About a second. The circumference of Earth is about 40,075 km. Light travels at about 299,792 km/s. So to find how long it takes to go around 7.5 times, we multiply the circumference of the Earth by 7.5.Then take that answer and divide it by the speed of light, which equals 1.0026 seconds.ight travels at about 299,792 km/s. So to find how long it takes to go around 7.5 times, we multiply the circumference of the Earth by 7.5. Then take that answer and divide it by the speed of light, which equals 1.0026 seconds.