Comet Hyakutake in March 1996

January 15, 2010

Summary Author: Doug Zubenel

On the morning of January 30, 1996, the late Japanese comet hunter Yuji Hyakutake, using a 25 X 150 binocular, swept up an 11th magnitude comet in the constellation of Libra. This discovery, made just one month after his first comet find (C/1995 Y1), was destined to bring him international fame. Of all the comets that have ever passed through the inner solar system, only a few dozen have come closer to the Earth than Comet Hyakutake – the closest being Comet Lexell, which passed by our planet at a distance of 0.0146 AU (Astronomical Units – the distance from the Earth to the Sun), or 1.35 million miles, on July 1, 1770. Following Yuji’s discovery, it was quickly determined that this new comet would pass only 0.1018 AU, or 9.5 million miles from Earth, on March 25th at 07:00 UT (Universal Time).

I had my first look at Comet Hyakutake on the morning of March 8th from rural eastern Kansas, and began photographing it on March 16th. During this time, as it rapidly approached its March 25th pass by Earth - and subsequent perihelion passage on the first of May - it underwent an incredible transformation as it grew brighter and larger. While it was not a particularly dust-rich comet, Hyakutake’s primary feature was its long ion tail.

The top photo shows the comet as it appeared to the camera on the morning of March 21st. This is a 10 minute exposure (hand-guided with the camera piggyback on an old Tasco equatorial refractor) centered at 10: 15 UT with a 135mm NIKKOR lens @ f/2.8 on Fujicolor Super G 400 film, from Linn County, Kansas. On this morning, the photographic length of the ion tail was 22 degrees, but to emphasize the structure in the tails close to the comet’s coma, the telephoto lens was used and records only 11 degrees of the ion tail. Clicking on the image will allow a rollover of your cursor to yield comet and star-field details.

The bottom photo - taken just over 26 hours after the comet’s closest approach to Earth - was from the frigid morning of March 26th, and is an 11 minute, hand-guided exposure centered at 09: 40 UT with a 24mm NIKKOR lens @ f/4 on the same film as the first image, from Carroll County in northwest Missouri. It shows the ion tail stretching an amazing 60 degrees from near Kochab (Beta Ursae Minoris), all the way into the cluster of stars making up part of the constellation of Coma Berenices. A disconnection is clearly visible halfway down the tail. As with the first image, clicking on this one will allow a cursor rollover for details.

To my naked eye on this crystalline morning in early spring, the comet’s coma was a large, glowing body over 1.5 degrees in diameter. The false nucleus was similar in brightness to Polaris, and it was possible to see 50 degrees of Hyakutake’s ghostly ion tail stretching from near the bowl of the Little Dipper in the north, up overhead, and down into Coma Berenices.

As Comet Hyakutake continued accelerating sunward for its May 1st perihelion, the ion tail was oriented more broadside to Earth each day after the 26th, and on April 12.25, the well-known astronomy writer Stephen James O’Meara, observing from Volcano National Park in Hawaii, reported the ion tail to be 100 degrees in length!!!

Comet Hyakutake, and Comet Hale-Bopp (visible the following year), are both considered to be “Great Comets.” Had Comet Hale-Bopp passed as close to the Earth as Comet Hyakutake did the previous year, its tails would have nearly spanned the entire sky, and would most likely have been one of, if not the, brightest comets in recorded astronomical history!!

Thanks to Stephen J. O’Meara, Gary Kronk’s Cometography, JPL’s interactive orbital diagram for comet Hyakutake, and Dan Green at the Harvard-Smithsonian Center for Astrophysics, for invaluable information.