Frank Tipler argues that the Star of Bethlehem was, most probably, a supernova in the Andromeda galaxy.
Gazing skywards on a clear night, the stars appear to be speckled across the inner surface of an inverted bowl. This is one hemisphere of what astronomers call the celestial sphere. To understand some of the terminology in Tipler's article, note that declination and right ascension are the names for the equatorial system of coordinates upon the celestial sphere. In this system, the intersection of the plane of the Earth's equator with the celestial sphere determines a great circle on the celestial sphere called the celestial equator. Right ascension (R.A.) provides a coordinate upon the celestial equator, starting at the vernal equinox (see below) and running Eastward. Declination specifies the angular distance North or South of the celestial equator.
To define the vernal equinox, one first needs to introduce the ecliptic. The ecliptic is the great circle which the Sun traces upon the celestial sphere due to the Earth’s annual orbit around the Sun. It can also be thought of as the intersection of the Earth’s orbital plane with the celestial sphere. Because the Earth’s axis, and therefore its equator, are inclined at approximately 23 deg to the orbital plane, the celestial equator is inclined at the same angle to the ecliptic. Now, the ecliptic intersects the celestial equator at two points: the vernal equinox and the autumnal equinox. The vernal equinox is the point of intersection of the ecliptic and the celestial equator at which the Sun moves from the Southern celestial hemisphere into the Northern celestial hemisphere.
Tipler asserts that "The Star of Bethlehem is a star. It is not a planet, or a comet, or a conjunction between two or more planets, or an occultation of Jupiter by the Moon. I shall assume that the Star of Bethlehem was an actual point of light fixed on the celestial sphere. Second, I am going to assume that the Matthean expression 'stood over' means exactly that. The star went through the zenith at Bethlehem...the Star was there, in the sky, directly above the Magi, at the time of their visit to the baby Jesus...Since the latitude of Bethlehem is 31 deg 43' north, the declination of the Star in the first decade B.C. (the range of estimates of Jesus' birth year) must have been 31 deg 43' N.
"Setting Babylon as the zero of longitude and identifying it with the zero of R.A. would give the R.A. of the Star of Bethlehem as 23h 23m in 5 B.C...This position in the first decade B.C. is far away from the galactic plane (the likely location of a galactic nova/supernova), but it is very close to the Andromeda Galaxy, whose center in 5 B.C. was 30 deg 13' [declination], 23h 1m [right ascension]. The galactic halo of the Andromeda Galaxy would have definitely included the declination of the zenith of Bethlehem. The R.A. of the Andromeda Galaxy would correspond to a position in the Mediterranean Sea, but the nearest large city with the indicated declination/latitude is Jerusalem, the city to which the Magi first traveled. The nearest small city is Jaffa, the main port of Palestine, and in Greek mythology, the home city of Andromeda, princess of Jaffa. Any astronomer of the first decade B.C. would immediately associate an event in the constellation Andromeda with Palestine. Our system of constellations is essentially that of Ptolemy, which can be traced back at least to Eudoxus of Cnidus (c. 350 B.C.) (through the poet Aratus), before the Seleucid period of Greek rule over Babylon. Astronomical techniques at the time were sufficiently accurate to allow observers to determine that a star’s declination was at the zenith of a given location to within a minute of arc, or within a nautical mile, using a dioptra and plumb bob. A supernova in M31 could indeed have 'stood over' Bethlehem."
Star of Bethlehem Frank Tipler