51 Pegasi
Where is 51 Pegasi?
Look south, about 59° up at 22:57 in Pegasus.
- Rises
- 15:02
- Highest
- 23:00
- Sets
- 06:58
- Best after dark
- 22:57 · 59°
Can I see 51 Pegasi?
No. The planets of 51 Pegasi can’t be seen with the eye, binoculars or any amateur telescope: they are lost in their star’s light. What you can do is point toward the star.
From London tonight, the star 51 Pegasi is above the horizon all night. It’s highest after dark at 22:57, in the south at 59°.
Why is 51 Pegasi interesting?
51 Pegasi has 2 known planets, discovered between 1995 and 2011 by the radial velocity and imaging, astrometry methods.
51 Peg b is a giant planet that orbits in under five days: a “hot Jupiter”.
What can you see?
Eyes
Direction onlyAround magnitude 5.5: a faint star visible under dark skies, not from cities.
Binoculars
Easy to see as a star just west of the Great Square of Pegasus.
Telescope
A yellowish star. The planets themselves can’t be seen with any backyard telescope.
About
51 Pegasi is a Sun-like star about 50 light-years away in Pegasus. In 1995 Michel Mayor and Didier Queloz discovered a planet orbiting it, the first planet found around a Sun-like star. The discovery earned them a share of the 2019 Nobel Prize in Physics.
The planet, 51 Pegasi b (also named Dimidium), was a surprise: a gas giant about half the mass of Jupiter, racing around its star every 4.2 days. Nobody expected a giant planet so close to its star, and it became the first known “hot Jupiter”.
It was found from the tiny back-and-forth wobble it causes in the star’s motion, a method that has since revealed hundreds of planets.
The star itself, also named Helvetios, is just visible to the naked eye under dark skies.
Since that discovery, astronomers have confirmed thousands of planets around other stars.
The 51 Pegasi system
| Planet | Mass | Radius | Orbit | From star | Found | Method |
|---|---|---|---|---|---|---|
| 51 Peg b | 0.61 M♃ | 1.20 R♃ | 4.23 days | 0.052 AU | 1995 | Radial Velocity |
| 51 Peg c | 10.00 M♃ | — | — | 37 AU | 2011 | Imaging, Astrometry |
Questions
Can I see 51 Pegasi b?
Why is 51 Pegasi famous?
Sources: The Extrasolar Planets Encyclopaedia (CC BY 4.0); star chart: Wikidata (CC0). Positions computed for your place and time with astronomy-engine. Data & Licences