SN 1604, also known as Kepler's Supernova, Kepler's Nova or Kepler's Star, was a Type Ia supernova that occurred in the Milky Way, in the constellation Ophiuchus. Appearing in 1604, it is the most recent supernova in our galaxy to have been unquestionably observed by the naked eye, occurring no farther than 6 kiloparsecs from Earth. Prior to the adoption of the current naming system for supernovae, it was named for Johannes Kepler, the German astronomer who described it in De Stella Nova.
Observation
Visible to the naked eye, Kepler's Star was brighter at its peak than any other star in the night sky, with an apparent magnitude of −2.5. It was visible during the day for over three weeks. Records of its sighting exist in European, Chinese, Korean and Arabic sources. It was the second supernova to be observed in a generation. No further supernovae have since been observed with certainty in the Milky Way, though many others outside our galaxy have been seen since S Andromedae in 1885. SN 1987A in the Large Magellanic Cloud was visible to the naked eye. Evidence exists for two Milky Way supernovae whose signals would have reached Earth 1680 and 1870 – Cassiopeia A, and G1.9+0.3 respectively. There is no historical record of either having been detected in those years probably as absorption by interstellar dust made them fainter. The remnant of Kepler's supernova is considered to be one of the prototypical objects of its kind and is still an object of much study in astronomy.
Controversies
Astronomers of the time were concerned with observing the conjunction of Mars and Jupiter, which they saw in terms of an auspicious conjunction, linked in their minds to the Star of Bethlehem. However, cloudy weather prevented Kepler from making any celestial observations. Nevertheless, his fellow astronomers Wilhelm Fabry, Michael Maestlin and Helisaeus Roeslin were able to make observations on 9 October, but did not record the supernova. The first recorded observation in Europe was by Lodovico delle Colombe in northern Italy on 9 October 1604. Kepler was only able to begin his observations on 17 October while working at the imperial court in Prague for Emperor Rudolf II. The supernova was subsequently named after him, even though he was not its first observer, as his observations tracked the object for an entire year. These observations were described in his book De Stella nova in pede Serpentarii.
Delle Colombe–Galileo controversy
In 1606, Delle Colombe published Discourse of Lodovico delle Colombe in which he shows that the "Star Newly Appeared in October 1604 is neither a Comet nor a New Star" and where he defended an Aristotelian view of cosmology after Galileo Galilei had used the occasion of the supernova to challenge the Aristotelian system. The description of Galileo's claims is as follows:
Galileo explained the meaning and relevance of parallax, reported that the nova displayed none, and concluded, as a certainty, that it lay beyond the moon. Here he might have stopped, having dispatched his single arrow. Instead he sketched a theory that ruined the Aristotelian cosmos: the nova very probably consisted of a large quantity of airy material that issued from the earth and shone by reflected sunlight, like Aristotelian comets. Unlike them, however, it could rise beyond the moon. It not only brought change to the heavens, but did so provocatively by importing corruptible earthy elements into the pure quintessence. That raised heaven-shattering possibilities. The interstellar space might be filled with something similar to our atmosphere, as in the physics of the Stoics, to which Tycho had referred in his lengthy account of the nova of 1572. And if the material of the firmament resembled that of bodies here below, a theory of motion built on experience with objects within our reach might apply also to the celestial regions. “But I am not so bold as to think that things cannot take place differently from the way I have specified.”
Kepler–Roeslin controversy
In Kepler's De Stella Nova, he criticised Roeslin concerning this supernova. Kepler argued that in his astrological prognostications, Roeslin had picked out just the two comets, the Great Comet of 1556 and 1580. Roeslin responded in 1609 that this was indeed what he had done. When Kepler replied later that year, he simply observed that by including a broader range of data Roeslin could have made a better argument.
