WHY PHASES
Where the Moon sits
Phases come from the positions of the Moon, Sun and Earth. Between us and the Sun it is new; on the far side of Earth it is full.
Name this moonAN INFORMATIONAL GUIDE: LUNAR CALENDAR LORE
Every month has
a moon in it.
The word month takes its root from the Moon.
Here LCL stands for lunar calendar lore: this is an independent informational guide, not an organisation. It explains the 29.5-day cycle of phases, the old names given to each full moon, and why the calendar and the Moon drift apart.
Name this moon Read the short answer
01 Half always lit02 Eight named phases03 Names from many culturesThe oldest calendar is overhead
THE SHORT ANSWER
Same Moon,
changing view.
Royal Museums Greenwich: at almost all times,
half of the Moon is lit by the Sun.
WHY ONE FACE
Tidally locked
The Moon rotates at the same speed it orbits Earth, NASA explains, so the same side always faces us.
See the numbers
WHY NAMES
Timekeeping by moons
Many familiar names reached us from Native American timekeeping, later adopted by colonial Americans and popular culture.
Go moon watchingNAME THIS MOON
Which full moon
is it?
Pick a season. The bar shows how widely the most popular name is used, going by the Royal Museums Greenwich guide.
Names follow the Royal Museums Greenwich guide to full moon names. Different cultures and tribes use different names; these are the most popular in English today.
TWO NUMBERS WORTH KNOWING
Close, but
not quite.
The gap between them is why
full moon dates drift through the calendar.
PHASES · RMG
Days for a full cycle of phases
29.5
That is not the same as the time the Moon takes to orbit Earth, which Royal Museums Greenwich gives as 27.3 days.
THE GAP · RMG
Days short of a calendar year
11
Twelve cycles of phases take about 354 days, so every two and a half years or so an extra, 13th full moon fits into the year.
That extra full moon is one meaning of blue moon. The term once named the third full moon of a season with four, and is now also used for a second full moon in one month.
FOUR TIPS FROM NASA
Eyes first,
then binoculars.
These tips follow NASA's moon viewing guide.
- Skip the full moonFor craters and mountains, try phases other than full. Shadows are stronger and make features easier to pick out.
- Follow the lineLook along the terminator, the line between light and dark, where features cast long shadows.
- Spot the seasThe grey patches, the maria, are old solidified lava flows. The lighter highlands show the Moon's earliest crust.
- Catch earthshineNear a crescent at dusk or dawn, the dark part can glow faintly with sunlight reflected off Earth.
MONTH AND MOON
Padded out
to fit the Sun.
Royal Museums Greenwich notes that a month was originally 29 or 30 days, close to the lunar cycle. Some calendar months were later given extra days so that twelve months make up a 365-day solar year.
That is why the old names sit loosely on the modern calendar: a named full moon can fall early or late in its month, and some years hold thirteen.
QUESTIONS PEOPLE ASK
Frequently asked
What does LCL stand for here?
Lunar calendar lore. This is an independent informational guide, not an organisation or observatory.
How many phases are there?
Eight named phases: new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter and waning crescent.
Where do the names come from?
Many came from Native American timekeeping and were adopted by colonial Americans. Names vary between cultures and tribes.
What is the harvest moon?
The nearest full moon to the autumnal equinox, usually in September. Its light was said to let farmers work late.
How much of the Moon can we see?
One face, because it is tidally locked. A wobble called libration lets experienced observers see about 59 percent over time, NASA says.
SOURCES
Where the facts come from
Each figure on this page comes from the sources below. Check them for the full detail and context.