Timocharis facts for kids

Timocharis of Alexandria was an ancient Greek astronomer and philosopher. He lived around 320 to 260 BC. He was probably born in Alexandria, a famous city in Egypt. He lived at the same time as Euclid, a very well-known mathematician.

Discoveries and Work

Most of what we know about Timocharis comes from the writings of another famous astronomer named Ptolemy. Ptolemy wrote about Timocharis in his important book, the Almagest. These writings show that Timocharis worked in Alexandria during the 290s and 280s BC.

Star Observations

Ptolemy wrote down the declination of 18 stars. Declination is like a star's height in the sky. These measurements were made by Timocharis or another astronomer named Aristillus around 290 BC.

Between 295 and 272 BC, Timocharis also recorded four times when the Moon passed in front of a star. This event is called a lunar occultation. He also recorded when the planet Venus passed very close to a star. This might have happened on October 12, 272 BC. At that time, Venus came very close to a star called Eta Virginis. He used both Egyptian and Athenian calendars to record these dates.

Early Records

Timocharis's observations are some of the oldest Greek records that we can link to a specific date. Only older records, like the summer solstice of 432 BC, are known. Those were noted by Euctemon and Meton.

Timocharis worked with Aristillus at an observatory. This observatory was likely part of the famous Library of Alexandria. Their tools were simple. They probably used gnomons (like sundials), sundials themselves, and armillary spheres. An armillary sphere is a model of objects in the sky. Timocharis and Aristillus lived at the same time as Aristarchus of Samos. Aristarchus was another important astronomer. But we don't know if they worked together.

Precession of the Equinoxes

During his sky observations, Timocharis noted something important about the star Spica. He saw that Spica was 8 degrees west of the Autumnal equinox. The Autumnal equinox is a specific point in the sky.

Later, another astronomer named Hipparchus observed Spica. He found it was only 6 degrees west of the Autumnal equinox. Hipparchus used older records of lunar eclipses to figure out when Timocharis made his observations. From this difference, Hipparchus realized that the positions of stars in the sky change over time. This led him to discover the precession of the equinoxes. This means the Earth's axis slowly wobbles. He figured out this wobble was at least 1/100th of a degree each year.

First Star Catalogue

Around the 3rd century BC, Timocharis and Aristillus created the first star catalogue in the Western world. A star catalogue is like a map or list of stars. It helps astronomers find and study them.

Mercury and the Moon

Timocharis is also known as the first astronomer to write down a mention of the planet Mercury.

A crater on the Moon is named after him. It is called Timocharis crater.

See also

In Spanish: Timocares de Alejandría para niños