It just appears to be texture corruption, but without more information I can't really be sure what's happening. I need to know what exact model of Mac you have, what version of OpenGL, the operating system (and version), along with the drivers you have, to see if it's possible to recreate your issue.
The output of your log files will let me know exactly what's going on. It's possible the textures are set to be too high resolution for your hardware (that skybox is really big). The logs should tell me exactly what's happening though.
Just as a guess, you can try to set the texture resolution to be lower, and bring down the anti-aliasing level to something lower. Both of those options are really intensive on the GPU memory.
To change the settings, go to the home menu in the top left, select the settings tab, and under the video section, change the texture resolution down to something simple, start with low, and set the AntiAliasing to off. Once you apply the settings, restart Universe Sandbox and see if the issue clears up.
If it does help, you can move the settings back up a little bit to see where the issue kicks in. Let me know if that helps out at all, and send those logs over. If you like, you can email them to me at chad@universesandbox.com or send them through the built in support system. (The little star in the top right hand window labeled feedback, be sure to check the bug category and the log file option)
Sending in a performance test would be helpful as well, you can run that through the home menu and select run performance test. After that ends, it will ask if you'd like to submit feedback. You can put in the notes Atten C7, and it will be forwarded to me.
Thanks!