Once upon a time, goes the Cherokee story, a turtle was talking to a raven. 'You get to see the world from above,' complained the turtle, 'but all I see is the ground. My horizons are, er, limited.'

'No problem,' said the raven. 'Hang onto this tree branch and I'll take you for a ride.' Grabbing the other end of the tree branch, the raven took the turtle on an aerial tour.

The turtle got so excited by the view that he let go of the branch – and fell, breaking his shell into pieces. The Creator saw this and repaired the turtle, putting him back together in 13 pieces for the 13 months of the lunar year. Around the edge of the shell he placed 28 smaller pieces, for the 28 days of the lunar month. Many Native American/First Nation peoples have used the turtle's back as a handy lunar calendar.

It's a convenient mnemonic for the lunar calendar of 13 × 28 = 364 days. The Cherokee celebrate one other day in midsummer, the Green Corn Day. On that day, a feast is held and offences are forgiven. To count by the calendar, start with 1 and go around the turtle. A month begins with each new moon: when a sliver of light can be seen in a crescent on the right side of the moon. Native Americans celebrate the new year in different seasons. The Algonquin people of the northwest US region start with the Wolf Moon after the winter solstice. Cherokee new year is in October.

Many cultures have ancient legends based on a flat or disc-shaped world. Whether this means that ancient peoples believed these stories, or merely found them to be convenient ways to pass on information, isn't clear. But the turtle's (or tortoise's) back makes a charming calendar. Just don't annoy the turtle.

It is fitting that the turtle plays a significant role in measuring time. After all, North America is referred to by many Native American nations as 'Turtle Island.'

FYI: The turtle's shell has a carapace (top) and a plastron (bottom). The carapace of most turtles contains 13 scutes, which is what those plates are called. So you can have fun figuring out which month you're in by counting around the turtle's carapace. If you would like to know more about the moons, try this Ojibway Calendar, courtesy of Ontario Parks. If you want some help pronouncing the names of the moons, listen to a recording from the US National Park Service.

In the foregoing, we have referred to 'turtles' because the lore applies equally to turtles (aquatic), tortoises (dry land), or terrapins (amphibious). Here is a video with helpful tortoise to show you. A word to the wise: using an alligator snapping turtle as your calendar is not a good idea.