Astronomical Images : The vapours near the Sun

Johannes Kepler

Astronomical Images

<p style='text-align: justify;'>Johannes Kepler's <i>Epitome astronomiae copernicanae</i> was published in three successive parts from 1617 to 1621. Intended as a new astronomical textbook for students, the <i>Epitome</i> covered much of the material traditionally associated with the <i>Theoricae planetarum</i> and works on spherical astronomy. Despite its title, the <i>Epitome</i> does not draw its information directly from Copernicus' <i>De revolutionibus</i> but is an original synthesis, mainly based on Kepler's own earlier works. It thus presents a comprehensive survey of Kepler's new astronomy. The text is illustrated by an abundance of images, with some figures printed multiple times. Though utilising illustrations traditionally belonging to the iconography of spherical astronomy, Kepler also included images concerning unusual topics, such as atmospheric vapours. For instance, Kepler stressed the importance of understanding the phenomenon of atmospheric refraction, which had been ignored by some other astronomers including Galileo. This effect was thought to be caused by the different densities of the Air surrounding the Earth and the celestial Aether. Though the two elements were distinct, there was no barrier existing between them and the vapours could move freely through the sky. As a consequence, fumes could collect around the Sun, obscuring its rays.These two rather crude illustrations demonstrate that the location of these vapours must be close to the Sun's body, for two reasons. Firstly, as the top figure is intended to illustrate, a more terrestrial location would obscure not only the rays of the Sun, but also the visibility of the stars. Secondly, as the bottom figure is intended to illustrate, the phenomenon sometimes lasts for up to a year (that is, in every position of the Earth in its orbit around the Sun). Therefore the vapours must be located close to the body of the Sun.</p>