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Paper Plate Education
"Serving the Universe on a Paper Plate"

Activity: Analemma Project

analemma_12-25_noon.jpg (45562 bytes)

analemma08656.JPG (25354 bytes)With the Sub-Solar Cup activity you can determine the position on the earth where an observer would see the sun directly overhead.  Plotting the sub-solar point at the same time each day should yield an analemma, the figure-eight shape on a globe that expresses the sun's declination and the equation of time.  

In this ongoing project, we hope to track the sub-solar point for one year, provided the weather and personal commitments permit regular observations at noon.  See the Analemma Project (same name, different project) for multiple exposure photographs that produce terrific visual image of analemmas.   Paper Plate Education, being a very casual pursuit, will likely undertake this Sub-Solar Cup  endeavor with less exactness.  Enjoy.

The results are in and appear at the bottom of this page...

  From the Sun Clock home page at http://www.mapmaker.com/sunclock.htm see the Sun Path diagram for depictions of analemmas.  It is a nice addition to this activity.

analemma_setup.jpg (40301 bytes) For continuity, we secure our globe in a base so our location (see figurine at left) is atop the globe.  Then we  align our globe base with cracks in a driveway that are nearly north-south.  Any minor offset from north-south will cause a slanted figure-eight.  

analemma12-25_noon.jpg (20849 bytes) analemma 12-25_afternoon.jpg (29085 bytes) Another way to check the north-south alignment is to track the path of the sun through several hours.  If the globe is properly aligned, the sun should move along one latitude for the entire day.

At the end of 12 months we will mark the globe to clarify the path of the analemma.


analemma_solstice_globe.jpg (40509 bytes) analemma_solstice_dec.jpg (32987 bytes)
December 25, 2002
Noon (Standard Time)

The sun appears just slightly above the Tropic of Cancer two days after the December solstice.  Please recognize the sub-solar image is an approximate position, dependent on the accuracy of the globe's alignment relative to the real earth.

analemma_01-06.jpg (45464 bytes) analemma_01-06_zoom.jpg (21752 bytes)
January 6, 2003
For the first image, the base was wobbly on ice.  The zoomed image is with the base steady.  Weather is mostly cloudy.
analemma01-09zoom.jpg (26122 bytes) 01-09.jpg (53783 bytes)
January 9, 2003
analemma01-12.jpg (34879 bytes)
January 12, 2003
analemma01-22.jpg (1324897 bytes) analemma01-22zoom.jpg (34811 bytes)
January 22, 2003
Hands shaky from bitter cold.  Intermittent snow, windy, temperature 10 degrees F.
01-30 afar.jpg (57018 bytes) 01-30.jpg (34579 bytes) 01-30zoom.jpg (32269 bytes)
January 30, 2003
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February 11, 2003
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February 27, 2003
Lesson learned: Do not align globe with intersection of four slabs of concrete running along cardinal points, for when the slabs heave in the winter the globe is not automatically level anymore.
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March 13, 2003
12:10 p.m.
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March 21, 2003
12:10 p.m.
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March 30, 2003
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April 15, 2003
Noon (Standard Time)
An upside not to move the clock forward to daylight time (DT): the time remains noon, Standard Time (ST).
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April 24, 2003
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April 29, 2003
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May 21, 2003
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June 17, 2003
Has been a large gap since last observation.
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June 22, 2003
By tracking the summer solstice sun across the length of the day, we can see the globe is slightly skewed from ideal.  In the morning the sub-solar point is slightly under the globe's Tropic of Cancer line; in the afternoon the solar dot is well above the line.
06-24.jpg (40284 bytes)
June 24, 2003
approx. noon
Dsc01131.jpg (36066 bytes) 07-09zoom.jpg (33533 bytes)
July 9, 2003
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July 16, 2003
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July 25, 2003
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August 12, 2003
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August 19, 2003
12:05 p.m.
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August 28, 2003
Meanwhile, Mars at opposition is making its closest approach to earth in nearly 60,000 years.
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September 10, 2003
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September 15, 2003
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September 23, 2003
September Equinox.  The sun's position just above the equator hints that the globe is slightly out of alignment.  As long as that error is kept nearly constant, we should still be able to plot a figure-8 (albeit misaligned) onto the globe at the end of one year.
10-12.jpg (42729 bytes)
October 12, 2003
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October 27, 2003
11:55 a.m. EST
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November 6, 2003
12:05 p.m. EST
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November 26, 2003
Meanwhile, the big sunspot groups of 2003 come round again--a bonus while tracking the sun.


Image courtesy of SOHO (ESA & NASA).

12-02.jpg (29626 bytes)
December 2, 2003
12-21.jpg (34288 bytes)
December 21, 2003
eric.jpg (30131 bytes)We're done!  We have tracked the sun for 12 months.  Now we just have to plot the points on the globe.  To be more scientific about this, we could continue tracking the sub-solar point to see if its path is repeatable.  You may notice that the sun does not exactly coincide with the tropic of Capricorn.   In the past year, the globe has settled into the padded base and repeated handling has affected the positioning of the base, globe, and cup.



The results are in, with mixed success.  We first plotted the sub-solar point with yellow circles on the Tropic of Capricorn and moved up to the Tropic of Cancer.  From there the red circles descend back to the Tropic of Capricorn.  If the three points immediately after the vernal equinox were better positioned, then the figure-8 of the analemma would be more apparent.  Again, the globe was repositioned after each observation, so plenty of error is introduced.


globe-plot.jpg (292368 bytes)globe-plot.jpg  (286 KB) globe-plot2.jpg (51557 bytes)globe-plot2.jpg  (50 K
globe-plotzoom.jpg (282014 bytes)globe-plotzoom.jpg (275 KB) globe-plotzoom2.jpg (35225 bytes)globe-plotzoom2.jpg  (34 KB)




[Note: The Sub-Solar Cup activity is detailed in the Paper Plate Astronomy video.]


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