Moon Replaced by Planets
The full Moon is only half a degree wide. Give Mars the same orbit and it becomes a rust-red disk twice that width; give it to Jupiter and the planet spans 21 degrees, two fists at arm's length. This simulator renders each body at its exact angular size over a night landscape, with a phase control and a distance slider from a quarter of the Moon's distance to sixteen times it.
10⁹ m · 384,400 km (the Moon's distance) · Three.js · WebGL
Keep exploring the scale
Every toy changes one assumption. Try another and see what moves.
Ten bodies, one orbit
How much sky would each planet take?
The Moon looks big only because nothing else in the night sky is close. Park a planet at the same 384,400 km and the scene changes completely: Mercury is barely wider than the Moon, Earth would look four Moons across, and the gas giants would dominate the view like weather. The table below is the whole thought experiment in numbers; the simulator above lets you stand under it.
Each body at the Moon’s distance
| Body | Full Moons across | Angular diameter | Width vs Earth |
|---|---|---|---|
| Moon (as it is) | 1 | 0.52° | 0.27× |
| Mercury | 1.4 | 0.73° | 0.38× |
| Mars | 2.0 | 1.0° | 0.53× |
| Venus | 3.5 | 1.8° | 0.95× |
| Earth | 3.7 | 1.9° | 1.00× |
| Neptune | 14 | 7.4° | 3.9× |
| Uranus | 15 | 7.6° | 4.0× |
| Saturn, globe only | 35 | 18.0° | 9.5× |
| Saturn, rings face-on | 77 | 40.1° | 22× |
| Jupiter | 41 | 21.4° | 11.2× |
| Sun | — | Earth would be inside it | 109× |
A handy ruler: your outstretched fist covers about 10 degrees of sky and your little finger about 1 degree. Mars in the Moon’s place would be one finger wide, Jupiter two fists, and Saturn’s rings four fists from tip to tip.
Using the simulator
- Choose a body; the scene opens with the real Moon so you have a reference.
- Drag, use the arrow keys, scroll, or pinch to look around and zoom.
- Slide the phase from full to a thin crescent. The Sun has no phase control, because it makes its own light.
- Change the distance from a quarter of the Moon’s distance to sixteen times it and watch the disk shrink or swell.
Why real planets are dots
Jupiter is about 11 Earths wide, yet at its closest it is roughly 630 million km away, about 1,600 times the Moon’s distance. Divide its 21-degree disk by 1,600 and you get under an arcminute, a bright point to the naked eye. Distance, not size, keeps the giants small.
What happens when the Sun takes the Moon’s place
It cannot, at that distance. The Sun’s radius is about 696,000 km, nearly twice 384,400 km, so Earth would be inside the Sun. The simulator says so instead of drawing nonsense. Push the distance slider all the way out to sixteen times the Moon’s distance and the Sun’s disk still spans about 13 degrees, twenty-five full Moons wide. Planet textures are adapted from the Solar System Scope texture pack, built on NASA imagery and released under CC BY 4.0.
Related scale tools
Questions about planets in the Moon’s place
What would Jupiter look like in place of the Moon?
A disk about 21 degrees across, roughly 41 full Moons wide, or two fists held at arm's length. Its cloud bands and the Great Red Spot would be obvious to the naked eye, and its four large moons would swing out to the edges of the view.
How wide would Saturn's rings appear?
The A to C rings span 280,440 km, which at 384,400 km works out to about 40 degrees face-on: nearly half the arc from the horizon to the zenith. Saturn's globe alone would cover about 18 degrees.
Could the Sun replace the Moon at all?
Not at the Moon's distance. The Sun's radius is about 696,000 km, almost twice 384,400 km, so Earth would sit inside it. The simulator warns when you are inside a body and lets you push the Sun out along the distance control until its disk fits in the sky.
Would any of this be survivable?
No, not for the large bodies. A gas giant at the Moon's distance would raise catastrophic tides and disturb Earth's orbit. The simulator deliberately ignores gravity, atmosphere, and heat and shows only what the eye would see.
How large does the real Moon look?
About 0.52 degrees across, small enough to hide behind a pea at arm's length. It seems bigger because it is bright and alone in the sky, and because of the well-known Moon illusion near the horizon.
How is the apparent size calculated?
From the exact limb-to-limb formula for a sphere, 2 × asin(radius ÷ distance), using NASA fact-sheet diameters and the Moon's mean distance of 384,400 km. The distance control multiplies that baseline from 0.25× to 16×.
A visual thought experiment: gravity, tides, and radiation are deliberately left out.