Mekbuda — Stella variabile in Gemelli

Mekbuda, Zeta Geminorum, is a classical Cepheid variable — a yellow supergiant of spectral type G1 Ib that pulsates regularly between magnitudes 3.62 and 4.18 with a period of 10.15 days. It lies about 1,350 light-years away, and at maximum light it shines at roughly 3,000 solar luminosities. As a Cepheid, Mekbuda follows the period-luminosity relation that Henrietta Leavitt discovered in 1912 and that Edwin Hubble later used to measure galactic distances.

Mekbuda is an ideal naked-eye Cepheid project: compare its brightness to Lambda Gem (3.58) and Nu Gem (4.15) every clear night and you can construct its own light curve in a few weeks. The variation is a full half magnitude — easily detected by eye. Mekbuda marks the western knee of Pollux, the southern Gemini twin. Best observed December through May.

The name comes from the Arabic "maqbūdah," meaning "the contracted" or "folded paw" — a pre-Islamic astronomical image of a lion's paw. The variability was discovered by Julius Schmidt in 1825. Mekbuda was one of the first Cepheid variables used to calibrate the period-luminosity relation: because it is close enough for accurate parallax measurement, it anchors the brightness scale that leads outward to other galaxies.