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Caesar's Comet (also ''Sidus Iulium'' ("Julian Star"); ''Caesaris astrum'' ("Star of
Caesar Gaius Julius Caesar (; ; 12 July 100 BC – 15 March 44 BC), was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in a civil war, and ...
"); Comet Caesar; the Great Comet of 44 BC; numerical designation C/−43 K1) was a seven-day cometary outburst seen in July 44 BC. It was interpreted by Romans as a sign of the
deification Apotheosis (, ), also called divinization or deification (), is the glorification of a subject to divine levels and, commonly, the treatment of a human being, any other living thing, or an abstract idea in the likeness of a deity. The term has ...
of recently assassinated dictator, Julius Caesar (100–44 BC). It was perhaps the most famous comet of antiquity. Based on two dubious reports from China (May 30) and Rome (July 23), an infinite number of orbit determinations can fit the observations, but a retrograde orbit is inferred based on available notes.The Comet of 44 B.C. and Caesar's Funeral Games (John T. Ramsey, A. Lewis Licht
p. 125
/ref> The comet approached Earth both inbound in mid-May and outbound in early August.Cometography Vol
p. 22
by
Gary W. Kronk Gary W. Kronk (born 1956) is an American amateur astronomer and writer. Biography Kronk was born in Granite City, Illinois, United States, on March 23, 1956. He developed an interest in space at an early age, during the time of the first manned ...
It came to perihelion (closest approach to the Sun) on May 25, −43 at a solar distance of about . At perihelion the comet had a
solar elongation In astronomy, a planet's elongation is the angular separation between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given inferior planet occurs when this planet's position, in its orbital path around t ...
of 11 degrees and is hypothesized to have had an
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
of around −3 as the Chinese report is not consistent with daytime visibility during May.See Ramse
pp. 122–23:
(Comet absolute magnitude H1 of 3.3) + 2.5 * (n of 4) * log (Sun distance of 0.220 AU) + 5 * log (Earth distance of 1.09 AU) = perihelion apparent magnitude of −3.1.
Between June 10 and July 20 the comet would have dimmed from magnitude +1 to around magnitude +5. Around July 20, −43, the comet underwent an estimated 9 magnitude outburst in apparent magnitudeThe Comet of 44 B.C. and Caesar's Funeral Games (John T. Ramsey, A. Lewis Licht
p. 123
/ref> and had a solar elongation of 88 degrees in the morning sky. At magnitude −4 it would have been as impressive as Venus. As a result of the cometary outburst in late July, Caesar's Comet is one of only five comets known to have had a negative
absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...
(for a comet, this refers to the apparent magnitude if the comet had been observed at a distance of 1 AU from both the Earth and the Sun) and may have been the brightest daylight comet in recorded history. In the absence of accurate contemporary observations (or later observations confirming an orbit that predicts the earlier appearance), calculation of the comet's orbit is problematic and a parabolic orbit is conventionally assumed. (In the 1800s a possible match was speculated which would give it a period of about 575 years. This has not been confirmed because the later observations are similarly insufficiently accurate.) The parabolic orbital solution estimates that the comet would now be more than from the Sun. At that distance, the Sun provides less light than the full Moon provides to Earth.


History

Caesar's Comet was known to ancient writers as the ''Sidus Iulium'' ("Julian Star") or ''Caesaris astrum'' ("Star of Julius Caesar"). The bright, daylight-visible comet appeared suddenly during the festival known as the '' Ludi Victoriae Caesaris''—for which the 44 BC iteration was long considered to have been held in the month of September (a conclusion drawn by
Edmund Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Hal ...
). The dating has recently been revised to a July occurrence in the same year, some four months after the
assassination of Julius Caesar Julius Caesar, the Roman dictator, was assassinated by a group of senators on the Ides of March (15 March) of 44 BC during a meeting of the Senate at the Curia of Pompey of the Theatre of Pompey in Rome where the senators stabbed Caesar 23 ...
, as well as Caesar's own birth month. According to Suetonius, as celebrations were getting underway, "a comet shone for seven successive days, rising about the eleventh hour, and was believed to be the soul of Caesar." The Comet became a powerful symbol in the political propaganda that launched the career of Caesar's great-nephew (and adoptive son)
Augustus Caesar Augustus (born Gaius Octavius; 23 September 63 BC – 19 August AD 14), also known as Octavian, was the first Roman emperor; he reigned from 27 BC until his death in AD 14. He is known for being the founder of the Roman Pri ...
. The Temple of Divus Iulius (Temple of the Deified Julius) was built (42 BC) and dedicated (29 BC) by Augustus for purposes of fostering a "cult of the comet". (It was also known as the "Temple of the Comet Star".) At the back of the temple a huge image of Caesar was erected and, according to Ovid, a flaming comet was affixed to its forehead:
To make that soul a star that burns forever
Above the Forum and the gates of Rome.


