Megrez — おおぐまの恒星

Megrez, Delta Ursae Majoris, is an A-type main-sequence star about 80 light-years away and the faintest of the seven stars of the Big Dipper. It marks the junction where the Dipper's "handle" meets its "bowl." Megrez is about 1.6 times the Sun's mass, twice the radius, and 14 times the luminosity. It is also a suspected debris-disk star, with mid-infrared excess suggesting a surrounding ring of dust.

Megrez's relative faintness (magnitude 3.31) is a classic sky-quality check — if you can see Megrez clearly with the naked eye, you have a reasonably dark site. From light-polluted suburban skies, the Big Dipper looks "incomplete" because Megrez disappears first. Use a pair of binoculars to confirm its white color and position at the corner of the Dipper's bowl, at the base of the handle. Circumpolar from all of the northern hemisphere.

The name Megrez comes from the Arabic "al-maghriz," meaning "the root of the tail" — referring to the tail-root of the great bear. All seven Dipper stars carry Arabic-derived names. Megrez's relatively modest brightness puzzled pre-modern astronomers; some ancient records refer to it being "fainter than expected," possibly due to observer uncertainty about the star's real appearance.