Drag the sun-position slider to see why Shackleton crater's floor - a real permanently shadowed crater at the lunar south pole - never sees light, while points right on its rim stay lit almost year-round.
The shadow on the crater floor is a real WebGL shadow cast by the rim geometry from the current sun direction - not a painted-on darkening. Drag to orbit and scroll or pinch to zoom on the scene above.
For the Moon's visible-face phase and libration geometry, see the Moon Phases 3D Explorer and the Moon Libration 3D Explorer. For how the Moon itself formed, see the Moon Formation (Giant Impact) 3D Explorer.
Lunar South Pole Ice 3D Explorer
Drag the sun-position control on this browser explorer to see why Shackleton crater's floor - a real permanently shadowed crater at the lunar south pole - never receives direct sunlight, while a few points right on its rim stay lit almost year-round.
Shackleton crater sits almost exactly on the Moon's south pole, its rim about 21 km across and its floor about 4.2 km below the rim (NASA's Lunar Orbiter Laser Altimeter measured 4.1 ± 0.05 km rim-to-floor). The reason its floor never sees light traces back to one number: the Moon's axial tilt is only about 1.54 degrees, compared with Earth's 23.5 degrees. At the pole, that tiny tilt means sunlight grazes in almost parallel to the ground all through the roughly 29.5-day lunar day - it never climbs high enough to clear a crater's own rim and reach the floor inside. The same low angle that keeps the floor dark also keeps a few points right on the rim lit more than 90% of the year, an effect astronomers call "peaks of eternal light." This scene renders both effects with a real WebGL shadow, computed live from the sun's current direction and the crater's own geometry, not a painted-on darkening - drag the sun-position slider all the way around and the floor stays shadowed at every position, because the real angle is that low.
Cold, permanently shadowed floors like Shackleton's - and nearby Cabeus crater's - can trap water ice for billions of years, because anything that lands there has almost no way to warm up and evaporate again. Permanently shadowed lunar polar craters generally never warm above about 100 K (-173 C); Shackleton's floor averages about 90 K (-183 C), among the coldest measured surfaces in the solar system. On 2009-10-09, NASA's LCROSS mission tested that idea directly: it deliberately crashed a spent rocket stage into Cabeus crater's permanently shadowed floor, and spectrometers analyzing the resulting debris plume detected about 5.6% ± 2.9% water ice by mass (Colaprete et al., "Detection of Water in the LCROSS Ejecta Plume," Science, 2010) - the first direct confirmation of water ice at the lunar south pole. The smaller bowl beside Shackleton in the scene represents that nearby Cabeus crater.
- Sun-position slider (0 to 360 degrees) moves the sun around the pole at the Moon's real, near-constant grazing elevation
- A real WebGL directional-light shadow, cast by the crater's own rim geometry, darkens the floor - genuinely computed, not a fixed overlay
- 3 gold rim markers illustrate the "peaks of eternal light" effect (illustrative positions, not exact NASA-surveyed coordinates)
- "Compare to Earth tilt" button raises the sun elevation to 23.5 degrees so you can see light reach the floor at some sun positions - and why that never happens at the Moon's real 1.54-degree tilt
- Facts panel states Shackleton's real diameter, depth, and floor temperature, plus the LCROSS water-ice figures
- Drag to orbit, scroll or pinch to zoom
- Runs fully in the browser with the vendored three.js engine - no account, no upload
| Figure | Value | Source |
|---|---|---|
| Shackleton rim diameter | about 21 km | NASA LOLA (Lunar Orbiter Laser Altimeter) |
| Shackleton depth (rim to floor) | about 4.2 km (4.1 ± 0.05 km measured) | NASA LOLA |
| Floor temperature (average) | about 90 K (-183 C) | Published lunar polar temperature surveys |
| Moon's axial tilt | about 1.54 degrees | Standard lunar orbital parameters |
| Cabeus ejecta water ice (LCROSS) | about 5.6% ± 2.9% by mass | Colaprete et al., Science, 2010 |
For the Moon's visible-face phase and libration geometry, see the Moon Phases 3D Explorer and the Moon Libration 3D Explorer. For how the Moon itself formed, see the Moon Formation (Giant Impact) 3D Explorer.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached.
This is an educational approximation, not a physics simulation. The sun's polar elevation is simplified as a constant angle through the whole azimuth sweep (in reality it varies slightly through the month, since the Moon's orbit is not a perfect circle); the 3 "peaks of eternal light" markers are illustrative rim positions, not exact NASA-surveyed coordinates; and the fill light that keeps the shadowed floor visible on screen is a rendering aid, not a claim that the real floor receives ambient light. Shackleton's 21 km by 4.2 km measurements and the LCROSS 5.6% ± 2.9% water-ice figure are real, published numbers.
Frequently Asked Questions
Why does Shackleton crater's floor never get sunlight?
The Moon's axial tilt is only about 1.54 degrees, so at the pole the sun grazes in nearly parallel to the ground all through the lunar day. That angle is too low to clear the crater's own rim and reach the floor, at any point in the roughly 29.5-day cycle.
How big and how deep is Shackleton crater?
About 21 km across the rim and about 4.2 km deep (NASA's Lunar Orbiter Laser Altimeter measured 4.1 ± 0.05 km rim-to-floor).
What is a "peak of eternal light"?
A point right on a polar crater's rim that stays illuminated more than 90% of the lunar year, because it sits high enough to catch the grazing sunlight from almost every angle. The 3 gold markers in this scene illustrate the effect at approximate rim positions.
How cold is the floor of a permanently shadowed crater?
Shackleton's floor averages about 90 K (-183 C). Permanently shadowed lunar polar craters generally never warm above about 100 K (-173 C), among the coldest measured surfaces in the solar system.
What did NASA's LCROSS mission actually find?
On 2009-10-09, LCROSS deliberately crashed a spent rocket stage into the permanently shadowed floor of nearby Cabeus crater. Spectrometers analyzing the ejecta plume detected about 5.6% ± 2.9% water ice by mass - the first direct confirmation of water ice at the lunar south pole.
Is Cabeus the same crater as Shackleton?
No - Cabeus is a separate, nearby permanently shadowed crater at the lunar south pole. LCROSS impacted Cabeus, not Shackleton; this scene shows Cabeus as the smaller bowl beside Shackleton for context.
Is Shackleton crater an Artemis III landing site?
Shackleton itself is not one of the 9 candidate regions NASA narrowed the list to in October 2024, but it sits on the rim of the same South Pole-Aitken basin area those regions are in, including "Peak near Cabeus B" and de Gerlache Rim 2 - the same permanently-shadowed-region science that makes this crater notable.
Is the shadow in this scene a real 3D shadow?
Yes - it is a real WebGL directional-light shadow computed live from the sun's current direction and the crater's own rim and wall geometry, not a fixed painted-on darkening.
What happens if I switch to the Earth-tilt comparison?
The button raises the sun's elevation to Earth's 23.5-degree axial tilt. At that steeper angle, sunlight clears the rim and reaches parts of the floor at some sun positions - showing why Earth's own poles do not have permanently sunless crater floors the way the Moon's do.