Zeta Puppis (Zeta Pup, ζ Puppis, ζ Pup) is a star in the constellation of Puppis. It is also known by the traditional names Naos ( /ˈneɪ.ɒs/, from the Greek ναύς "ship") and Suhail Hadar (سهيل هدار, possibly "roaring bright one") in Arabic.
Its spectral class is O4If, making it an exceptionally hot star, and it is one of the sky's few naked-eye class O-type stars. It had been assumed to be part of the Vela complex near the Gum nebula and at over 400 parsecs, but the 2008 reduction of Hipparcos data gave a distance of 335 parsecs (1,093 ly) ± 4%. Its surface temperature is 42,000 K, the current mass is calculated at 22.5 M☉ and the radius at 14 R☉ but these values are highly uncertain. Older derivations assumed the larger distance and were correspondingly larger, but some new calculations still give values up to twice these.
Zeta Puppis is an extreme blue supergiant, one of the brightest stars in the Milky Way in terms of absolute magnitude. Visually, it is 12,500 times more powerful than the Sun, but being an extreme blue star most of its radiation is in the ultraviolet, and when this is considered it is over 500,000 L☉.
For comparison, at the distance of Sirius, Naos would cast strong shadows on Earth, with a visible magnitude of -8 (near that of the quarter moon). In order for Naos to appear equal to the Sun's apparent magnitude of -26.8 combined with Earth-like temperatures, a planet would need to be over 100 AU away from Naos, more than twice Pluto's maximum distance.
Zeta Puppis, being typical of O-type stars, is also notable for its extremely strong stellar wind, and it has garnered increasing attention for this over the past decade. Its stellar wind velocity has been estimated at 2,500 km/s, which sees the star shed more than a millionth of its solar mass each year, or about 10 million times that shed by our own Sun over a comparable time period. This mass ejection is highly evident in non-visible wavelengths such as radio and X-ray.