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 (5,818 °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
- Computed from mass and radius
- Spectral type
- G0V (yellow-white dwarf)
Motion through space
- Proper motion
- 0.0348 arcseconds per year · its drift across our sky
- SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
- Radial velocity
- -14.7 km/s · approaching the Sun
- SIMBAD — 2020yCat.1350....0G, 2018A&A...616A...7S
- Speed across our line of sight
- 7.94 km/s
- Computed from proper motion and parallax
- Speed through space, relative to the Sun
- 16.7 km/s
- Computed from proper motion, parallax and radial velocity
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 (5,818 °C)
Radiation & temperature
- Luminosity
- 6.72 × 10²⁶ W · 1.76 L☉
- Surface temperature
- 6,091 K (5,818 °C)
- Peak wavelength
- 476 nm · blue light
- Computed (Wien's law) from the surface temperature
Discovery & history
- Method
- Telescope
- 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
Images from open archives · credit shown per image