The Sun’s Southward Journey

You may have noticed that it is getting darker earlier now. Today we’ll discuss a simple project to help you experience this phenomenon more fully and, as my undergrad astronomy professor would say, “feel connected to the universe!”

Quiz time: In what part of the sky does the Sun rise and set?

It rises in the east and sets in the west, right? Mostly.

For a good, detailed description of what is going on with the sunset position, see http://www.astronomynotes.com/nakedeye/s5.htm

The only time it is directly east and west is on the equinoxes (first day of spring/fall). In the summer, it rises more in the northeast and sets in the northwest, and now, as we head towards winter, it rises more in the southeast and sets in the southwest. Its sunset location is “traveling” further south along the horizon each day. It is quite noticeable. You can do a simple activity with your kids at sunset to see this happening.

THE ACTIVITY

The activity to connect you with the sun’s southward journey involves treating yourself to watching some beautiful sunsets. Pick a spot outside with a view of the sunset to the southwest horizon, one that has some landmarks along it like electrical poles, small hills, trees, houses, et cetera. You’ll be returning to this exact spot for several days. Arrive a bit before the sunset. (You can find your local sunset time from a site like this.)

If you or your little astronomonster is a budding artist, bring a sketch pad and draw your southwestern horizon. Otherwise, bring a camera and take a picture of the sunset. DO NOT LOOK DIRECTLY AT THE SUN. STARING AT THE SUN WILL DAMAGE YOUR EYES. Record the position of the sun as it sets against the horizon. Do this for several days (they don’t have to be consecutive), and notice how much the sun moves over time. Make sure you are at the exact same spot each time so you will have an accurate record.

You could also do this project for sunrise instead of sunset. Another interesting activity would be to mark the height of the Sun at your local apparent noon each day. As we approach the winter solstice, it will get lower and lower in the sky.

HISTORY AND SCIENCE NOTES

This graphic shows a solar horizon calendar in action. To learn more about solar calendars, see http://medicinewheel.vcsu.edu/ and take the PowerPoint Tour of Medicine Wheel Park.

People from long ago, such as the Hopi People, used to do just such an activity to make a solar horizon calendar. They would watch the sunset throughout the year, and special days would be recorded. The motion of the Sun along the horizon would alert them to the arrival of special days in their calendar. You can read more about this (and get more in-depth tips for this project) from Project ASTRO UTAH.

The sunrise/sunset positions and the amount of daylight we receive is due to the Earth’s tilt as it orbits the Sun. We in the Northern Hemisphere will be getting less direct sun rays now through winter as our hemisphere is tilted away from the Sun. On the autumnal equinox, or first day of fall, the Sun appeared directly over the equator and our day and night were of roughly equal length. Now the Sun journeys further south of the equator daily until the December solstice when it reaches its southernmost point above the Tropic of Capricorn in the Southern Hemisphere. The Sun will appear to be lower in our sky and further south until the solstice, and then it will begin to turn around and come back north.

This graphic from an online astronomy text shows how the sun ray angles change from summer to winter. You can view the online text here: http://physics.weber.edu/schroeder/ua/default.html

ASTRONOMOMMY NOTE: This activity was one we did in an undergraduate astronomy class. I enjoyed going to my sunset spot. I would bring a different CD to listen to each time, so it was also sort of a music history project for me (I brought things like Mussorgsky to listen to; music was one of my majors). You can use the sunset-viewing time to catch up on some music or audiobooks or with your child/spouse/friend/whoever-you-want-to-view-the-sunset-with. If you send me some pictures of the calendars you create, I will publish some of them here. Enjoy!

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