Which is bigger, the star TRAPPIST-1 or the planet Jupiter?
Compare 21 objects by diameter: 17 stars from red dwarfs to red supergiants, the white dwarf Sirius B, the neutron star PSR J0030+0451 (25.4 km across), and Earth and Jupiter for scale. 4 of the stars are smaller than the Sun and 12 are larger; 2 are more than a thousand times its width.
How to play
- Two stars appear side by side (stacked on a phone). The first shows its diameter; the second keeps its value hidden.
- Decide whether the second one is larger or smaller and press Larger or Smaller.
- The hidden value counts up and your answer is judged. When you are right, the second card moves across and a new one takes its place.
- One wrong answer ends the run. There is no timer, and values stay fixed for the whole run. Most star pictures are illustrations, and none are to scale. Two objects are only paired when one is at least 10% wider and their published uncertainties do not overlap.
- Your result is saved in this browser. Once enough people have played a game, the results also show how your score ranks, and you can copy or share an image of your result, or replay.
Understanding the comparison
Use the Sun as your ruler: each card gives the size as a multiple or a fraction of the Sun’s diameter. The red dwarfs here are a fraction of the Sun’s width, the giants tens of times wider, and the red supergiants hundreds to more than a thousand times wider.
All 21 stars and objects, largest first
Show all 21 objects
| Rank | Object | Type | Diameter | Compared with the Sun |
|---|---|---|---|---|
| 1 | UY Scuti | Red supergiant | 2.38 billion km | 1,710 × the Sun’s diameter |
| 2 | VY Canis Majoris | Red supergiant | 1.98 billion km | 1,420 × the Sun’s diameter |
| 3 | Betelgeuse | Red supergiant | 1.06 billion km | 764 × the Sun’s diameter |
| 4 | Antares | Red supergiant | About 970 million km | about 700 × the Sun’s diameter |
| 5 | Deneb | Blue-white supergiant | 282 million km | 203 × the Sun’s diameter |
| 6 | Rigel | Blue supergiant | 110 million km | 78.9 × the Sun’s diameter |
| 7 | Aldebaran | Orange giant | 61.5 million km | 44.2 × the Sun’s diameter |
| 8 | Arcturus | Orange giant | 35.3 million km | 25.4 × the Sun’s diameter |
| 9 | Vega | White main-sequence star | 3.79 million km | 2.73 × the Sun’s diameter |
| 10 | Procyon A | Yellow-white star | 2.85 million km | 2.05 × the Sun’s diameter |
| 11 | Sirius A | White main-sequence star | 2.38 million km | 1.71 × the Sun’s diameter |
| 12 | Alpha Centauri A | Yellow main-sequence star | 1.7 million km | 1.22 × the Sun’s diameter |
| 13 | The Sun | Yellow main-sequence star | 1.39 million km | 1 × the Sun’s diameter |
| 14 | Alpha Centauri B | Orange main-sequence star | 1.2 million km | 0.863 × the Sun’s diameter |
| 15 | Epsilon Eridani | Orange main-sequence star | 1.03 million km | 0.74 × the Sun’s diameter |
| 16 | Proxima Centauri | Red dwarf | 215,000 km | 0.154 × the Sun’s diameter |
| 17 | TRAPPIST-1 | Red dwarf | 166,000 km | 0.119 × the Sun’s diameter |
| 18 | Jupiter | Planet | 142,984 km | 0.103 × the Sun’s diameter |
| 19 | Earth | Planet | 12,756 km | 1/109 of the Sun’s diameter |
| 20 | Sirius B | White dwarf | About 12,000 km | about 1/116 of the Sun’s diameter |
| 21 | PSR J0030+0451 | Neutron star | 25.4 km | 1/54,700 of the Sun’s diameter |
Diameters are twice the published radius. Red supergiant sizes carry wide uncertainties; the game only pairs stars whose published ranges do not overlap.
Frequently asked questions
What is the biggest star in the game?
UY Scuti, with a radius of about 1,708 times the Sun’s in a 2013 interferometric study. That size depends on the star’s distance, which is uncertain, so the game only pairs it with stars under 40% of its size. Next is VY Canis Majoris, at 1,420 solar radii.
