A distant comet that was as faint as magnitude 18 on October 20th has suddenly brightened by a millionfold, altering the naked-eye appearance of the constellation Perseus.

This startling outburst of Comet Holmes (17P) may be even stronger than the one that occurred 115 years ago, in November 1892, when the comet was first spotted by English amateur Edwin Holmes.

©Babak Tafreshi
On the evening of October 24th, through bright moonlight and light pollution over Tehran, Iran, Babak Tafreshi took this wide-field panorama. "This is unbelievable!" he writes. "I was amazed to find Comet Holmes so easily with the naked eye in the light-polluted skies of metropolitan Tehran."

According to IAU Circular 8886, issued Wednesday October 24th by the Central Bureau for Astronomical Telegrams in Cambridge, Massachusetts, A. Henriquez Santana at Tenerife, Canary Islands, was the first to notice the outburst shortly after local midnight on the 24th. The comet was then about 8th magnitude, but within minutes Ramon Naves and colleagues in Barcelona, Spain, caught it at magnitude 7.3.

Periodic Comet Holmes (17P) is currently located in east-central Perseus. Although this finder chart shows the northeastern horizon at dusk, the comet will be easier to spot late at night, when Perseus is more nearly overhead. Click on image for a larger view.

Internet discussion groups came alive with the news. "To my amazement, 17P had brightened to naked-eye visibility," exclaimed Bob King when he spotted Comet Holmes shortly before dawn in Duluth, Minnesota. "What a sight!" he posted to the Comets Mailing List. Alan Hale of Cloudcroft, New Mexico, concurred. To Hale (well-known codiscoverer of Comet Hale-Bopp) it appeared essentially starlike in a telescope until he switched to high power.

Then things only got better. As Earth continued to turn, nightfall arrived in Japan. "It is visible with naked eyes in a large city!" posted Seiichi Yoshida, who observed the comet from beside Tsurumi River in Yokohama. By 17:15 Universal Time he was describing Comet Holmes as magnitude 2.8.

Comet expert Gary Kronk expects this object to remain bright and grow from a starlike point to several arcminutes across over the next few nights as it makes its way slowly westward across Perseus. Its position on October 25th (0h UT) is right ascension 3h 53m, declination +50.1° (equinox 2000), and by October 30th it will have moved only to 3h 48m, +50.4°. For those living in the Northern Hemisphere, Perseus is visible all night at this time of year.

©Clay Sherrod / ASO
This 12-arcminute-wide frame from Arkansas Sky Observatory shows the comet as a brilliant, near-circular disk on the morning of October 25th. Clay Sherrod used a 0.4-meter (16-inch) Schmidt-Cassegrain telescope at f/3.

Update Oct. 25: "This object is amazing!" posted Brian Cudnik of Houston, Texas, on the Yahoo CometChasing group after coming in from his telescope on the evening of the 24th. "I have just observed it with an 8-inch f/10 Cassegrain, boosting the power up to 163x then to 508x.... The bright inner coma seems displaced off-center toward position angle 315°. The inner coma opens up into a fan toward position angle 300°, and I have noticed one ripple, akin to the hoods/ripples seen in Comet Hale-Bopp ten years ago. The coma is uniform in brightness, aside from this fan-shape material emanating from the central condensation, and has a well-defined edge." He measured the coma to be 69 arcseconds wide using using the drift method. "The entire object has a nice yellow-white color; no sign of any tail. The apparent magnitude is +2.8 (estimated using Mirfak at +1.9 and the other two bright stars adjacent to it at +3.0 each) and has remained rather steady all evening."

©Griffith Observatory / Anthony Cook
Despite moonlight and smoke from wildfires near Los Angeles, Anthony Cook captured the comet at the prime focus of Griffith Observatory's 12-inch Zeiss refractor at 8:30 UT on October 25th. This frame, cropped to 4 arcminutes wide, shows the comet's nucleus slightly off-center in the larger coma. In longer exposures the coma had a well-defined edge, allowing Cook to measure its growth rate. He got a diameter of 86 arcseconds at 7:46 UT, then 89 arcseconds an hour later.

Posted Dan Laszlo of Fort Collins, Colorado: "In an 18-inch Newtonian at 90x, the yellow orb is like a bright spherical planetary nebula. Diameter of the bright portion is about equal to the lunar crater Tycho, so magnification helps. I can detect a very faint spherical outer envelope, about equal in radius to the diameter of the bright portion, tough with the moonlight."

From Florian Boyd, Palm Springs, California: "I think this is about the most amazing thing I've ever seen in the sky!"