The ancient Greek astronomer Meton lived in Athens during the 5th century B.C. He is most famously associated with the Metonic Cycle (although this was also known to the Babylonians and the Chinese before him). The Metonic Cycle (or Enneadecaeteris, from ancient Greek meaning “nineteen years”), is based on the fact that 235 lunar months are almost equal to 19 solar years. Considering that 235 is equal to 19 multiplied by 12, plus another 7 months, then by adding 1 lunar month seven times in a 19-year cycle, a calendar can be formulated that will very nearly follow both the lunar phases and the seasons. Such calendars are called lunisolar. Examples of this are the Hebrew Calendar (used today predominantly for Jewish religious observances) and the Christian Orthodox Church calendar used to calculate the date of Easter. In contrast, the calendar many of us are more familiar with (used in most western countries), the Gregorian one, is a solar calendar and only follows the seasons of the year but not the phases of the moon. So by specifying, for example, a date as being the 15th of January, we immediately know that it is winter but have no idea of the phase of the moon on this day. A lunisolar calendar on the other hand would, within a degree of accuracy, inform us both of the season and the lunar phase. The lunar phases were very important to ancient Athenians as they defined the timing of their festivals.
Historical sources suggest that Meton (together with his assistant Euktemon), placed his observation instrument (the “heliotropion” or “helioscopion”), just above the podium on the hill of the Pnyx where the ancient Athenians hosted their popular assemblies.
Meton may have aligned his heliotropion (which according to ancient scholars was a type of advanced sundial – i.e a solar clock), in order to facilitate the calculation of those important astronomical parameters. From his chosen position the sunrise at the summer solstice is seen from the peak of mount Lycabettus, while six months later, at the winter solstice, the sun rises from the summit of Hymettus. Finally, at the equinoxes, sunrise aligns with the Acropolis rock. He reportedly performed calculations on the summer solstice of 432 B.C. The summer solstice was important to ancient Athenians as it signalled the beginning of a new year. The first month of the new year, Hekatombaion, began with the first new moon after the summer solstice.
Where to digest your knowledge:
The Islamic Art museum may not be directly related to science (although definitely worth a visit) but its beautifully decorated top floor cafe is one of the hidden gems of Athens. It also boasts a terrace with a view worthy of an astronomical observatory! Note that the cafe access is free of the museum admittance charge.