Lunar phases
Lunar phases refer to the distinct stages of the Moon as it orbits Earth, resulting in varying appearances based on the angle of sunlight illuminating it. This lunar cycle includes several primary phases: the new moon, when the Moon is not visible; the full moon, when it is fully illuminated; and the first and last quarter moons, which appear half-lit. Additional phases, such as gibbous and crescent, describe the Moon's illumination levels beyond or below 50%. The Moon's orbit is elliptical, causing it to vary in distance from Earth, which can affect its apparent size in the sky.
Lunar phases significantly influence ocean tides due to the Moon's gravitational pull, with notable effects during spring tides (full and new moons) and neap tides (quarter moons). The Moon's illumination also affects wildlife behavior; for instance, nocturnal predators may alter their hunting patterns according to its phases, with lions being less active during a full moon. Eclipses, both lunar and solar, occur due to the alignment of the Earth, Moon, and Sun, creating dramatic astronomical events that can be observed by a significant portion of the Earth's population. Understanding lunar phases enhances our appreciation of this celestial body's influence on both natural phenomena and cultural beliefs.
Subject Terms
Lunar phases
Lunar phases, or the different stages of Earth’s moon as it orbits around the planet, have long fascinated humans. People have attributed everything from success in the stock market to transformation into wolves to the phase of the moon. Medical workers often blame particularly disastrous emergency-room nights on the full moon. These ideas may or may not be true. However, from a scientific perspective, lunar phases have been proven to correlate with ocean tides and the hunting cycles of some animals.
Overview
Lunar phases are related to the location of the moon in orbit and the subsequent changes in the way this celestial body appears when viewed from Earth. These apparent changes to the moon’s size and shape are caused by the angle at which the sun's light hits the moon at a specific time. In reality, the moon is always spherical (round) and half-illuminated by the sun, just like Earth. However, because Earth rotates on its axis faster than the moon rotates around Earth, the angle at which we see the partially lit moon changes. This gives the illusion that the moon changes size and shape.
The moon shifts through its full set of phases over the course of about a month. The primary phases are the new moon, during which the moon doesn’t appear to be illuminated at all; the full moon, during which the moon appears fully illuminated; and the first and last quarter moons, during which the moon appears half-lit. Additionally, the moon is called gibbous when it appears more than 50 percent illuminated, and crescent when it is less than 50 percent illuminated.
The size of the moon in the night sky often varies throughout the year. This is because the moon's orbit around Earth is not spherical, but elliptical. An elliptical orbit means that at certain times, the moon is more or less distant from Earth. In fact, it may be up to 6 percent closer or farther away than its average distance, depending on the time of year. This means the moon can be anywhere from 225,622 miles to 252,088 miles away from Earth.
Eclipses
The shifting orbit of the moon is the cause of both lunar and solar eclipses. A lunar eclipse occurs when Earth moves directly between the moon and the sun, covering the moon in Earth's shadow. At first, the moon appears to slowly disappear. Then, it turns a blood red or deep orange color as it returns. This effect, commonly called a blood moon, can last for hours. The dramatic coloring occurs because the gases in Earth's atmosphere block out several colors of light, making the edges of Earth's shadow appear red or orange in space. Lunar eclipses are completely visible to anyone who can see the moon at the time of the eclipse; that means they are visible to about half the population on Earth at a time.
Another type of eclipse, called a solar eclipse, is more complicated. Solar eclipses occur when the moon's orbit takes it between the sun and Earth, blocking out the sun to Earth’s viewers. The sun is about four hundred times as large as the moon. However, coincidentally, the moon is about four hundred times closer to Earth. For this reason, the two appear to be almost the same size when viewed from Earth. Thus, during a solar eclipse, the moon appears to block out all or part of the sun. A partial solar eclipse occurs when the moon is not close enough to Earth to appear large enough to block out the entire sun. In a partial eclipse, very little of the moon's shadow, if any at all, reaches Earth.
An annular solar eclipse, also known as a total eclipse, is more rare and dramatic. In an annular eclipse, the moon is large enough to block out all but the outermost ring of the sun. The section of Earth within the moon's shadow at that time is cast into a twilight-like state. During this eclipse, the sun looks like a dark black disk surrounded by a ring of fire, occasionally with stars visible around it in the diminished light. Needless to say, an annular solar eclipse is an incredible show on Earth.
Ocean Tides
Lunar phases heavily influence ocean tides. In fact, the moon's gravitational pull is, in large part, the reason ocean tides exist at all. The moon causes uneven gravitational pull on Earth during its monthly circuit through the sky. This circuit isn't perfectly aligned with the daily rotation of Earth on its axis. As Earth wobbles along its axis, different parts of the oceans are pulled by the gravity of both the sun and moon. This causes different parts of the ocean to rise.
During the full moon and new moon, the gravitational pulls of the sun and moon pull in the same direction, creating dramatic tides, called spring tides. On rare occasions, a spring tide occurs when the moon is at the closest point to Earth in its cycle. This is called a proxigean spring tide and produces the strongest tides of the tide cycle. On the other hand, during quarter moons, when the sun and moon are farthest from alignment, tides are at their weakest. These are called neap tides.
Hunting Cycles
The moon also carries significant influence farther inland. Nocturnal species have had centuries to evolve to make the best use of all available light at night, including that of the moon. Thus, many species change their behavior with the moon's cycle. For example, lions and other nocturnal predators are less likely to hunt under the full moon. Additionally, many prey species remain inactive during a full moon, knowing it makes them more visible. However, in the nights following the full moon, the moon rises later and later after the sun has gone down, producing several hours of moonless dark. Lion attacks are statistically most likely to occur during this window because these large predators have learned to exploit the darkness.
Bibliography
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MoonConnection. "Understanding the Moon Phases." MoonConnection. MoonConnection.com. Web. 28 Jul. 2014. <http://www.moonconnection.com/moon‗phases.phtml>
NOAA. "Tide Waters and Levels." NOAA. National Oceanic and Atmospheric Administration. Web. 28 Jul. 2014. <http://oceanservice.noaa.gov/education/kits/tides/tides02‗cause.html>
Walker, Cameron. "Moonstruck." Aeon Magazine. Aeon Media Ltd. 22 April 2014. Web. 28 Jul. 2014. <http://aeon.co/magazine/nature-and-cosmos/how-moon-phases-affect-life-on-earth/>