Comet Lights Up the Night Sky

17:42

I am so going outside to see this tonight!

11/08/2007

Discovery
E. Holmes (London, England) was a regular observer of the Andromeda galaxy (M31), so he knew the region very well. On the evening of 1892 November 6, with skies that were not very favorable, he finished making a few observations of Jupiter and some double stars with his 32-cm reflector, and then decided to take a quick look at the faint companions of Mu Andromedae and the nearby galaxy M31 before quitting for the night. Upon turning the reflector toward that region, he saw what he thought was M31 enter the field of the finder, but when he looked through the eyepiece he saw something different.

Holmes said he "called out involuntarily, 'What is the matter? There is something strange here.' My wife heard me and thought something had happened to the instrument and came to see." The object in the field of Holmes' telescope was a comet with a coma about 5 arc minutes across and with a bright nucleus. The date was then November 6.98. Holmes was able to determine a rough positon on November 7.03, before clouds moved in. He immediately wrote to E. W. Maunder (Royal Observatory, Greenwich, England), W. H. Maw (England), and Kidd (Bramley, England). Kidd immediately expressed some skepticism about Holmes' find because of its nearness to M31; however, on November 7.75, Kidd and Bartlett (Bramley) spotted the comet with the naked eye. The comet was independently discovered by T. D. Anderson (Edinburgh, Scotland) on November 8.9 and by J. E. Davidson (Mackay, Queensland, Australia) on November 9.5.

Historical Highlights
The comet's perihelion distance of over 2 AU made the initial orbits somewhat discordant, especially in the perihelion date. The first orbit was calculated by H. C. F. Kreutz using positions from November 9, 10, and 11. The resulting perihelion date was 1892 August 16.24. During the next several days, the perihelion date was given as April 19.92 by E. Weiss and April 20.04 by A. Berberich. Using positions obtained through November 17, Kreutz demonstrated the difficulty in determining the orbit, as he gave four parabolic orbits with perihelion dates ranging from February 28.82 to June 7.30 that each fit the available positions in a similar fashion.

Prominent astronomers on both sides of the Atlantic Ocean noted something particularly interesting about the orbit of this comet around mid-November. Berberich reported in a November 11 Circular issued by the Astronomische Nachrichten and Boss reported in the November 18 issue of the Astronomical Journal that this comet might be the lost comet 3D/Biela. The perihelion date was given as December 28 by Berberich and December 27 by Boss.

The first elliptical orbits were independently calculated by Kreutz and Searle using positions spanning the period of November 9 to 17. Kreutz gave the perihelion date as June 10.46 and the period as 7.09 years. Searle gave the perihelion date as October 12.48 and the period as 6.14 years. Additional orbits by L. Boss, L. Schulhof, Berberich, V. Cerulli, and J. R. Hind eventually established the perihelion date as June 13 and the period as 6.9 years. These orbits proved that this comet was not a return of 3D/Biela.

The comet had passed perihelion nearly five months before discovery and had passed closest to Earth just a month before. As astronomers would later realize, it was discovered during an apparent outburst in brightness. Nearly every astronomer reported the comet was visible to the naked eye through the first half of November, but few made actual total magnitude estimates. E. E. Barnard (Lick Observatory, California, USA) said the comet "was easily visible to the naked eye, as a small hazy star, and almost exactly as bright as the brightest part" of the galaxy M31 on the 9th. The comet faded throughout the second half of November, but it was still a naked-eye object until the last days of this period. Although no actual total magnitude estimates were made, a couple of astronomers made observations that give clues to the comet's brightness. G. Gruss (Prague, Czech Republic) said it was very easy to see in the 5-cm finder on the 23rd and he said it seemed brighter on the 24th, while M. Updegraff (State University of Missouri) said it was barely visible to the naked eye after the moon had set on the 26th.

Moonlight blocked the comet from view as December began. On the December 6, H. A. Kobold (Strasbourg, France) described the comet as a shapeless nebulosity, without a distinct condensation. F. Ristenpart (Karlsruhe, Germany) said the comet could barely be seen by averted vision in the 15-cm refractor on the 7th. J. Tebbutt (Windsor, New South Wales, Australia) said the comet was "of the last degree of faintness" in the 11-cm refractor on the 7th and 8th. On 1893 January 5, Barnard viewed the comet at low power in the 30-cm refractor and said the comet appeared very large and very faint, while Kobold said the 46-cm refractor revealed a faint spot of nebulosity about 2 arc minutes across which was only visible with great effort. Kobold noted the comet was next to a star of magnitude 10 on the 12th and was very difficult to see. The coma was about 30 arc seconds across.

