Was Comet McNaught the best or brightest?

Great January comet of 1910: The first people to see this comet—then already of first magnitude—were workmen at the Transvaal Premier Diamond Mine in South Africa on Jan. 13.  Two days later, three men at a railway station in nearby Kopjes casually watched the object for 20-minutes before sunrise, assuming that it was Halley’s Comet.  Later that morning, the editor of the local (Johannesburg) newspaper telephoned the Transvaal Observatory for a comment.  The observatory’s Director, Robert Innes, must have initially thought this sighting was a mistake, since Halley’s Comet was not in that part of the sky and nowhere near as conspicuous. Innes looked for the comet the following morning, but clouds thwarted his view.  But on the morning of the 17th, he and an assistant saw the comet, shining sedately on the horizon just above where the Sun was about to rise. 

Later, at midday, Innes viewed it as a snowy-white object, brighter than Venus, several degrees from the Sun.  He sent out a telegram alerting the world to expect “Drake’s Comet”—for so “Great Comet” sounded to the telegraph operator.  It was visible during the daytime for a couple of more days, then moved northward and away from the Sun, becoming a stupendous object in the evening sky for the rest of January for the Northern Hemisphere. Ironically, many people in 1910 who thought they had seen Halley’s Comet, instead likely saw the Great January Comet that appeared about three months before Halley.

Comet Skjellerup-Maristany, 1927: Another brilliant comet, first seen as a third magnitude object in early December, had the unfortunate distinction of being situated under the poorest observing circumstances possible.  The orbital geometry was such, that the approaching comet could not be seen in a dark sky at any time from either the Northern or the Southern Hemisphere.  But it reached tremendous magnitude at perihelion on Dec. 18.  Located at a distance of 16.7 million miles from the Sun, it was visible in daylight about 5-degrees from the Sun at a magnitude of -6. As the comet moved out of the twilight and headed south into darker skies, it faded rapidly, but still threw off an impressively long tail that reached up to 40-degrees in length by the end of the month. 

Comet Ikeya-Seki, 1965: This was the brightest comet of the 20th century, and was found just over a month before perihelion passage in the morning sky moving rapidly toward the Sun.  Like the Great Comets of 1843 and 1882, Ikeya-Seki was a Kreutz Sungrazer and on Oct. 21 swept to within 744,000 miles of the center of the Sun.  The comet was then visible as a brilliant object within a degree or two of the Sun, and wherever the sky was clear, the comet could be seen by observers merely by blocking out the Sun with their hands.   From Japan, the homeland of the observers who discovered it, Ikeya-Seki was described as appearing “ten times brighter than the Full Moon” corresponding to a magnitude of -15. Also at that time, the nucleus was observed to break into two or three pieces.  Thereafter, the comet moved away in full retreat from the Sun, the head fading very rapidly but its slender, twisted tail, reaching out into space for up to 75 million miles, and dominating the eastern morning sky right on through the month of November.

Comet West, 1976: This comet developed into a beautiful object in the morning sky of early March 1976 for Northern Hemisphere observers.  It was discovered in November 1975 by Danish astronomer, Richard West on photographs taken at the European Southern Observatory in Chile. Seventeen hours after passing within 18.3 million miles of the Sun on Feb. 25, it was glimpsed with the naked eye 10 minutes before sunset by John Bortle—the last daylight comet sighting until McNaught in 2007. In the days that followed, Comet West displayed a brilliant head and a long, strongly structured tail that resembled “a fantastic fountain of light.” Sadly, having been “burned” by the poor performance of Comet Kohoutek two years earlier, the mainstream media all but ignored Comet West, so most people unfortunately failed to see its dazzling performance!

What’s next for Comet McNaught?
Viewers in the Southern Hemisphere will now have Comet McNaught pretty much all to themselves in the days ahead.  It should continue to be a striking object in the west-southwest sky as darkness falls. 

If a parallel can drawn between Comet McNaught and any of the above-mentioned comets, it’s that it should gradually fade as it moves away from both the Earth and Sun.  As we have previously noted, new comets can be notoriously unpredictable to forecast, but it appears now that McNaught should be shining somewhere between magnitude 0 and 2 on Jan. 21, then fade to perhaps magnitude 5 by the end of January or early February.

Although the comet is fading as it moves higher into the sky and sets progressively later, its tail should appear to impressively lengthen. 

Amazingly, the end of the tail (called the "terminus") has been glimpsed as far north as Colorado; the multiple streamers protruding above the southwest horizon resemble faint auroral rays in binoculars.

It should, in fact, appear at its longest this upcoming week—before the increasing brightness of the waxing Moon begins to compromise the view.  Skywatchers should look for two tails.  The one appearing slender and straight and pointing nearly directly upward from the horizon, will be due to gas, while the other, appearing as broad and gentle curving fan is composed of dust expelled from the comet’s head and made visible by reflected sunlight. 

Without doubt, however, Comet McNaught’s performance will stand as one of the most spectacular in recent years. For those fortunate enough to have seen it, it will always be a comet to remember.

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