n and position of the Moon as viewed from Tokyo, Japan and from Houston, Texas at the same moment. The first image pair is a close-up of the full Moon showing that observers in the two locations see a slightly different set of features at the eastern and western edges of the Moon. The second pair of images is a wider field of view showing how much the Moon's position is shifted against the background stars when seen from the two locations. A single observer can see these same parallax effects by viewing the Moon at different times during the night. Between moonrise and moonset, the Earth's rotation carries the observer from one side of the globe to the other. The resulting change in the apparent orientation of the Moon during the night is called diurnal libration . The Moon's position against the background stars also changes, but this is the combined effect of parallax and the Moon's motion in its orbit, which partially cancel each other out: In 12 hours, parallax can move the Moon's apparent position 2° to the west while its orbital motion moves it 6° to the east. Lunar parallax was used for over 2000 years to measure the distance to the Moon. Although the specific techniques vary, the essence of the method is the solution of the triangle formed by the Moon and two widely separated observers. By the early 1960s, this approach had produced a distance accurate to within a mile. It's now measured with lasers to within a fraction of an inch. Download Images diurnal2.gif (1024x1024) [69.1 KB] A two-frame animated GIF comparing the views of the full Moon from Tokyo and from Houston at the same instant. In these wider views, the position of the Moon among the background stars is significantly different when viewed from the two locations. Planets & Moons Lunar Surface Lunar Topography Moon Credits Please give credit for this item to: NASA's Scientific Visualization Studio Visualizer Ernie Wright (USRA) Technical support Laurence Schuler (ADNET Systems, Inc.) Ian Jones (AD