The comet experienced another outburst in brightness around January 16. Kobold noted the comet was visible to the naked eye on January 16.81 and said a telescope revealed a nucleus of magnitude 8 and a coma 41 arc seconds across. At about the same time, J. Palisa (Vienna, Austria) also found the comet shining like a star of magnitude 8, and gave the coma diameter as 20 arc seconds. Observations made on the 17th indicated the comet had not changed in brightness, but exhibited a larger coma than on the previous night. A 30-minute exposure by I. Roberts (England) revealed "a very dense circular nucleus surrounded by symmetrical nebulosity, which gave the comet the appearance of a nebulous star." He measured the coma as 39 arc seconds across and the nuclear condensation as 14 arc seconds across.

The comet steadily faded after the mid-January outburst. Its position was measured for the final time on March 13.79, when Palisa found it with the 69-cm refractor and described it as extremely faint. The final observations of the comet were made by H. C. Wilson (Goodsell Observatory, Northfield, Minnesota) on April 4 and Kobold on April 6.9. Wilson observed with a 41-cm refractor and described the comet as "exceedingly faint" with a coma about 2 arc minutes across and "very slight" central condensation. Kobold said it as "extremely faint" and added that it was impossible to measure the position "on this and on several following evenings." Wilson again looked for the comet in the 41-cm refractor on August 16 and September 14, but no trace was found. He took a photograph of the region where the comet was expected to be on 1894 January 12. The exposure was made with the 15-cm camera and the exposure was one hour in duration. Although a slightly oval stain about 20 arc minutes across and with no condensation was seen at the correct spot, He noted it was "so suspiciously like a dirty water stain that we hesitate to say anything about it without verification."

Apparition of 1899: Predictions for the 1899 return came from E. Kohlschütter (1896) and H. J. Zwiers (1895, 1897, 1899). Both astronomers made careful investigations of the comet's discovery apparition of 1892-3, but where Kohlschütter did not apply perturbations between that apparition and 1899, Zwiers carefully determined the effects Jupiter and Saturn would have on the comet's motion. The ultimate result was that Kohlschütter predicted a perihelion date of 1899 May 8.51, while Zwiers ultimately predicted it as April 28.17. Zwiers (1899) wrote that the comet would have been favorably situated for recovery during the Spring of 1898 for observers in the Southern Hemisphere though it could have been just out of range of their telescopes. The failure to find the comet made a recovery during the autumn of 1899 very important. The comet was recovered by C. D. Perrine (Lick Observatory, California) with a 91-cm refractor on 1899 June 11. His measured position indicated Zwiers' perihelion date required a correction of only +0.43 day.

Perrine said the comet was not brighter than magnitude 16. He described it as a "round nebulous mass about 30" in diameter, with only a slight brightening at the center." The comet was only observed at Lick Observatory and Yerkes Observatory (Wisconsin) using large refractors of 91-cm and 102-cm, respectively. Although the magnitude estimates seem to jump around a bit, their sparse distribution and lack of confirming observations makes it difficult to determine if the variations were because the comet was still experiencing outbursts or because of other factors. The comet's brightest reported magnitude was 13 by E. E. Barnard (Yerkes Observatory) on August 16. The comet was last detected on 1900 January 21 by Perrine. The observation was made with the 91-cm refractor and he described the comet as very faint, with a magnitude of 16.

Apparition of 1906: A prediction for this comet's recovery in 1906 was provided by H. J. Zwiers. He refined the orbit for the 1899 apparition, applied perturbations by Jupiter, and determined the perihelion date as 1906 March 14.68. M. F. J. C. Wolf (Königstuhl Observatory, Heidelberg, Germany) recovered this comet on a photographic plate exposed on 1906 August 29. He gave the magnitude as 15.5 and noted "a concentric halo is rather round, but the west side is brighter than the east side." He also suspected a nucleus. Interestingly, a search plate exposed by Wolf for 4 hours and 6 minutes on August 28 revealed absolutely no trace of 17P/Holmes! According to Wolf, the comet attained a magnitude of 15 on September 26. Observations thereafter indicated the comet was fading and some astronomers failed to find the comet after mid-October. The comet was last detected by Wolf on December 7. He was using he new 71-cm reflector and estimated the magnitude as 16.

The comet was lost after the 1906 apparition, despite predictions at virtually every return thereafter. By the time of the 1942 return, a rough prediction by J. T. Foxell and K. Pollock noted that recovery seemed doubtful.

