Due: in class on January 17, 2008
1. Determine local noon in Eugene and the highest point
in the sky reached by the Sun for a random winter day. First off,
what is meant by local noon?
In what direction is the Sun
(N, E, S, W) at local noon? ________
To perform this exercise, find a flat spot and place a stick (pole) into the ground vertically. (You could also find a flat spot of ground which already has a vertical stick (pole) for this exercise such as the large sundial in the Memorial Quad across from Lillis Hall. The height of the obelisk in the Memorial Quad is ~10.25 meters.) This vertical stick is referred to as a gnomon (see the Figure below). We will measure the length of the shadow cast by the gnomon to accomplish our goals.
Date:
Gnomon Height, H:
Between the times say, 11:15 am and 1:30 pm, measure the length of the shadow cast by the gnomon. Record your measurements in the table below:
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2. Plot your data on the graph below:
At what time is the length of the shadow the smallest? ________ At what time is the Sun the highest in the sky? _________ At what time does the Sun pass through the Celestial Meridian, the semi-circle which connects the north point on the horizon, the zenith, and the south point on the horizon? ________ At what time is local noon? ________ Does local noon lead or lag clock time at this time of year? ________
3. What is the maximum altitude above the horizon reached by the Sun (on the day you performed your observations)? ________ Use the table below to estimate your answer. (For a more precise result note that the Altitude A = tan-1 (H/L), that is, the altitude is the inverse tangent of the ratio (H/L).) The longer the shadow (the smaller the H/L), the lower the altitude of the Sun.
For fun, perform this exercise in the summer and compare your answers to those found here.
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