Do you struggle to tell the difference between a waxing and waning gibbous? Was your last imaging session interrupted by a lunar light show? Trying to guess when and where the Moon will make an appearance can feel like playing a poorly coordinated game of hide and seek. It is nowhere to be found when you want to see it, and when you are hoping for clear, dark skies, it is sure to show up shining bright as ever. So, why does the Moon seem so elusive?
Like with many of the problems we face in life, this celestial drama traces back to lack of clear communication. Fortunately, understanding our cosmic companion doesn’t require the assistance of a professional. Below, you’ll find an interactive lunar calendar that will give you the know-how needed to predict the phases of the moon and more!
TL;DR:While predicting the phases of the Moon can be a great way to learn about the orbital dynamics of our solar system, it isn’t always the most convenient way to stay up-to-date with the Lunar cycle. For real-time updates on all things celestial, star guiding, and more, download a night sky simulator like Star Walk or Stellarium.
Things to Know Before We Get Started
- The Moon follows a repeating 29.5-day cycle.
- The word month comes from the 29.5 lunar cycle (Moonth). However, lunar calendars inevitably fall out of sync with the solar year, making it difficult to keep track of seasonal shifts.
- The lunar cycle is predictable. The new moon always rises with the Sun in the morning, the first quarter rises around noon, the third quarter rises at midnight, and the full moon rises as the Sun sets in the evening.
- The Moon’s orbital path moves west to east, following the same direction as the Earth's rotation around its axis. This means the Moon moves about 14° closer to the eastern horizon every day.
- The Moon orbits at 5° incline to the ecliptic plane, which causes subtle shifts in its path, wandering at about +/- 0.5° north to south.
- The Moon crosses the ecliptic twice per cycle. When the Moon passes one of these transit points, or nodes, it can result in either a lunar or solar eclipse if the timing and alignment are right. Want to know more?
Interactive Lunar Calendar
Now that we’ve identified the pieces to this lunar puzzle, let's put it all together. Check out the lunar calendar below!
To learn how to predict the phases of the Moon, begin by saving a copy of the above image, or use the following link to download a PDF copy: Lunar Phase Calendar. Once you have a copy of the calendar, print it out and follow the steps below!
Mechanics
The mechanics of this calendar are straightforward; you have three main points of interest: the two cut-out pieces, the 24 hour time gauge around the innermost circle, the 29 lunar placeholders, and eight lunar phase icons.
Step 1
Cut out the two pieces. If you don’t have a pair of scissors, you can simply use a few coins instead!
Step 2
Place the dial cut-out in the middle of the calendar and orient the arrow towards 12 pm.
Step 3
Next, place the lunar cut-out on the position directly below the new moon phase icon.
Rules
From here, look to the outer ring around the 29 lunar place holders. You'll see the closest phase icon to the lunar cut-out is "New Moon". This is the first day of the lunar cycle. During this stage in the lunar cycle, the Sun and Moon rise at the same time, so the Moon is not observable, as it’s reflecting the sunlight back towards the Sun and away from the Earth. You will also see the arrow on the dial cut-out is pointing towards 12 pm. This means that at 12 pm, the Moon will be positioned directly above you, or at your zenith. If you move the inner dial so the arrow points at a different time, you'll see the Moon will now be in a different position relative to your zenith. Why is this? Well, the Moon only traverses 14° of it's orbital path each day, but during that same period of time, you traverse a full 360° as the earth rotates around its axis. The inner dial accounts for this rotation, so as you move the dial is various points of time, you will see how your position changes relative to the position of the Moon. To account for the slower movement of the Moon through its orbital path, you only need to move the lunar cut-out counter-clock wise to the next placeholder for each passing day.
Before moving on, play around with the model and get a feel for how the different positions correlate to the various phases of the Moon. Once you have the mechanics down, it's time to put your skills to the test. Move on to the next phase to begin calibrating your lunar calendar!
Phase One (Lunar Observation)
To begin calibrating your lunar calendar, you’ll need to gather some data. Go outside and see if you can find the Moon. This might take a couple of tries, as the Moon isn’t always above the horizon. Once you’ve located the Moon, you’ll need to write down some observational notes. First, note the current time of night or day.
