by The Great Christ Comet- Revealing the True Star of Bethlehem (retail) (epub)
With our range of possible values of n, the apparent magnitude at first observation, and the orbit, we are in a position to determine the comet’s absolute magnitude, that is, the brightness of the coma as a whole if it were precisely 1 AU from both the Sun and Earth. Since we know the range of dates within which the Bethlehem Star was first observed, we can work out a range of possible absolute magnitude values for each brightness slope (i.e., n=3, n=4, and n=5; see table 9.2).
Magnitude Slope (value of n)
Absolute Magnitude if it was first observed on November 21–28, 8 BC
Absolute Magnitude if it was first observed on December 10–17, 7 BC*
3
-8.1
-5.2
4
-10.4
-6.8
5
-12.7
-8.5
TABLE 9.2 The range of the Christ Comet’s possible absolute magnitude values.
NOTE: *The absolute magnitude values given here (and the apparent magnitudes based on them) are for December 17, 7 BC. Had the comet first been spotted on December 10, 7 BC, its absolute magnitude would have been -5.2 (n=3), -6.9 (n=4) or -8.6 (n=5).
If n=3, the absolute magnitude was between -5.2 and -8.1. If n=4, the absolute magnitude was between -6.8 and -10.4. If n=5, the absolute magnitude was between -8.5 and -12.7. Those familiar with comets will immediately grasp how astonishing these values are. The intrinsically brightest comets observed in recent centuries are Sarabat’s Comet of 1729, with its absolute magnitude of between -3 and -6, and Hale-Bopp, which had an absolute magnitude of -2.7 in the early stages of its apparition. Even if we adopt a brightness slope (n) of just 3 and assume that the 6 BC comet was first observed at the latest possible time (December 10–17, 7 BC), the Bethlehem Star comet finds itself in an exclusive league with Sarabat’s Comet and the progenitor of the Kreutz Sungrazers. If n=4, then the Christ Comet is distinguished as the intrinsically brightest comet in recorded history.
With an estimated value of absolute magnitude, we are in a position to calculate how bright a comet should become over the course of its visit to the inner solar system—that is, what its apparent magnitude will be. With respect to the Christ Comet, if we consider September 30, 6 BC, just a few days after perihelion, the comet’s apparent magnitude would have been dramatic (table 9.3).
Magnitude Slope (value of n)
Apparent Magnitude on Sept. 30, 6 BC if it was first observed on November 21–28, 8 BC
Apparent Magnitude on Sept. 30, 6 BC if it was first observed on December 10–17, 7 BC
3
-13.6
-10.7
4
-17.7
-14.1
5
-21.8
-17.6
TABLE 9.3 The range of possible apparent magnitude values of the Christ Comet on September 30, 6 BC.
If n=3, then the comet would have been between -10.7 and -13.6 when it was seen in Virgo’s belly before dawn on September 30, 6 BC. If n=4, the comet would have attained to between -14.1 and -17.7. If n=5, it would have been between -17.6 and -21.8.
If we remember that the apparent magnitude of the full Moon is -12.6 and that of the Sun -26.7, we can get some idea of how remarkable the comet’s brightness would have been according to these statistics.
One major caveat should be mentioned: comets do not always develop in a very neat and orderly manner. With respect to the brightness curve and hence absolute and apparent magnitude values, they can vary within a single apparition. Comets may shift from one pattern of brightness development to another at a certain distance from the Sun or have one pattern before perihelion and quite another one afterwards.33 Comets with perihelion distances of less than 1 AU, like the Bethlehem Star comet, often display a very different pattern of activity and brightness after perihelion than before. Moreover, sometimes comets have outburst events that dramatically increase their brightness and size. Therefore, as Schaaf points out, “Absolute magnitude and the brightening factor can only be regarded as useful, not perfect, guides for helping to predict and characterize a comet’s brightness and brightness behavior during an apparition, or during part of one.”34
At this point it is important to pull together some of the historical data that speaks to the Bethlehem Star’s brightness. Ignatius, in his letter To the Ephesians, wrote of the Star in terms that suggested it was especially brilliant:
A star shone in heaven [with a brightness] beyond all the stars; its light was indescribable, and its newness caused astonishment. And all the rest of the stars, together with the Sun and the Moon, formed a chorus to the star, yet its light far exceeded them all. And there was perplexity regarding from where this new entity came, so unlike anything else [in the heavens] was it.
