The Moon, seen from Earth, is the brightest and most easily identifiable object in the night sky. … [+] Only by observing it and its appearance in detail over time, can we learn an enormous amount of science.
kasabubu by pixabay / public domain
The brightest object in the night sky, our Moon is an unmistakable sight.
The Moon, in the crescent phase, can be seen set with the Statue of Liberty in the foreground. The … [+] The moon phases change from new to half-full to half-full to full to full to half-full to half-full to half-full to new again periodically every 29.53 days. (Tayfun Coskun / Anadolu Agency via Getty Images)
Anadolu Agency via Getty Images
Beyond its skyward movement and shifting phases, naked-eye lunar observations produce enormous scientific knowledge.
Seen from the Northern Hemisphere with respect to the Southern Hemisphere in its various phases, … [+] the Moon will appear differently oriented due to the spherical shape of the Earth. The perspectives of observers at different latitudes ensure that the Moon will be tilted with respect to the horizon and the sky, as dictated by a person’s orientation on Earth.
Open University / Creative Commons
1.) The Earth is round.
Depending on the latitude and perspective of an observer, he will see the Moon oriented differently, like … [+] their horizon and orientation is determined by their position on a round Earth. Someone at the north pole would see the Moon turned 180 degrees by someone at the south pole. The diagram is not to scale; the Moon is much further away than illustrated.
Kelvin case / public domain
Arctic versus Antarctic perspectives are completely reversed, with latitudinal variations indicating the shape of the Earth.
By observing the curvature of the Earth’s shadow falling on the Moon, we can reconstruct the … [+] relative size of the Moon with respect to the shadow cone of the Earth, allowing us to geometrically reconstruct the Earth-Moon distance. The shadow of the Earth falling on the Moon teaches us that our planet is more than 3 but less than 4 times the diameter of the Moon and spheroidal in shape.
Fred Espenak / MrEclipse.com
Furthermore, the shadow of the Earth during lunar eclipses reveals the spheroidal nature of our planet.
Compared to an apogee Moon (more distant), a full Moon perigee (closer) can be about 14% … [+] bigger and 30% brighter. The apparent size of the Moon not only changes from full moon to full moon, but throughout the lunar month as it travels in an elliptical orbit around the Earth.
Tomruen / Wikimedia Commons
2.) The Moon’s orbit is elliptical, not circular.
Before understanding how the law of gravity worked, we were able to establish with respect to any object in … [+] orbit around another obeyed Kepler’s second law: it plotted equal areas in equal amounts of time, indicating that it must move slower when farther away and faster when closer. This effect was clearly visible for the Moon since ancient times, as the smaller angular size and slowest velocity near the apogee and the largest angular size and fastest velocity near the perigee are evident.
RJHALL / PAINT SHOP PRO
Changes in the apparent size of the Moon indicate large variations in its distance from Earth.
The cycle from new moon to full moon to new moon again coincides with increases and decreases in … [+] apparent size as the Moon moves along its elliptical orbit. Since it moves faster at the perigee and slower at the apogee, but has a constant rotation speed, we see just over 50% of the Moon over the course of a lunar month: this is the phenomenon of lunar libration.
Tomruen, Wikimedia Commons user.
Furthermore, more than 50% of its face is visible over time, as it orbits the Earth faster when it is closer and slower when it is further away.
Seen from Earth, a non-full Moon will have part of its face illuminated by reflection … [+] sun, but the rest of the moon is not completely dark. Instead, it is illuminated by Earthshine – sunlight reflected from the Earth falling on the Moon. By looking at the portion of the Moon illuminated by the Earth, we can determine the reflectivity of the Earth: known as the Earth’s albedo. (Alan Dyer / VWPics / Universal Images Group via Getty Images)
VWPics / Universal Images Group via Getty Images
3.) How reflective is the Earth?
The brightness of the portion of the Moon not directly illuminated by the Sun, but instead illuminated by … [+] Earthshine, will change over time, depending on how reflective the Earth is, which depends on a number of factors, including cloud cover, ice cover, time of day and Earth’s rotation, and even seasons. (Frederic Larson / San Francisco Chronicle via Getty Images)
Hearst Newspapers via Getty Images
The unlit part of the Moon is illuminated by Earthshine: sunlight reflected from the Earth.
This amateur photograph shows in detail a crescent moon: where part of the moon is illuminated … [+] from the Sun, where the craters are particularly visible along the terminator (the line between night and day), and the rest of the Moon is dimly illuminated by sunlight reflected from the Earth: Earthshine.
Rob Pettengill / flickr
Observing the light from the unlit side teaches us the reflectivity of the Earth.
The Moon as seen from a view over most of the Earth’s atmosphere. Earthshine illuminates the … [+] most of the moon, which has only a tiny sliver illuminated by the sun. The light from the moon passes a little through the earth’s atmosphere, with the atmospheric color slightly affecting the camera’s view.
NASA
4.) Earth’s atmosphere bends red light more than blue.
When viewed very close to the horizon, the moon’s light must pass through the maximum amount of … [+] Earth’s atmosphere. The atmosphere preferentially disperses blue light while allowing red light to pass more easily, resulting in a redder appearance near the horizon. (Gary Hershorn / Getty Images)
Corbis via Getty Images
During moonset / moonrise, the Moon appears redder, as blue light is scattered.
When the Moon appears farther from the horizon, its light passes through less than that of the Earth … [+] atmosphere before reaching our eyes, making its color appear more faithful to its original color: white, that of reflected sunlight. The closer the Moon is to your apparent horizon, the more red it will appear.
Steven Schimmrich / Hudson Valley Geologist
That red light is bent, meanwhile, preferentially illuminating the Moon during lunar eclipses.
During most total lunar eclipses, a partial eclipse is followed by a dark red that takes over the Moon … [+] on the one hand, with one limb that always remains brighter and whiter than the other. If the Moon passes through the direct center of the Earth’s shadow, it may appear uniformly red and faint, but the more blue light falls on the Moon the closer the side of the Moon is to the edge of the Earth’s shadow cone.
KAZUHIRO NOGI / AFP / Getty Images
5.) The Moon has mountains, valleys and high crater walls.
While the Moon blocks most of the Sun, the deeper craters continue to let sunlight through, … [+] giving the effect known as Baily’s Beads. The amount of time these spheres are visible, along with their intensity, allows us to infer the heights and depths of crater walls and valleys during solar eclipses.
Phil Hart / http://philhart.com/content/solar-eclipse-queensland-14th-november-2012
During solar eclipses, Baily’s pearls reveal the lunar topography.
When the moon’s shadow falls to Earth, as it did during this 1999 total solar eclipse, yours … [+] the whole shadow can be seen from the right perspective. Contrary to the expectations of many, the Moon’s shadow will not be perfectly spherical, but will be elongated and irregular due to the geometric alignments and cratered and mountainous terrain found on the Moon.
Mir / Roscosmos
The irregular shape of the moon’s shadow on Earth, during total eclipses, reveals the heights of the crater walls.
Mostly Mute Monday tells an astronomical story in pictures, images and no more than 200 words. Talk less; smile more.
