That was and still is a challenge I am wrestling with.

I think we we all understand the calendar and its history well enough. It all started with the advent of agriculture and a means to track growing and harvesting seasons on a yearly cycle.

The year was further subdivided by the lunar period, or at least guided by it, but that had it's share of difficulties, so eventually a dynamic length month was selected. There were a number of revisions to this plan and there are still efforts by some groups to modernize the Gregorian calendar.

Many of the problems are attributed to the orbital period of the Earth. Earth does not orbit the sun at an integer number of days. It takes 365.256 sidereal days to complete a full orbit, so we opted for leap years to periodically readjust our calendars to prevent drift with respect to the true seasons.

I'll digress momentarily to address sone vocabulary. When we talk about a fun day we think in terms of 24 hours with high noon at the same point in the sky (ignoring seasonal tilt). That actually is slightly more than a full revolution of the earth because we are orbiting our sun. Consider placing an object at the center of a room and drawing a large circle around it. If you stand facing that object on the circle then repeat the same thing, but move along the perimeter of the circle 90° you are still facing the object, but you are not facing the same direction with respect to the walls of the room.

Sidereal time is based on your orientation to the room, not the object. Or, in the actual world, it is based on the Earth's orientation with respect to other stars. Okay, let's get back to business.

We can design an alien planet's calendar based on the same principles we designed ours. That seems pretty clear and believable, but what about the hours and minutes?

That's where things get screwy. Have you ever wondered why 12 and 60 is used for delineation of the Earth day? Well, 12 probably came about due to the position of some key stars. At first we only cared about daylight hours and the sundial became our first clock. Not that an hour was not always the same length due to seasonal changes and the amount of daylight in a day. It wasn't until the invention of the mechanical clock that the hour was standardized. I'll buy that.

For us Pentadactyl apes, base ten rules because of the number of digits on our hands and feet. So, we use 1, 10, 100, 1000, fluently. But why 60 minutes in an hour?

My first thought was a smart alien society would simply use the base that they counted in. I am assuming that they are smart, perhaps smarter than we are. Let's say they also use base-10 for simplicity's sake. Where did 60 come from?

Well, it turns out that there may have been some logic to the number 60 after all. Remember that no one had calculators thousands of years ago, so ancient time engineers may have made something that was easy to manage. It turns out that 60 is an easy number to reckon with.

60 is easily divided by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. That's not only convenient for time, but it seems that ancient mathematicians also found it simple for geometry. With a little help from our lunar cycle and the period of the year, 360 seems to have been a worthy compromise for the number of degrees in a full circle. Again, 60 divides into 360 nicely, eliminating those pesky decimals and fractions we all hated in grade school.

Much of this is what I call strong conjecture, but the evidence I have found in my research seems pretty compelling.

So, my quest to world build a logical time system for my alien societies has taken on a new twist. What appears to have been arbitrary divisions for time by humans seems to have its roots grounded in solid logic.

I would be interested in hearing other opinions on developing time counting schemes for other worlds. Using Earth hours and minutes by an alien race to describe events or actions would be a little silly. For instance, I suspect that a dinner date for another race wouldn't ask to be picked up at 8 O'Clock.

What do you think?