From the FAQ http://en.spaceengine.org/index/faq/0-29:

Q: Will there be a version for Mac and Linux?

A: Yes, this is planned for in the near future. There is a donation campaign ongoing for this. If you would like to get SpaceEngine to Mac soon, please donate here.

the linux support goal has been reached months ago, and still nothing..

not really complaining, since it runs out of the box in wine.

Don't forget that Rift also seemed to support Linux, but then decided to push that to the back of their planning. So even if it's in the list of things to do, that doesn't mean it will happen in the near future, or even at all.

I got really excited about this until I saw it only runs on something called "Windows".

What you said was sarcastic, but you make a serious point.

I absolutely refuse to expose myself on the internet to virus and other malicious digital attacks, that I do not have to be exposed to. Dropping windows entirely was one of the single best steps I took in minimizing that attack surface.

I do not have resources to dedicate to having yet another untrusted machine with expensive software for the sake of one "free" piece of software that amounts to little more than a game (even though I really like games).

Luckily it (appears to) runs on linux.

Since it is not open source how do I know it doesn't contain a virus? It would not be the first time such has happened.

I got seriously downvoted on that one, but it was worth it.