You may or may not know that the International Space Station is visible from Earth with the naked eye. If you didn't know, NASA wants to make sure you do. The space agency has created a service that will send e-mail and text alerts when the ISS is above your location. It's called Spot the Station. The system allows you to give your e-mail address and receive notices when the ISS, the third brightest object in the sky after the sun and moon, is orbiting above your area. Given that the ISS passes over roughly 90 percent of the Earth's population, most people will have a chance to spot the space station sooner or later. The Web site for "Spot the Station" emphasizes that alerts will only be sent out for "good" observations -- that is, times when the space station is high enough over the horizon and in view long enough to make sky-gazing worthwhile. Even with these restrictions, NASA estimates that "Spot the Station" will offer viewing opportunities several times a month.