Welcome to the Fort Lewis College Sky Steps Horizon Calendar

What is a horizon calendar?

A horizon calendar is an ancient observational timekeeping method for tracking the seasons and time of year by noting the position the Sun rises or sets on the horizon. The first thing to know to understand how a horizon calendar works is that the Sun rises (and sets) in a slightly different position almost every day of the year. A horizon calendar works year after year because the sunrise and sunset positions for every day of the year are predictable. For example, if you make your observation from the same location, the Sun will rise (or set) in the exact same location every year on your birthday.

People made horizon calendars before the invention of the modern calendar, by noting the location of sunrise or sunset regularly, likely over multiple years. By noting the location on the horizon where the Sun rose (or set) when important events occurred, these events could be predicted in future years by watching for time when the sunrise (or sunset) position was nearing that location on the horizon.

How does a horizon calendar relate to the 250/150 project?

The 250/150 project is about understanding our sense of place. Cultures from the Four Corners region have used horizon calendars for over a thousand years. By following along with the content below, you will learn how a horizon calendar works by using this example from the Fort Lewis College campus. Our hope is that you create your own horizon calendar where you live. Before the invention of the modern calendar where we can just look up the date on our phones, our ancient relatives relied on this knowledge to live!

Safety message: If you plan to observe sunsets (or sunrises) at the Sky Steps or anywhere else, take care. Looking directly at the Sun is bad for your eyes. Your goal when observing the Sun’s setting or rising position is to notice the general area where this occurs, not the precise location. The safest time for sunrise is just as the Sun is beginning to be visible. The safest time for sunset is just as the Sun is finally disappearing over the western horizon or just after it sets and sky still glows where the Sun had set.

How a horizon calendar works.

Let’s get started. First, look at the Birthday Sunset Activity Poster shown here.

For the poster shown here, where do you think the Sun would set on your birthday?

On the Birthday Sunset Activity Poster, the turquoise letters of the word “SUNWATCHER” (spelled backwards) are just there to help us refer to places on the horizon above them. Use these letters to share your estimate of where on the horizon the Sun sets on your birthday. Sample answers could be, “at horizon position A” or “Between horizon positions A and T”.

Here are some tips to help you with the BIRTHDAY SUNSET ACTIVITY POSTER:

• The photos from this panorama were taken from just behind the black bench at the top of the Sky Steps on the Fort Lewis College campus.
• The yellow disks mark the horizon positions of sunset on the Winter and Summer solstices and the Spring and Fall Equinoxes when observed from the top of the Sky Steps.
• The slanted arrows pointing to the Sun disks mark the end of the Sun’s longer path across the sky shortly before it sets on the labeled date.
• Sunsets that occur northward (right) of west occur on days when the Sun climbs higher and spends more time in the sky. These are days with more hours of daylight than nighttime [see the higher, red dotted line path in Sun Motion Diagram below].
• Sunsets that occur southward (left) of west occur on days when the Sun stays lower and spends less time in the sky. These are days with fewer hours of daylight than nighttime [see the lower, blue dashed line path in the Sun Motion Diagram below].

Understanding the Sun Motion Diagram ×

How does the Sun Motion Diagram shown above relate to the Birthday Sunset Poster? The guided exploration below allows you to answer this question.

Imagine you are standing inside the Sun Motion Diagram at the position of the little orange “stick person.” You are in the center of a round, green field with the blue sky above you. You are facing eastward to watch the Sun rise on the eastern horizon.

As the Earth turns each day, the Sun appears to make an arc across the sky from sunrise to sunset. The starting and ending points of these arcs change daily over a year’s time. All of these daily paths are parallel to each other.

The Sun Motion Diagram shows the Sun’s path on only two days of the year in the Northern Hemisphere. All the other daily paths occur between them. Trace each of these two paths on the diagram with your finger, starting at sunrise and ending at sunset.

RED DOTTED LINE: At the Summer Solstice (red dotted line), the Sun rises north of east (Northeast) and sets north of west (Northwest). The higher path of the summer Sun means that it spends MORE time above the horizons, so we have more hours of daylight.

BLUE DASHED LINE: At the Winter Solstice (blue dashed line), the Sun rises south of east (Southeast) and sets south of west (Southwest). The lower path of the winter Sun means that it spends LESS time above the horizons, so we have fewer daylight hours.

When you traced the two paths with your finger, did you notice how the Summer Solstice path is longer than the Winter Solstice path?

Did you also notice that the Sun does not rise straight up from the eastern horizon but instead rises and sets at a slanted angle?

That’s why the Birthday Sunsets Poster has slanted arrows pointing to the Sun’s positions on the horizon. These arrows represent the end of the Sun’s longer path across the sky on that day. We do not see the whole path from sunrise to sunset on the poster.

On the Birthday Sunsets Poster, notice how the location of sunset on the horizon is different depending on the time of year. On the Sun Motion Diagram, we can see that this seasonal difference in horizon position occurs at both sunrise and sunset.