If you stood on the shore looking across the sea to the horizon (the line appearing to separate earth from sky), you might be able to see about two and a half miles. But he higher you stood the farther you would be able to see. As the earth is curved, the horizon would appear farther away with every increase in the height above sea level.
At a height of 20 feet you might see for six miles. From the top of a 300-foot cliff your view could extend for 23 miles, while on the summit of a 3,500-foot mountain, it could lengthen to 80 miles. From an aircraft flying at 16,000 feet you might have an uninterrupted panorama for 165 miles.
If you look straight up into the sky, the distance you can see is immense. The moon is about 239,000 miles away and the stars are millions of miles distant.
Picture credit: google