Next, you need to note the position of the Moon relative to the eastern or western horizon. To do this, use a compass or GPS-enabled smartphone to find the northern horizon. If you are completing this step at night, you can use Polaris as a point of reference. Facing the northern pole, look directly above. Imagine a line dividing the sky in half. From this position, everything on your left side will be your western hemisphere, and everything to your right will be your eastern hemisphere. Now, find the Moon and note which hemisphere best describes its location. If it is close to the imaginary division, just note that it is at your zenith. Finally, either draw a picture of what the Moon looks like or note the current phase.
After collecting the relevant information, move on to the next phase!
Not sure how to determine the current phase? Check out our What are the Phases of the Moon article!
Phase Two (Calibrating the Calendar)
With your observation notes close by, prepare your calendar for calibration. Position the dial cut out so that the arrow is roughly aligned to the time of day you noted in your observations. Now, review the lunar placeholders on the diagram. There should be about thirteen available placeholders for any given orientation.
Check your notes to see what position the Moon was in during the previous step. If you noted that the Moon was in the western hemisphere, place the lunar cut-out on one of the positions to the right of the arrow. If the Moon was at or near your zenith (the point directly above you when standing upright), place it in the position directly above the arrow. Finally, if the Moon was near the eastern horizon, place the lunar cut-out on one of the left-hand positions. It’s important to remember that for this step, the position doesn’t need to be perfect, just place the lunar cut-out where you think it should go. Once you’ve completed this step, your lunar calendar should be initialized. In the next step, you will do a little fine-tuning to fully calibrate your lunar calendar.
Phase Three (Checking for accuracy)
Now that you’ve initialized your lunar calendar, you should be able to roughly determine the current phase of the Moon, but with a little fine-tuning, you will be able to make much more confident predictions. Review your notes from step one. Compare the phase of the Moon you noted or sketched, with the phase listed nearest the position you placed the lunar cut-out.
If your notes match the model, congratulations, you have successfully calibrated your lunar calendar! If things don’t line up, try moving the lunar cut-out one or two steps to the left or to the right. If you are still having trouble, reset the calendar and go back to the first step.
What’s next?
With your successfully calibrated lunar calendar, you should be able to start making accurate phase predictions. Remember, for every day that passes, you need to move the lunar cut out one position counter clockwise. Once you’ve returned to the new moon phase, reset the calendar by repeating the calibration steps.
That's it! Now, you have everything you need to start predicting the phases of the Moon. Simply rotate the inner dial to the time of day you plan to do your viewing or imaging, and you’ll not only be able to locate the Moon, but you’ll also be able to predict its phase, when it will rise, when it will set, and how long it will be in the sky!
Troubleshooting
If you find that your calendar is out of sync, repeat the steps outlined above to recalibrate. If you are still having trouble, review our Why Does the Moon Have Phases article to get a better understanding of our cosmic companion. You can also download a night sky simulator like Star Walk or Stellarium if you are having trouble finding the Moon. Of course, during the new moon phase of the lunar cycle, you will not be able to see the Moon. If you find yourself in this moonless predicament, simply wait a few days and try again.
Latitude
It’s important to remember that the Moon’s position in the sky changes slightly depending on your latitude. If you are in the northern hemisphere, the moon will be near or south of your zenith, and if you are in the southern hemisphere, it will be near or north of your zenith. If you are located near the equator, it will ebb north-south of your zenith, and if you are at or near one of the poles, it will stay low on the horizon facing the opposing pole.
Predicting the Future
If you want to take things even further, use this equation to make far out predictions! You need to gather some information first, then simply plug the information into the equation, do some calculations, and you'll be able to make accurate predictions beyond the current cycle. Here what you need: Find the number of days between the current day and the prediction date. Then, count the number of placeholders between the new moon position and the lunar cut out. Once you have these two values, its time to start crunching the numbers! Check out the equation below.
Start by dividing the number of days between the current date and prediction date by 29.53. This will provide the number of cycles between the two dates. Next, take the value after the decimal point and multiply it by 29.53. This will covert the percentage of the cycle leftover to a value that can be mapped on to the 29 spaces of the lunar calendar. The last step is to determine how many spaces you need to move the lunar cut out. Round the product of the second equation to the nearest whole number. If the resulting number is less than 29, then move the lunar cut out that many spaces (starting from the calibrated position). If the number exceeds a full cycle (29 days), simply subtract 29 from the number and the difference will be the number of spaces you need to move the lunar cut out. If done properly, you should be able to accurately predict the phase and positioning of the Moon for any date ranging between 3000 BCE and 3000 CE.
Put your lunar calendar to the test! To verify the accuracy of your lunar phase predictions, set a reminder to view the Moon on the date of the prediction. Then, take an image of the Moon and share it with your friends and family!
Learn More
Interested in learning more about astronomy and astrophotography? Not sure where to begin? Check out our Astronomy Hub!
Glossary
Annular Eclipse
“Annulus” refers to a ring shaped object, and is where the Annular Eclipse gets its name. As the Moon has an elliptical orbit around the Earth, it is not always the same distance away. An annular eclipse occurs when the Moon is at or near its farthest point from the Earth, making it appear smaller in the sky. Due to this, when the moon passes in front of the Sun it does not entirely block its light, resulting in a thicker ring around the Moon than what is visible in a total eclipse. While still rare, this type of eclipse is more frequent than a total solar eclipse.
Astrophotography
This refers to photography of astronomical bodies and phenomena. Astrophotography is not new, for example the popular T threading still used today harkens from Tamron’s T-mount developed for their 35 mm cameras - however it has seen a notable increase in popularity with improvements in cameras, mounts, filters, and software making astrophotography much more accessible. This is not limited to celestial bodies such as nebulae, planets, or galaxies either, as solar imaging is now more within the reach of the average consumer than ever before.
Crescent Moon
A crescent moon refers to two of the eight major phases of the Moon. When the Moon is in a crescent phase, the illuminated side faces away from the earth, making the Moon appear slim and inwardly arced.
Ecliptic Plane
First described by the Greek astronomer and mathematician Hipparchus, the ecliptic plane is an imaginary two dimensional plane on which planets orbit their host star. Not all celestial objects are confined to the ecliptic plane. For example, Pluto's orbit is tilted by about 17° when compared to the other planets and dwarf planets, making it the largest object to deviate from the ecliptic plane.
Full Moon
When the Moon passes through the far side of its orbit, and it is completely illuminated by the sun, it's considered a full moon. Since the shadow is no longer visible, the Moon appears as a bright disc in the night sky.
Gibbous Moon
A gibbous moon refers to two of the eight major phases of the Moon. When the Moon is in a gibbous phase, the illuminated side appears to bulge outward, but does not look quite as circular as a full moon.
Hemisphere
A hemisphere is a mathematical term that describes half of a sphere or globe. While the dividing line between hemispheres can be arbitrary, when talking about our planet or the celestial sphere, we tend to divide the hemispheres into west, east, north, and south.
Latitude
Latitude is one of two coordinates used to find a position on a globe. Lower latitudes are closer to the equator, while higher latitudes are closer to the poles.
Lunar Calendar
A lunar calendar is an algorithm that uses the lunar cycle to keep track of the date or phase of the Moon. Lunar calendars can be useful for keeping track of the various lunar phases and predicting eclipses, however, they inevitably fall out of sync with the solar year because the 29.5 day lunar cycle does not align with the 365.25 day orbital period of the earth around the sun.
Lunar Cycle
A lunar cycle refers to the 29.5 day orbital period of the Moon around our planet, in which the Moon transitions through all 8 of its main phases.
Lunar Eclipse
A lunar eclipse occurs when the Moon passes through Earth’s shadow. One of the reasons for this celestial event is orbital inclination of the Moon to the ecliptic plane of the solar system. Since this orbital inclination is constantly shifting, lunar eclipses can happen at various different times of year and have been historically difficult to predict.
Lunar Phases
Lunar phases are the various shapes caused by the shadow of the Moon as it moves around our planet. These phases are normally categorized into eight major phases: waxing crescent, 1st quarter, waxing gibbous, full moon, waning gibbous, 3rd quarter, waning crescent, and new moon.
The Moon
A moon is a naturally occurring object that orbits a planet or other celestial bodies (excluding stars). These are also called natural satellites. The Moon, capitalized, is the Earth's only natural satellite and is the brightest object in the night sky. The Moon stabilizes the tilt of Earth's orbit, causing the seasons, and tides.
