The Great Christ Comet Read Online Free Page A

behavior. There is no indication of the comet’s behavior thereafter. However, the fact that it was observable for so long prior to perihelion suggests that it could have remained visible for many months afterwards.
    Determining the Orbit
    We have already seen that astronomers have determined the orbits of many historical comets. In fact, we are in the fortunate position of knowing the orbits of comets as far back as the fourth and third centuries BC. 13 Astronomers are able to calculate a comet’s orbit when they can derive sufficient positional information from the surviving records of observers. Remarkably, just three observations are adequate to determine the six orbital elements that fully describe any orbit. In the case of the Christ Comet, Revelation 12:1–5 provides more than enough observational data to make a reasonably precise determination of its orbital elements at that time. It is important to realize that only a comet with a very particular orbit can do what Revelation 12:1–5 describes. Everything has to be just right: the placement of Earth on its orbit around the Sun, the time and place of the comet’s perihelion, the comet’s inclination and the direction of its motion, and the whole orientation of its orbit. Accordingly, we are able to deduce the six orbital elements that describe the Christ Comet’s orbit ( table 9.1 ; see fig. 9.1 for a portrayal of the comet’s orbit). 14
    Eccentricity
1.0
Perihelion Distance (AU)
0.119
Inclination
178.3
Argument of Perihelion
9.47
Longitude of Ascending Node
200.08
Perihelion Date
    (Julian)
1719500.7/
    September 27, 6 BC
    TABLE 9.1 The orbital elements of the Christ Comet.
    FIG. 9.1 The Christ Comet’s orbit viewed from the time of perihelion on September 27, 6 BC. The outermost circle is Uranus’s orbit. The green line is the comet’s eccentric orbit, and the orange arrows are directed to the First Point of Aries, a base line for astronomical measurements. The comet is under the ecliptic plane on its way toward the Sun and over it on its way away from the Sun. However, because the comet is so narrowly inclined, it is above the orbital paths of the major planets (other than Earth) on its way toward perihelion. On its way out, the comet is above the orbital paths of all the major planets except for Mercury (because of the significant tilt in Mercury’s orbit). Image credit: Sirscha Nicholl.
    Of course, the big question is whether this orbit is compatible with what Matthew records concerning the comet’s behavior on the final stage of the Magi’s journey (Matt. 2:9–11). Astonishingly, it is. Shortly after the cometary baby’s birth in the eastern predawn sky, the comet shifts to the western evening sky and quickly migrates to the southern sky. 30 to 40 days after leaving the eastern sky, the comet is appearing at sunset in the south-southeast and, over the following couple of hours, is moving to the south-southwest, the direction of Bethlehem from Jerusalem. Then some 5 hours later it sets near-vertically over the western horizon. This remarkable compatibility is overwhelmingly strong evidence that our approximate orbit is correct, that Revelation 12:1–5 is indeed the key that unlocks the mystery of the Bethlehem Star, and that Matthew 2’s account of the Star is grounded in history.
    Since cometary orbits are so susceptible to change due to gravitational and nongravitational effects, it cannot be assumed that a calculated orbit is applicable a long time before or after the observations which were the basis of the orbit determination. In the case of the Bethlehem Star, our orbit suggests that the comet had a relatively close encounter with Saturn on the way toward the inner solar system and so the orbital elements before that would have been different.
    Chronological Considerations
    Before we consider the comet and its orbit in more detail, it is important to pause to fill in some of the