Astronomers spot a mystery interstellar visitor
Comets have always been of particular interest. Appearing without warning, and sometimes with impressive tails, it was not surprising that they were regarded as portents of battles to be won or lost and of the passing of kings.
It was in 1705 that Edmond Halley first published the orbit of the comet that now bears his name. This, and the more than 5,000 comets that have been studied since, have all proved to be members of our solar system.
Some, like Halley, follow closed elongated orbits, returning to perihelion in the Sun’s vicinity every few years. Many more, though, trace almost parabolic paths as they dive towards the Sun from the Oort cloud, a spherical reservoir of icy worlds at the edge of the Sun’s influence – if they ever return to perihelion it may not be for millions of years. A handful, though, receive a sufficient gravitational boost as they pass a planet that they are flung beyond the Oort cloud into interstellar space, never to return.
Now astronomers have sighted a faint object which appears to have originated far beyond the Oort cloud, perhaps as an escapee from another star. Discovered by the Pan-STARRS 1 telescope in Hawaii on 18 October, it had already reached its perihelion within 38 million km of the Sun nine days before and passed 24 million km from the Earth on the 14th. Dubbed at first Comet/2017 U1 (PanSTARRS) because of its highly eccentric comet-like orbit, its name was changed to A/2017 U1 on 25 October when observers failed to detect any trace of a tail or hazy coma surrounding its small nucleus, probably less than 200 metres wide. So, for the moment, it is classed as an asteroid.
Its path though is certainly hyperbolic, having entered the solar system at a relative speed of 26 km per second from a direction close to the bright star Vega in the constellation Lyra. This is also close to the direction that our solar system is moving at 20 km per second with regard to the stars around us, so it may be expected that interstellar intruders, be they comets or asteroids, are most likely to appear from this region. As our first known visitor from interstellar space, frantic efforts are underway to investigate its spectrum and nature before it recedes forever from view in the direction of the Square of Pegasus.
Vega, itself, is the brightest object very high in the south-west at nightfall, falling into the west by our star chart times as Pegasus and Andromeda occupy our high meridian. Orion is rising in the east below Taurus whose brightest star, Aldebaran, is occulted by the bright Moon on the morning of the 6th. Use a telescope to watch it slip behind the Moon’s lower-left limb between 02:27 and 03:26 as seen from Edinburgh
Our sole bright evening planet, Saturn at magnitude 0.5, is easy to miss as it hangs low in the south-west at nightfall, sinking to Edinburgh’s horizon at 18:40 on the 1st and by 16:58 on the 30th. We may need binoculars to spy it in the twilight 5° left of the young earthlit Moon on the 20th and 8° below-right of the Moon a day later. Mercury stands 22° east of the Sun on the 24th but is unlikely to be visible from our latitudes.
The other naked-eye planets are all in our predawn sky. Mars rises in the east just before 04:00 throughout November, climbing to stand 15° to 20° high in the south-east before its magnitude 1.8 pinprick is swallowed by the twilight. This month, it tracks 19° east-south-eastwards in Virgo to pass 3° north of Virgo’s leading star Spica on the 28th. Mars stands to the right of the waning Moon on the 15th when a telescope show it as only 4 arcseconds wide – too small to see any detail.
Venus continues as a brilliant morning star of magnitude -3.9, but it stands lower each morning as it approaches the Sun’s far side. Currently above and left of Spica but speeding east-south-eastwards into Libra, it rises a little more than two hours before the Sun on the 1st and one hour before sunrise by the 30th.
Jupiter, about to emerge from the Sun’s glare below-left of Venus, climbs to pass a mere 16 arcminutes, or half the Moon’s diameter, below-right of Venus on the 13th. Conspicuous at magnitude -1.7, the Jovian disk appears 31 arcseconds wide as compared with only 10 arcseconds for Venus. On the 17th, the incredibly slim earthlit Moon lies above-left of Venus and to the left of Jupiter while the later stands 18° above-right of Venus by the 30th.
