A brief history of solar science

Today solar science is a diverse and rapidly evolving discipline. But the roots of solar science can be traced back to ancient times and beyond. Especially the observation of dark sunspots has a long tradition. While the oldest plausible record dates back to Chinese astronomers (800 BC), the first sunspot drawing was made in 1128 by the monk John of Worcester observing large sunspot formations visible to the naked eye. At the beginning of the 17th century, several astronomical milestones were set to modernize the human understanding of the Sun. In 1609, Johannes Kepler expanded the heliocentric system to include elliptical orbits of the planets around the Sun. In the same year, the invention of the telescope became the starting shot in a new era of solar and stellar observations.

Zeitstrahl der wichtigsten Ereignisse in der Geschichte der Sonnenphysik.

The most prominent and pioneering solar observers were Galileo Galilei and Christoph Scheiner who performed the first sunspot observations with telescopes between 1610 and 1612. The interpretations of sunspots were diverse, though. They reached from objects orbiting the Sun, to clouds in the solar atmosphere or even holes in the luminous atmosphere showing the cool (possibly habitable) solar surface.

In the 19th century, the field of solar and astronomical research was revolutionized by the birth of spectroscopy. Already in the late 1660s, Isaac Newton has used a prism to separate sunlight into its chromatic components, which served as the basis for solar spectroscopy. By the beginning of the 19th century the groundbreaking discoveries followed in quick succession. William Herschel and William Wollaston detected the Sun’s invisible infrared and ultraviolet radiation. The latter also found dark lines crossing the continuous solar spectrum and interpreted the lines as the marked boundaries between the natural colors. The optician Joseph von Fraunhofer made certainly one of the most important steps in 1814. He mapped more than 500 spectral lines in the visible range and linked them to the solar atmosphere. Shortly later, scientists like John Herschel or Gustav Kirchhoff compared the solar absorption lines with the emission spectrum of flames and concluded that the spectral lines reveal the chemical composition and properties of the Sun’s atmosphere.

With this knowledge, many milestone discoveries were made in the field of Solar Physics. In 1858, Richard Carrington and Gustav Spörer discovered the Sun’s differential rotation. At the beginning of the 20th century, groundbreaking findings were made by George Ellery Hale. With new high-resolution telescopes, he detected the magnetic field of sunspots and investigated the magnetic 22-year cycle of the Sun.

The picture and additional information can be found in the PhD thesis (Chapter 1) of J. Löhner-Böttcher.