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Creating a Sundial & What Makes Day & Night

Understanding What Makes Day and Night to Make a Sundial to Tell Time

Frequently, we take it for granted that when the hands on the clock are positioned at a certain point; we know what time it is. However, what creates the 24-hour phenomenon of day and night, and what would we do if there weren't any clocks?

At only two points, exactly twice per year, is the amount of daylight and darkness the same. Telling time without the convenience of a clock takes a little understanding of the stars and how the orbit and rotation of the earth makes day and night, including the length of each.

Let's take a look at what causes day and night. We'll begin by touching on the factors that dictate how long each of these is and then discuss what creates them. Finally, we'll show you how to make a sundial to tell what time it is, even if all the clocks on the planet stopped.

What Causes Day and Night?

You've probably become accustomed to the fact that the sun comes up in the morning and then goes away, eventually. It happens every day. While there are never two points during a 24-hour period with exactly the same amount of sunlight or lack thereof, most take it for granted.

But what causes day and night to occur, and what causes the length of daylight and darkness to change throughout the year. Well, there are two factors that blend together to make this happen. The simplest place to start is with what causes longer periods of day and night.

Seasonal Changes in the Amount of Daylight

One day on earth is 24-hours. This is counted by clocks, but dictated by the sun and the earth's rotation. For good reason, each 24-hour period on earth is called a solar day. However, seasonal changes alter the amount of daylight throughout the year.

As the earth rotates every 24 hours, it also tilts very slightly during each of these 24-hour periods. It might appear that the days and nights are the same during much of the year. Nevertheless, we all appreciate those days when the amount of daylight is at a minimum.

Because the earth is round, this gradual tilting is what causes the seasons. In addition, since land masses are fixed, the tilting creates different seasons depending on where you're standing on this gigantic sphere.

If you stayed in one exact spot for 365 days, keeping data on the amount of daylight and darkness every day, you'd find it's never exactly the same. Two times each year are marked on the calendar as the earth's solstice.

One will record the most daylight during a single calendar year, while the second will be the shortest. The point on the clock, or sundial, when daylight begins and ends changes each day because of the tilt. The earth tilting on its imaginary axis causes longer or shorter days, but what causes the sun to appear and then disappear, creating day and night?

The Cause of Day and Night

The principles that affect the length of day and night are more involved than what actually causes day and night to occur. While the earth tilts slowly to cause the seasons and corresponding changes in the amount of daylight, there is also a constant rotation.

The earth rotates on this same invisible access once every 24 hours. Not be coy, but this daily rotation happens repeatedly "like clockwork". An interesting twist to this 24-hour daily rotation is that it's actually not quite a full 24 hours.

Every day on earth is four-minutes shy of a complete 24 hours. We make up for this four-minute disparity with what is called a leap year. Every four years we compensate for this loss of four daily minutes by adding another full 24-hour day to balance our calendars with our solar clocks.

So, speaking in terms of a solar day, how did the human race tell what time it was before some wise person invented the clock? There is some debate about when the first actual clock was invented, but there is one fact that cannot be debated.

People were telling and recording time long before any true clock was invented. We determined what time it was during the day by using the principles behind the solar day. While we learned to determine time at night via the stars, the only star visible during the day was the sun.

Ancient sundials have been unearthed, methods of telling time dating back centuries. The earliest recorded use of sundials dates back to Babylon over six thousand years ago. So, what if all technology failed, how would you know what time it was? Well, you'd make a sundial of course.

How Do You Make a Sundial?

Now that we appreciate the science behind night and day, is there any method for telling time during the day. Of course, there is the sarcastic reply which is to tell someone asking to purchase a watch. But what if you don't have a watch, or a clock of any kind?

Is there a way to tell what time it is by using the scientific principles behind what causes day and night? Thankfully, long before the first mechanical clocks were invented, humans were able to tell time. Stargazers, so to speak, documented the position of the stars during the night.

However, there were rarely situations where any of the stars were visible, except the biggest one of all. The sun is a star, a star that can be seen big and bold during a particular period during earth's daily rotation.

Factoring in the seasonal tilt of the earth during its 365-day orbit around our solar system's biggest star, we get a particular number of hours of daylight. One way to tell time during daylight hours is by using a sundial. Here's how to make your own.

Making a sundial uses the concept of shadows. In the middle of every sundial, even the ancient ones, there is a gnomon. This is what casts the shadow on the dial and the corresponding markers that indicate time.

First step is to find a sunny spot to place your sundial. While there are intricate plans for constructing colorful sundials cut out of wood, we're going to suggest a simple garden sundial using a stick and some stones.

Step 1 – Gather 12 small, preferably flat stones and number them 1 through 12.

Step 2 – Take a four-foot dowel or metal rod, about a quarter-inch in diameter and drive it into the ground.

Step 3 – Step 3 is actually a multi-stage process. At a given hour in the morning, preferably 7:00AM, note the exact point where your gnomon or center post is casting a shadow.

Step 4 – Mark this point with your first stone that indicates it is seven o'clock in the morning.

Step 5 – Continue to do this once every hour until you set the twelfth stone at dusk.

Once you've completed this simple garden sundial, you can use the same concept to make smaller sundials out of things such as paper plates. Regardless of what type of sundial you make, you'll notice how the dial's accuracy changes slightly as the seasons change.

Using a sundial to tell time is an excellent source of enjoyment. However, it will also help you appreciate how the angle of the sun is affected not only by the earth's rotation but also how time changes during the earth's year-long trip around the sun.