Skip to content
Overview From Space
Imagine you’re in a spaceship, traveling away from Earth. As you sail onward, you see our planet and its Moon locked together in their endless, circling, gravitational embrace. Your distant view gives you a unique perspective on the Moon that can be hard to visualize from the ground, where the Moon appears to sweep through the sky as an ever-changing globe of light.
The Moon orbits Earth from a viewpoint above the North Pole in this animation. The blue gridlines show how the same side of the Moon always faces Earth. The size of the Earth and Moon are enlarged 20 times. Credit: NASA's Scientific Visualization Studio
From your astronaut’s viewpoint, you can see that the Moon is an average of 384,399 km from Earth, or about the space that could be occupied by 30 Earths. It travels around our planet once every 27.322 days in an elliptical orbit, an elongated circle. (It takes about 27.3 days to complete a revolution, but 29.5 days to change from new moon to new moon.) The Moon is with Earth, which means that it spins on its axis exactly once each time it orbits our planet. Because of this, people on Earth only ever see one side of the Moon. We call this motion synchronous rotation.
Our Wobbly Moon
When we think of the way the Moon seems to change over the course of a month, we think of phases. But frequent Moon observers know that the Moon also appears to twist, nod, and roll slightly during its journey across the sky, allowing us to peek around the Moon's shoulder and catch glimpses of the farside. This phenomenon is called libration.
This visualization of the Moon’s phases throughout the year 2021 also shows lunar libration, the apparent rolling motion that changes our view of the Moon slightly over time. NASA’s Science Visualization Studio.
Because the Moon's orbit is not perfectly circular, its distance from Earth and its speed in orbit both change slightly throughout the month. The Moon’s rate of rotation around its own axis, though, always stays the same.
When the Moon is at its closest to Earth and moving most quickly along its orbital path, the Moon itself doesn’t rotate quite fast enough to keep entirely the same side facing us, and we get to see a little more of the eastern side of the Moon. When the Moon is farthest from Earth and orbiting at its slowest, its rotation gets a little ahead, and we see a bit more of its western side. We call this motion “libration in longitude.”
The 5 degree tilt of the Moon’s orbit also causes it to appear to nod, as though it were saying “yes.” The tilt sometimes brings the Moon above Earth’s northern hemisphere, and sometimes below Earth’s southern hemisphere, allowing us to see slightly more of the northern or southern hemispheres of the Moon. We call this motion “libration in latitude.”
Finally, the Moon appears to tilt back and forth like a metronome. The tilt of the Moon’s orbit contributes to this, but it’s mostly due to the tilt of our Earth. Earth has a tilt of 23.5 degrees on its axis, which means that when we observe the Moon from Earth, it’s a little like we’re standing sideways on a ramp. If you look left, the ramp slopes up. If you look right, the ramp slopes down. In front of you, the horizon looks higher on the right and lower on the left. If you turn around, the horizon appears to tilt the opposite way.
The tilted ramp works the same way as the tilted “platform” of the Earth beneath our feet. Every two weeks, we have to look in the opposite direction to see the Moon, and the ground beneath our feet is then tilted the opposite way as well.
Eclipses
The Moon's Tilted Orbit
This animation illustrates how the tilt of the Moon’s orbit often keeps it out of alignment with the Sun and Earth, preventing frequent eclipses.
NASA's Scientific Visualization Studio
Solar Eclipses
What is a solar eclipse?
A solar eclipse occurs when the moon is the position between Earth and the Sun. Covering the Sun, it casts a shadow over the Earth. This phenomena happens only during the New Moon phase which is during the day time.
What is an annular solar eclipse?
An annular solar eclipse happens when the Moon covers the Sun’s center, leaving the Sun’s visible outer edges to form a “ring of fire” around the Moon. Annular comes from the Latin word, annulus, meaning ring.
What is a total solar eclipse?
A total solar eclipse happens when the Moon covers the Sun’s disk completely. The Moon passes between the Earth and the Sun during the new moon phase. A solar eclipse happens about every 6 months somewhere on Earth.
Solar vs. Lunar Eclipses
Movement of the Moon
Calendars
Most cultures started using the moon cycles to mark a month. Doing some simple calculations, if each moon cycle is about 28 days, then a year in this 13-cycle calendar works out to 364 days, not 365 days! Over several decades, that one day difference can add up to be a whole month off the seasons. This was different for other cultures that used a twelve-moon calendar. That’s why the Gregorian calendar, which is widely used around the world today, uses 12 longer months (30 or 31 days) plus one shorter month (February). You may also know that February 29th comes once every 4 years because a year is about 365 ¼ days long so the calendar needs to catch up!
The following image from the Oneida nation depicts the 13 moons of Turtle Island. There are 13 segments on the turtle’s back that are named according to the activities that occur during each moon cycle. The edge of the shell has 28 small plates, one for each day in the cycle.
Explore the following interactive entitled Oneida Moon Calendar to learn more about how the cycles of the moon relate to the activities of the community month to month, over the course of the year.
Religion
The importance of the moon cycle can be found in many cultures and religions. They help individuals keep track of important events and mark celebrations. The following image depicts the phases of the moon in the night sky.
image.jpeg
Phases of the Moon
Studying the phases of the Moon we can clearly observe that the Moon must move around the Earth as depicted in the following animation.
All Moon Phases
Let’s take a look at the individual phases, and how the movements of the Moon and Sun appear to us as we watch from the Northern Hemisphere on Earth:
New Moon
Waxing Crescent
First Quarter
Waxing Gibbous
Full Moon
Waning Gibbous
Last Quarter
Waning Crescent
The Tides
The gravity from the Moon tugs on the Earth.
The Moon pulls the most on the part of the Earth nearby, which raises the atmosphere, the tides, and even the surface (a little).
The Moon pulls the least on the part of the Earth far away, which allows the atmosphere and tides to be further from the Moon.
The Sun’s gravity does the same thing because of its size, but to a lesser extent because of its distance.
Moon Formation
Want to print your doc?
This is not the way.
This is not the way.
Try clicking the ··· in the right corner or using a keyboard shortcut (
CtrlP
) instead.