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Night Sky Simulator
Stand under a night sky and swap the Moon for Jupiter, Saturn, or even the Sun — every body rendered at its true angular size at the Moon’s distance. Drag to look around.
If the Moon Were Replaced by Planets
The full Moon covers only half a degree of sky, yet it dominates the night. This simulator swaps the Moon for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or the Sun at the Moon's distance of 384,400 km, rendering each one at its true angular size over a night landscape. Drag to look around, change the phase, and pull the planet closer or farther to see how the view changes.
Angular size falls with distance. Jupiter is 40 times wider than the Moon, but it orbits about 1,600 times farther away, so it shrinks to under an arcminute — a bright point. Placed at the Moon's distance instead, the same planet would stretch across 21 degrees of sky, more than forty full Moons side by side.
| Body | Diameter | Apparent size in the sky | Vs full Moon |
|---|---|---|---|
| Moon (actual) | 3,475 km | 0.52° | 1× |
| Mercury | 4,879 km | 0.73° | 1.4× |
| Mars | 6,779 km | 1.0° | 2× |
| Venus | 12,104 km | 1.8° | 3.5× |
| Earth | 12,742 km | 1.9° | 3.7× |
| Neptune | 49,528 km | 7.4° | 14× |
| Uranus | 51,118 km | 7.6° | 15× |
| Saturn (rings) | 120,536 km (280,440 km) | 18.0° (rings 40.1° face-on) | 35× (77×) |
| Jupiter | 142,984 km | 21.4° | 41× |
| Sun | 1,391,400 km | Earth would be inside it | — |
Apparent size is the full angular diameter of the sphere's limb, 2·asin(radius ÷ 384,400 km). The ring figure is the face-on reference span, 2·atan(radius ÷ distance) — tilt the rings and perspective stretches the widest chord slightly, to about 42° at this simulator's default pose; the 3D scene handles that naturally. For comparison, your fist at arm's length covers about 10 degrees — Jupiter in the Moon's place would be two fists wide, and Saturn's rings would span four.
This tool answers only what your eyes would see. Gravity is another story: a gas giant at 384,400 km would raise ocean tides hundreds of times stronger than the Moon's, stress Earth's crust, and in Jupiter's case place Earth inside its Roche limit and radiation belts. The Sun is the extreme case — its radius of 696,000 km is nearly twice the Moon's distance, so Earth would simply be inside it. The simulator flags that scenario when you select the Sun.
Jupiter at the Moon’s distance of 384,400 km would span about 21 degrees of sky — roughly 40 full Moons side by side, or two fists held at arm’s length. Its cloud bands and the Great Red Spot would be visible to the naked eye, and its reflected light would make the night thousands of times brighter than a full Moon.
Saturn’s globe would cover about 18 degrees, and the A–C ring system, 280,440 km across, would stretch roughly 40 degrees from tip to tip — nearly half the distance from the horizon to straight overhead.
You could not see it from outside, because Earth would be inside it. The Sun’s radius is about 696,000 km — almost twice the Moon’s distance of 384,400 km — so a Sun centered where the Moon is would engulf Earth entirely. The simulator shows this case and lets you slide the Sun farther away until its disk fits in the sky.
No, for the larger bodies. This is a visual thought experiment only: a gas giant that close would raise enormous tides, destabilize Earth’s orbit and crust, and in Jupiter’s case put Earth inside its Roche limit and intense radiation belts. The simulator ignores gravity and shows only what your eyes would see.
The full Moon has an angular diameter of about 0.52 degrees — small enough to cover with a pea held at arm’s length. It looks large mainly because it is the biggest and brightest object in the night sky, and the well-known “Moon illusion” makes it seem bigger near the horizon.
It uses the exact angular-diameter formula for a sphere: 2 × asin(radius ÷ distance), with planet diameters from NASA planetary fact sheets and the Moon’s mean center-to-center distance of 384,400 km. The 3D scene then renders each sphere at that exact angular scale, so the view matches what a camera with the same field of view would photograph.