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X-treme stars you can see

Find the hottest, coolest, largest, and farthest stars visible to the naked eye.
Zeta (ζ) Puppis
Zeta (ζ) Puppis
Astronomy: Richard Talcott
In "X-treme stars of the cosmos," we took you on a tour of some the galaxy's biggest, hottest, and most distant stars. But you don't need a space telescope to see stellar extremes; you just have to know where to look.

The table below guides you to a handful of stars visible without a telescope. Zeta Puppis tops the list as the hottest star naked-eye observers can see. R Cassiopeiae is truly an extreme star, taking top ranking as both the coolest (1/3 the surface temperature of our Sun) and the largest. Exchanged with our Sun, R Cassiopeiae would engulf all the planets except Uranus, Neptune, and Pluto. And S Carinae, the most distant naked-eye star at 12,000 light-years away, is a Mira-type variable star that brightens to magnitude 5.6.

There's one other object on the list, but it's no longer visible. Still, its incredible distance when it was visible — 2.5 million light-years — establishes its extreme-star credentials. In 1885, the light from a star that exploded in our neighboring galaxy, M31, finally reached Earth.

Astronomers gave it a standard variable star designation, S Andromedae, but had no idea how far away it was. The scientific concepts of an event as violent as a supernova, of the vast gulf between our Milky Way and M31, and even of galaxies themselves wouldn't exist until the 20th century's opening decades.
Naked-eye extreme stars
RecordName R.A.*Dec.*DistanceMag.Note
Hottest Zeta (ζ) Puppis 8h03m35s –40° 00' 11" 1,400 light-years 2.2 Surface temperature: 42,000 K — 7 times hotter than the Sun; 20 times the Sun's size; 60 times the Sun's mass; 800,000 times the Sun's brightness.
Coolest and largest R Cassiopeiae 23h58m25s 51° 23' 19" 350 light-years 4.8 Surface temperature: 2,000 K — 1/3 the Sun's; 1,800 times the Sun's size; would extend nearly to orbit of Uranus; Variable star; mag. 4.8 is its brightest.
Farthest S Carinae 10h09m22s –61° 32' 56" 12,000 light-years 5.6 Variable star; 5.6 is the brightest it gets.
Farthest S Andromedae 0h42m43s 41° 16' 04" 2.5 million light-years 6.0 Supernova in M31 (SN 1885, no longer visible — although you can see its galaxy)
* Right ascension is the celestial equivalent of longitude.
** Declination is the celestial equivalent of latitude.
Zeta (ζ) Puppis
Zeta (ζ) Puppis
Astronomy: Richard Talcott
R Cassiopeiae
R Cassiopeiae
Astronomy: Richard Talcott
S Carinae
S Carinae
Astronomy: Richard Talcott
S Andromedae
S Andromedae
Astronomy: Richard Talcott
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