Size It Up

Size It Up Space

WORLD AGAINST WORLD · FIVE ROUNDS A DAY · 60 CELESTIAL BODIES

DAILY No. —
DailyNo. — 
ROUND 1/5 today’s five
0 / 1,000

Versions & measurements

Slide anywhere on the board to resize · then Lock inSlide anywhere on the board to resize

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Choose a lookSAME SIZES · SAME SCORING

How to play Size It Up

  1. Compare. The black silhouette is the reference. It is at true scale and never changes.
  2. Resize. Slide anywhere on the board — or drag the grip, tap the ruler, pinch, or use the arrow keys — until the white silhouette looks right next to the reference. Zoom out if you need room.
  3. Lock in. The true size is drawn in red over your guess. Within 6% scores 100; twice or half the size scores 45; five times off scores 0.

SIZES IN

01 / A whole world on your ruler

Meet Size It Up Space

You can recognise Jupiter in a photograph. But how wide should it look beside another world? Size It Up Space turns familiar names into a test of proportion: resize one celestial body against another, lock in your guess, then see the real relationship.

Size It Up Space explores eight planets, thirty-four moons, two dwarf planets and sixteen stars, including the Sun. Compact stars such as TRAPPIST-1 bridge the gap between Jupiter and larger stars. Every round compares body diameter. There are no country outlines, rockets or animal silhouettes to supply an everyday reference.

Play today’s five above, then use this field guide to build a few reliable anchors. Size It Up Space Unlimited keeps the same collection and supplies fresh pairs when you want another round.

Voyager photograph of Jupiter showing cloud bands and the Great Red Spot.
Jupiter fills this frame, but the frame supplies no size reference. Size It Up Space supplies another world. Enhanced-colour Voyager image: NASA/JPL/USGS.

02 / Read · resize · reveal

How to play Size It Up Space

The black disk is your reference. The white disk is your guess. Size It Up Space scores the ratio between your chosen diameter and the recorded one; five rounds, from easy to hard, can earn 1,000 points.

  1. Read the two names

    Check which world is the reference and read its ruler. A moon’s label also names the body it orbits. The reference keeps its real size.

  2. Resize the whole disk

    Estimate half, one, two or more reference diameters. Use the resizing controls to adjust the white disk. Moving it or changing the view does not change the measured dimension.

  3. Learn from the reveal

    Lock in to see the true outline against your guess. Size It Up Space shows the direction and size of your error, giving you a better anchor for the next comparison.

03 / Across, through the centre

The ruler in Size It Up Space

Diameter runs from one side of a body to the other, through its centre. Radius stops at the centre, so diameter is twice radius. Size It Up Space consistently asks for the full width, not the distance from the centre to one edge.

Most worlds are not perfect spheres. Size It Up Space uses twice the published mean radius for planets and moons: the radius of a sphere with the same volume. The Sun uses a nominal photospheric diameter; other stars use labelled radius estimates. Each disk is a scale diagram, not an exact map of the limb.

A crescent Moon has the same body diameter as a full Moon. Illumination changes the visible bright area, not the size you should estimate in Size It Up Space.

Galileo photograph of the Moon, with dark plains and bright crater rays inside its full disk.
Follow the full disk, not a crater or bright patch. Lunar diameter is the measurement in Size It Up Space. Galileo image: NASA/JPL.
A diameter is twice a radiusA schematic disk has a line across its centre labelled diameter, and a line from centre to edge labelled radius. Schematic disk

ONE FULL WIDTH

Diameter = 2 × radius

Edge → centre → opposite edge

White line: diameter. Red line: radius. The same measurement runs across every game disk.

04 / Three relationships to remember

Size It Up Space, at one scale

These fixed examples use the same records as Size It Up Space. Within each panel, both disks share one linear scale. Each panel has its own scale; the diagrams compare diameters, not orbital positions.

Use the relationship as your anchor. Size It Up Space becomes easier when “a little wider” or “about a quarter as wide” means something you can picture. These are general comparisons, independent of today’s puzzle.

COMPARISON / 01

A familiar world, a smaller neighbour

About four Moon diameters span Earth. Compare the full disks, not the bright part of a lunar phase.

3.67×Earth’s diameter
compared with Moon

Earth Moon
Earth12,742 kmMean diameter sourceMoon3,474.8 kmMean diameter source

COMPARISON / 02

A moon can be wider than a planet

Ganymede edges past Mercury in diameter. The word “moon” describes what it orbits, not how small it must be.

1.08×Ganymede’s diameter
compared with Mercury

Ganymede Mercury
Ganymede5,262.4 kmMean diameter sourceMercury4,878.8 kmMean diameter source

COMPARISON / 03

Two giants, almost the same width

Their colours look different in photographs, but their mean diameters differ by only about three percent.

1.03×Uranus’s diameter
compared with Neptune

Uranus Neptune
Uranus50,724 kmMean diameter sourceNeptune49,244 kmMean diameter source

05 / Saturn without the extra width

What counts in Size It Up Space?

Saturn’s rings dominate its appearance. Including them would answer a different question from measuring the planetary globe. Size It Up Space uses the mean diameter of Saturn itself and excludes the rings, so its game silhouette is a globe.

This convention applies to every ringed planet in Size It Up Space. If you have seen a ring-inclusive Saturn in Mixed, read the label: that is a different measurement. The photograph shows why the distinction matters; it is not the scoring outline.

