This volume is the first part of notes that evolved during my teaching of a small class for junior and senior physics students at MIT. The course focused on a physical, analytical approach to astronomy and astrophysics. The material in this volume presents methods, tools and phenomena of astronomy that the science undergraduate should incorporate into his or her knowledge prior to or during the practice and study of quantitative and analytical astronomy and astrophysics.

The content is a diverse set of topics ranging across all branches of astronomy, with an approach that is introductory and based upon physical considerations. It is addressed primarily to advanced undergraduate science students, especially those who are new to astronomy. It should also be a useful introduction for graduate students or postdoctoral researchers who are encountering the practice of astronomy for the first time. Algebra and trigonometry are freely used, and calculus appears frequently. Substantial portions should be accessible to those who remember well their advanced high school mathematics.

Here one learns quantitative aspects of the electromagnetic spectrum, atmospheric absorption, celestial coordinate systems, the motions of celestial objects, eclipses, calendar and time systems, telescopes in all wavebands, speckle interferometry and adaptive optics to overcome atmospheric jitter, astronomical detectors including CCDs, two space gamma-ray experiments, basic statistics, interferometry to improve angular resolution, radiation from point and extended sources, the determination of masses, temperatures, and distances of celestial objects, the processes that absorb and scatter photons in the interstellar medium together with the concept of cross section, broadband and line spectra, the transport of radiation through matter to form spectral lines, and finally the techniques used in neutrino. cosmic-ray and gravitational-wave astronomy.