Polaris

Star

Polaris — the North Star, a yellow supergiant about 430 light-years away that sits almost exactly above Earth's north pole, so it appears to stand still while the whole sky wheels around it. It is a Cepheid variable and the brightest star of a small family.

Open in 3D viewSee Polaris in the live, interactive 3D map

Key facts

Mass

1.07 × 10³¹ kg

5.4 M☉

Radius

0.174 AU

37.5× wider than the Sun

Surface temperature

6,015 K (5742 °C)

Luminosity

4.82 × 10²⁹ W

Spectral type

F7 Ib (yellow supergiant Cepheid variable)

Science

Physical

Mass: 1.07 × 10³¹ kg · 5.4 M☉
Radius: 0.174 AU · 37.5× wider than the Sun
Density: 0.144 kg/m³ · 0.00014× water
Spectral type: F7 Ib (yellow supergiant Cepheid variable)

Composition

By mass: A yellow supergiant that pulsates as a Cepheid variable, its brightness cycling over about four days. The nearest and brightest Cepheid, it anchors the cosmic distance ladder. It heads a small multiple-star system (Polaris Aa, its close companion Ab, and the wider Polaris B). Its distance has been genuinely debated (~99–137 pc); ~133 pc (≈433 ly) is the modern value used here.

Temperature

Surface: 6,015 K (5742 °C)

Radiation & temperature

Surface temperature: 6,015 K (5742 °C)
Peak wavelength: 482 nm · blue light

Discovery & history

Method: Naked-eye star
Name: 'Polaris' — the pole star (Latin stella polaris); Alpha Ursae Minoris, in the Little Bear.

Used to find true north for millennia — but only for now: Earth's slow axial precession will hand the pole-star title to other stars over the coming thousands of years. As the nearest, brightest Cepheid, it is a key rung on the cosmic distance ladder.

Images

Where to find it — Polaris, the North Star, at the tip of the Little Bear's tail (Ursa Minor); it marks true north (IAU chart) — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image