Zeta Puppis

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Zeta Puppis
Zeta Puppis.jpg
Observational Data
Designation HD 66811
HR 3165
Right ascension 08h 03m 35.04754s[1]
Declination -40° 00′ 11.3321″[1]
Constellation Puppis
Type of object Blue supergiant
Magnitude Apparent Mag: +2.21[2]
Absolute Mag: -5.41[3]
Distance from Earth 1,093 ly[4]
Radial velocity -23.9±2.9 km/s[1]
Proper motion RA: -29.71 mas/yr[1]
Dec.: 16.68 mas/yr[1]
Parallax 3.01±0.10 mas[1]

Zeta Puppis, also called by its traditional name Naos from the Greek ναύς "ship", or less commonly, Suhail Hadar, is one of the hottest stars in the galaxy and one of the few rare class O stars visible with binoculars in the night sky.[2] It is the second brightest such star in terms of its apparent magnitude, with only Zeta Orionis appearing brighter. Located in the constellation of Puppis, Zeta Puppis is situated 1,093 light years away according to the 2008 data from the Hipparcos mission.[4]

Properties and Structure

Zeta Puppis is a blue supergiant star of spectral class O5IAf, making it one of the hottest stars in the galaxy with a surface temperature of 42,400 K (in comparison, the Sun has a surface temperature of 5,780 K).[5] The star’s mass is 22.5 times that of our Sun, and 14 times its diameter.[2] However, there is large uncertainty in these measurements due to an uncertainty in the stars distance, so some put these higher at a mass of 40 solar masses.

Since Zeta Puppis is an exceptionally large class O supergiant, it is one of the brightest stars in the galaxy in terms of absolute magnitude, at -5.96. The star is 21,000 times as luminous as our Sun visually. However, because it is a class O blue star, most of the radiation from the star is in the ultraviolet. When this is considered, the star is 790,000 times more luminous then the Sun overall.

Because of its temperature and luminosity, if Zeta Puppis was at the same distance as Sirius from our Solar System, it would appear as bright as a quarter-moon. If Zeta Puppis was our Sun, the Earth would have to be 450 AU away in order to maintain the same temperature and climate, or about 11 times the mean distance of Pluto from our Sun.

As it is so bright and hot, it is fusing helium into carbon and oxygen in its core.[6] The star generates a very strong stellar wind with a velocity between 2,300-2,500 km/s[2][6] This results in the star loosing around a millionth of a solar mass of material each year. This may sound small but it is over 10 million times more than the Sun looses and is some 1.99×1024 kg/yr.

Zeta Puppis is a fine example of a class O "runaway" star and is moving at a speed of over 100 kilometers a second.[6] This is likely to it having been ejected from another star system. Like many runaway stars, Zeta Puppis rotates very quickly, at some 220 km/s around its equator which is 100 times faster than the Sun.[6]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Zeta Puppis from the SIMBAD Astronomical Database
  2. 2.0 2.1 2.2 2.3 Puppis Constellation from constellation-guide.com
  3. From definition of absolute magnitude, using apparent magnitude (+2.21) and distance (1,090 ly) given here.
  4. 4.0 4.1 Maíz Apellániz, J.; Alfaro, E. J.; Sota, A. (2008). Accurate distances to nearby massive stars with the new reduction of the Hipparcos raw data. arΧiv:0804.2553
  5. Lamers & Cassinelli 1999, accurate to 200 K
  6. 6.0 6.1 6.2 6.3 Naos from stars.astro.illinois.edu