Matar — ペガススの恒星

Matar, Eta Pegasi, is a bright-giant binary system about 215 light-years away in the constellation Pegasus. The primary is a G-type bright giant (G2 II-III) roughly 5 times the Sun's mass and 175 times its luminosity, accompanied by a closer F-type companion in a 813-day orbit. Matar marks one of the corners of the fainter Pegasus "neck," north of the Great Square. It shines at magnitude 2.94 and has a soft yellow-white color in binoculars.

Matar is an easy naked-eye target in moderately dark skies, forming the northwestern corner of a prominent asterism above the Great Square of Pegasus. Use the line from Scheat (Beta Peg) northward toward Polaris; Matar sits roughly one-third of the way along. The stellar companion is far too close (tens of milliarcseconds) to split visually in any amateur telescope — Matar is effectively a single point of warm yellow light at the eyepiece. Best observed August through December when Pegasus dominates the evening sky.

The name Matar derives from the Arabic "al-Sa'd al-Matar," meaning "the lucky star of rain," an allusion to its heliacal rising at the start of the rainy season on the Arabian peninsula. The International Astronomical Union formally adopted the name in 2016 as part of the Working Group on Star Names standardization effort. Along with Scheat, Markab, and Algenib, Matar has been used for centuries as a celestial marker of Pegasus.