According to Ignatius’s authoritative-sounding statement (which was apparently rooted in first-century tradition), the Star was far brighter than all the stars, by which he is evidently including the planets such as Venus, which has a maximum apparent magnitude of -4.89.
Is Ignatius claiming that the Star was brighter than the Moon and even the Sun? That is certainly what commentators believe. If he is claiming this, we must allow for hyperbole but should probably take it to mean that the Star had an apparent magnitude more impressive than that of the full Moon (-12.6).
According to the less reliable Protevangelium of James (21:2–3), the Magi reported, “We saw an immense star shining among these stars and causing them to become dim, so that they no longer shone; and we knew that a king had been born in Israel.”35 This description suggests that the comet’s brightness was greater than the Moon’s. Moreover, this document portrays the Star as exceptionally large. For a very large comet to be extraordinarily bright means that the apparent magnitude must be most remarkable.36
Apparent magnitude compares the brightness of complete entities to the star Vega (the second brightest star in the northern celestial hemisphere, after Arcturus). It does not compare the entity based on the brightness of a set portion of its area, that is, its “surface brightness.” For a large object to be bright enough to bleach out the light of the stars, its apparent magnitude has to be extraordinary, because its overall brightness is distributed over a wider area, which means it is diluted. It is much like the brightness of a beam of light on a wall cast by a flashlight. When the beam is small, the brightness is more concentrated. When it is large, the brightness is more diffuse. If you compare a set area of the beam when small to a set area of it when large, the brightness of the set area of the more compact beam would, of course, be more intense than that of the more extended beam. That, in a nutshell, is surface brightness. On the other hand, do not forget that the same amount of light is being distributed—think of that as the apparent magnitude. The difference between apparent magnitude and surface brightness is the difference between the overall brightness of your whole computer display screen and the brightness of the average pixel on it. In the case of a large comet, the brightness of the whole coma (the apparent magnitude) needs to be high for the brightness of each small section of it (the surface brightness) to be really intense.
We have mentioned Ignatius and the Protevangelium of James, but what did the first generations of Christians claim about the brightness of the comet?
First, Revelation 12:2, 5 would seem to imply that the coma of the comet, in playing the role of the baby that grew in Virgo’s womb and then seemed to cause her intense agony as it was “born,” grew very large. It may possibly be inferred from this account that the coma became as large relative to Virgo as a newborn baby is in comparison with its mother: something like 9–12 degrees long (major axis), on October 20, 6 BC. That would be astonishing, because only a coma that had a strong apparent magnitude value would have a sufficiently great surface brightness at that size to be clearly visible to the naked eye. At apparent magnitude -9 to -11 (n=3, assuming that the comet was first seen between May and December, 7 BC), the large coma would have been
easily detectable but it would not have been stunningly bright. At apparent magnitude -11 to -13 (n=4) it would have been more striking, with a surface brightness like that of Neptune (seen through a telescope).37 Magnitude -13 to -16 (n=5) would have made for a stunning sight, with a “surface brightness” like that of Saturn.38
Second, we may perhaps tentatively glean indirect clues about the comet’s brightness from texts that speak of Jesus in terms of the comet that heralded his birth. In particular, it is possible to detect some information about the comet’s brightness from how New Testament texts draw upon Isaiah 9:2’s great oracle concerning the coming of the Messiah and the great natal star: “The people who walked in darkness have seen a great light; those who dwelt in a land of deep darkness, on them has light shone.” Luke 1:78–79 and Matthew 4:16 speak of the Messiah’s coming in terms drawn from Isaiah’s oracle, as does the Gospel of John.
