Eight Phases of the Moon

• The Moon has eight phases during its 29.5 day rotation of the earth, which are described below.

1. New Moon (or Dark Moon)

• • When visible:
    • Cannot be seen.
  • Location after Sunset:
    • Setting with the Sunset.
    • The New Moon is not visible because it rises at Sunrise and sets at Sunset.
  • It is not visible because the Sun and the Moon are on the same side of the Earth, and we can only see the unlit side.
    • The Moon starts to become visible about 36 hours after the New Moon.
  • Position: In a line between the Sun and the Earth. It is at the starting point of its path describing a full circle around the Earth, away from the Sun.

2. Waxing Crescent Moon (Evening Crescent)

• • When visible:
    • Briefly, just after Sunset in the West.
    • Only visible as a crescent, shortly after Sunset, when it is low in the West.
  • Location after Sunset:
    • Low in the West.
  • Waxing means increasing.
  • A line joining the points of the Crescent Moon to the Horizon will always point due South in the Northern Hemisphere and due North in the Southern Hemisphere.
  • In the Northern Hemisphere, the right side of the Moon forms the crescent.
  • In the Southern Hemisphere, the left side of the Moon forms the crescent.
  • Earthshine: During this phase sunlight reflected off the Earth can faintly illuminate the unlit side of the Moon.

3. First Quarter Moon (Also known as a Half Moon)

• • When visible:
    • Rises in the East at Noon and sets in the West around Midnight.
  • Location after Sunset:
    • After Sunset, high above the southern Horizon.
  • Only half of the Moon is visible and this is why it is known as a Half Moon.
  • In the Northern Hemisphere, the right half of the Moon is lit.
  • In the Southern Hemisphere, the left half of the Moon is lit.
  • Position: 90 degrees of a full circle away from the Sun.

4. Waxing Gibbous Moon (very bright Moon)

• • When visible:
    • Passes due South during the evening, sets in the West before Sunrise.
  • Location after Sunset:
    • Already high in the southeast.
    • Rises in the East during the afternoon, passes due South during the evening, sets in the West before Sunrise.
  • Gibbous means hump-backed. Three quarters of the Moon is now visible.

5. Full Moon

• • When visible:
    • The Full Moon is the only Moon phase to shine all night from Sunset to Sunrise. Around Midnight it is in the South.
  • Location after Sunset:
    • Rises in the East after Sunset and sets in the West at Sunrise.
  • The Full Moon is the only Moon to be overhead in the middle of the night.
    • Position: The Earth is between the Sun and the Moon. It has completed 180 degrees of a full circle away from the Sun.

6. Waning Gibbous Moon

• • When visible:
    • Rises in the East after Sunset, passes due South before Sunrise, and sets in the West after Sunrise.
  • Location after Sunset:
    • Rises in the East long after Sunset.
  • In the Northern Hemisphere, the left side of the Moon forms the crescent.
  • In the Southern Hemisphere, the right side of the Moon forms the crescent.

7. Last Quarter Moon (also known as a Half Moon)

• • When visible:
    • Rises in the East at Midnight and Sets in the West before Noon.
  • Location after Sunset:
    • Does not rise in the East until Midnight.
  • Only half of the Moon is visible and this is why it is known as a Half Moon.
  • In the Northern Hemisphere, the left half of the Moon is lit.
  • In the Southern Hemisphere, the right half of the Moon is lit.
  • Position: The Moon has completed 270 degrees of a full circle away from the Sun.

8. Waning Crescent Moon (Morning Crescent)

• • When visible:
    • Rises in the East about two hours before Sunrise and sets about two hours after Sunset.
  • Location after Sunset:
    • sets in the West about two hours after Sunset.
    • A line joining the points of the Crescent Moon to the Horizon will always point due South in the Northern Hemisphere and due North in the Southern Hemisphere.

Names of the 12 Full Moons

Blue Moon

• • Because the Moon cycle takes 29.5 days, every 3 years there are two Full Moons in one calendar month. In modern times, the second Full Moon has become known as a ‘Blue Moon’. As February only has 28 days, sometimes it has no Full Moon.
  • The older meaning of ‘once in a Blue Moon’ derives from the rare occurrence of a blue tinged Moon due to high altitude dust.

How the Moon can be used in Navigation

• The Moon acts as a Compass:
  • For Navigation at Night the Moon will give an approximate guide to East, South and West.
  • The Moon is only invisible for 3 to 4 days each month during the New Moon Phase.
  • Like the Sun, the Moon will always rise in the Eastern sky and set in the Western sky.
  • A line joining the points of the Crescent Moon to the Horizon will always point due South in the Northern Hemisphere and due North in the Southern Hemisphere.
• Anomalistic Month
  • However, the position of Moonrise and Moonset will vary from True East or True West by up to plus or minus 30 degrees, due to its elliptical orbit known as the Anomalistic Month, which takes 27.5 days to complete.
• Synodic Month
  • Unlike the Sun, the time of Moonrise and Moonset will vary according to the Moon’s cycle known as the Synodic Month of 29.5 days, and in addition to the observer’s Latitude and Longitude.

• The Moon acts as a Calendar:
  • The Time taken for the complete Moon cycle from the New Moon to the next New Moon is always 29.5 days. This is known as the Synodic Month.
  • The time from New Moon to Full Moon is approximately two weeks.

• The Moon acts as a Clock:
  • The New Moon rises and sets at almost the same time as the Sun.
  • The First Quarter Moon rises at mid-morning and sets at Midnight. It is at its highest around Sunset.
  • The Full Moon rises at Sunset and sets at Sunrise. It is at its highest around midnight.
  • The last Quarter Moon rises around Midnight and sets around mid-morning. It is at its highest around Sunrise.
• The Almanac
  • The Tables in an Almanac are constructed for predicting the local times of Moonrise and Moonset throughout the year, as well as the times of rising and setting of the other planets.

• The Moon provides light
  • The Full Moon reflects the Sun’s light during the whole night. The intensity of the Moonlight varies according to its altitude in the sky, its distance from the Earth (it has an elliptical orbit) and the prevailing atmospheric conditions.
  • Moonlight reaches its maximum brightness on the night of the Full Moon. It then falls to half that brightness during the two days on either side of the Full Moon. Therefore, the reflected Moonlight is useful only during a four day period during the Moon’s cycle.