Sunrise/sunset times for Edinburgh change from 07:20/16:32 on the 1st to 08:18/15:45 on the 30th. The Moon is full on the 4th, at last quarter on the 10th, new on the 18th and at first quarter on the 26.
The annual Leonids meteor shower lasts from the 15th to the 20th and peaks on the night of the 17th-18th. Its meteors, all of them very fast and many leaving glowing trains in their wake, emanate from the Sickle, the reversed question-mark of stars above Regulus in Leo. This rises in the north-east at 22:00, with most Leonids visible during the predawn hours as it climbs through our eastern sky. The shower has given some spectacular meteor storms in the past, notably in 1966 and 1999, but the parent comet, Comet Tempel-Tuttle, is now near the farthest point of its orbit and rates may be around a dozen meteors per hour. For once, though, moonlight is no hindrance.
This is a slightly revised version of Alan’s article published in The Scotsman on October 31st 2017, with thanks to the newspaper for permission to republish here.
Almost every Christmas an astronomer attempts to explain the Star of Bethlehem. The Sky at Night team did so in their programme broadcast on 2015 Dec 30. They concluded that it was most likely to have been a comet and showed Giotto’s painting of the Nativity with a comet in the sky (see below). Other artists portraying the Nativity usually just showed a distant star.
I am a member of the ASE because I am interested in astronomy and cosmology. But I also have an abiding interest in the origin of Christianity and the life of Jesus. This is the result of a youth misspent as a Christian, a religion I abandoned a long time ago. This interest deepened until I found that I could write a book on the subject, which covers all aspects of the gospel story (see The Rise and Fall of Jesus, by Steuart Campbell). Necessarily the book examines Jesus’ birth and the story of the Star of Bethlehem.
The story comes only from Matthew’s Gospel, chapter 2, as follows (Authorised version):
Now when Jesus was born in Bethlehem of Judæa in the days of Herod the king, behold, there came wise men from the east to Jerusalem, saying, Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him. When Herod the king had heard these things, he was troubled, and all Jerusalem with him. And when he had gathered all the chief priests and scribes of the people together, he demanded of them where Christ should be born. And they said unto him, In Bethlehem of Judæa: for thus it is written by the prophet,…Then Herod, when he had privily [secretly] called the wise men, enquired of them diligently what time the star appeared. And he sent them to Bethlehem, and said, Go and search diligently for the young child; and when ye have found him, bring me word again, that I may come and worship him also. When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was.
Several things about this account should trouble astronomers. Does the account mean that the magi saw the ‘star’ in the east, i.e. rising, and followed it during a night as it travelled west? Or does it just mean that, being in the east themselves (Arabia?), they saw the ‘star’ in the west, over Palestine. If the latter, the ‘star’ would have set before they even came to Jerusalem. It is not clear.
The question of the time of the appearance of the ‘star’ is also obscure. No answer is given to this question and one wonders how it could be answered. Herod seems to have thought it significant, but we are not told why.
Most puzzling of all is the idea that the magi could follow the ‘star’ to identify a particular building in Bethlehem. Astronomers especially know that a celestial object or phenomenon cannot be identified with a particular location on the surface of the earth. Perhaps they are ignorant of this account or choose to ignore it as they search for any celestial phenomenon that might explain it. The entire confused account should alert astronomers to the possibility that it is unreliable and that they might not be looking for a real ‘star’.
It is important to understand that the two accounts of Jesus birth, one here in Matthew and another incompatible one in Luke’s Gospel are additions to the first Gospel, that of Mark. Both Matthew and Luke, took Mark as their basis and made additions to give Jesus an origin and background commensurate with his later deification and to elevate him the status of a Saviour God at least equal to contemporary such gods. The obvious comparison is with Mithras, the god of the Roman Army. Indeed, Matthew may have borrowed from the Mithraic books, which, it is reported, tell how, when Mithras was born, a star fell from the sky and was followed by Zoroastrian priests called ‘Magi’ on the way to worship him (by the way, Mithras birthday was Dec 25!).
