Observational astronomy refers to the branch of astronomy that deals with the study of the universe through observation. It involves various methods such as telescopes, cameras, and other instruments to observe and measure the celestial objects. Some common synonyms for observational astronomy include astrometry, which refers to the measurement of the positions and motions of celestial objects; photometry, which is the measurement of the brightness of celestial objects; spectroscopy, the study of the electromagnetic spectrum of celestial objects; and cosmology, which deals with the origin and evolution of the universe. These terms are often used interchangeably with observational astronomy, and they all play a crucial role in our understanding of the cosmos.