Lunar and Earth Curvature of Horizon ```Name: Annie Status: other Grade: other Location: NV Country: N/A Date: 1/25/2006 ``` Question: Why is the curvature of the horizon on the moon so obvious? I do not understand how since you cannot really make out much with your eyes or a sophisticated camera past 2 city blocks. Replies: Annie, There are several possible reasons why the curvature of the Earth is not as easily observable as opposed to pictures you have seen taken by astronauts on the Moon. (1) Since the average diameter of the moon is 3,500km as opposed to the Earth's which is 6,400km (nearly double) - then the curvature is not so pronounced. (2) Depending on where you are there are many intervening structures, fog, dust, trees, buildings (etc) that break up your view of the Earth's horizon - if you were to stand on a boat in the middle of the ocean, or on a particularly flat and featureless land (like where I live in South-East Texas), you can readily see the Earth's curvature. Greg (Roberto Gregorius) Annie, To keep the answer as simple as possible, the curature of the moon's horizon is so noticable because its diameter is quite small. To make an analogy to a two-dimentional object, think of a pizza. As you cut slices it is easy to see that the crust is round. But imagine that you made a pizza larger than the Earth. Now when you cut the pizza, the crust would be so large, that it would be very difficult for you to tell if the crust was round or not. To put the answer in terms of math, think of the pizza as a geometric shape--an isocelese triangle, with the base curved instead of straight. Now, the tip of the pizza (the tip being the point that was in the center of the pizza) makes an angle with the two long sides of the pizza. If that angle is held constant and the diameter of the pizza is increased (let us say from a 10" pizza to an 18" pizza), the length of the crust is increased. As the crust gets longer and longer it also has to become less curved in order to keep the angle at the tip the same! So back to the moon and the Earth, since the moon is so much smaller than the Earth, it is much easier to see its curvature since it IS more curved than the Earth! Matthew Voss Click here to return to the Astronomy Archives

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