Bill Logan / For The Bulletin

What's an analemma you ask? According to Merriam Webster's online dictionary: “A plot or graph of the position of the sun in the sky at a certain time of day (as noon) at one locale measured throughout the year that has the shape of a figure 8; also: a scale (as on a globe or sundial) based on such a plot that shows the sun's position for each day of the year or that allows local mean time to be determined.” When finished, it becomes a neat calendar. In the movie “Castaway,” Chuck Nolan, played by Tom Hanks, who was stranded on a remote island, constructed an analemma on the wall of a cave — thus he knew when the trade-winds changed directions in order to make his escape. You'll also find an analemma, that mysterious figure 8, on most globes.

Are you looking for a cool science project that takes at least one year to construct? Well, I have one in which your whole family can participate. This is also an excellent science project for children. You can make an analemma on your back deck, driveway, school sidewalk or any flat surface. At precisely noon, the sun will cast a shadow on your flat surface. Mark the shadow with any round object such as a bottle cap or coin every 10 days or so. The trick for an accurate analemma is to have an accurate time piece synced to the National Bureau of Standards. One of the goofs in the movie “Castaway” is that Nolan's pocket watch was broken from being drenched with seawater making it impossible to construct his analemma.

The size of your analemma will depend on the distance from the object casting the shadow and the flat surface. The shadow can be produced by most any object, but whatever you choose, it must be stationary. Fastening an eyelet on a live tree will not work. The eve of a house or garage would be better options. When marking the shadow with a date, use a permanent marker.

When your analemma is finished, you'll have a keen understanding of the Earth's tilt throughout the year in relation to the sun, and a nice calendar.

— Bill Logan is an expert solar observer and a volunteer amateur astronomer with University of Oregon's Pine Mountain Observatory. He lives in Bend. Contact: