Earth's Lunar Cycle
This chart is a 2D model representing Earth’s Lunar Cycle. THE SUN In this chart, we pretend that the Sun is motionless. It isn’t. It’s revolving around the center of the galaxy once every 250 billion years. But that revolution doesn’t affect earthly experience of the Lunar cycles, so for now, you can pretend it’s holding still. EARTH Likewise, Earth is revolving around the Sun, which we experience as the changing seasons. To understand Lunar phases, we can ignore this orbit. As we’ll soon see, we can’t ignore the Earth’s rotation on its own axis. While one hemisphere faces the Sun and experiences daytime, the other hemisphere faces away from the Sun and experiences night. THE MOON Outer ring: what the Moon would look like from an extraterrestrial perspective, as if you were in a starship watching over the whole scene. The side of the Moon facing the Sun is always illuminated, the side facing away is always dark. The Moon is a mirror. Moonlight is simply sunlight reflected off the Lunar surface. Inner ring: the Lunar phases as we see them from Earth. Shapes: The Moon itself does not change shape over time; we witness distinct phases as it revolves around us, changing its angle to the Sun. Each day (or night) we are able to see the Sun’s light on a slightly larger sliver (waxing) until full, and a slightly smaller sliver each day (waning) until it goes dark again. Then the cycle repeats, again and again. Time Length of a Lunar Cycle: a Lunar Cycle, approximately 28 days, is the time it takes the Moon to revolve around Earth. Thus there are 28 days between one new Moon and the next new Moon. When Can We See the Moon?: On Earth, we tend to feel stationary and to perceive the Moon and Sun as moving across the sky. But the truth is, we are actually rotating. When we turn enough to catch a glimpse of the Sun or Moon on the horizon, we say they are “rising.” When we turn away from these bodies and they begin to slip from our view, we say they are “setting.” The time of day or night that we can see the Moon changes because as it revolves the distance between the Moon and the Sun changes too. This is easiest to visualize on the chart by choosing a spot for yourself on Earth, then imagining yourself rotating to face the sun (dawn) and then the Moon. Each day the time between dawn and the next moonrise increases by approximately one hour. Looking at it another way, the amount of time between moonrise and the following dawn decreases.
PHASES
THE NEW OR DARK MOON Day: 1 or 28 Moon rises at sunrise Moon sets at midday We can’t see the Moon during this phase, because it’s between the Earth and the Sun. As you can see from the outer ring, half of the Moon is still illuminated, but the lit half is facing directly away from our view. WAXING MOON PHASES Crescent Moon rises ≈ 1 hour later each day Waxing is when the fraction of the Moon we can see increases. As we rotate, we first face the Sun (dawn), then we spin a little further to face the Moon. Thus you can see the crescent Moon in the morning time, an hour later past dawn each day. From the extraterrestrial viewpoint, you’ll see that one half of the Moon is still illuminated by the Sun. But because of Earth’s angle, only a tiny slice of this light is visible to us. First Quarter or Half Moon Day: 7 Moon rises at high noon Moon sets at mid-night Some people like to call this the “half Moon.” I prefer “first quarter.” It takes the Moon about 7 days to go from New to First Quarter, which is ¼ the total 28 day cycle. On a first quarter day, by the time Earth has spun enough to bring the Moon into view, we’ve made a quarter turn away from the Sun, which is now in the middle of the sky at high noon. Thus, in the first quarter, the Moon rises at noon and sets at midnight. Gibbous Moon Moon rises ≈ 1 hour later each day The Moon is known as “gibbous” (pronounced GIB-us) when more than half of the visible side of the Moon is lit. During this phase the moon rises about one hour closer to sunset each evening. FULL MOON Day: 14 Moon rises at sunset Moon sets at mid-night The moon is now on the opposite side of the Sun, with the Earth in between. Earth rotates to face the Moon rise just as we turn out back to the sunset. The entire surface of one side of the moon is
now glowing in the reflection of the Sun’s rays. The moon sets at mid-night; that is, exactly half-way between sundown and sunset, which doesn’t always line up perfectly with human’s 12:00 a.m. WANING MOON PHASES, Disseminating Moon During the waning period smaller and smaller sections of the Moon are visible to us each day, and the moon rises an hour later past sunset each night. Third Quarter Day: 21 Moon rise at mid-night Moon set at high noon Balsamic Moon Also known as the “waning crescent,” the balsamic moon rises one hour closer to the following dawn each night before becoming completely dark and returning to new moon phase. OTHER MOON MYSTERIES The Dark Side of the Moon Just in case you’re head’s not spinning enough, know this: the Moon also spins on its own axis, but this takes about the same amount of time as it does to orbit the Earth because Earth’s gravity “locks” the moon in this position. Thus Earthlings only ever see one side of the moon. The famed “dark side of the Moon” refers not to the dark phase of the Moon, but to the Lunar hemisphere that remains eternally invisible to us on Earth. Eclipses These orbits are not all happening on the same plane. The moon’s orbit is around Earth is tilted askew in relationship to Earth’s orbit of the Sun. But occasionally the orbits line up just so, creating eclipses. A solar eclipse is when the new Moon lines up between Earth and the Sun, casting a shadow on Earth. During a total eclipse of the sun, the moon lines up perfectly to temporarily block all sun light from reaching earth. During a lunar eclipse, the Moon moves into Earth’s shadow. Earth blocks sunlight from reflecting off the Moon, so we see the full moon go dark.
