This is primarily a travel blog in which I write about traveling in our motorhome. Our travels have

Nacogdoches, TX, United States
I began this blog as a vehicle for reporting on a 47-day trip made by my wife and me in our motorhome down to the Yucatan Peninsula and back. I continued writing about our post-Yucatan travels and gradually began including non-travel related topics. I often rant about things that piss me off, such as gun violence, fracking, healthcare, education, and anything else that pushes my button. I have a photography gallery on my Smugmug site (

Sunday, October 28, 2012

The "Time-Compensated Sun Compass"

We left Mission this morning at 9:15 AM, drove 340 miles and decided to stop in Sugar Land (3 to 4 hours south of Nacogdoches).  We will finish our 10-week trip tomorrow.  It will be nice to get home.

We found a nice big Walmart with a Sam's Club next door, both sharing the same parking lot.  The place was busy and it was hard finding a section of parking space on the fringe of the lot into which I could maneuver the motorhome with toad. I drove around the entire parking lot twice without running over anything or looking any of the people staring at me in the eye.  I'm only taking up about 10 parking spaces but there are 2 other motorhomes with toads close by and taking up almost as much space (they aren't as long).  As a matter of boon-docking ("dry camping") etiquette we will not extend the slide outs.  It will be a little cramped but we are only here for the night.

The temperature here is Sugar Land is a very pleasant 71 degrees and a soft cool breeze is flowing in through our open windows.  Since our only power source is the generator it's good that we don't need A/C or heat (at the moment, anyway).  We are parked on the Sam's Club side of the lot, which is good, as they have free wi-fi for their customers and with my USB amplified antenna I am able to write this note and surf the web while sitting in the comfort of my motorhome.

Now we can finish the butterfly lessons by discussing the Monarch's navigation system.

How does the migrating Monarch butterfly find its way?  It’s not easy, that’s for sure.  You will need a clear head to follow my explanation.  So, pay attention!  There will be a test.

An airplane requires several different navigational instruments and aids to follow a defined flight path.  Especially for a flight of 2,000 to 3,000 miles.  The Monarchs have none of these devices, not even a map or a compass.  At least not a physical map or compass, as we would use.  They do utilize a very complex navigational system that is built into their genetic code, which uses their pin-head sized brain and their antennae to give them direction.  It’s like having a built-in GPS in your car.

Scientists call the Monarch’s genetic navigational system a “time-compensated sun compass” with time being measured by “circadian clocks” located in their antennae.  The “sun compass” uses the sun’s position during the day with timing information from the “circadian clocks” to maintain a constant heading.  A “circadian clock” is basically a 24-hour rhythm that repeats daily without the presence of any known external cues.    The rhythms can be adjusted to match the local time.  That just means that they can adjust themselves as the days lengthen or shorten during the year. 

The Monarch has 2 of these clocks.   One is incorporated into each of the Monarch’s two light-sensitive antennae.  Scientist refer to this as a “dual timing system”.  Only one antenna is required for the system to work sufficiently.  Therefore, if an antenna is damaged or lost the Monarch just keeps right on trucking without skipping a beat.  It is therefore a “redundant” system. 

The Monarch’s navigation system works by computing its position relative to the sun to keep it on course.  Timing is required for the Monarch to adjust his course for the position of the sun at any time of the day (think of it as a moving target as it moves across the sky).  The sun’s movement means that the angle of the sun relative to the Monarch is continually changing and therefore is continually being recomputed during the day.  The sunlight is processed through the Monarch’s eyes and antennae to adjust the “sun compass” so that the Monarch knows his position relative to the sun at any time during the day. 

I realize that I may have over simplified the explanation.  But at least you didn’t have to read science-speak such as; “the core mechanism relies on a negative transcriptional feedback loop, which drives self-sustaining rhythms in the mRNA and protein levels of a distinctive set of core clock components.”

By the way, I never did find out if they taste like chicken.  It takes about 400 to 500 Monarchs to make a pound and I never even found one.

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