Tepee and star trails

I took this image of a tepee and the night sky at f2.8 for about 15-20 minutes. I realized the hard way that about 15 minutes is the limit for long exposures of Velvia, especially when there is some ambient light. All my 40 mins+ exposures are green. This one was okay. I converted it into black and white to prevent viewers from recoiling at the sight of a slightly weird green/orange tepee. Your comments are welcome. Thanks in advance.