A page from the "Calendars" exhibit...

Do it yourself

You can make a calendar page, watch the moon everyday for a month, and learn about the phases of the moon. The moon changes in appearance and location in the sky everyday, which is why we refer to the moon by its phases: new moon, new crescent moon, 1st quarter moon, waxing gibbous, full moon, waning gibbous, 3rd quarter, and old crescent. After 29 days you will have a visual record of the phases of the moon, and a better understanding of all the phases. In other words, you can gain the first-hand experience of an astronomer by watching the sky everyday. To see how your observations of the real sky match up with predictions, see also a simulation of whole month or single day at a time.


  • A calendar page where you can record information in each box. (Note: you can make your own calendar page on a sheet of paper or a piece of poster board.)
  • Pen, pencil, marker, and ruler (if you make your own calendar page).

How To Do It

  1. Start your project on the day of a new moon. Most calendars label the days of four of the moon phases (new, 1st quarter, full, and 3rd quarter). You can consult a chart of this month’s 29.53-day cycle.
  2. Each day, look in the sky for the location of the moon. The moon rises in the east and sets in the west. (Note: The east is where the sun rises and west is where the sun sets.)
  3. If it’s cloudy, you can draw or sketch a cloud in the box for that day or see a picture of the moon for that day.
  4. Since a new moon is not visible, you will not find it in the sky. You should write the word ”nothing” in the box for that day and the next day, because it will still not be visible.
  5. On the third day of your project, you may see the new crescent moon in the early afternoon high in the sky, or in early evening in the west. Draw a thin sliver of a moon in your calendar box and note the time of day.
  6. On the fourth and fifth days, the new crescent will get a little larger. Draw what you see and note the time of day.
  7. Seven days after the new moon, you will see a first quarter moon from noon to midnight. Draw a half circle in the box for that day (this is one quarter of the whole moon).
  8. After the 1st quarter, the moon will get a little larger each day. This is called a waxing gibbous moon. It rises in the east in early afternoon and sets in the west after midnight. Record what you see in the appropriate box of your calendar.
  9. The waxing gibbous continues for a few days, after which you’ll see a full moon. It rises in the east at sunset and sets in the west at sunrise. Draw a circle and note the time of day.
  10. After the full moon, the moon will start to get a little smaller. This is the waning gibbous moon. It will rise in the east after sunset and set in the west after sunrise. Continue to fill in the boxes on the calendar.
  11. A week after the full moon, you will see the 3rd quarter moon. It doesn’t rise in the east until midnight and it sets in the west at noon. So, you could see it in the morning!
  12. Three or four days after the 3rd quarter moon, you will start to see a crescent again. This is the old crescent. It gets smaller and smaller and is visible in the morning. It sets in the afternoon.
  13. After the old crescent, you are back where you started 29 days ago - with another new moon. You have finished your calendar of all the phases of the moon.
Moon phases

How It Works

The moon revolves around the earth while the earth is rotating on it axis to give us day and night. It takes the moon 29.53 days to revolve around the earth. During those 29 days we see different proportions of the visible moon from our position on earth.

If the sun is to your right, and the earth is to your left, the moon will be in the middle of this model. The dark side of the earth, where it is nighttime, is not facing the moon. Half of the moon is lit by the sun, but it is not visible on earth (except during a solar eclipse). Some people in rural areas can see what is called “earthshine,” the reflection of the sunlight hitting the earth and bouncing off the earth to the moon and back to earth.

As the moon moves around the earth, we can start to see a little sliver of the moon as we move towards nighttime. Over the course of a week, the moon moves one quarter of its way around the earth and is visible from the dark side of the earth for part of the night.

With the sun still on the right, and the earth in the middle with the moon to the left, you see the whole side of the moon illuminated by the sun; this is a full moon. Sometimes the shadow of the earth covers the moon; this is a lunar eclipse.

Each day, the moon continues to move around the earth. By the time of the 3rd quarter moon, you can see it in the morning. The earth is facing the sun and half of the moon is still receiving sunlight, but you can only see half of the half that is lit.

When the moon moves back to the daylight side of earth, the half of the moon that is lit by the sun is facing away from you. You cannot see it; it is another new moon.


Using a flashlight, a tennis ball, and a golf ball in a darkened room, you can simulate the model described above. Move the moon (the golf ball) around the tennis ball. Put a little Post-it flag on the tennis ball to represent where you are. You will understand why you cannot see a new moon and why you can see a full moon.

On any given day, you can compare what you see with the predicted moon phase for today.

Visit http://www.usno.navy.mil/USNO/astronomical-applications/data-services/phases-moon, where you can look up the phase of the moon on your birthday or any other day. You can add to each calendar box the height of the moon above the horizon and it direction (east or west). If you do this, it’s best to always measure at the same time of day. Your numbers will be in degrees from 0 (horizon) to 90 (directly overhead.) The altitude is the distance the moon appears to be above the horizon. The angle is measured up from the closest point on the horizon.

The azimuth of an object is the angular distance along the horizon to the location of the object. By convention, azimuth is measured from north towards the east along the horizon. North is 0 degrees, East is 90 degrees, South is 180 degrees, and West is 270 degrees.

Share your observations

Calling all would-be astronomers! Help us grow this exhibit by sending in a scan or photo of your homemade moon calendar. Read more about sharing.