Stars are basic building blocks of the visible Universe and have received astronomers' attention throughout history. Since the late nineteenth century astronomers have been able to investigate the physical processes occuring inside stars and have unravelled their structure, evolution, and death. Current research focusses on their interior structure through measurements of their pulsations, the elemental abundances in their atmospheres and attempts to identify primordial Population III objects, and the mass-loss phenomena during the late stages of their evolution.
Many stars are surrounded by planets, and since the discovery of these extrasolar planets the Solar System is no longer unique. Still, the characteristics of our Solar System can tell us much about its origin and evolution. The composition and dynamics of asteroids and comets hold a valuable record stretching back 4.5 Gyr, while the atmospheres of the planets (and the Saturnian moon Titan) offer important comparison for the Earth atmosphere and climate. Finding new planetary systems around other stars is at the forefront of astronomical research nowadays. It allows us to explore the full range of environments where planets can exist and places our own Solar System in context. The characterization of extrasolar planets, such as their density and atmopsheric composition, is in its infancy, but technological advances hold much promise for this budding field.
Research into stars and planetary systems at Leiden Observatory has many facets. Building on a strong research tradition over the last decades, research is ongoing on stellar variability, on the post-main-sequence evolution of stars, and on the nature and content of OB associations. Leiden reseachers are also active in the fields of minor Solar System bodies and comets, the latter especially through molecular spectroscopy of their volatiles. Much new activity is being developed at Leiden Observatory in the areas of finding and characterizing extrasolar planets, ranging from developing and building the required instrumentation to exploring new detection and characterization methods.