Overview
Rome produced few original astronomical theories. Much of its sky knowledge was inherited from Greek astronomers, and Roman contributions were mostly practical: calendars, writing, teaching, navigation and the cultural uses of astronomy. That is still a significant legacy, since many of the names we use for planets and constellations are Latin.
The Greek inheritance
Greek astronomers developed geometric models of the sky and catalogued stars. Hipparchus (2nd century BCE) is credited with an early star catalog and with discovering the precession of the equinoxes. Later, Ptolemy, who worked in Roman Egypt in the 2nd century CE, wrote the Almagest, which presented an Earth-centered model and listed 48 constellations. He wrote in Greek and lived under Roman rule, but he is usually counted as part of the Greek scientific tradition rather than as a Roman.
Romans studied and translated Greek ideas. Educated Romans often read Greek, so Greek texts circulated directly.
The calendar and Julius Caesar
The Roman calendar originally had irregularities, and months drifted out of step with the seasons. In 46 BCE, Julius Caesar reformed it with advice from astronomers, usually associated with Sosigenes of Alexandria. The result was the Julian calendar, with a year of 365 days and a leap day every fourth year. It was slightly too long compared to the true year, and was later replaced in many countries by the Gregorian calendar.
Roman writers on the sky
- Vitruvius, an architect, wrote about the zodiac, the planets and sundial design in his work on architecture.
- Lucretius wrote a philosophical poem touching on the nature of the heavens.
- Pliny the Elder included astronomy in his encyclopedic Natural History.
- Manilius wrote a Latin poem on astrology.
- Cicero translated a Greek poem on the constellations by Aratus, which helped spread constellation lore in Latin.
These authors are valuable sources, though they were often summarizing rather than observing.
Did the Romans know about planets?
Yes. They knew the five planets visible to the naked eye (see seeing planets with a telescope for what they look like through modern optics): Mercury, Venus, Mars, Jupiter and Saturn, together with the Sun and Moon as wandering bodies. The planets carry Roman god names, which came partly from earlier Greek names matched to Roman gods. Romans did not have telescopes (see telescope types explained for the instruments that came later), so they knew nothing of Uranus or Neptune, or of the moons of Jupiter.
Astrology and religion
Astronomy and astrology were often intertwined. Many Romans consulted astrologers, and the zodiac was widely used in art and in popular belief. Astrology is not supported by scientific evidence, but it does help explain why sky records were kept. Religious festivals also followed the calendar, and some officials interpreted celestial events as omens. The stories behind the figures are covered in constellations and the stories behind them.
Practical uses
- Timekeeping: sundials and water clocks divided the day into hours.
- Farming: writers such as Columella and Pliny linked stars’ rising and setting to farm tasks.
- Navigation: sailors steered by stars, although Roman sea travel was often coastal.
What Romans left behind
Latin names remain throughout the sky: the planets, many constellations such as Ursa Major and Scorpius, and the names of months. The zodiac figures described by Roman authors are still used. For a modern look at these patterns, see our guide to the most famous constellations.
Frequently asked questions
Who were some famous Roman scientists? Pliny the Elder, Vitruvius and Lucretius are often named, though they were writers rather than observers. Ptolemy lived in Roman Egypt but is classed with the Greek tradition.
Did the Romans make original astronomical discoveries? Few are recorded; they mainly preserved, taught and applied Greek knowledge.
What did ancient Greek astronomers discover? Examples include precession (Hipparchus), early estimates of the size of Earth (Eratosthenes) and planetary models (Ptolemy).