With masked spectators watching from below, hundreds of drones lit up the night sky in South Korea’s capital on Friday in a synchronized display to encourage citizens to remain vigilant against the coronavirus. More than 300 drones flew in the performance above Olympic Park in southern Seoul, forming images of people wearing masks and spelling out messages thanking people and medical workers for the country’s anti-virus gains. The steady spread of the virus has alarmed government officials, who eased social distancing measures to the lowest level since October to soften the pandemic’s shock on the economy.