Celestium
by ItzGreenCat
Celestium lets players swap the in-game skybox while they play, using two keys to add or clear a skybox image.
What it does
A skybox is chosen in the game and applied on the fly: the Page Up key opens selection of a new skybox image, and the Page Down key removes the current one. The mod supports two image types, HDRI cube maps with a 2:1 width to height ratio and normal cube maps with a 4:3 ratio. An image with the wrong ratio is rejected and the skybox stays unchanged.
The mod is small and focuses only on skybox management, so it changes the sky and nothing else. It runs on Fabric in the client only, so the server does not need it and players can join a server without installing it. Files are released for 1.21.5 and 1.21.10, and the latest Fabric build, 2, is for 1.21.10 and was published on 2025-10-11. The code is open source under the MIT License.
Key features
Change skybox
Page Up opens selection of a new skybox image, which then replaces the current sky while playing.
Remove skybox
Page Down clears the active skybox and returns the sky to its default look.
HDRI cube maps
Cube maps with a 2:1 width to height ratio are accepted as high dynamic range skybox images.
Normal cube maps
Cube maps with a 4:3 width to height ratio are accepted as standard skybox images.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Changing atmosphere
A player building or exploring can switch the sky to suit a scene without leaving the world.
Who it’s for: Players who want a different sky in single-player or multiplayer worlds, and builders who set up scenes with different atmospheres. Because the mod is client-only, it is installed by players and not by server owners.
How it compares
Skybox at Home is an alternative for Fabric 1.20.4 that runs on client and server and is open source under the MIT License. Fogbox targets Fabric and Quilt for 1.18.2 – 1.19, is client-side only and is open source under the GNU Lesser General Public License v3.0 only. aspect ratio is client-side only for 1.21 – 1.21.4 and is not open source, released under All rights reserved.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| Celestium | Fabric | 1.21.5 – 1.21.10 | Client-side only | 2025-10-11 |
| Skybox at Home | Fabric | 1.20.4 | Client and server | 2024-02-07 |
| Fogbox | Fabric and Quilt | 1.18.2 – 1.19 | Client-side only | 2022-06-11 |
| aspect ratio (width screen) | Fabric | 1.21 – 1.21.4 | Client-side only | 2026-03-16 |
Questions
Does Celestium need to be installed on the server?
What happens if an image has the wrong aspect ratio?
Which game versions does Celestium support?
More from ItzGreenCat
What the author says
This is a small mod that lets you easily change the in-game skybox. It's perfect for spicing up your world with different atmospheres, whether you're building, exploring, or taking screenshots.
Official listing
- Modrinth page
- modrinth.com/mod/celestium
- Owner
- ItzGreenCat
- Published
- 2025-08-31
- Updated on Modrinth
- 2025-10-11
- Facts verified
- 2026-10-15