- Main sequence (Wikipedia)
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of stars on and off the band are believed to indicate their physical properties, as well as their progress through several types of star life-cycles. These are the most numerous true stars in the universe and include the Sun. Color-magnitude plots are known as HertzsprungโRussell diagrams after Ejnar Hertzsprung and Henry Norris Russell.
- Ur (Wikipedia)
Ur (/สษr/; Sumerian: ๐ถ๐ , ๐๐๐ , or ๐๐๐ Urim; Akkadian: ๐๐๐ Uru; Arabic: ุฃูููุฑ, romanized: สพลซr; Hebrew: ืืึผืจโ) was an important Sumerian city-state in ancient Mesopotamia, located at the site of modern Tell el-Muqayyar (Arabic: ุชู ูฑููู
ููููููุฑ) in south Iraq’s Dhi Qar Governorate. Although Ur was once a coastal city near the mouth of the Euphrates on the Persian Gulf, the coastline has shifted and the city is now well inland, on the south bank of the Euphrates, 16 km (10 mi) from Nasiriyah in modern-day Iraq. The city dates from the Ubaid period circa 3800 BC, and is recorded in written history as a city-state from the 26th century BC, its first recorded king being Mesannepada.