PHASES
THE NEW OR DARK MOON Day: 1 or 28 Moon rises at sunrise Moon sets at midday We can’t see the Moon during this phase, because it’s between the Earth and the Sun. As you can see from the outer ring, half of the Moon is still illuminated, but the lit half is facing directly away from our view. WAXING MOON PHASES Crescent Moon rises ≈ 1 hour later each day Waxing is when the fraction of the Moon we can see increases. As we rotate, we first face the Sun (dawn), then we spin a little further to face the Moon. Thus you can see the crescent Moon in the morning time, an hour later past dawn each day. From the extraterrestrial viewpoint, you’ll see that one half of the Moon is still illuminated by the Sun. But because of Earth’s angle, only a tiny slice of this light is visible to us. First Quarter or Half Moon Day: 7 Moon rises at high noon Moon sets at mid-night Some people like to call this the “half Moon.” I prefer “first quarter.” It takes the Moon about 7 days to go from New to First Quarter, which is ¼ the total 28 day cycle. On a first quarter day, by the time Earth has spun enough to bring the Moon into view, we’ve made a quarter turn away from the Sun, which is now in the middle of the sky at high noon. Thus, in the first quarter, the Moon rises at noon and sets at midnight. Gibbous Moon Moon rises ≈ 1 hour later each day The Moon is known as “gibbous” (pronounced GIB-us) when more than half of the visible side of the Moon is lit. During this phase the moon rises about one hour closer to sunset each evening. FULL MOON Day: 14 Moon rises at sunset Moon sets at mid-night The moon is now on the opposite side of the Sun, with the Earth in between. Earth rotates to face the Moon rise just as we turn out back to the sunset. The entire surface of one side of the moon is
now glowing in the reflection of the Sun’s rays. The moon sets at mid-night; that is, exactly half-way between sundown and sunset, which doesn’t always line up perfectly with human’s 12:00 a.m. WANING MOON PHASES, Disseminating Moon During the waning period smaller and smaller sections of the Moon are visible to us each day, and the moon rises an hour later past sunset each night. Third Quarter Day: 21 Moon rise at mid-night Moon set at high noon Balsamic Moon Also known as the “waning crescent,” the balsamic moon rises one hour closer to the following dawn each night before becoming completely dark and returning to new moon phase. OTHER MOON MYSTERIES The Dark Side of the Moon Just in case you’re head’s not spinning enough, know this: the Moon also spins on its own axis, but this takes about the same amount of time as it does to orbit the Earth because Earth’s gravity “locks” the moon in this position. Thus Earthlings only ever see one side of the moon. The famed “dark side of the Moon” refers not to the dark phase of the Moon, but to the Lunar hemisphere that remains eternally invisible to us on Earth. Eclipses These orbits are not all happening on the same plane. The moon’s orbit is around Earth is tilted askew in relationship to Earth’s orbit of the Sun. But occasionally the orbits line up just so, creating eclipses. A solar eclipse is when the new Moon lines up between Earth and the Sun, casting a shadow on Earth. During a total eclipse of the sun, the moon lines up perfectly to temporarily block all sun light from reaching earth. During a lunar eclipse, the Moon moves into Earth’s shadow. Earth blocks sunlight from reflecting off the Moon, so we see the full moon go dark.
