Moon Phases

The Moon orbits the Earth approximately every 27.3 days, a period known as a sidereal month. At the same time, the Earth is also moving in its orbit around the Sun.

From our perspective, the Moon appears to complete its cycle (from new moon to new moon) in about 29.5 days, known as a “synodic”, “lunar cycle” or a month.

We have 8 defined stages, or phases, that the moon goes through in the course of this cycle.

8 Phases Of The Moon

 

New Moon

The moon is between the earth and the sun. The side of the moon facing us doesn’t get any sunlight, so it looks like it’s not there.

Lit Portion Northern Hemisphere = Moon in Sun’s shadow, lit only by earthshine

Lit Portion Southern Hemisphere = Moon in Sun’s shadow, lit only by earthshine

Visibility = Nearly invisible

Average Moonrise = 6 am

Average Moonset = 6pm

 

Waxing Crescent

A tiny sliver of the moon starts to light up. “Waxing” means it’s getting bigger.

Lit Portion Northern Hemisphere = Right side 0%-50% lit

Lit Portion Southern Hemisphere = Left side 0%-50% lit

Visibility = Late morning to after sunset

Average Moonrise = 9 am

Average Moonset = 9 pm

 

First Quarter

Half of the moon is lit up. It’s called ‘quarter’ because the moon has completed a quarter of its orbit around the earth, not because only a quarter is lit.

Lit Portion Northern Hemisphere = Right side 50.1% lit

Lit Portion Southern Hemisphere = Left side 50.1% lit

Visibility = Afternoon and early evening

Average Moonrise = Noon

Average Moonset = Midnight

 

Waxing Gibbous

More than half of the moon is visible. It’s not full yet, but it’s getting there

Lit Portion Northern Hemisphere = Right side 50%-100% lit

Lit Portion Southern Hemisphere = Left side 50%-100% lit

Visibility = Late afternoon to most of the night

Average Moonrise = 3 pm

Average Moonset = 3 am

 

Full Moon

The moon is on the opposite side of the earth from the sun. Now, the sun’s light fully illuminates the moon, making it look like a big, bright circle

Lit Portion Northern Hemisphere = 100% illuminated

Lit Portion Southern Hemisphere = 100% illuminated

Visibility = Sunset to sunrise

Average Moonrise = 6 pm

Average Moonset = 6 am

 

Waning Gibbous

The moon starts to look smaller. “Waning” means it’s shrinking.

Lit Portion Northern Hemisphere = Left side 100%→50% lit

Lit Portion Southern Hemisphere = Right side 100%→50% lit

Visibility = Most of the night to early morning

Average Moonrise = 9 pm

Average Moonset = 9 am

 

Third Quarter

Again, half of the moon is lit up, but this time it’s the other half compared to the first quarter phase.

Lit Portion Northern Hemisphere = Left side 50.1% lit

Lit Portion Southern Hemisphere = Right side 50.1% lit

Visibility = Late night and morning

Average Moonrise = Midnight

Average Moonset = Noon

 

Waning Crescent

Only a small part of the moon is visible again. It’s winding down to go back to the new moon phase.

Lit Portion Northern Hemisphere = Left side 50%→0% lit

Lit Portion Southern Hemisphere = Right side 50%→0% lit

Visibility = Before dawn to early afternoon

Average Moonrise = 3 am

Average Moonset = 3 pm

QUIZ

 

1. Why do you think it is important to know the phases of the moon and be able to correctly identify them?
2. How long does it take for the moon to orbit around the Earth?
3. What is a lunar cycle.
4. How much light does the moon emit by itself?
5. Explain “waxing” and “waning”?
6. Explain the difference between third quarter phase and the first quarter phase.
7. What causes the phases of the moon?
8. Why do we see different phases of the moon in different hemispheres?
9. What is the lit portion of the waxing cresent moon in the Northern Hemisphere?