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Mintaka /?m?nt?k?/, designation Delta Orionis (? Orionis, abbreviated Delta Ori, ? Ori) and 34 Orionis (34 Ori), is a multiple star system some 1,200 light-years from the Sun in the constellation of Orion. Together with Alnitak (Zeta Orionis) and Alnilam (Epsilon Orionis), the three stars form Orion's Belt, known by many names among ancient cultures. When Orion is near the meridian, Mintaka is the rightmost of the Belt's stars when viewed from the Northern Hemisphere facing south.
The name Mintaka is derived from an Arabic term for 'belt': man?aqa.
Mintaka is the westernmost of the three stars of Orion's belt. It is easily visible to the naked eye, one of the brightest stars in the sky, and has been known since antiquity.
Radial velocity measurements taken by Henri-Alexandre Deslandres in 1900 at Paris Observatory showed that Mintaka had a variable radial velocity and therefore was a spectroscopic binary. His preliminary orbital period estimate of 1.92 days was shown to be incorrect in 1904 when Johannes Franz Hartmann using photographic plates taken at Potsdam Observatory showed that the orbital period was 5.7 days. Hartmann also noticed that the calcium K line at 393.4 nanometres in the stellar spectrum did not share in the periodic displacements of the lines due to orbital motion of the star and theorized that there was a cloud in the line of sight to Mintaka that contained calcium. This was the first detection of the interstellar medium.

? Orionis is a multiple star system. There is a magnitude 7 star about 52 arcseconds away from the second-magnitude primary and a much fainter star in between.
The primary component is itself a triple system: a class O9.5 bright giant and a class B main-sequence star orbit every 5.73 days and exhibit shallow eclipses when the star dims about 0.2 magnitudes, and a B-class sub-giant is resolved 0.26" away. At the primary eclipse, the apparent magnitude (of the whole system) drops from 2.23 to 2.35, while it only drops to 2.29 at the secondary eclipse.

The distance derived from the Hipparcos satellite parallax is 21230 pc, while spectroscopic distances, comparisons to similar stars, and cluster membership all suggest a value more than double that. This type of unreconcilable discrepancy is not unique to Mintaka and the reasons for it have yet to be clarified. In Gaia Data Release 2, components B and C are listed with parallaxes of 3.45310.0371 mas and 2.57270.0767 mas, respectively, implying distances considerably further than the Hipparcos-derived value for the primary.

The puzzle consists of two intersecting circles rotating with four steps each. The radii are different and the bigger one intersects deeper that the center of the smaller circle. It is completely doctrinaire.



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