Neither Mark’s nor John’s Gospel know anything about Jesus’ origin. Biblical scholars believe that the entire Birth Narratives of Matthew and Luke are inventions, for the purpose explained above.
Matthew in particular, writing for the Jewish community in Alexandria, was at pains to show fulfilment of Jewish prophecy, or at least to show links between Jesus’ origin and the Jewish Scriptures. Consequently he may have borrowed from a Jewish apocryphal book like The Testament of Levi (one of the Jewish patriarchs). In that book, in a description of the last days (18:3), one finds the statement that ‘his star shall arise in heaven as of a king. Lighting up the light of knowledge as the sun the day’. Also, in 24:1, the statement that ‘shall a star arise to you from Jacob in peace’. One can even see forecast of a star in Numbers 24:17 (‘There shall come a star out of Jacob’). In the Old Testament, the word ‘star’ often stood for the Messiah.
Jewish readers would easily see the connection and be persuaded that Jesus really was the Messiah, the point Matthew was trying to convey. I understand that The Talmud, a central text of Rabbinic Judaism, contains a statement that ‘when the Messiah is to be revealed a star will rise in the east…and seven other stars round it will fight on every side’.
It is common knowledge that ancient peoples saw celestial phenomena as signifying or celebrating some important event, such as the birth of a king, on Earth. It is not so obvious, but equally logical, that an important historical Earthly event must somehow have been reflected in the sky. Consequently, even though nothing appeared at the time, such an event was easily invented to convince people that the event described had great significance. Miraculous events were often invented to accompany the births or deaths of Roman Emperors. Such was the case here. Believing that Jesus was the expected Messiah, Matthew invented a celestial event to convince his readers of Jesus’ importance.
Astronomers even make a mistake about the date. Our year dating system was invented in 525 by a Scythian monk called Dionysius Exiguus. He based it on the assumed age of Jesus, by then thought to be in Heaven (we still keep to this system which was adopted by Bede in the 8th century). However, astronomers and many others are misled by the reference in Matthew’s account to king Herod. They assume that it must be Herod the Great, known for his cruelty and who died in 4 BCE. Consequently, they look for a celestial phenomenon prior to that date, perhaps 5 or 6 BCE and sometime they find one. However, ‘Herod’ was a family name and all of Herod the Great’s sons also carried the name. So merely calling a king ‘Herod’ was not sufficient identification and Dionysius’ calendar should not be accused of making a mistake. He almost certainly worked from Luke’s account of when John the Baptist began to preach (chapter 3). Note the reference to ‘Herod the Tetrarch’, whose name was actually ‘Antipas’:
1 Now in the fifteenth year of the reign of Tiberius Cæsar, Pontius Pilate being governor of Judæa, and Herod being tetrarch of Galilee, and his brother Philip tetrarch of Ituræa and of the region of Trachonitis, and Lysanias the tetrarch of Abilene
2 Annas and Caiaphas being the high priests, the word of God came unto John the son of Zacharias in the wilderness.
Also a statement about the age of Jesus:
23 And Jesus himself began to be about thirty years of age
Tiberias’ 15th year was the year we call, using Dionysius’ system, 28 CE. Making allowances for the period between the appearance of John and Jesus’ mission, his birth must be place in the year 1 BCE (there was no year zero). There is no reason to abandon Dionysius’ calendar and every reason to eschew the idea that he made a mistake. Consequently, even if there had been a celestial phenomenon at the time of Jesus’ birth, astronomers have been looking in the wrong time.
The mistake made by astronomers is a classic example of ‘the law of the instrument’ or over-reliance on a familiar tool. It means that astronomers have been looking at the biblical record only from their own point of view, ignorant of the fact that the record does not lie within their competence. There are other examples of experts in one discipline believing that they can explain something that lies in another discipline. In this case, astronomers have seen what appears to be an astronomical record and assumed that they would be able to explain it. But the star is imaginary. It never really existed.
Please remember this when you next hear, as you will, of an astronomer trying to explain The Star of Bethlehem.