Saturn with broad rings extending far beyond the planetary globe.
The ring system stretches beyond the globe. Size It Up Space measures the globe alone. Cassini image: NASA/JPL/Space Science Institute.

06 / Bigger is not farther

Size It Up Space measures bodies, not orbits

A solar-system poster often enlarges the planets and compresses the gaps to fit the page. Its spacing cannot tell you how wide a planet is. Size It Up Space brings two bodies together on a comparison board; their separation is not a clue.

Keep three questions separate in Size It Up Space: diameter asks how wide, distance asks how far, and mass asks how much matter. A line across a disk measures diameter. A line between two centres measures a separation.

Body diameterWhite ruler · across one disk

Centre-to-centre distanceRed ruler · between two worlds

Body diameter and separation measure different thingsTwo schematic disks. A short white ruler crosses one disk; a separate red line joins the two centres. Their separation and sizes are not to scale.
The gap is not the answer. Two different rulers. This diagram explains the dimensions; body sizes and separation are schematic, not an orbital scale model.

07 / 60 bodies, one dimension

60 bodies in Size It Up Space

The Size It Up Space collection extends beyond the eight planets. Ganymede, Titan and Triton provide larger moon references; Mimas, Enceladus and Miranda bring the scale down. Pluto and Ceres add dwarf planets, while Proxima Centauri, TRAPPIST-1 and the Sun introduce stellar sizes.

Size It Up Space deals pairs with a usable size reference: the smaller body is at least one fifth of the larger body’s diameter. Not every possible pairing is dealt; a tiny moon beside the Sun would make a poor ruler.

Planets

08

Moons

34

Dwarf planets

02

Stars

16

08 / Make your next guess count

Three habits for Size It Up Space

Build intuition through comparison, rather than memorising a table. Try these habits during your next Size It Up Space run.

01

Count widths

Imagine reference disks in a straight line across the target. Counting how many fit inside its area is a different calculation and leads to a different answer.

02

Ignore the photograph’s crop

A small moon and a giant planet can each fill a picture. In Size It Up Space, use the named reference and its ruler to restore the missing scale.

03

Keep the close calls close

Some worlds really are similar in diameter. Do not enlarge a target just because its name sounds more impressive. Start near equal, then adjust.

09 / Measurements, photographs, diagrams

Sources behind Size It Up Space

Size It Up Space derives planetary and lunar diameters from JPL’s published mean radii. The Sun uses the IAU nominal solar radius, a defined reference value rather than a claim that the solar surface is perfectly fixed. Other stellar radii are estimates from the NASA Exoplanet Archive, converted using that solar reference. Displayed numbers are rounded; scoring uses the recorded value.

The photographs come from NASA/JPL missions and retain their individual credits. The Voyager montage includes grey areas where imaging coverage is missing. In Size It Up Space, photographs explain the subject; reused Classic disks and calculated diagrams explain scale.

Voyager montage of Miranda, Ariel, Umbriel, Titania and Oberon; incomplete coverage is filled with grey.
Five moons of Uranus, from Miranda at left to Oberon at right. Voyager montage: NASA/JPL. The Size It Up Space roster links every measurement to its source.

10 / Questions from the observatory

Questions about Size It Up Space

Does Size It Up Space include every planet?
Yes. All eight solar-system planets are in the collection, alongside thirty-four moons, Pluto, Ceres and sixteen stars. A Daily draws five pairs from this collection, so it does not show every planet every day.
Does Size It Up Space count Saturn’s rings?
No. Saturn uses its planetary globe’s mean diameter. Rings are excluded from all planet measurements in this category. A ring-inclusive entry elsewhere on the site has a different label and value.
Why are the Sun and Pluto in Size It Up Space?
This is a celestial-body comparison game, not a list restricted to planets. The Sun is a star; Pluto and Ceres are dwarf planets. They supply different sizes; nearby stars extend the collection beyond our solar system.
Are the circles in Size It Up Space exact shapes?
They are schematic disks used to compare stated diameters. Worlds can be flattened or irregular. Surface details, lunar phases and rings do not change the measured span. The Sun uses a nominal photospheric diameter; other stars use estimates rather than exact boundaries.
Does Size It Up Space compare distance or volume?
Neither. You compare a linear diameter, straight across a body through its centre. Distance, mass and volume are different quantities. The gap between the two objects on the board is just space to play.
Can I keep practising Size It Up Space after the Daily?
Yes. Choose Space Unlimited for fresh pairs from the same collection. The Daily refreshes at local midnight, and past Space games remain available from the category’s opening date.

11 / Keep exploring

Keep playing Size It Up Space

Finished today’s Size It Up Space? Stay with planets, moons and stars in Unlimited, revisit a past Space puzzle, or compare country outlines in Geography. Each category gives your ruler a different job.

Choose a categoryPLAYING DAILY
MixedAnimals, planets and everyday things. AnimalsLength, height or wingspan — every round names the axis. GeographyEast–west or north–south span, never area. Pop CultureCheck the version. Compare the measured dimension. VehiclesLength end to end, or height for the ones that stand upright. DinosaursCompare estimated body length, from snout to tail tip. SpaceCompare body diameter. Rings and orbital distances are excluded. Everyday ObjectsLength, height or width — every round names the axis. InsectsBody length or wingspan — read the named measurement. LandmarksRead the named height, length or main span — including its endpoints. Food & DrinkRead the selected size and axis — length, diameter or container height.
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