Spaceship and planets by MillionthVector under CC BY 4.0 license

http://millionthvector.blogspot.com

http://millionthvector.blogspot.de

Moon by Saroman under CC BY 3.0 license

http://opengameart.org/content/moon

 

Earth and Atmosphere by Justin Nichol under CC BY 3.0 license

http://opengameart.org/content/earth

“Deus Ex Tempus” by Trevor Lentz  under CC-BY-SA 3.0 License

https://opengameart.org/content/deus-ex-tempus

“Stasis” by Trevor Lentz  under CC-BY-SA 3.0 License

https://opengameart.org/content/stasis

“Hero Immortal” by Trevor Lentz  under CC-BY-SA 3.0 License

https://opengameart.org/content/hero-immortal

“Church Bell” by Ulrich Metzner  under CC-BY-SA 3.0 License

https://opengameart.org/content/church-bell

CC BY-SA 3.0 license link

https://creativecommons.org/licenses/by-sa/3.0/

CC BY 3.0 license link

https://creativecommons.org/licenses/by/3.0/

CC BY 4.0 license link

https://creativecommons.org/licenses/by/4.0/

No changes made.

Note that providing attribution does not suggest in any way that the licensor endorses the use of credited items.