aguirre and I. Joson. Reproduction requires written permission from both photographers.