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.
Lunar South Pole Ice 3D Explorer
This browser explorer puts you above Shackleton crater at the Moon's south pole, a real permanently shadowed crater whose floor never receives direct sunlight while a few points right on its rim stay lit almost year-round.
Why Shackleton's floor never sees sunlight
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 stays dark 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. Move the sun all the way around in this scene and the floor stays dark at every position, because the real angle is that low. The same low angle keeps a few points right on the rim lit more than 90% of the year, an effect astronomers call "peaks of eternal light."
Permanently shadowed floors trap water ice for billions of years
A floor that cold can hold on to water ice, because anything that lands there has almost no way to warm up and evaporate again. Lunar polar craters in permanent shadow 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 crashed a spent rocket stage into the shadowed floor of nearby Cabeus crater, and spectrometers reading 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 is that Cabeus crater.
What you can change in this scene
- 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
- "Compare to Earth tilt" button raises the sun elevation to Earth's 23.5 degrees, so you can watch light reach the floor at some sun positions
- Facts panel restates the figures in the table below for the current view
- Drag to orbit, scroll or pinch to zoom
- Runs on 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.
The whole Shackleton crater scene - the shadowed floor, the rim-cast light, and the sun sweep around the pole - renders on your own device with WebGL. Nothing about the crater view is uploaded to a server. The 3D engine downloads just once (about 0.7 MB) and is then cached, so revisiting this lunar south pole explorer loads straight from your browser with no account needed.
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 gold rim markers sit at illustrative 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 measured dimensions and the LCROSS 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.