Astronomers say a loud explosion heard across a large swath of Nevada and California on Sunday morning was likely caused by a meteor.The sound of the explosion around 8 a.m. prompted a flood of calls to law enforcement agencies on both sides of the Sierra Nevada in the two states.The explosion rattled windows and shook houses from Reno to Winnemucca in Nevada, and from the Sacramento to Bakersfield areas in California.Some people in the two states reported seeing a fireball streak across the sky at the same time. Dan Ruby of the Fleischmann Planetarium at the University of Nevada, Reno, …