Astronomers of the time (including Kepler) 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 ("On the new star in Ophiuchus's foot", Prague 1606).