PLANET SIZE COMPARISON GAME
Size It Up Space
Compare the diameter of planets and moons in a visual space size guessing game. Resize a celestial body beside a known reference and make enormous scale feel understandable.
How to play the space size comparison game
Space rounds compare the physical diameter of a planet or moon, not the distance it travels around the Sun. The fixed reference is your anchor; resize the violet target until its body looks correct beside it, then reveal the true outline and selected measurement.
Start with the order of magnitude. Is the target a small moon, a planet, or a star-sized object compared with the reference? Once the broad relationship is right, use the controls to make the final adjustment.
Name the body
Read whether the round shows a planet, moon, or other celestial body.
Estimate diameter
Compare the body itself, excluding orbital paths and rings.
Reveal scale
Check the red outline, real diameter, error, and score.
030 / SCALE LIBRARYWhy space scale breaks intuition
A planet in a photograph has no familiar object beside it. Images often show a small moon and a giant planet at convenient display sizes, not at the ratio your eye would see in space. The game restores that ratio with silhouettes drawn to one shared scale.
Space also spans orders of magnitude. A moon can be thousands of kilometres across, while a planet or star can be millions or billions of metres. The best estimate starts with the category of object before it reaches for an exact number.
Use a short ladder of celestial anchors
Earth and the Moon are useful first anchors because they appear in many comparisons. Once you can picture their relationship, Mars, Mercury, and the larger moons become easier to place. You are building a ladder of diameters, not memorising a planet fact sheet.
The reveal gives you a durable relationship: one body may be half the reference, similar in size, or several times larger. Carry that ratio into the next round before worrying about the unit.
Read what the space measurement includes
The page treats body diameter as the measured dimension. Rings, orbital distance, and the empty space around a planet are not part of the score. If a silhouette looks visually wide because of a ring or label, use the field note and the selected body measurement instead.
Space values can be expressed in kilometres even though the game’s internal library stores metres. The display converts the unit for readability while keeping one consistent numeric scale for comparison.
A daily space puzzle with unlimited practice
Five daily space rounds make a quick test of cosmic scale. Unlimited practice lets you keep exploring planets and moons after the daily set, with extra attempts separate from your streak.
Alternate a familiar body with an unfamiliar moon. That rhythm helps you use known anchors without turning every answer into a memory test.
Planets and moons in the Size It Up library
Every entry below is part of the playable library and keeps a traceable measurement record. Open the full list to browse this category by real-world scale.
Sun
1,391,400 kmSun has a nominal photospheric diameter of about 1,391,400 km. This is the body’s size, not an orbital distance.
Jupiter
139,822 kmJupiter has a mean diameter of about 139,822 km. This is the body’s size, not an orbital distance.
Triton
2,705.2 kmTriton, a moon of Neptune, has a mean diameter of about 2,705.2 km. This is the body’s size, not an orbital distance.
Miranda
471.6 kmMiranda, a moon of Uranus, has a mean diameter of about 471.6 km. This is the body’s size, not an orbital distance.
Mimas
396.4 kmMimas, a moon of Saturn, has a mean diameter of about 396.4 km. This is the body’s size, not an orbital distance.
