- A Hipparcos Census of the Nearby OB Associations (iopscience.iop.org)
A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound “moving groups,” which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V ≲ 6 mag), with spectral types earlier than ∼B5. The Hipparcos measurements allow a major improvement in this situation.
- History of the alphabet (Wikipedia)
The history of the alphabet goes back to the consonantal writing system used for Semitic languages in the Levant in the 2nd millennium BCE. Most or nearly all alphabetic scripts used throughout the world today ultimately go back to this Semitic proto-alphabet. Its first origins can be traced back to a Proto-Sinaitic script developed in Ancient Egypt to represent the language of Semitic-speaking workers and slaves in Egypt. Unskilled in the complex hieroglyphic system used to write the Egyptian language, which required a large number of pictograms, they selected a small number of those commonly seen in their Egyptian surroundings to describe the sounds, as opposed to the semantic values, of their own Canaanite language. This script was partly influenced by the older Egyptian hieratic, a cursive script related to Egyptian hieroglyphs. The Semitic alphabet became the ancestor of multiple writing systems across the Middle East, Europe, northern Africa, and Pakistan, mainly through Ancient South Arabian, Phoenician, Paleo-Hebrew (closely related and initially virtually identical to the Phoenician alphabet or even derived from it) and later Aramaic (derived from the Phoenician alphabet), four closely related members of the Semitic family of scripts that were in use during the early first millennium BCE.