This star appeared in the constellation Ophiuchus, the Greek (Ὀφιοῦχος Ophioukhos) "serpent-bearer" which is also known in Latin as Serpentarius.

With a typical error of less than one minute of arc, remarkable for observations made with the naked eye, he established that it had no noticeable movement.

Thus, as suggested by the supernova observed 32 years previously by Tycho Brahe (SN 1572), were too far away for any kind of parallax to be noticed with the instrumentation of the time.

Kepler also mentioned his measures of the object’s brightness, which compared it with Jupiter, Venus, Mars and several nearby stars.

These were sufficiently precise and extended over a year, allowing the supernova’s light curve to be reconstructed.