On Roman coinage

Tracing the coinage from 44 BC through the developing rule of Augustus reveals the changing relationship of Julius Caesar to the Sidus Iulium. Robert Gurval notes that the shifting status of Caesar's Comet in the coinage follows a definite pattern. Representations of the deified Julius Caesar as a star appeared relatively quickly, occurring within several years of his death. About twenty years passed, however, before the star completed its transformation into a comet. Starting in 44 BC, a money maker named P. Sepullius Macer created coins with the front displaying Julius Caesar crowned with a wreath and a star behind his head. On the back, Venus, the patron goddess of the Julian family, holds a starred scepter. Gurval maintains that this coin was minted about the time of Caesar's assassination and thus probably would not have originally referred to his deification. As it circulated, however, it would have brought that idea to mind because of Caesar's new cult. Kenneth Scott's older work ''The Sidus Iulium and the Apotheosis of Caesar'' contests this by assuming that the comet did indeed spark this series because of similarity to other coins he produced. A series of Roman aurei and denarii minted after this cult began show Mark Antony and a star, which most likely represents his position as Caesar's priest. In later coins likely originating near the end of Octavian's war with Sextus Pompey, the star supplants Caesar's name and face entirely, clearly representing his divinity. One of the clearest and earliest correlations of Caesar to a comet occurred during the
Secular Games The Saecular Games ( la, Ludi saeculares, originally ) was a Roman religious celebration involving sacrifices and theatrical performances, held in ancient Rome for three days and nights to mark the end of a and the beginning of the next. A , s ...
of 17 BC when money maker M. Sanquinius fashioned coins whose reverse sports a comet over the head of a wreathed man whom classicists and numismatists speculate is either a youthful Caesar, the Genius of the Secular Games, the Julian family, or
Aeneas In Greco-Roman mythology, Aeneas (, ; from ) was a Trojan hero, the son of the Trojan prince Anchises and the Greek goddess Aphrodite (equivalent to the Roman Venus). His father was a first cousin of King Priam of Troy (both being grandsons o ...
' son
Iulus Ascanius (; Ancient Greek: Ἀσκάνιος) (said to have reigned 1176-1138 BC) was a legendary king of Alba Longa and is the son of the Trojan hero Aeneas and Creusa, daughter of Priam. He is a character in Roman mythology, and has a divine l ...
. These coins strengthened the link between Julius Caesar and Augustus since Augustus associated himself with the Julians. Another set of Spanish coins displays an eight-rayed comet with the words DIVVS IVLIVS, meaning Divine Julius.


In literature

The poet Virgil writes in his ninth eclogue that the star of Caesar has appeared to gladden the fields. Virgil later writes of the period following Julius Caesar's assassination, "Never did fearsome comets so often blaze." Gurval points out that this passage in no way links a comet to Caesar's divine status, but rather links comets to his death.
Calpurnius Siculus Titus Calpurnius Siculus was a Roman bucolic poet. Eleven eclogues have been handed down to us under his name, of which the last four, from metrical considerations and express manuscript testimony, are now generally attributed to Nemesianus, who li ...
makes mention of the comet in his epilogues as a boding sign of the civil strife that would plague Rome after Caesar's death. It is Ovid, however, who makes the final assertion of the comet's role in Julius Caesar's deification. Ovid describes the deification of Caesar in ''
Metamorphoses The ''Metamorphoses'' ( la, Metamorphōsēs, from grc, μεταμορφώσεις: "Transformations") is a Latin narrative poem from 8 CE by the Roman poet Ovid. It is considered his ''magnum opus''. The poem chronicles the history of the w ...
'' (8 AD):
Then Jupiter, the Father, spoke..."Take up Caesar's spirit from his murdered corpse, and change it into a star, so that the deified Julius may always look down from his high temple on our Capitol and forum." He had barely finished, when gentle Venus stood in the midst of the Senate, seen by no one, and took up the newly freed spirit of her Caesar from his body, and preventing it from vanishing into the air, carried it towards the glorious stars. As she carried it, she felt it glow and take fire, and loosed it from her breast: it climbed higher than the moon, and drawing behind it a fiery tail, shone as a star.
It has been argued recently that the idea of Augustus's use of the comet for his political aims largely stems from this passage. In Shakespeare's '' Julius Caesar'' (1599), Caesar's wife remarks on the fateful morning of her husband's murder: "When beggars die there are no comets seen. The heavens themselves blaze forth the death of princes."


Modern scholarship

In 1997, two scholars at the University of Illinois at Chicago—John T. Ramsey (a classicist) and A. Lewis Licht (a physicist)—published a book comparing astronomical/astrological evidence from both
Han China The Han dynasty (, ; ) was an imperial dynasty of China (202 BC – 9 AD, 25–220 AD), established by Liu Bang (Emperor Gao) and ruled by the House of Liu. The dynasty was preceded by the short-lived Qin dynasty (221–207 BC) and a war ...
and Rome. Their analysis, based on historical eyewitness accounts, Chinese astronomical records, astrological literature from later antiquity and
ice core An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains i ...
s from Greenland glaciers, yielded a range of orbital parameters for the hypothetical object. They settled on a perihelion point of 0.22 AU for the object which was apparently visible with a tail from the Chinese capital Chang'an (in late May) and as a star-like object from Rome (in late July): * May 18, 44 BC ( China) * July 23–25, 44 BC ( Rome) * Apparent magnitude: −4.0The Comet of 44 B.C. and Caesar's Funeral Games (John T. Ramsey, A. Lewis Licht
pg 121
/ref> A few scholars, such as Robert Gurval of
UCLA The University of California, Los Angeles (UCLA) is a public land-grant research university in Los Angeles, California. UCLA's academic roots were established in 1881 as a teachers college then known as the southern branch of the California St ...
and
Brian G. Marsden Brian Geoffrey Marsden (5 August 1937 – 18 November 2010) was a British astronomer and the longtime director of the Minor Planet Center (MPC) at the Center for Astrophysics Harvard & Smithsonian (director emeritus from 2006 to 2010). ...
of the Harvard–Smithsonian Center for Astrophysics, leave the comet's very existence as an open question. Marsden notes in his foreword to Ramsey and Licht's book, "Given the circumstance of a single reporter two decades after the event, I should be remiss if I were not to consider this .e., the comet's non-existenceas a serious possibility."Marsden, Brian G., "Forward"; In: Ramsey and Licht, ''Op. cit.''


See also

* List of hyperbolic comets


References

{{DEFAULTSORT:Caesar Non-periodic comets Julius Caesar Augustus 44 BC
Comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are ...
Astronomical objects known since antiquity Great comets