Nadir
Nadir is a geometrical term which describes an imaginary line running below and perpendicular to a two dimensional plane. In the context of visual astronomy, it refers to the point directly below you when standing upright. While less commonly used than its complimentary term zenith, it can be useful when describing the location of objects that are below your celestial horizon.
New Moon
New moon marks the beginning of a new cycle of moon phases. This is where the Moon seemingly disappears from the sky, as its non-illuminated side is facing us. Because of the lack of moonlight shrouding dim celestial objects, this phase of the Moon is important to astronomers and astrophotographers. The moon will soon appear as a crescent as it continues to orbit the Earth.
Orbit
An orbit is a predictable and periodic path an object follows as it moves through space-time warped by a more massive celestial object. We have known about celestial orbits since early antiquity, however, it was not until Johannes Kepler formalized the three laws of planetary motion that we gained the ability to acutely predict the orbits of our planetary neighbors.
Orbital Incline
An orbital incline is the degree to which a celestial body tilts above or below the ecliptic plane of the solar system. These tilts are caused by the conservation of the celestial body’s momentum as it’s pulled towards a massive star or planet. Our Moon has a slight orbital incline of around 0.5°.
Orbital Nodes
When describing the Moon's position in relation to a solar eclipse, a node is a point along its orbit that would place the Moon in line with the Sun. This isn't necessarily where an eclipse will happen, just a location where it can happen as the Moon still needs to be in the New Moon phase when passing through this point for an eclipse to occur. There are two nodes in the Moon's orbit, one where a solar eclipse can happen and one where a lunar eclipse can happen.
Solar Calendar
A solar calendar is a timekeeping algorithm that keeps track of the 365.25 day solar year, as well as the associated seasonal shifts. The widely adopted Gregorian Calendar is one example of a solar calendar. Solar calendars often incorporate leap days, weeks, months or years, to account for the gradual drift caused by Earth’s 365.25 orbital period around the Sun.
Solar Eclipse
A phenomena that occurs when the Moon passes in front of the Sun, blocking some or most of its light. These events happen every year at one point or another around the globe, and last from a matter of seconds to a few minutes. While the Moon does block a large amount of the Sun’s light, it is still not safe to view or image an eclipse directly without special equipment such as solar eclipse glasses or a solar filter.
Stellarium
Stellarium celestial simulator that you can download on your smartphone. This software works with your phone’s GPS to give you real-time positioning of objects in the sky, night or day. It also allows you to see past or future positioning by changing the date and time. It is free with ads, or you can purchase a subscription for full access.
Star Walk
Star Walk celestial simulator that you can download on your smartphone. This software works with your phone’s GPS to give you real-time positioning of objects in the sky, night or day. It also allows you to see past or future positioning by changing the date and time. It is free with ads, or you can purchase a subscription for full access.
The Sun
The sun is the star which our planet (as well as the other planets in our solar system) orbit around. Like other stars, the sun is a luminous sphere of plasma held together by the collective gravitational attraction of hydrogen and helium atoms.
Visual Observation
Visual observation is the study of celestial objects using specialized visual equipment like telescopes and binoculars, or simply viewing the sky with your naked eye. Born from our species' first attempts to understand the many mysterious objects that fill our night sky, visual astronomy has blossomed into an expansive field of study, and inspired many to join in the pursuit of knowledge that beckoned our curious ancestors.
Waning Moon
As the Moon begins to move towards the sun in its orbit around the earth, the illuminated side appears to shrink with each passing day. This period of the lunar cycle is labeled “waning” to distinguish it from the opposing, yet similar, waxing phases.
Waxing Moon
As the Moon begins to move away from the sun in its orbit around the earth, the illuminated side appears to grow larger each passing day. This period of the lunar cycle is labeled “waxing” to distinguish it from the opposing, yet similar, waning phases.
Zenith
The zenith is a commonly used geometrical term which describes an imaginary line running above and perpendicular to a two dimensional plane. For visual astronomy, the zenith simply refers to the point directly above your head when standing upright, and can be a useful point of reference when describing the position of celestial objects in our night sky.
