Final answer:
Hipparchus used apparent magnitudes to classify stars by brightness. He established the foundation for the modern system of measuring stellar brightness and discovered the precession of the equinoxes.
Step-by-step explanation:
An ancient Greek astronomer named Hipparchus used apparent magnitudes to rate the stars based on how bright they looked in the night sky.
Hipparchus and Stellar Magnitudes
Considered one of the greatest astronomers of antiquity, Hipparchus was born in Nicaea, in what is now Turkey. Around 150 BCE, he established an observatory on the island of Rhodes. His contributions to astronomy include compiling a detailed star catalog containing the positions and estimated apparent brightness of nearly 1,000 stars. This catalog was significant for the designation of celestial coordinates, analogous to the latitude and longitude used on Earth, for each star.
Hipparchus's work on stellar brightness led to the division of stars into different categories of apparent magnitudes. He labeled the brightest stars as 'stars of the first magnitude' and continued to categorize the others in descending order of brightness. Although the system has been modified, it forms the basis for the modern stellar magnitude system used in astronomy today.
Besides documenting stellar brightness, Hipparchus made other significant contributions, including the discovery of the precession of the equinoxes, noting that the celestial sphere's axis shifts over time.