![]() ![]() ![]() However, they are opposite to the lunar phases that we see from the Earth. The moon is actually a little brighter at first quarter than at last quarter, since at that phase some parts of the moon reflect sunlight better than others.Ħ) The Earth, seen from the moon, also goes through phases The end result is that at first quarter, the moon appears only one eleventh as bright as when it's full. Also, the moon's face is splotched with dark regions. Especially near and along the day/night line (known as the terminator), the lunar landscape appears riddled with innumerable shadows cast by mountains, boulders and even tiny grains of lunar dust. In such a case, it would indeed appear half as bright.īut the moon has a very rough topography. If the moon's surface were like a perfectly smooth billiard ball, its surface brightness would be the same all over. So you could fill up the entire sky, including the half that lies below our feet, with 206,264 full moons - and still come up short by 191,836 in the effort to match the brightness of the sun.Ĥ) The first- or last-quarter moon is not one half as bright as a full moon The moon measures only a half degree across, which gives it an area of only 0.2 square degrees. The sky is 360 degrees around (including the half we can't see, below the horizon), so there are over 41,200 square degrees in the sky. But this all a moot point, because there is no way that you could fit that many full moons in the sky. So that's how many full moons you would need to equal the brightness of the sun. The ratio of brightness of the sun versus the moon amounts to a difference of 398,110 to 1. The full moon shines with a magnitude of -12.7, but the sun is 14 magnitudes brighter, at -26.7. The remaining 41 percent can never be seen from our vantage point and if anyone were on that region of the moon, they would never see the Earth.ģ) It would take hundreds of thousands of moons to equal the brightness of the sun So the moon "rocks" in the east and west direction, allowing us to see farther around in longitude at each edge than we otherwise could. We call this effect libration of longitude. Put another way, the two motions do not keep perfectly in step, even though they come out together at the end of the month. The moon's rate of rotation is uniform but its rate of revolution is not, so we're able to see just around the edge of each limb from time to time. The truth, however, is that we actually get to see more of it over the course of its elliptical orbit: 59 percent (almost three-fifths). Most reference books will note that because the moon rotates only once during each revolution about the Earth, we never see more than half of its total surface. (Image credit: Karl Tate/)Ģ) We see slightly more than half of the moon from Earth Learn what makes a big full moon a true 'supermoon' in this infographic. Supermoons can appear 30 percent brighter and up to 14 percent larger than typical full moons. ![]()
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