main-sequence star: see Hertzsprung-Russell diagram.

Class	Color	Surface Temperature	Strong Lines
O	blue-white	35,000°C;	ionized helium
B	blue-white	21,000°C;	helium
A	white	10,000°C;	hydrogen
F	creamy	7,000°C;	ionized calcium
G	yellow	6,000°C;	calcium
K	orange	4,500°C;	titanium oxide
M	red	3,000°C;	titanium oxide

Spanish Main, mainland of Spanish America, particularly the coast of South America from the isthmus of Panama to the mouth of the Orinoco River. Spanish treasure fleets, sailing home from the New World, passed through the Caribbean N of the Main and were attacked by English buccaneers raiding from the islands and coast. Pirates congregated there until the 19th cent., and the words "Spanish Main" have become the symbol of piratic romance.

Offenbach am Main or Offenbach, city (1994 pop. 116,870), Hesse, S central Germany, on the Main River. It is an industrial center long famous for the manufacture of leather goods; chemicals, electrical products, textiles, and machinery are also produced. Offenbach was first mentioned in the late 10th cent.; it passed to the counts of Isenburg in the 15th cent. and was annexed by Hesse-Darmstadt in 1816. A Renaissance-style palace (1564-78) and museums of leathercraft, typography, and graphics are located in the city.

Main, river, c.310 mi (500 km) long, formed near Kulmbach, E central Germany, by the confluence of the Roter Main and the Weisser Main, both of which rise in the Fichtelgebirge. It then winds generally west through the rich farmland of central Germany and past the industrial areas of Schweinfurt, Würzburg, Aschaffenburg, and Frankfurt to the Rhine River at Mainz. Navigable from its junction with the Regnitz River, its chief tributary, the Main is an important east-west route. The Ludwig Canal connects it with the Danube River. A recently completed addition to the canal links the Danube with the Rhine, allowing barge traffic from the North Sea to the Black Sea, a distance of more than 2,000 mi (3,200 km). There are about 40 hydroelectric power plants on the Main, of which Griesheim (62,000-kW capacity) is the largest.

Frankfurt am Main, Germany: see Frankfurt.

City (pop., 2002 est.: city, 641,076; metro. area, 1,896,741), western Germany. Located on the Main River, it was the site of a Roman military settlement in the 1st century AD. It served as a royal residence of the Carolingians from the 9th century through the Middle Ages. A free imperial city (1372–1806), it lost its status under Napoleon but regained it in 1815. It was the capital of Germany from 1816 until it was annexed by Prussia in 1866. Its Old Town, once the largest surviving medieval city in Germany, was mostly destroyed in World War II; some landmarks survive, including its red sandstone cathedral, dedicated in 1239. International trade fairs have been held in Frankfurt since 1240; in the modern era, book, automobile, and computer fairs are popular annual events. The city's manufactures include machinery and printing materials, as well as the high-quality sausages known as frankfurters. Frankfurt is the birthplace of Johann Wolfgang von Goethe.

Learn more about Frankfurt (am Main) with a free trial on Britannica.com.