Ice & Stone 2020 WEEK 44: OCTOBER 25-31 Presented by The Earthrise Institute # 44 Authored by Alan Hale COMET OF THE WEEK: Ikeya-Seki 1965f Perihelion: 1965 October 21.18, q = 0.008 AU What would prove to dramatically, and be the 20th Century’s throughout the U.S. it brightest comet was was widely viewed as discovered on the a naked-eye object morning of September during full daylight. 18, 1965 – in a sky Merely covering recently swept clean up the sun with an by a typhoon – by two outstretched hand Japanese amateur would allow the astronomers, Kaoru comet and up to two Ikeya and Tsutomu degrees of tail to be Seki (both of whom visible, and numerous were veteran brightness estimates comet discoverers), at the time indicated independently and that it was as bright within about 15 as magnitude -10 or minutes of each other. -11. It may have been The comet was an even brighter when 8th-magnitude object Daytime photograph of Comet Ikeya-Seki when near perihelion it passed through at the time, and on October 21, 1965, taken with a coronagraph at the Mount perihelion a few hours traveling eastward Norikura Solar Station of the Tokyo Astronomical Observatory. The later; this took place at approximately sun is hidden behind the black occulting disk. Courtesy Tokyo after sunset from the one degree per day; Astronomical Observatory. U.S., but from Japan it within a couple of was easily visible in the weeks it had brightened to 6th magnitude and had noontime sky just a few arcminutes from the sun itself. developed a short tail a couple of degrees long. By about this time orbital calculations were beginning to The comet was again a naked-eye daylight object on show that it was a Kreutz sungrazer, and furthermore October 21, although it faded noticeably as the day would be appearing under just about the best viewing progressed. Telescopically it was a daytime object geometry possible for such for another day or two, an object, and thus hopes but meanwhile it was were high that it would put beginning to reappear on a spectacular display. back in the morning sky, and on the morning of Comet Ikeya-Seki the 25th it was reported brightened rapidly during as being as bright as October, being close to magnitude -2 with a bright 4th magnitude around tail 20 degrees long. As the 7th and as bright as it climbed higher each 2nd magnitude, with a successive morning it 10-degree-long tail, by faded, but at the same mid-month. Observations time the tail grew longer became difficult and more impressive, and thereafter as it slipped into at the end of the month morning twilight, but by it was reported as being the 18th observers in the Comet Ikeya-Seki in daytime, October 20, 1965. Courtesy about 30 degrees long or southern hemisphere were Life magazine. longer, bright, slender, and reporting it to be as bright slightly curved. as magnitude 0 deep in the dawn sky, and it began to be visible telescopically during the day. By early November the comet had faded to 3rd or 4th magnitude, although it continued to exhibit its bright, By October 20 the comet had brightened long tail, which even late in the month was still being Comet Ikeya-Seki in the morning sky, after perihelion. Left: From Kitt Peak National Observatory in Arizona, October 29, 1965. Courtesy Roger Lynds/NOAO/ AURA/NSF. Right: Close-up of the coma and inner tail, taken by Alan McClure from north of Los Angeles on November 1, 1965. Photo copyright Alan McClure. reported as being 15 degrees long as seen with the successful, although it didn’t produce much in the unaided eye. It dropped below naked-eye visibility way of significant scientific results. by early December, and thereafter faded rapidly and grew vague and diffuse; it was only about 10th Japanese observers reported a pair of small magnitude in early January 1966, and was little more apparent fragments of the comet’s primary nucleus than a hazy patch of light when the last photographs as it rounded perihelion, but these were apparently of it were taken shortly before mid-February. short-lived objects that soon evaporated. However, in early November a secondary nucleus began to Comet Ikeya-Seki ended up being the most be detected within the inner coma, and over time scientifically studied comet up until the time of its its separation from the primary nucleus increased, appearance. Indeed, plans to obtain observations of eventually reaching almost a full arcminute by the it had been scheduled for NASA’s Gemini 6 mission beginning of January. Individual orbital calculations which had been originally scheduled for launch on for the two nuclei indicate that the primary nucleus October 25, however a failure of the planed Atlas- has an approximate orbital period of 880 years, while Agena rendezvous vehicle – the primary reason for that of the secondary nucleus is in the neighborhood the mission – caused the mission to be delayed for of 1110 years. several weeks. Spectroscopic observations revealed the presence of numerous metallic atoms within Comet Ikeya-Seki was the second – and brightest – the comet’s dust, and one interesting experiment of three Kreutz sungrazers that appeared during a carried out at Sacramento Peak Solar Observatory seven-year period between 1963 and 1970, and as in New Mexico attempted to see if the sun’s corona “Ice and Stone 2020” participants have undoubtedly was affected by the comet’s passage through it; no noticed, several previous “Comets of the Week” have effects were detected. The comet’s appearance been Kreutz sungrazers. This most remarkable “family” also brought the first attempts to obtain ultraviolet of comets has produced some of the brightest comets observations by means of sounding rocket launches, in history and has been the subject of numerous from Wallops Island in Virginia and White Sands Missile scientific investigations, and it is the subject of this Range in New Mexico; only the White Sands flight was week’s “Special Topics” presentation. special Topic: Kreutz Sungrazers Observers following the Great Southern Comet of 1880, ostensibly on February 14, 1880. It was one of the Kreutz sungrazing comet that appeared around the time of the Great Comet of 1882. Courtesy State Library of Victoria. The Great Comet of 1882 – a recent previous “Comet about 3rd magnitude, although with a tail 50 to 60 of the Week” – attracted a lot of attention from degrees long – had briefly been observed from the around the world from both astronomers and the southern hemisphere, and this comet’s orbit bore a lay public. One of the many interesting facets of this striking resemblance to that of the Great Comet of comet had been its very small perihelion distance, 1882. One person in particular who noticed this was just a few hundred thousand km above the solar the German astronomer Heinrich Kreutz, who noted photosphere. It so happened that 2½ years earlier, that the Great Comet of 1843 – another previous i.e., in February 1880, a somewhat dimmer comet – “Comet of the Week” – also traveled in a very similar orbit. Since the calculated orbital periods were in Boyden Observatory in South Africa, Daniel du Toit, the neighborhood of several centuries it was clear discovered a 7th-magnitde comet – Comet du Toit that these could not be returns of the same comet, 1945g – that appeared to be traveling in a Kreutz and Kreutz soon speculated that they were instead sungrazing orbit. Unfortunately, it was only followed returning fragments of a larger comet that had split for four days before disappearing into twilight, and it up during a previous return. Since the Great Comet never reappeared after perihelion, suggesting that it of 1882 had split into at least four separate fragments had disintegrated. as it passed through perihelion such an occurrence would seem highly plausible. Meanwhile, there have been efforts to identify previous members of the Kreutz sungrazing group, The appearance of another comet with a similar orbit although these efforts are hampered by the fact that in January 1887 reinforced Kreutz’s ideas in this matter. the positional information in earlier centuries is often (This particular not good enough comet, which to allow for the was visible only determination from the southern of reliable orbits. hemisphere, is The Great Comet unusual in that it of 1668 (new never exhibited style designation anything in the C/1668 E1) looks to way of an actual be a likely Kreutz “head;” instead, sungrazer, and two it appeared as a bright comets that long straight tail that appeared later that reached a maximum century, the first length of 35 to 40 in late 1689 (new degrees, and it is style designation often referred to C/1689 X1) and the as the “headless other in 1695 (new wonder.”) Kreutz style designation also speculated that C/1695 U1), are Comet Tewfik (new also reasonable style designation candidates, X/1882 K1), which although for both had appeared only objects the positional during the total solar information eclipse on May 17, is not reliable 1882 – and which enough for an is another previous unambiguous orbital “Comet of the determination. Week” – was another Another comet member of this observed from the comet group. In an southern hemisphere attempt to identify a for two weeks in Motion and tail development of the “headless wonder” Comet of 1887, possible progenitor another Kreutz sungrazing comet that appeared around the general February 1702 (new comet of these time of the Great Comet of 1882. From “Knowledge” by Richard style designation “sungrazing” comets, Proctor.