A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2013 Jan 25, 18:47 -0500
I'm not going to defend the research. I haven't read the peer reviewed article or subjected the dung beetles to my own tests
The article did briefly mention test right along the lines of your inquiry, overcast, milky way with & without stars, & etc. Further, they brought the beetles into a planetarium so as to further investigate the theories, for example changing the orientation of the milky way, relative to true.
So it seems that they do use the milky way to keep a straight line! They are using stars (in conglomeration, as a bright band of nocturnal light) to navigate in their environment.
Of course, no little sextants. No Beetle Naval Observatory. No Beetle Time Services. No Beetle Maskelyne.
Hah! Back to lunars!
"Turns out that the South African dungbeetle orients direction vis the milky way."
They're doing something very simple --naturally... tiny bug brains and all that. They're obviously not doing any position finding --no teeny, tiny insect sextants in their claws. They're also not using the Milky Way as an astro-compass to provide a true orientation, which would be very difficult even for a human navigator if all you have is the glow of the Milky Way. Assuming the theory is correct (and I am skeptical since there's little incentive for anyone to double-check this sort of claim), all the beetles are really doing is using the Milky Way to maintain a course, whatever direction that may be, for some relatively short period of time. The Milky Way is a stripe of light across the sky, and whatever orientation it has over the beetle's head when it starts, it presumably keeps that relative orientation as it's rolling along. Very simple bug brain software could accomplish this. And if the model is correct, any comparably bright stripe of light across the sky would work just as well. I can think of some observational tests. Do the beetles perform more poorly on nights with a featureless overcast? On such nights, if we shine a spotlight beam over their little bug heads, do they use that instead of the Milky Way for orientation?
For marine navigation (humans now), this sort of aid wouldn't work as well because the orientation given by the Milky Way changes as the Earth turns. Like the bugs, you could steer a course by it for a short period of time but your course will change by the usual rate of 15 degrees per hour. You can't steer by the stars unless you're careful in your selection. The Milky Way is, at least, visible nearly all night long, almost everywhere on the globe. And since the star clouds of the Milky Way lie about the galactic equator, it's a band along a great circle, which means it always looks like a "straight line" across the sky wherever you are. One of these days, I'll have to visit some spot along latitude 27.1 (N or S) at the right time of night to see a dark sky full of stars but with NO Milky Way (or really, with the star clouds of the Milky Way running right along the horizon and therefore made invisible by extinction). It is interesting to note that this research on beetle orientation was conducted partly in Johannesburg, South Africa, close to 27.1S, which just happens to be one of those places where the Milky Way can be aligned right along the horizon for a portion of each night, rendering it completely invisible. Do the dung beetles panic when that happens??
Here's a better beetle, the famous "Beetle Cat": http://en.wikipedia.org/wiki/Beetle_cat.
Those Beetles also built most of the whaleboats that hung from the davits of the ships of the great American whaling fleet in the mid-19th century. And those Beetle boats were out there on those years-long, globe-circling voyages thanks to lunars. Lunars made global whaling by the New England fleet an economic reality.
Ha! I did it: dung beetles to lunars in five easy steps. :)
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
View and reply to this message: http://fer3.com/arc/m2.aspx?i=122116