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First Stonehenge monument constructed
The first henge monument at Stonehenge dates to about 3000 BCE.
Solar-aligned Stonehenge stone circle erected
Stonehenge’s central stones were arranged to align with solstitial movements of the Sun.
Egyptian calendars documented by the Old Kingdom
Calendars based on lunar cycles and agricultural seasons had developed by about 2450 BCE.
Nebra Sky Disc deposited near Nebra
The Nebra Sky Disc was buried on the Mittelberg near Nebra around 1600 BCE.
Early Chinese sunspot observations recorded
NASA’s solar history associates sunspot observations in the Book of Changes with approximately 800 BCE.
Pythagorean astronomy develops
Pythagoras is included in NASA’s chronology of the early mathematical study of astronomy.
Meton introduces a calendar in Athens
Meton introduced a calendar connecting lunar months with the solar year.
Aristarchus proposes a Sun-centered arrangement
Aristarchus estimated the Sun’s size and distance and proposed that Earth moves around the Sun.
Eratosthenes estimates Earth’s size
Eratosthenes used geometrical reasoning to estimate the size of Earth.
Chankillo solar observatory operates
Chankillo’s towers and observation points served as a solar calendar in ancient Peru.
Halley’s Comet recorded in China
Chinese observations provide the first reliably recorded appearance of Halley’s Comet.
Antikythera mechanism dates to the late Hellenistic period
The National Archaeological Museum dates the mechanism and its astronomical inscriptions to around 150–100 BCE.
Hipparchus identifies precession
Hipparchus identified precession of the equinoxes and estimated the Moon’s distance.
Roman calendar reform instituted
Julius Caesar reformed the Roman calendar, establishing the basis of the Julian calendar.
Ptolemy compiles the Almagest
Ptolemy’s astronomical synthesis set out a geocentric mathematical model of planetary motion.
Chinese observers record the guest star SN 185
Chinese records describe a guest star associated by modern astronomers with supernova SN 185.
Chinese observers record SN 393
Chinese astronomers recorded a guest star interpreted as supernova SN 393.
Aryabhatiya composed
Aryabhata composed the Aryabhatiya, an influential work on mathematics and astronomy.
Brahmasphutasiddhanta written
Brahmagupta wrote the Brahmasphutasiddhanta, addressing mathematical and astronomical calculations.
House of Wisdom develops under al-Ma’mun
The Baghdad institution supported the study and transmission of scientific and astronomical knowledge.