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Zeta Puppis (ζ Pup / ζ Puppis) is a star in the constellation of Puppis. It also has traditional names Naos (nay'-os, from the Greek ναύσ "ship"), as well as Suhail Hadar, which literally means "bright star of the ground" in Arabic.

Its spectral class is O5Ia, making this an exceptionally hot star, and one of the sky's few naked eye class O stars. The surface temperature is 42,400K (Lamers & Cassinelli 1999, accurate to 200K) and the star's mass is 59 solar masses.

Unlike many other stars at such great distance, we do have rather precise parameters for Zeta Puppis since we know its velocity and can extrapolate back to the region where it was formed, a molecular cloud in Vela, thus can derive a much more accurate distance than we can with, for example, Deneb.

It is an extreme blue supergiant, one of the brightest stars in the Milky Way in terms of absolute magnitude. Visually, it is 21,000 times more powerful than the Sun; although being an extreme blue star most of its radiation is in the ultraviolet, and when this is considered, it is approximately 790,000 (Lamers & Cassinelli 1999) solar. Blue stars are never very large and Naos is no exception, being 'merely' 20 times the solar radius. It is up to red supergiants such as Betelgeuse to set the size records.

At the distance of Sirius, Naos would cast strong shadows on Earth, with a visible magnitude(-9) close to that of the quarter moon, but if it was placed at the center of our Solar System, its intense heat would cause the oceans to evaporate and afterwards heat the Earth's surface to over 1000 degrees Celsius and its intense ultraviolet and gamma rays would destroy all life within seconds. The Earth's surface trapped beneath a thick Venus-like atmosphere would glow red hot in the process and eventually melt into an ocean of lava. In several hundred thousand years, Naos will cool on its way to becoming a red supergiant and will pass through spectral classes B, A, F, G, K and M as it cools. When this occurs, the star's output will mostly be in the visible spectrum and any humans still around will view Naos as one of the brightest stars in the sky. Within 2 million years, Naos will turn into a Class M5 red giant 100 times its current size (1AU) will explode into a hypernova so powerful and bright that even at 1400 light years, would appear much brighter than the full Moon and might even resemble a gamma ray burst. A black hole would be formed in the process and the innermost exploded material will form an accretion disk, a hot vortex sucked in by the hole and blasted into space via plasma jets emerging from its poles which will last millions of years. Any companion stars, gas giants and brown dwarf planets will also have their atmospheres pulled inward. The rest of the hypernova would form a spectacular nebula where new stars will eventually form.

It is the brightest star in Puppis, with an apparent magnitude (visual) of 2.21. It is around 1,400 light years distant and has an absolute magnitude of −6.1 although given the slightly uncertain 1,400ly distance, this could be as high as −6.0 or as low as −6.2. The visual magnitude is dimmed by approximately 1 magnitude by intervening dust.

Naos was formed in the Vela star forming region and since birth has travelled over 400 light years relative to this area, making it a fine example of a runaway star. There is evidence of an ionisation front, a 'bow shock', ahead of Naos. Howarth et al. in 1995 determined an anomalously high rotational velocity of 211 km/s at the equator, which also seems to be a common trend in O runaway stars, as well as an apparent enrichment in helium and nitrogen on the surface.

In 1896, Edward C. Pickering observed mysterious spectral lines from ζ Puppis, which fit the Rydberg formula if half-integers were used instead of whole integers. It was later found that these were due to ionized helium.

• Daniel Schaerer et al, 1997, "Fundamental stellar parameters of zeta Pup and gamma^2 Vel from HIPPARCOS data", ApJ Letters.