Moon Phase
From FFXIclopedia, the free Final Fantasy XI encyclopedia
As the world turns, the moon goes through phases. Each phase refers to how much of the moon's face is visible. As the moon moves through these phases it is decribed as either "Waxing" (the moon is getting visibly "bigger") or "Waning" (the moon is getting visibly "smaller"). Waxing refers to the moon as is passes from New Moon (0% visible) to Full Moon (100% visible), while Waning refers to the opposite.
The moon phase affects certain aspects of parts of the environment, as well as some pieces of equipment. It is also rumored that moon phases affect certain luck-based elements of the game, such as the chances of getting item drops off an enemy, or crafting results. (See below)
You can check the current moon phase, as well as its percentage, by using the /clock command. This command also toggles the display of the game clock on your screen. To keep the clock on your screen, use the /clock command again, or use "/clock on" instead.
Each full lunar cycle (lasting from 0% New Moon to 100% Full Moon and back to 0% again) lasts for 84 game days (3 days, 8 hours, 38 minutes, and 24 seconds, Earth time).
On an interesting side note, the moon's face will be tinted the color of the current day as the days change (i.e. on Firesday the moon will tint red and on Windsday the moon will tint green).
Another interesting side note; due to tidal locking, Vana'diel's moon appears to orbit in synchoronous rotation around the planet, showing the same face to Vana'diel at all times. This behavior is not unlike what is found on the moon orbiting the distant planet Earth.
Full Moon
The moon phase where the entire face of the moon is illuminated (90%->100%->95%)
When the moon is in this phase, it is rumored that certain effects are improved/degraded: 
- Item drops from monsters increase.
- Fishing results improve (except in Rabao, where results degrade).
- Crafting skill ups are improved.
- The number of High Quality items synthesized is decreased.
- Gardening yields are higher. (rumored to be 150% normal yield)
- Chocobo Digging is more accurate.
Certain Notorious Monsters will only spawn during a full moon:
Some items have effects that are affected by this moon phase:
- Horror Head - Enmity -50
- Luna Subligar - Dexterity +2, Agility +2, Charisma +7
- Selene's Bow - Ranged Attack +5, Ranged Accuracy +25
- Gnole Sainti / Gnole Sainti +1 - STR +2/3, DEX +2/3
- Diana Corona - Magic Attack Bonus +4
Certain items and key items can only be obtained during this moon phase:
Gibbous Moon
The moon phase where most of the moon's face is illuminated (60%-90%). Also known as "waxing gibbous" when the moon is waxing towards a full moon and "waning gibbous" when the moon is waning towards a new moon.
Certain items have effects that are affected by the "waxing gibbous" phase:
- Selene's Bow - Ranged Attack +10, Ranged Accuracy +20
Certain items have effects that are affected by the "waning gibbous" phase:
- Selene's Bow - Ranged Attack +20, Ranged Accuracy +10
Half Moon
The moon phase where the face of the moon is halfway in shadow, and halfway in light. Also known as "first quarter moon" when the moon is waxing and "last quarter moon" when the moon is waning (40%-60%).
When the moon is in this phase, it is rumored that certain effects are improved/degraded:
Some items have effects that are affected by this moon phase:
- Selene's Bow - Ranged Attack +15, Ranged Accuracy +15
- Amood - Occasionally attacks twice (First Quarter Moon only)
- Amood +1 - Occasionally attacks twice (First Quarter Moon only)
- Dark Amood - Occasionally attacks twice (First Quarter Moon only)
Crescent Moon
The moon phase where most of the moon's face is obscured (10%-40%). Also known as "waxing crescent" when the moon is waxing and "waning crescent" when the moon is waning.
Certain items have effects that are affected by the "waxing crescent" phase:
- Selene's Bow - Ranged Attack +10, Ranged Accuracy +20
New Moon
The moon phase where the entire face of the moon is obscured (10%->0%->5%)
When the moon is in this phase, it is rumored that certain effects are improved/degraded:
- Item drops from monsters decrease.
- Fishing results improve (except in Rabao, where results degrade).
- Crafting skill ups are decreased.
- The number of High Quality items synthesized is increased.
- Chocobo Digging is more accurate.
Certain Notorious Monsters will only spawn during a new moon:
Certain Notorious Monsters can not spawn during a new moon:
Some items have effects that are affected by this moon phase:
- Horror Head II - Enmity +50
- Inferno Sabots - INT +1, Dark Magic Skill +3
- Selene's Bow - Ranged Attack +25, Ranged Accuracy +5
Moon in Real Time
Each 1% of moon phase is equivalent to 24 minutes and 11'52 seconds of real world time.
To calculate how many minutes moon needs to be in a percentage you want to know, just need to multiply the difference of percentages by 24,192.
To know the percentage difference you have to take in count:
- When moon is waxing:
- If desired percentage is greater than current: difference = desired - current.
- If current percentage is greater than desired: difference = 200 - current - desired.
- When moon is waning:
- If desired percentage is lower than current: difference = current - desired.
- If current percentage is lower than desired: difference = current + desired.
