Lunar phase
Lunar phases (or Phases of the Moon) are the result of looking at the illuminated half of the Moon from different viewing geometries; they are not caused by shadows of the Earth -- this would be a lunar eclipse. The Moon exhibits different phases as the relative geometry of the Sun, Earth and Moon change, appearing as a full moon when the Sun and Moon are on opposite sides of the Earth, and as a new moon (also named dark moon, as it is not visible at night) when they are on the same side.
Names of lunar phases
The phases of the Moon have been given the following names, in sequential order:
| Phase | Northern Hemisphere | Southern Hemisphere | Visibility | |
|---|---|---|---|---|
| New moon | Not visible, or traditionally, the first visible crescent of the Moon | |||
| Waxing Crescent moon . | Right 1-49% visible | Left 1-49% visible | afternoon and post-dusk | |
| First Quarter Moon | Right 50% visible | Left 50% visible | most of the day and early night | |
| Waxing gibbous moon | Right 51-99% visible | Left 51-99% visible | afternoon and most of night | |
| Full Moon | Fully visible | Fully visible | sunset to sunrise (all night) | |
| Waning gibbous Moon | Left 51-99% visible | Right 51-99% visible | most of night and morning | |
| Last Quarter Moon | Left 50% visible | Right 50% visible | late night and most of the day | |
| Waning Crescent Moon | Left 1-49% visible | Right 1-49% visible | pre-dawn and morning | |
| Darkened moon | Not visible | Not visible | ||
The average calendrical month, which is 1/12 of a year, is about 30.4 days, while the Moon's phase (synodic) cycle repeats every 29.53 days. Therefore the timing of the Moon's phases shifts by an average of about one day for each successive month
Cumulus Webtag
Cumulus has three webtags relating the phase of the Moon.
Cumulus processes a <#moonphase> representing the current phase of the Moon. By default, as these can be modified, one of the following eight strings will be returned:
- New moon
- Waxing Crescent
- First Quarter
- Waxing Gibbous
- Full moon
- Waning Gibbous
- Last Quarter
- Waning Crescent
These default values can be overridden by editing the Strings.ini file.
Cumulus also has two webtags relating to the percentage illumination of the Moon.
<#MoonPercent> returns the percentage of the visible surface illuminated, with positive values for a waxing Moon and negative values for a waning Moon.
<#MoonPercentAbs> returns the percentage of the visible surface illuminated, and is always positive.