14 November 2004

Eid Mubarak 1425

Today (or tomorrow, in some parts of the world) is Eid-ul-Fitr, the Muslim holiday after the end of the fast of Ramadan. The reason it is celebrated on different days in different regions is that the Muslim liturgical calendar is based on lunar months, each beginning with the sighting of the new moon. Astronomical positions and atmospheric conditions determine when that new moon can first be seen, and where.

The importance of predicting astronomical events is one reason astronomy flourished in Muslim lands while Europe was falling into the Dark Ages. One legacy of mediaeval Islamic science is that we still use Arabic names for most of the prominent stars. If you go out this evening and the sky is clear you will probably be able to see the big square made up of stars in the constellations of Pegasus and Andromeda. The four corners are:
Modern NameArabic NameMeaningModern Designation
MarkabMankib al-FarasThe shoulder of the horseAlpha Pegasi
ScheatAs-SaqThe legBeta Pegasi
AlgenibAl-JanbThe flankGamma Pegasi
Alpheratz (or SirrahSurrat al-FarasNavel of the horseAlpha Andromedae

Create a sky map for your location. Here is a list of Arabic star names. What does "Betelgeuse" mean?

If it is really clear, and you are away from the lights of the city, you will be able to see the spiral galaxy in Andromeda, the most distant object visible to the naked eye. The photons hitting your eye when you see this nearest-neighbor galaxy have been traveling for 2.2 million years. (They were emitted before human beings like us evolved -- though our extinct relative Homo erectus was already making tools.)

The Andromeda galaxy was known to Islamic astronomers at the beginning of the 10th century. It was illustrated and called "a little cloud" by Abd-al-Rahman Al Sufi, of the court of the Emire Adud ad-Daula in Isfahan, Persia, in his famous "Book of Fixed Stars" in 964.

More on mediaeval Islamic astronomy:

Islamic Gateway
University of Nevada at Reno
King Fahd University of Petroleum and Minerals

No comments: