I took this series of photos likely showing the Carnival Cruise Ship Elation coming out of Jacksonville, FL shown as the blue boat in the upper center of the attached photo. I was on the St Augustine pier with my ETX90 and Fuji camera. The ship was between 30-35 miles. According to our pals at NASA, there should be over 600 feet of curvature. I wasn't able to stick around for an entire series of photos as it approached, maybe next time. I could see it around 40 miles when it was brighter out, but easier to get photos after the lights were visible as the sun was setting. I watch it for 1 1/2 -2hrs. It was just a spec at first and not easily resolved. I took the photos and screen shot at the same time and that is how I estimated the distance. One photo is cropped to show more detail. You can see the milage scale at the bottom of the screenshot of my ship tracking app. Anyone at the seashore can do this type of testing with a telephoto lens on a clear day. I could actually see it with some 8x30 binoculars.