I'm looking for a clical music piece, most likely by Brahms.?

I'm almost positive it was Brahms, and I thought it was part of the German Requiem, but I couldn't seem to find the bit that I remember. It sounds really spacey and futuristic, and I always thought of the stars when I heard it. I vaguely remember asking what the instrument was, so I have this idea that it was organ, but I can't be sure. I've searched and searched, and I just can't figure it out.