The Reigns of Roman Emperors 

Seneca's descriptions. One could make a case for either comet (

A.D.

 39 or 

A.D.

 54) as being a better fit for the 

observed location of Claudius' comet. 

    On the other hand, Suetonius describes Claudius' comet as  a long haired star, known as a comet. 

930

 This 

description can only fit a comet with a long tail. The 

A.D.

 39 comet's tail was 30 degrees in length, but the 

A.D.

 54 comet's tail was only 5 degrees.

931

 The comet of 

A.D.

 39 is therefore a much better fit for Suetonius' 

description of a long haired comet. 

    Dio tells us an interesting story about a solar eclipse that occurred during the reign of Claudius.

932

 The 

emperor Claudius knew from the calculations of Roman astronomers that a solar eclipse would coincide with 

his birthday. The Roman people considered eclipses in general to be omens of impending events, either of a 

change in leadership or of some misfortune. An eclipse coinciding with the birthday of an emperor is a very 

rare event and would have been interpreted by the Romans as very significant. They would likely have 

interpreted this event as indicating either an end to Claudius' reign, or the beginning of some misfortune or 

disaster during his reign. 

    In order to forestall any disturbance among the people as a result of this eclipse, Claudius issued a 

proclamation about the eclipse. His proclamation explained when the eclipse would occur and how long it 

would last, and gave a fairly scientific explanation as to why eclipses occur.

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  Dio's description of this 

proclamation shows us that the Roman scholars of that time period could predict eclipses with a fair degree of 

accuracy. Dio is therefore unlikely to have been mistaken that a solar eclipse coincided with Claudius' 

birthday, both because the proclamation about the eclipse was an historical event and because the scholars of 

Dio's time period could have verified when the eclipse occurred. 

    In the usual chronology, the solar eclipse on August 1 of 

A.D.

 45 is considered to be this eclipse mentioned 

by Dio. That eclipse occurred in the morning and was centered in Africa, but would have been visible from 

much of Europe, including Rome, as a partial eclipse. Claudius' birthday was August 1 and the usual 

chronology has his reign extending from Jan. of 

A.D.

 41 to Oct. of 

A.D.

 54. The generally accepted chronology 

places this eclipse a few years into the reign of Claudius. Dio apparently believed that this eclipse occurred a 

few years into Claudius' reign, for he places it in that context.

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    In my revised chronology, the solar eclipse on August 1 of 

A.D.

 26 is the eclipse mentioned by Dio. That 

eclipse also occurred in the morning and was centered in Africa, but would not have been visible from Europe. 

The scholars of Claudius' time could predict the day and time when a solar eclipse would occur. However, it is 

another matter altogether to be able to predict where on earth the shadow of the moon will fall during a solar 

eclipse. To predict the day and time, one must know the relative positions of the sun, earth, and moon. This 

same information is also used to predict lunar eclipses and the moon's phases. Lunar eclipses and the moon's 

phases are generally visible from any location on earth from which the moon would be visible. So, predicting 

the day and time of a lunar eclipse or a lunar phase is sufficient to predict whether the event will be visible 

from a particular location. Not so with solar eclipses. A solar eclipse is not visible from everywhere on earth 

where the sun is visible. 

    The Roman scholars could predict the day and time of the solar eclipse, and they knew that the eclipse 

would occur in the morning, when the sun would be above the horizon, so they assumed that the eclipse 

would be visible. They could not accurately predict the places on earth where the solar eclipse would be seen. 

In order to predict where the shadow of the moon will fall during a solar eclipse, one needs to know the 

distance of the moon from the earth (which varies within a certain range), the size of the moon, and the shape 

and size of the moon's shadow. They did not have this precise information (as is clear from Pliny's 

explanation of the solar system).

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    This eclipse coincides with the first year of Claudius' reign in my revised chronology (

A.D.

 26, revised). Dio, 

however, places the eclipse in the context of the fifth year of Dio's reign (

A.D.

 45, usual). Did Dio have 

documents indicating that the eclipse occurred in the fifth year of Claudius' reign? Or, did Dio check with 

Roman scholars to find out (by means of their calculations) when an eclipse coincided with Claudius' birthday 

during the time period he believed contained Claudius' reign? It is likely that he did check with Roman 

scholars, since he follows this story about the eclipse on Claudius' birthday with a fairly scientific explanation 

of both solar and lunar eclipses (this explanation seems to have come from Roman scholars).

936

 I conclude that 

he placed this eclipse in the incorrect time frame because he did not account for the overlap between Tiberius 

203