Kepler's Supernova
The first known European observations of SN 1604 are recorded in northern Italy
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Original prompt & settings (JSON) ↗Altobelli knew the light was new because he had been watching that exact patch of sky every night up to 8 October, following a planetary conjunction.
Sunset, 9 October 1604, Verona
At sunset on 9 October 1604, the astronomer Ilario Altobelli saw an unfamiliar stationary light in Verona, near the conjunction of Mars, Jupiter and Saturn in Ophiuchus. A modern historical study identifies him as the first known observer to report it.
He insisted in later letters that the object had not been present through 8 October; he had been watching the same part of the sky night after night to follow the conjunction.
As bright as Jupiter, and an odd colour
On that first evening Altobelli judged the new object comparable to Jupiter and described an unusual mixed yellow-green or orange colour.
What observers called a stella nova was the light from a supernova in the Milky Way, now catalogued as SN 1604. NASA gives its peak apparent magnitude as approximately −2.5 and its daylight visibility as about three weeks.
Kepler was clouded out
Additional observers reported the object in Italy on 10 October. Clouds kept Kepler from seeing it in Prague until 17 October, after which he monitored it for more than a year; his 1606 book gave the event its enduring name.
Modern secondary sources contest who saw it first: NASA names Lodovico delle Colombe, whereas the 2021 historical study identifies Altobelli and documents his repeated insistence on the date.
Historical naked-eye brightness estimates carry substantial uncertainty — a modern review assigns typical errors of roughly 0.25 to 0.5 magnitude.
Sources
Researched 23 Aug 2026 5 sources 2 audit passes
How this was checked
Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →
What the sources leave uncertain
- The 9 October date is well supported, but the identity of the first observer is contested in modern secondary sources. NASA names Lodovico delle Colombe, whereas a 2021 historical study identifies Ilario Altobelli as the first known reporter and documents his repeated insistence on the date.
- Historical naked-eye brightness estimates have substantial uncertainty; a modern review assigns typical errors of roughly 0.25–0.5 magnitude.
- The Type Ia classification is strong, but the exact progenitor system remains unresolved because no predicted surviving companion has been found.