Last summer, just after one of the large flares sent a blast of "solar wind" Earth's direction, we were able to see the aurora here in southeast Missouri. Most visible were the reds, but there were greens, too. The curtin effect was visible as the lights shifted around the sky. We don't see them often, but they are quite a treat when we do. Open Mike is correct about the cause. Often the news casts, both local and national, will carry a warning that we are the target of solar activity along with the admonition that there may be an effect on our communications and tv reception. When you hear that, keep an eye on the sky that night. It doesn't always produce the lights, but when it does it's often spectacular.