By knowing whether the moon is waxing or waning, we can determine the phase the moon goes through, the direction the waves move, and the moon's position in relation to the sun and the earth. You can also find out where the moon rises and sets according to its phase, if you want to see it on a certain night. The new moon is the moon whose bright part will increase if it continues to be monitored every night until it reaches the full moon. While the old moon is the opposite. There are several ways to tell if the moon is young or old. Although the details differ slightly, depending on your point of location on earth, the method will be the same.
Part 1 of 3: Understanding the Phases of the Moon
Step 1. Learn the names of the phases of the moon
The moon revolves around the earth so we will see its bright part from various angles. The moon does not produce its own light, but reflects light from the sun. The moon goes through several phases as it changes from new to full moon and back to new moon, including crescent and gibbous phases caused by its own shadow. The phases of the moon consist of:
- New month
- Young crescent
- 1st quarter month
- Young convex moon
- Full moon
- Old convex moon
- 3rd quarter moon
- Old crescent
- New month
Step 2. Know the meaning of the phases of the moon
The moon revolves around the earth in the same path every month, so the phases it goes through are the same every month. The phases of the moon arise as a result of our perspective on earth. We see various shapes of the moon's bright part as this satellite evolves on its path. Don't forget, actually half the moon is always illuminated by sunlight. It is our perspective on earth that changes and determines the apparent phases of the moon.
- During the new moon, the moon is between the earth and the sun so that when viewed from the earth, none of the bright parts of the moon are visible. In this phase, the bright part of the moon is facing completely towards the sun and we can only see the total shadow of the earth.
- During the first quarter moon, we see the bright half of the moon and half the shadow of the moon. The same goes for the 3rd quarter month, only I swap sides.
- When the full moon appears, we see all the bright parts of the moon and the shadow parts of the moon facing the sky.
- After the full moon, the moon continues its journey back to its initial position between the earth and the sun (new moon phase).
- The moon takes a little over 27.32 days to completely circle the earth. However, the length of a full moon (from new moon back to new moon) is 29.5 days because that is the time it takes the moon to return to its position between the earth and the sun.
Step 3. Find out the cause of the occurrence of young and old moons
When the bright part of the moon from day to day increases, this is called the young moon phase. Conversely, if the bright part of the moon from day to day is decreasing, this is called the old moon phase.
The phases of the moon always look the same. Therefore, although the moon is visible in various locations and orientations in the sky, you will be able to determine which phase it is in if you see certain signs
Part 2 of 3: Determining the Phases of the Moon in the Northern Hemisphere
Step 1. Understand that the bright part of the moon increases and decreases from right to left
The parts of the moon that are illuminated by the sun during the young and old phases of the moon are different. In the northern hemisphere, the increase in the bright part of the moon will appear from right to left until full, and then decrease also from right to left.
- The young moon will be illuminated by the sun from the right side, and the old moon will be illuminated from the left side.
- Extend your right hand, straighten the thumb, and face the palm up. Your thumb and index finger are bent as if to form the letter C. If the curve matches the curve of the moon, it means that the moon is in a young moon phase. If you make the same gesture with your left hand and the curve matches the curve of the moon, it means that the moon is in the old moon phase.
Step 2. Remember the letter pattern D, O, C
Since the moon always follows the same pattern, you can use the shapes of the letters D, O, and C to determine the phases the moon goes through. As it moves towards the 1st quarter phase, the shape of the moon resembles the letter D. At full moon, the moon forms like the letter O. When moving towards the 3rd quarter moon phase, the shape of the moon resembles the letter C.
- A crescent moon shaped like an inverted C occurs during the young moon.
- A convex moon that looks like the letter D occurs during the young moon.
- A convex moon that looks like an inverted D occurs during the old moon.
- A crescent shaped like the letter C occurs during the old moon.
Step 3. Know when the moon rises and sets
The moon doesn't always rise and set at the same time, and it depends on the phase it goes through. This means that you can use the moon's rising and setting times to determine its phase.
- The new moon cannot be seen because it is not illuminated by the sun, and the time of sunrise and sunset coincides with the sun.
- When the young moon moves towards the 1st quarter, it rises in the morning, reaches its peak at sunset, and sets in the middle of the night.
- The full moon rises when the sun sets and sets when the sun rises.
- When moving into the 3rd quarter phase, the moon will rise in the middle of the night and set in the morning.
Part 3 of 3: Determining the Phases of the Moon in the Southern Hemisphere
Step 1. Know the part of the moon that is bright during the young and old moons
In contrast to the northern hemisphere, the bright part of the moon in the southern hemisphere will increase from left to right until full, and then decrease also from left to right.
- On a young moon, the sun shines on the moon from the left side. On the other hand, in the old moon, the sun shines on the moon from the right side.
- Extend your right hand, straighten your thumb, and palm facing up. Curl your thumb and forefinger to form an upside-down C. If the curvature matches the curve of the moon, it means the moon is in the old moon phase. If you do the same with your left hand and the curve matches the curve of the moon, it means the moon is in its light moon phase.
Step 2. Remember the letters C, O, D
The moon goes through the same phases in the southern hemisphere, but the letters indicating the phases of the moon are young or old have an inverted shape compared to the northern hemisphere.
- The C-shaped crescent occurs during the young moon.
- A half or convex moon that looks like an inverted D occurs during the young moon.
- The full moon is circular (O).
- A convex moon shaped like the letter D occurs during the old moon.
- An inverted C-shaped crescent occurs during the old moon.
Step 3. Learn when the moon rises and sets
In the southern hemisphere, the sunlit side of the moon is opposite to the lunar side in the northern hemisphere. However, the moon's rising and setting times remain the same during the same phase.
- The first quarter moon will rise in the morning and set around midnight.
- The full moon rises and sets as the sun sets and rises.
- The 3rd quarter moon will rise at midnight and set in the morning.