Browse the full space libraryHide the full space library
| Object | Measurement | Notes & sources |
|---|---|---|
| Marsbody diameter · 6,779 km | 6,779 km | Mars has a mean diameter of about 6,779 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Ceresbody diameter · 939.4 km | 939.4 km | Ceres has a mean diameter of about 939.4 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Oberonbody diameter · 1,522.8 km | 1,522.8 km | Oberon, a moon of Uranus, has a mean diameter of about 1,522.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Tritonbody diameter · 2,705.2 km | 2,705.2 km | Triton, a moon of Neptune, has a mean diameter of about 2,705.2 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Moonbody diameter · 3,474.8 km | 3,474.8 km | Moon, a moon of Earth, has a mean diameter of about 3,474.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Charonbody diameter · 1,212 km | 1,212 km | Charon, a moon of Pluto, has a mean diameter of about 1,212 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Neptunebody diameter · 49,244 km | 49,244 km | Neptune has a mean diameter of about 49,244 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Titanbody diameter · 5,149.5 km | 5,149.5 km | Titan, a moon of Saturn, has a mean diameter of about 5,149.5 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Europabody diameter · 3,121.6 km | 3,121.6 km | Europa, a moon of Jupiter, has a mean diameter of about 3,121.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Mimasbody diameter · 396.4 km | 396.4 km | Mimas, a moon of Saturn, has a mean diameter of about 396.4 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Uranusbody diameter · 50,724 km | 50,724 km | Uranus has a mean diameter of about 50,724 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Earthbody diameter · 12,742 km | 12,742 km | Earth has a mean diameter of about 12,742 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Titaniabody diameter · 1,577.8 km | 1,577.8 km | Titania, a moon of Uranus, has a mean diameter of about 1,577.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Callistobody diameter · 4,820.6 km | 4,820.6 km | Callisto, a moon of Jupiter, has a mean diameter of about 4,820.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Mercurybody diameter · 4,878.8 km | 4,878.8 km | Mercury has a mean diameter of about 4,878.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Iobody diameter · 3,643 km | 3,643 km | Io, a moon of Jupiter, has a mean diameter of about 3,643 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Mirandabody diameter · 471.6 km | 471.6 km | Miranda, a moon of Uranus, has a mean diameter of about 471.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Rheabody diameter · 1,527 km | 1,527 km | Rhea, a moon of Saturn, has a mean diameter of about 1,527 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Iapetusbody diameter · 1,468.6 km | 1,468.6 km | Iapetus, a moon of Saturn, has a mean diameter of about 1,468.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Dionebody diameter · 1,122.8 km | 1,122.8 km | Dione, a moon of Saturn, has a mean diameter of about 1,122.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Sunbody diameter · 1,391,400 km | 1,391,400 km | Sun has a nominal photospheric diameter of about 1,391,400 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Jupiterbody diameter · 139,822 km | 139,822 km | Jupiter has a mean diameter of about 139,822 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Ganymedebody diameter · 5,262.4 km | 5,262.4 km | Ganymede, a moon of Jupiter, has a mean diameter of about 5,262.4 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Tethysbody diameter · 1,062.2 km | 1,062.2 km | Tethys, a moon of Saturn, has a mean diameter of about 1,062.2 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Umbrielbody diameter · 1,169.4 km | 1,169.4 km | Umbriel, a moon of Uranus, has a mean diameter of about 1,169.4 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Saturnbody diameter · 116,464 km | 116,464 km | Saturn has a mean diameter of about 116,464 km. This measures the globe, not its rings. Measurement sourceOriginal silhouette by Size It Up |
| Venusbody diameter · 12,103.6 km | 12,103.6 km | Venus has a mean diameter of about 12,103.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Arielbody diameter · 1,157.8 km | 1,157.8 km | Ariel, a moon of Uranus, has a mean diameter of about 1,157.8 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Enceladusbody diameter · 504.2 km | 504.2 km | Enceladus, a moon of Saturn, has a mean diameter of about 504.2 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
| Plutobody diameter · 2,376.6 km | 2,376.6 km | Pluto has a mean diameter of about 2,376.6 km. This is the body’s size, not an orbital distance. Measurement sourceOriginal silhouette by Size It Up |
Space entries identify body diameter, measurement source, artwork record, and license details. The table keeps those references visible.
Tips for better space size estimates
- 01
Confirm that the round measures body diameter, not orbital distance.
- 02
Start with the order of magnitude before fine-tuning.
- 03
Use Earth and the Moon as familiar celestial anchors.
- 04
Ignore rings and empty space when judging the body itself.
- 05
Use Unlimited to practise unfamiliar planets and moons.
Questions about Size It Up Space
Does the space game compare planet diameter?
Yes. Space rounds compare the physical body diameter of planets and moons. Orbital distance and rings are not the scored dimension.
What units are used for space measurements?
The library stores one consistent metre value and the page formats large bodies in kilometres for easier reading.
How many space objects are playable?
The current scheduled space library contains 30 playable entries, including planets and moons.
Can I play more space rounds?
Yes. Select Space in Unlimited mode to continue practising after the daily five.
Where do the space measurements come from?
Each celestial entry stores a measurement source and an artwork record. The library table links to the source information used for the comparison.