Is the Sun a big star?
It is bigger than most: the majority of stars in the Milky Way are red dwarfs, smaller and dimmer than the Sun, such as Proxima Centauri and TRAPPIST-1 in this game. Giants and supergiants are far larger, and this game includes many famous bright ones, so 12 of its 17 stars are larger than the Sun, including 6 supergiants, and 4 are smaller. The Sun’s diameter is 1.39 million km.
Is any star smaller than Jupiter?
Not in this game. The smallest star, the red dwarf TRAPPIST-1, is 166,000 km across, about 1.2 times Jupiter’s 142,984 km.
What is smaller than Earth?
Two stellar remnants. The white dwarf Sirius B is about 12,000 km across, a little less than Earth’s 12,756 km, and the neutron star PSR J0030+0451 is only 25.4 km across.
Why are star sizes uncertain?
A star has no solid surface. Many radii come from interferometry, which measures a star’s angular size; combined with its distance, that gives the radius, so any error in the distance carries into the size. Each card shows the published value and its uncertainty.
How the sizes are measured
The game shows each star’s diameter: twice the published radius, taking the Sun’s radius as 695,700 km. Many of the radii come from interferometers such as ESO’s Very Large Telescope Interferometer, the CHARA Array and the Navy Optical Interferometer; others come from spectroscopic analysis, stellar models (Betelgeuse) or the transits of a star’s planets (TRAPPIST-1).
Fast spinners such as Vega bulge at the equator, so the card gives the equatorial radius and notes the smaller polar one. Red supergiants have extended, uneven atmospheres, and their published radii carry wide uncertainties.
Where the sizes come from
The Sun, Earth and Jupiter come from NASA’s fact sheets, Sirius B from ESA/Hubble, Antares from ESO, and the other stars and the neutron star from the peer-reviewed papers listed under Sources.
Sources
Source: Peer-reviewed measurements, NASA, ESA/Hubble and ESO · Sources reviewed 2026-10-01
Each star’s radius is taken from the paper or agency release linked below, with its published uncertainty, and doubled for the diameter (Sun’s radius 695,700 km). Most star pictures are illustrations; the Sun, Earth and Jupiter are NASA images and Betelgeuse an ALMA image (ESO/NAOJ/NRAO) under CC BY 4.0.
- Peer-reviewed measurements, NASA, ESA/Hubble and ESO
- Arroyo-Torres et al. 2013, Astronomy & Astrophysics 554, A76: UY Scuti
- Wittkowski et al. 2012, Astronomy & Astrophysics: VY Canis Majoris
- Joyce et al. 2020, The Astrophysical Journal 902: Betelgeuse
- ESO: Antares
- Schiller & Przybilla 2008, Astronomy & Astrophysics: Deneb
- Moravveji et al. 2012, The Astrophysical Journal 747, 108: Rigel
- Richichi & Roccatagliata 2005, Astronomy & Astrophysics: Aldebaran
- Ramírez & Allende Prieto 2011, The Astrophysical Journal 743, 135: Arcturus
- Monnier et al. 2012, The Astrophysical Journal Letters 761, L3: Vega
- Kervella et al. 2004, Astronomy & Astrophysics 413, 251: Procyon A
- Kervella et al. 2003, Astronomy & Astrophysics 408, 681: Sirius A
- Kervella et al. 2017, Astronomy & Astrophysics 597, A137: Alpha Centauri A, Alpha Centauri B
- NASA Sun Fact Sheet: The Sun
- Baines & Armstrong 2012, The Astrophysical Journal 748, 72: Epsilon Eridani
- Kervella et al. 2017, Astronomy & Astrophysics 598, L7: Proxima Centauri
- Agol et al. 2021, The Planetary Science Journal: TRAPPIST-1
- NASA Planetary Fact Sheet: Jupiter, Earth
- ESA/Hubble: Sirius B
- Riley et al. 2019, The Astrophysical Journal Letters 887, L21 (NASA NICER): PSR J0030+0451
- Every size, source quote and image credit (JSON)
Found an incorrect answer or a source that needs updating? Send a correction with the game name and a reference.