HD 209458

Star

HD 209458 — a yellow-white G0V star a little larger and hotter than the Sun, 158 light-years away in Pegasus. Ordinary in itself, it became a landmark of science as the first star watched to have a planet transit its face.

Open in 3D viewSee HD 209458 in the live, interactive 3D map

Key facts

Mass

2.45 × 10³⁰ kg

1.23 M☉

Radius

827,883 km

1.19× wider than the Sun

Surface temperature

6,091 K (5818 °C)

Luminosity

6.72 × 10²⁶ W

Spectral type

G0V (yellow-white dwarf)

Science

Physical

Mass: 2.45 × 10³⁰ kg · 1.23 M☉
Radius: 827,883 km · 1.19× wider than the Sun
Density: 1,029 kg/m³ · 1× water
Spectral type: G0V (yellow-white dwarf)

Rotation

Note: A quiet, slowly-rotating Sun-like star — ideal for the precise photometry that first caught a transit.

Composition

By mass: A hydrogen/helium main-sequence star a little larger and hotter than the Sun. Unremarkable in itself, it became a cornerstone of exoplanet science as the first star seen to have a planet transit it.

Temperature

Surface: 6,091 K (5818 °C)

Radiation & temperature

Luminosity: 6.72 × 10²⁶ W · 1.76 L☉
Surface temperature: 6,091 K (5818 °C)
Peak wavelength: 476 nm · blue light

Discovery & history

Name: A Henry Draper catalogue designation; no proper name.

Catalogued long ago as HD 209458, it drew attention only in 1999 when its wobble revealed a hot Jupiter — then, within weeks, that planet was seen transiting, opening the entire field of transit exoplanet science.

Images

Where to find it — in Pegasus, the Winged Horse (IAU constellation chart). To the eye it is a single point of light; no telescope has imaged its surface. — IAU / Sky & Telescope, R. Sinnott & R. Fienberg (CC BY 3.0) · Wikimedia Commons

Images from open archives · credit shown per image