Watching the Sun

A part of ASTRONOMY 101 is actual observing experience -- real time spent observing the heavens.

This project, added on March 26, will satisfy that requirement, and serve as an alternative to the observatory visit project (which may be difficult if observatories are closed on account of COVID-19).

From Earth, we see the stars circle around us every 23 hrs 56 minutes. We see the sun circle around us every 24 hours. This difference between sun and stars causes the sun to drift through the stars, passing through the constellations of the zodiac. The tilt of the zodiac versus the equator means the sun moves northward in the spring and southward in the fall, causing the seasons for those of us in Kentucky.

You can observe this yourself. To do this project, you will first download a sky app to your phone. These apps turn your phone into a “sky map”, which changes as you move your phone around, to help you find and identify objects in the sky. There are many of these apps, such as Google Sky Map, Stellarium Mobile, Night Sky, etc. Many are free. Those that are not free are usually cheap. The most elaborate ones work with your phone’s camera to provide an “augmented reality” view of the sky.

For this project, you also need a gnomon—a pole that casts a shadow on a flat surface. This can be a mailbox, a fence post, a streetlamp, etc. You need to be able to observe the shadow every day at the exact same time, for about half an hour (setting a regular reminder will help with this project). You choose the time, but it should be during the middle of the day (not near sunrise or sunset). As the sun moves northward or southward, the shadow length will change.

Every sunny day, go to your gnomon at your chosen time. Record the date and time. Measure the length of the shadow. Take a photo of the gnomon and its shadow. Wait half an hour and take another photo. If you have consecutive sunny days, you can do this every other day rather than every day. On each day, use your phone app to see where the sun is in the zodiac. Save a screen shot of the app, showing the sun location.

You need a lot of observations to see changes, so you should start this project in late March and continue it through the end of the semester.

When you are finished, write up a 500-word discussion on what you learned. Include a large selection of photos and app screen shots from across the entire period that illustrate what you observed. Also include a table of all your dates and shadow measurements.

What to turn in (all in one WORD or PDF document):

· Your 500-word discussion

· Your selection of photos and app screen shots.

· Your table of dates, time, and shadow measurements.