PHILADELPHIA—A string of lights that lobbed across the night sky in parts of the U.S. on Wednesday, Thursday and Friday had some people wondering if a fleet of UFOs was coming, but it had others—mostly amateur stargazers and professional astronomers—lamenting the industrialization of space. The train of lights was actually a series of relatively low-flying satellites launched by Elon Musk’s SpaceX as part of its Starlink internet service earlier last week. Callers swamped TV stations from Texas to Wisconsin reporting the lights and musing about UFOs. An email to a spokesman for SpaceX was not returned Saturday, but astronomy experts said the number of lights in quick succession and their distance from Earth made them easily identifiable as Starlink satellites for those who are used to seeing them. “The way you can tell they are Starlink satellites is they are like a string of pearls, these lights traveling in the …