Apparition of 1964: In the December 1963 issue of the Astronomical Journal B. G. Marsden integrated the motion of comet Holmes from 1899 to 1975 using a high-speed computer. He found that between the comet's last observed appearance in 1906 and the upcoming apparition of 1964, the orbital period should have increased from 6.86 years to 7.35 years, and the perihelion distance should have increased from 2.121 AU to 2.347 AU. The resulting prediction for the comet's next perihelion date was 1964 November 15.36. The comet was recovered by E. Roemer (U. S. Naval Observatory, Flagstaff station, Arizona) on 1964 July 16. She determined the magnitude as 19.2 and described the comet as very sharply condensed, with only a trace of coma. Additional plates were obtained on July 17, which revealed the same physical characteristics. Due to the weakness of the July images, additional confirmation was needed, and Roemer obtained this on September 11. The magnitude was determined as 18.7, and the comet was again described as very sharply condensed, with only a trace of coma. The precise positions indicated Marsden's prediction needed to be corrected by only +0.7 day.

The comet has been observed at every return since 1964.

Apparition of 2007: OUTBURST The comet was observed at about magnitude 14.5 since July and had showed signs of a slow fading; however, very early on the morning of October 24, Juan Antonio Henriquez Santana (Spain) reported that the comet was much brighter than expected.

This was all rapidly confirmed. One comet observer, Bob King (Minnesota, USA), made one of the confirming observations on October 24.17 and gave the magnitude as 7.1. He described it as appearing like a yellowish star. Interestingly, he reobserved the comet on October 24.47 and gave the magnitude as 4.0 with the naked eye! Seiichi Yoshida (Japan) observed the comet on October 24.55 and gave the naked-eye magnitude as 3.5. Further observations by Yoshida gave the naked-eye magnitude as 3.0 on October 24.63 and 2.8 on October 24.72. Through the end of October, most observers were reporting the comet holding at magnitude 2.6-2.8.

Close approaches to planets: During the 20th century, this comet made two close approaches to Jupiter. There are also two close approaches to Jupiter during the 21st century. (From the orbital work of Kazuo Kinoshita and G. W. Kronk)

0.54 AU from Jupiter on 1908 December 9
increased perihelion distance from 2.12 AU to 2.34 AU
increased orbital period from 6.86 to 7.33 years


1.03 AU from Jupiter during 1968 April
decreased perihelion distance from 2.35 AU to 2.16 AU
decreased orbital period from 7.35 to 7.05 years


1.50 AU from Jupiter during 2004 January
decreased perihelion distance from 2.17 AU to 2.05 AU
decreased orbital period from 7.07 to 6.88 years


0.85 AU from Jupiter on 2051 April 8
increased perihelion distance from 2.06 AU to 2.21 AU
increased orbital period from 6.89 to 7.21 years


11/10/2007
Blue tail of Comet Holmes breaks off from green nucleus

Astronomers observed through telescopes with large time exposures what they called a “big disconnection event.” They saw the tail separate from the nucleus (head) of the comet. The astronomers stated that gusts of solar wind from large magnetic storms in the vicinity of the comet most likely caused the disconnect.

The tail of the comet points behind its nucleus and away from the Sun and Earth. The colors are caused by ions (charged particles) coming from the comet and fluorescing (emitting radiation [light]) from its interaction with the Sun. Specifically, the greenish colors of the nucleus are caused by charged particles such as carbon ions and the bluish colors of the tail by carbon monoxide ions within the comet.

The comet is made up of pieces of ice, frozen gas, and tiny rocks and dust. However, when it approaches the Sun in its orbit around the star a comet begins to heat up (or sublimate) due to its cold surface getting closer to the heat of the Sun.

Material from the nucleus of the comet begins to be ejected from the dense nucleus. The gases and dust form a tenuous atmosphere or cloud (sometimes called the coma) around the nucleus. Since the comet has very little mass, it doesn’t have much gravity. Thus, it cannot keep these gases and dust near to it. The solar wind blowing past the comet throws off the material and it forms a gaseous (ion) tail behind it and curving away from the Sun.

Comet Holmes brightened a million of times over its normal brightness over the past several weeks due to some major event in the nucleus of the comet—possibly a collapse of some of the comet that was hollow or less dense than other portions, or a collision with another object.

When this happens the frozen gases heat up and are ejected, causing a tail to appear. Astronomers think that Comet Holmes may likely produce more tails and more dramatic pictures in the future. Only time will tell what we will see as we observe Comet Holmes in the night sky.

Saturday, 10 November, 20:02

Luis and I went out for a walk and went down to the lower portion of Volunteers Park. It was dark there, little light pollution, and many stars. I started scanning the northeastern sky and suddenly, there it was! About 20 times larger than any star, but kind of fuzzy, indistinct around the edges. I looked at and exclaimed to Luis, "I found it! It is incredible!" We finally came back, and I am waiting a little while until I'm warmed up again and then I'll go back out with my telescope. And my camera - I hope to get a shot of that. I'll keep you posted!