This textbook presents a comprehensive and didactic discussion of the observations of stars and planetary systems. Aimed at upper-undergraduate and graduate students of astrophysics and scientists and researchers, alike, this textbook brings together the clarity of a traditional teaching approach with the excitement of today’s scientific discoveries.

Over the past decade, large surveys that measure the positions, motions, spectra, and images of stars—together with new spacecraft exploring the Solar System and major advances in exoplanet research—have greatly deepened our understanding of the universe. These rapid developments highlight the need for a book that draws on real observations and explains what they reveal about the physical world.

The book starts with fundamental concepts and develops them to the graduate-level detail. The reader is encouraged to delve deeper into the covered material independently. Numerous figures, illustrations and analogies will be especially valuable to students as they develop curriculum assignments or prepare visual materials for their own projects. Suggested discussion topics at the end of each chapter and over 650 cited references contribute to the same goal.

Tomaž Zwitter is a full professor at the Faculty of Mathematics and Physics, University of Ljubljana, where he teaches introductory astronomy, observational astrophysics, and stellar astrophysics. His research spans a wide range of topics, including the interstellar medium, single and binary stars, and the structure, evolution, and composition of our Galaxy.

From 2004 to 2023, he led Slovenia’s national research program Astrophysics and Physics of the Atmosphere, funded by the Slovenian Research Agency, and he has also directed several projects supported by the European Space Agency.

Prof. Zwitter has co‑authored more than 260 peer‑reviewed research papers, which have been cited over 50,000 times. He served as a project scientist of the RAdial Velocity Experiment (RAVE) and is a core member of the Galah (galah-survey.org) and Gaia‑ESO (gaiaeso.eu) spectroscopic survey teams. Since 2000, he has been deeply involved in the Gaia mission, particularly in analyzing data from its Radial Velocity Spectrometer.

He has received several major awards, including the Golden Plaque of the University of Ljubljana (2013), the Zois Recognition for significant research achievements (2013), and the Zois Award for outstanding research achievements (2021).

Beyond research and teaching, he is active in public outreach. He frequently gives public lectures, translates Astronomy Picture of the Day (APOD) and other science materials into Slovene, appears regularly in the media, and prepares a monthly astronomy program broadcast on national radio.