The Great Christ Comet
Page 39
As great as the Great Comet of AD 400 undoubtedly was, it pales in comparison to the Great Comet of 6 BC, that is, the Great Christ Comet. The comet of 6 BC was intrinsically and apparently brighter and was larger in coma and tail size than the Comet of AD 400.
Good Viewing Opportunities
With regard to viewing opportunities, the general rule is that cometary apparitions should occur in the evening and in the northern hemisphere to be regarded as great. It should be qualified that, in the ancient world, rather more people would be expected to be awake in the hour or two before dawn than in the modern world. Nevertheless, as now, so then, a comet would have been more widely observed in the evening hours. The ideal time for a comet to be on show is the early part of a night when the Moon is not very bright. At the same time, comets are best seen against the backdrop of a dark sky, meaning earlier mornings or later evenings.
The Bethlehem Star was visible for a long time, but, like most comets, it saved its most magnificent display for the weeks before and after perihelion.
Prior to perihelion it put on a stunning show as it made its way across the sky from Pisces to Virgo. Much of that glorious procession occurred in the evening and early-night sky when most people were out and about and liable to notice anything unusual in the skies. Among other things, we have suggested that they might have perceived the comet to be Aquarius’s water-jar and the water coming out of it, to be an arrow fired from the Archer’s bow flying through the sky to slay the Scorpion in August, and to be a trumpet and bright “evening star” in September. For the latter part of its procession it may well have been visible during the daytime.
The comet as a whole, taking the form of a spectacular scepter, began to rise heliacally around the time of perihelion. Two or three days later, at the point when the coma heliacally rose in the eastern sky, it beamed with the brightness of the full Moon, or greater, looking like a baby in Virgo’s belly. It was an extraordinarily “bright morning star.” At that time the comet would also have been a dramatic daytime object. Over the following days the comet moved to a higher altitude before the Sun rose, so that it could be seen in a darker sky, although the growth in the comet’s size would have diluted the intensity of its brightness. The comet climaxed its apparition in the eastern sky on October 20. At that time the coma looked like a newborn baby and the comet as a whole like a massive iron scepter stretching across the whole sky and resting on the ground in the west. Over the following days it would have appeared very large, long, and bright as it made its close pass by Earth.
Then the comet shifted to the west of Earth and hence the focus of the majestic show moved from the morning sky to the evening and night sky, and from the eastern sky to the western sky. The comet’s long-tailed appearances dominated the skies for at least another 30–40 days. At that time, as on its procession to the Sun, the celestial visitor to the inner solar system made its presence abundantly clear to everyone.
Extraordinary Productivity
Regarding productivity, the Christ Comet was very active, beginning its degassing farther from the Sun than any other comet on record, including Hale-Bopp. Moreover, it remained in view from the point at which it was first observed, at least 9½ months before perihelion,16 until 2 or more months after it.17 As mentioned above, the hyperactivity of the comet is reminiscent of Hale-Bopp, which pumped out dust and gas like a locomotive, becoming visible to the naked eye almost 10½ months before rounding the Sun. Hale-Bopp maintained naked-eye visibility for 18 months. That was double the time that the previous record-holder, the Great Comet of 1811, had remained observable to the naked eye (9 months, becoming visible 5 months before perihelion), and that comet had been a long way in front of the next in line.18 We do not know how long in total the Christ Comet remained visible to the naked eye, but it is likely that it at least rivaled Hale-Bopp, and, quite possibly, surpassed it. Hale-Bopp was first observed by the naked eye at magnitude +6.7, because Terry Lovejoy knew exactly where to look, thanks to published data and telescopic and binocular aid.19 Needless to say, the Christ Comet lacked this advantage and would have been first observed only when considerably brighter (approximately +3.4). Of course, the Bethlehem Star Comet’s productivity is why its coma and tail were so large and bright immediately before and after perihelion.
