Moondial
Encyclopedia
Moondial is also the name of a television series.
Moondials are time pieces similar to a sundial
. The most basic moondial, which is identical to a sundial, is only accurate on the night of the full moon
. Every night after it becomes an additional (on average)* 48 minutes slow, while every night preceding the full moon it is (again on average)* 48 minutes fast, assuming there is even enough light
to take a reading by. Thus, one week to either side of the full moon the moondial will read 5 hours and 36 minutes before or after the proper time.
More advanced moondials can include charts showing the exact calculations to get the correct time, as well as dials designed with latitude and longitude in mind.
Moondials are very closely associated with lunar gardening (night-blooming plants) and some comprehensive gardening books may mention them.
Sundial
A sundial is a device that measures time by the position of the Sun. In common designs such as the horizontal sundial, the sun casts a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, often a thin rod or a...
. The most basic moondial, which is identical to a sundial, is only accurate on the night of the full moon
Full moon
Full moon lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. More precisely, a full moon occurs when the geocentric apparent longitudes of the Sun and Moon differ by 180 degrees; the Moon is then in opposition with the Sun.Lunar eclipses can only occur at...
. Every night after it becomes an additional (on average)* 48 minutes slow, while every night preceding the full moon it is (again on average)* 48 minutes fast, assuming there is even enough light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
to take a reading by. Thus, one week to either side of the full moon the moondial will read 5 hours and 36 minutes before or after the proper time.
More advanced moondials can include charts showing the exact calculations to get the correct time, as well as dials designed with latitude and longitude in mind.
Moondials are very closely associated with lunar gardening (night-blooming plants) and some comprehensive gardening books may mention them.
- The Moon's orbit is not circular, so it does not move around the Earth at a uniform rate. Thus while the average difference between moonrises is 48 minutes, the actual time can vary considerably (roughly 20min to 1hr50min depending on the time of year and the location of the Moon in its orbit). The time read by a moondial will also vary in a similar, though not so drastic manner.