Luke speaks of a rising star that “shall visit us from on high to give light to those who sit in darkness and in the shadow of death, and to guide our feet into the way of peace” (Luke 1:78b–79). The language describes a celestial entity that will rise and become so bright that it will powerfully overcome the darkness, enabling travelers to walk safely by its light during the night hours. The point made by Zechariah (John the Baptist’s father) and by Luke is that the Messiah’s ministry will be like the great comet that marked his nativity, powerfully dispelling the darkness of night.
Matthew 4:16 claims that, through Jesus’s ministry in Galilee, Isaiah’s prophecy concerning a great light shining in the deep darkness came to fulfillment: “The people dwelling in darkness have seen a great light,” and “a light has risen” on “those dwelling in the region and shadow of death.” We remember that in Genesis 1:16–17 there are only two “great lights,” so denominated because of their large size and more intense brightness. Matthew, following Isaiah, is claiming that there was a third great light. It powerfully vanquished the darkness, penetrating even into dark shady places. This great light is Jesus. As we observed earlier, Matthew’s rewording of Isaiah 9:1–2 hints that what the Star at the time of Jesus’s birth did literally in fulfillment of that oracle (“has risen”), Jesus did morally and spiritually in fulfillment of it.
Luke and Matthew therefore describe Jesus in terms drawn from Isaiah’s oracle about the great light that would attend the Messiah’s birth. These Gospel writers seem to assume that this great light had a brightness at least equal to that of the full Moon—probably greater.
The Gospel of John may also offer some indirect clues as to the brightness of the great light that announced Jesus’s birth. In this Gospel Jesus is said to be “the light of men” (John 1:4b) and “the true light, which gives light to everyone” (v. 9), and he calls himself “the light of the world” (8:12). Moreover, John describes this light as shining in the darkness but not overcome by the darkness (1:5), and Jesus claims that the light is sufficiently bright to dispel darkness (8:12). No light other than an astronomical entity can shine very bright light on all of humanity in the whole world. Jesus is probably being portrayed in terms of the celestial luminary that announced his birth (cf. Num. 24:17; Isa. 9:2). The light is more like the Moon than the Sun in that it shines during the hours of darkness, but in its intense brightness it seems brighter than the Moon, the planets, and the stars.
From Luke, Matthew, and John therefore we may possibly derive indirect clues regarding the brightness of the great light that marked the occasion of Jesus’s birth. What we find is consistent with the other, more explicit evidence that we have discovered regarding the comet’s brightness: the comet marking Jesus’s birth was astonishingly bright, and this great brightness was a literal picture of the moral and spiritual effect of the Messiah’s ministry.
With regard to the brightness of the Bethlehem Star’s tail, we have reason to believe that it was at the very least clearly visible around the time of its heliacal rising and specifically on October 20, 6 BC, when, together with the coma, it seems to have formed a scepter stretching across the whole sky. Also, on a night between November 23/24 and November 30/December 1, 6 BC, the comet tail stood up on the horizon and was bright enough to be seen when the Moon was present in the sky.
As a side note, it should also be borne in mind that any comet with a very low inclination (where tail curvature is essentially unobservable, because it occurs on the ecliptic plane) would have a brighter tail than more highly inclined comets, because “there is more material [i.e., dust] along the line of sight.”39 Moreover, a comet narrowly inclined to the ecliptic has a single, combined gas-dust tail, which is brighter by virtue of this union. In addition, the phenomenon of the forward-scattering of light would have intensified the brightness of the comet when it was in the general area between Earth and the Sun in the period of Virgo’s pregnancy and delivery.40 Consequently, the Bethlehem Star comet, with its close perihelion pass, would have a dust tail that was strongly curved in outer space but that seemed straight and especially bright, brighter even than its apparent magnitude values would suggest. Furthermore, comets are subject to outbursts, small and large, which boost their brightness.41
In light of this evidence regarding the brightness of the Christ Comet, we suggest that, while the value of n could have been 3, it is more likely that it was closer to 4 (or even 5). We shall generally assume n=4 when we overview the comet’s apparition in 7–6 BC in the following chapter.
