**What did Ptolemy do in astronomy?** Ptolemy made contributions to astronomy, mathematics, geography, musical theory, and optics. He **compiled a star catalog and the earliest surviving table of a trigonometric function** and established mathematically that an object and its mirror image must make equal angles to a mirror.

**What is Ptolemy most famous for?** Key facts. Claudius Ptolemy was a 2nd century Greek mathematician, astronomer and geographer famous for **his controversial geocentric theory of the universe**, which would form the basis of our understanding of the motions of stars and planets for over than a thousand years.

**What did Ptolemy believe in astronomy?** Based on observations he made with his naked eye, Ptolemy saw the Universe as a set of nested, transparent spheres, with Earth in the center. He posited that **the Moon, Mercury, Venus, and the Sun all revolved around Earth**.

**What is an interesting fact about Ptolemy?** **Ptolemy was a great mathematician, astronomer, and geographer**. While his most famous work is in the field of astronomy, he was more successful as a geographer. His world map was the most accurate point of reference for many years.

## What did Ptolemy do in astronomy? – Additional Questions

### What discoveries did Ptolemy make?

Ptolemy |

Citizenship |
Roman; ethnicity: Greco-Egyptian |

Known for |
Ptolemaic universe Ptolemy’s world map Ptolemy’s theorem |

Scientific career |

Fields |
Astronomy, Geography, Astrology, Optics |

### What did Ptolemy discover about light?

Defending the theory that vision is due to a flow emanating from the eye, Ptolemy analyzed **the reflection of light on flat and spherical mirrors, and its refraction when it crosses the surface between two transparent media**.

### Did Ptolemy have a family?

After Ptolemy I divorced Artacama, he married the Macedonian noblewoman Eurydice. Unhappy with this political alliance, Ptolemy put her aside, and **by 317 B.C.E. had married his widowed half-sister and lover, Berenice**.

### Where was Ptolemy born?

Alexandria, Egypt

Ptolemy / Place of birth

### When was Ptolemy born?

100 AD

Ptolemy / Date of birth

### What is the Ptolemaic model of the universe?

Model of the universe

Ptolemy placed the Earth at the centre of his **geocentric model**. Using the data he had, Ptolemy thought that the universe was a set of nested spheres surrounding the Earth. He believed that the Moon was orbiting on a sphere closest to the Earth, followed by Mercury, then Venus and then the Sun.

### Why is Ptolemy important to the history of astronomy?

Why is Ptolemy important to the history of astronomy? **developed the first model of the solar system that made sufficiently accurate predictions of planetary positions**.

### How many planets are in the Ptolemaic system?

### How many stars did Ptolemy count?

For example, whereas Hipparchus had compiled a star catalog (the first of its kind) containing 850 stars, Ptolemy expanded the number in his own catalog to **1,022 stars**.

### Did Ptolemy believe the Earth rotates?

There were astronomers who realised that this apparent motion could also be explained, from a purely mathematical point of view, by assuming that the earth rotates on its axis, but they rejected this option. By the way, **neither Ptolemy nor any other serious astronomer believed that the earth was flat**.

### How does Ptolemy’s model explain day and night?

As far as I understand, the Ptolemaic model explains day and night **by postulating that the whole celestial system revolves around the Earth once every day**. Since we observe the sun to move from East to West over a day, the whole system would have to move in an East to West direction once a day.

### What did Ptolemy think about how planets move?

The most important solution to this problem was proposed by Claudius Ptolemy in the 3rd century AD. He argued that **planets move on two sets of circles, a deferent and an epicycle**. This explained retrograde motion while keeping the planets in their circular orbits around the Earth.

### Where was the sun in Ptolemy’s model?

– It placed the Sun **at the center** so that the planets’ apparent retrograde motion was seen as the earth passed each one in its orbit.