A Long Tail
With respect to the criterion that a great comet must have a tail at least 10 degrees in length, the Christ Comet excels.20 We have seen that calculations suggest that the comet tail was majestically long, longer than most of Yeomans’s great comets, in the western sky prior to perihelion. In addition, of course, after perihelion, on October 20, 6 BC, it seems to have sported an impressively long tail that caused the comet as a whole to look like an iron scepter that stretched from the eastern horizon to the western.21 The tail would have continued to stretch across the entire dome of the sky for a few days after this. Moreover, its long tail streamed across much of the evening/night sky for the 28–37 days that the Magi were journeying from Babylon to Jerusalem, seeming to go before them to the west. Then one night, between November 23/24 and November 30/December 1, after ushering the Magi to Bethlehem in the south-southwest, the comet stood over the house where Jesus was, about 33–38 degrees in length.
The longest tail lengths among Yeomans’s great comets are Tebbutt’s Comet of 1861, which grew to 120 degrees, and the Great comet of 1618 (C/1618 W1), which was 104 degrees long. In regards to tail length, the Great Christ Comet seems to have surpassed even these impressive comets.
The Christ Comet’s tail is reminiscent of the Great March Comet of 1843. On March 1, 1843, that comet was 30 degrees long, by March 4 it was between 69 and 90 degrees, on March 21 about 64 degrees, and on March 30 approximately 38 degrees.22 Such a sustained period of tail length is most impressive. However, it is outdone by the Christ Comet, for its tail was longer and remained so for a considerably greater time. Nevertheless, if one wants to get a good idea of what the Christ Comet looked like as it processed from Pisces to Virgo or as the Magi journeyed westward to Judea and then found the house in Bethlehem, one can do little better than look at images of the Great March Comet of 1843.23 See figs. 5.27–28; 6.6, 10; 10.16.
A Large Coma
As for the size of the Christ Comet’s coma: in view of the very early first observation of the comet and its close perihelion and perigee distances, the coma, not surprisingly, grew very large. Revelation 12:1–5 may imply that the coma appeared to be the size of a newborn baby at the point of the baby’s birth. Our calculations suggest that it may have been about 11 degrees long (and something like 4.4 degrees wide). It should also be appreciated that, had the comet not also been extremely bright, observers would not have been able to see the large coma.
In the recorded history of comets, comets Lexell in 1770, Hyakutake in 1996, and IRAS-Araki-Alcock in 198324 stand out as having had especially large comas when they made a close approach to Earth—2–4 degrees in diameter. The size of these comas was due to the proximity of the comet to Earth, for each of these comets’ nuclei was relatively small. Only one of the three was a great comet—Hyakutake. Comet Holmes grew as large as 3 degrees by March 2008 due to a major outburst, but it is not classified as a great comet. Another coma worthy of note is that of the Great Comet of 1811. Even though this comet never came closer to the Sun than 1.04 AU or closer to Earth than 1.22 AU, its coma nevertheless at one point was reckoned to be larger than the Sun, approximately 2 million km in diameter in space.25
As we have already commented, had Hale-Bopp come as close as 0.1 AU from the Sun and Earth, its coma would probably have been some 4 or perhaps even 5 degrees in diameter.26 With respect to coma size, therefore, the Christ Comet was a much greater comet even than Hale-Bopp. In space, Hale-Bopp’s coma extended up to 3 million km in diameter. The Christ Comet’s coma may have been something like 5.75 million km long and 2.3 million km wide (equivalent to a round coma with a diameter of 3.6 million km—about the same overall size as the coma of Come
t Holmes in late November or early December of 2007). As such it was larger than all known comet comas in history except for that of Comet Holmes in 2007/2008. It would unquestionably have been the largest object in the inner and outer solar system at the time and indeed one of the largest in recent millennia. The Christ Comet’s great coma size was due to the larger nucleus size and greater productivity.
A Large Nucleus
For the coma to have grown so big, the nucleus must have been very large as well.27 Small nuclei can produce relatively large comas if they are especially active. But the remarkable size and sustained brightness of the coma of the Christ Comet would seem to require both that it was very productive and that it had a large nucleus.