The Shape of the Coma
The Christ Comet’s coma was probably elliptical (oval), with the nucleus relatively close to the top of the sunward side, in the month after perihelion. The oval shape is strongly suggested by the fact that it was judged to be playing the part of Virgo’s baby during that period. Many comets, especially large, productive comets (such as Hale-Bopp) and comets that pass within the orbit of Mercury (such as the Comet of 1677 [C/1677 H1] and Comet West during part of its apparition in 1975–1976), have this shape of coma. What its form was in the preceding and succeeding period we do not know for sure. Cometary comas are capable of changing shape to a considerable extent during the course of a single apparition. For example, the Great September Comet of 1882 was round until perihelion, when it became notably oval.42 However, in view of how large and productive the Christ Comet was, it is very possible that it remained oval-shaped throughout its time in the inner solar system.
Naming the Comet
The technical name of the Christ Comet, if we assume the latest possible date of first observation, between December 10 and 17, 7 BC, should perhaps be C/-6 X1 (Magi) or C/-6 Y1 (Magi). “-6” is 7 BC. Comets are assigned a prefix P, C, or D, depending on whether they have been observed at two or more passages around the Sun or judged to have a period of less than 200 years (P),43 or not (C), or have disappeared or are considered extinct (D). In the case of long-period comets, after the prefix the year of the comet’s discovery is given, followed by the part of the year when this occurred (in the form of a letter44) and a number indicating the order of the comet’s discovery relative to others during that period (“1” for the first one discovered, “2” for the second, etc.). If the Christ Comet was spotted earlier in 7 BC than December 1, then the “X” or “Y” would be replaced by one of the previous letters of the alphabet (A–W, excluding I), depending on the half-month during which it was first seen. For example, if the comet was first observed on September 30, 7 BC, its proper designation would be C/-6 S1 (Magi). If the comet was first seen in 8 BC, “-6” would be replaced with “-7,” and the letter of the alphabet would be W–Y.
Over the last few centuries comets have generally been named after their discoverer(s) or the one(s) who determined their orbit. An example of the former is D/1993 F2 (Shoemaker-Levy 9), which is named after Gene and Carolyn Shoemaker and David Levy. An example of the latter is 1P/Halley, which is named after Edmond Halley (fig. 9.2). Since we do not know the name of the particular Magus who first observed the Christ Comet, we have no choice but to attribute the cometary discovery to the wh
ole group. Alternatively, since many historically great comets are designated “Great Comet” (e.g., C/1811 F1 [Great Comet]), “Great January Comet” (C/1910 A1 [Great January Comet]), “Great Southern Comet” (C/1880 C1 [Great Southern Comet]), or the like, it may be preferable to name it “Great Christ Comet” (hence C/-6 Y1 [Great Christ Comet], assuming the latest possible date of first observation).
FIG. 9.2 Halley’s Comet (1P/Halley) (NASA/W. Liller). A photograph taken on March 8, 1986, by W. Liller, Easter Island, as part of the International Halley Watch Large Scale Phenomena Network. Image credit: W. Liller/NASA.
Conclusion
In this chapter we have sought to develop a profile of the comet, in particular nailing down its orbit and establishing the parameters of its brightness. In the following chapter we shall overview the cometary apparition on the basis of our orbital elements. This will help us get a vision of what the Star of Bethlehem did.
10
“Following Yonder Star”
Tracking the Comet
In this chapter we will put together the story of the apparition of the Christ Comet, tracking its progress from the point of its first appearance until it stood over the house in Bethlehem. We can do this based on our orbital elements and brightness calculations, the Biblical data, observations of comets over the last few centuries and especially recent decades, and cutting-edge cometary research. It is important to remember that a celestial object’s orbital elements fully describe its orbit and enable us to plot the body’s location in space and in the sky at any given point in time (planetarium software makes this easy). Our earlier work on the Christ Comet’s absolute magnitude, in conjunction with the latest research on cometary brightness, enables us to figure out the comet’s apparent magnitude (within a range) at any given point in its orbit.1 Thanks to the Biblical text, extensive records of historical comets, and modern studies of the behavior of comets such as Hale-Bopp, we are in an excellent position to say something about the Christ Comet’s appearance and behavior throughout its apparition.2
