HD 209458 planetary system
HD 209458 is a Sun-like main-sequence star of spectral type G0 V approximately 158 light-years from Earth (48.30 parsecs). It hosts 1 confirmed exoplanet. 1 planet transits the host star from our line of sight, allowing direct measurements of size and atmosphere.
Host star
- Name
- HD 209458
- Spectral type
- G0 V
- Effective temperature
- 6,091 K
- Mass
- 1.23 M☉ (solar masses)
- Radius
- 1.19 R☉ (solar radii)
- Distance
- 48.30 pc (158 ly)
- Hipparcos catalog
- HIP 108859
Confirmed planets (1)
| Planet | Class | Mass (M⊕) | Radius (R⊕) | Period (d) | Distance (AU) | Eq. temp (K) | Discovered |
|---|---|---|---|---|---|---|---|
| HD 209458 b | Jupiter-like | 232.02 | 15.58 | 3.52 | 0.0471 | 1,459 | 1999 |
The planets in detail
HD 209458 b is a Jupiter-like gas giant with about 15.58 Earth radii and 232.02 Earth masses. It orbits HD 209458 at 0.0471 AU with a 3.5-day year, soaked in over 587× Earth's stellar flux, and an extreme equilibrium temperature exceeding 1459 K. The planet transits its host star, which is how its radius and (when combined with mass) bulk density are pinned down. It was confirmed in 1999 via radial velocity (Doppler) measurements.
Discovery
The single planet in the HD 209458 system was confirmed in 1999 using radial velocity (Doppler) measurements. Detection facilities: W. M. Keck Observatory.
Observing from Earth
Exoplanets cannot be resolved visually with amateur telescopes — the host star's glare is overwhelming and even space-based direct imaging requires sophisticated coronagraphs. What you can observe is the host star itself at right ascension 330.7950°, declination 18.8842°. Because 1 planet transits from our perspective, advanced amateurs with photometric setups can sometimes detect the resulting brightness dips. Use the 3D orrery above to inspect orbital geometry, planetary scale, and the habitable-zone overlay — the orbits are computed from the published Keplerian elements and animate at user-controlled time rates.
