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Subject:
From:
Mike Rossander <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Thu, 23 Jan 2014 06:46:48 -0800
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re: "My hypothesis is that the bees can detect the angle of the sun and it's 
apparent movement north and south of the equator as perceived from here 
on earth, and that as the sun's apparent position moves northward, the 
bees detect that and initiate increased brood rearing."
 
That's an interesting hypothesis and drags me back to my Physics roots.  Let's run some numbers.  The sun is massively larger than the earth but we are vastly further away from the center of the sun than we are from the center of the earth.  Gravitational force is a function of mass over the square of distance.  That means the gravitational force we feel from the sun is about 0.0006 g or about 1/1600th of the force of gravity you feel from the earth.

Gravity is a force vector.  That means the vector fields can be added.  That means you weigh slightly more at night when both the sun and the earth are pulling you on a line through the center of the earth than at noon when the sun is pulling opposite to the earth's pull.  I don't think you'll meet your New Year's resolution by changing when you weigh yourself, though.  It's a pretty tiny effect.  For a 200 pound man at mid-latitudes, it's a difference of about 2 ounces.  That said, it's enough to generate tides so yes it's possible to measure time of day by tracking the changes in your weight very carefully.  And it's theoretically possible to measure time of year by measuring the slight change in the angle of gravity.

Here are some complicating factors, though.
1) The amount that the direction of the sun's gravitational pull changes each day is small.  The axial tilt of the earth changes by about 45 degrees from midwinter to midsummer.  It takes 180 days to get there.  That averages 0.25 degrees per day.  To detect that difference would be roughly equivalent to putting on your coat tomorrow and being able to tell just by the difference in pressure on your two feet that a key in your pocket was an eighth of an inch further to the right than it was yesterday.
2) The moon also exerts a vector gravitational pull.  While it's gravitational force is lower than the sun's, it's proximity is such that the moon has a greater effect on tides than the sun does.  And since gravity is a vector force, all we can really feel is the sum of the three forces (gravity of earth, sun and moon) added together.  That would suggest that if the bees were reacting to any gravitational variance, it would more likely be observed on a lunar schedule than on a solar one.
3) Finally, the bees have no independent external reference against which to measure that the line of gravity has changed.  You could simulate the same change by slightly tilting your beehive each day.

Actually, that last point might not be strictly true...  You could theoretically measure not the absolute change in the sum of the gravitational vectors from day to day but instead measure the degree to which that vector shifts between midday and midnight.  That difference, though very slight, could be measured with only an internal reference point.

It should be possible to test the hypothesis by putting a clockwork 
mechanism to very slightly tilt your hive back and forth by slightly 
differing amounts each day.  At midwinter, the difference in the sun's contribution to the net gravitation vector between midday and 
midnight is equivalent to a deflection off true vertical of 0.028 degrees.  You'd want to 
offset that amount by 0.000156 degrees each day to simulate the daily change in deflection.  If you wanted to shim 
the back end of a langstroth hive by that amount, that would require lifting it by about 
0.00006 inches over 12 hours, then lowering it over the next 12 hours to either offset or to exaggerate the daily change in the sun's vector contribution.

So is it theoretically possible that the bees are reacting to the change in the gravitational vector?  Yes.  
Is it likely given the masses and the sensitivities that would be required?  I don't think so, no.

One final note.  All of these are back-of-the-envelope calculations.  Apologies in advance if I've slipped a digit anywhere.


Mike Rossander


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