Estimating the precise size of a nucleus is an uncertain business, based on the comet’s magnitude, activity, and coma diameter. The asteroidal comet Chiron is reckoned to be 166–233 km in diameter. Sarabat’s Comet of 1729 was at least 100 km (comparable in diameter to metropolitan New York City), possibly as large as 300 km. Neither is classified as a “great comet,” because they have never come close to the Sun—at its nearest, Comet Sarabat was still more than 4 AU from the Sun.28 Had Sarabat come close to the Sun and Earth, it would have been a truly spectacular comet. Certainly, the Bethlehem Star Comet nucleus seems to have been larger than all recorded historically great comets, including Hale-Bopp, the diameter of which was 40 km (think London) to 70 km (think Boston), and the Great Comet of 1882, which was about 50 km in diameter (think Seattle).29 The Christ Comet was probably 100 km or more in diameter, comparable to the more modest estimates of Comet Sarabat’s size.
Unprecedented Absolute Magnitude
In view of how long the Magi had been tracking the Christ Comet prior to perihelion, it is obvious that it had unprecedented intrinsic brightness.
In table 11.1, I set out the absolute magnitude if n=3, 4, or 5 for different points within the time period when the Star was first observed. The absolute magnitude values for the earliest and latest dates of the first sighting by the Magi are included. I also set out the absolute magnitude values assuming a first observation on February 5, 7 BC, when it would have been in conjunction with Jupiter. May 29 and September 30, 7 BC, are also included, because that is when the first two of the three conjunctions of Jupiter and Saturn in Pisces occurred. If the comet was first spotted during the peak of the third conjunction (i.e., on December 1–8, 7 BC), its absolute magnitude values would have been essentially the same as on December 10–17, 7 BC.30 I also include the values of absolute magnitude for August 17, 7 BC.31
Magnitude Slope
(value of n)
Absolute Magnitude if first observed on November 21–28, 8 BC
Absolute Magnitude if first observed on February 5, 7 BC
Absolute Magnitude if first observed on May 29, 7 BC
Absolute Magnitude if first observed on August 17, 7 BC
Absolute Magnitude if first observed on September 30, 7 BC
Absolute Magnitude if first observed on December 10–17, 7 BC
3
-8.1
-7.9
-6.9
-5.8
-5.5
-5.2
4
-10.4
-10.2
-9.0
-7.8
-7.4
-6.8
5
-12.7
-12.4
-11.0
-9.7
-9.2
-8.5
TABLE 11.1 The Christ Comet’s range of possible absolute magnitude values.
Assuming n=4, the absolute magnitude was between -6.8 (if first spotted on December 17, 7 BC) and -10.4 (if first spotted on November 21, 8 BC). Kronk, having done brightness calculations on the Christ Comet, commented that it would have been “the biggest comet ever observed.”32
Sarabat’s Comet (1729) had an absolute magnitude of between -3 and -6. Hale-Bopp, in the early stages of its apparition, had an intrinsic brightness as great as absolute magnitude -2.7, although this changed to about -0.8. The Great Comet of AD 418 is plausibly reckoned by Seargent to have been -2 or -2.5.33 The absolute magnitude of Tycho’s Comet of 1577 was -1.8 and that of the Great Comet of 1746 was -0.5. After that comes the Great Comet of 1811, the absolute magnitude of which was 0. These comets are intrinsically the brightest comets on record. However, the Christ Comet’s extraordinary absolute magnitude means that it surpasses even these to qualify as the intrinsically brightest comet in recorded history.34
Notable Apparent Magnitude
When one considers that a comet with such an extraordinary absolute magnitude made close passes by both the Sun and Earth and was clearly visible when extremely large in Virgo, one realizes that its apparent magnitude must have been extraordinary. Indeed the Christ Comet may have been the brightest comet in human history. It is certainly in the super-league of cometary brightness.
The historical comets with the most notable values of maximum apparent magnitude are the Great Comet of 1680 (-18), the Great September Comet of 1882 (-17 or -15 to -20), Ikeya-Seki in 1965 (-15), the Comet of 1577 (-8), and the Great Southern Comet of 1865 (-8). Kronk observes that the Christ Comet would have been “a spectacular object that was visible in daylight for a time” and that its “maximum brightness is similar to what was observed for the Great September Comet of 1882 and Ikeya-Seki in 1965.”35
The climax of the Christ Comet’s apparent magnitude would have occurred at perihelion on September 27, 6 BC.36 However, while part of the tail would have been observable at that point, the coma was not. The coma may have become visible on September 29, 6 BC, when its apparent magnitude was between -14.8 and -18.4.37 On September 30, 6 BC, when it was almost certainly observable, its apparent magnitude was between -14.1 and -17.7.38 In view of the possibility that the brightness slope may have been higher than 4, and in view of the unpredictable nature of comets, it is conceivable that the comet was even brighter than these estimates, particularly in the period after perihelion. Moreover, throughout the month of October in 6 BC, the comet benefited from a brightness boost as it was in the zone between Earth and the Sun (at that time the nucleus had a phase angle from 90 to 180 degrees); it peaked on October 22 at 174.75 degrees, which would have meant a boost in brightness of some 7.5 magnitudes in the sunward side of the coma due to forward-scattering! Joseph Marcus has pointed out that this special geometry is a factor that endows comets, particularly those of medium or large size, with greatness.39 At the same time, the massive size of the Christ Comet’s coma at some stages of the apparition would have meant that the brightness was being distributed over a large surface area, diluting some of the effect of the impressive apparent magnitude values.
Long Spell of Better-than-Zero Apparent Magnitude
With regard to maintaining a minimum apparent magnitude of 0 for the longest period, Hale-Bopp is the record-holder, having maintained this level of brightness for 8 weeks. It is followed by de Chéseaux’s Comet of 1744 and Tycho’s Comet of 1577, both of which maintained better-than-zero magnitude for approximately 6 weeks, and by the Great Comet of 1882, which managed it for about 5 weeks. The Bethlehem Star Comet, however, easily trumps all of these great comets. Our calculations of its overall brightness suggest that it was zero or greater in apparent magnitude for more than 8 months (May 13, 6 BC, to January 30, 5 BC),40 although the Bible gives us no information about its behavior after its climactic performance on the night when the Magi found the baby Messiah (between November 23/24 and November 30/December 1, 6 BC), and the rate at which comets fade is famously variable!41
Conclusion
In conclusion, the Christ Comet satisfies the criteria for cometary greatness. In fact, all things considered, it is undeniably the single greatest comet in recorded history. Even if one considers only the combination of its perihelion and perigee distances, its status as an elite comet is clear. When one adds to this the great viewing opportunities, the long tail length, the extremely large c
oma, the remarkable productivity, the long duration of the apparition, and the extraordinary brightness, it is seen to be in a league of its own. Truly the Bethlehem Star comet is sitting at the top of the tree of cometary greatness! The Christ Comet is the only very large and intrinsically very bright comet we know of that made very close passes by both the Sun and Earth.
David Seargent, in his book Comets: Vagabonds of Space, commented that “People sometimes ask ‘What was the best comet ever seen?’ To this there is no positive answer. No single object can definitely be said to have wiped the rest off the field.”42 “No single object stands out from the rest as obviously the greatest comet.”43 However, in light of what we have discovered about the Great Comet of 6 BC, this statement is in need of revising. The Christ Comet stands out from the rest as obviously the greatest comet of recent millennia.
Ignatius’s description (in chapters 18–19 of his letter To the Ephesians) fits excellently with what we have discovered concerning the Christ Comet, and it is well worth citing as we close this chapter.44 Most scholars believe that Ignatius is, in 19:2–3a,45 quoting from very early Christian tradition (many believe it was a hymn46) that goes back well into the first century AD.47 It certainly appears to be independent of Matthew, which makes it a very important source concerning the Star.48 Strikingly, Ignatius makes it clear that the Star was a mystery hidden in the Hebrew Prophets.49 In particular, his reference to “Mary’s virginal conception and her giving birth” suggests that the fulfillment of Isaiah 7:14 was on his mind:50