Sunday, February 17, 2008

New "Stupid Sheet"

FFC's diagram of directions, including magnetic deviation for this area: a quick way to relate compass readings to directions of sky events. This is rev 2. You can carry around a print of it and check for standard alignments.


Norman said...

I don't get it -- why is this chart oriented to magnetic north, when everything to the Indians was based on true north? This simply throws everything off and leads to confusion.

pwax said...

The chart is not oriented to magnetic north. Rather, it shows the relation between various directions and magnetic north - which is useful if you have a compass. In particular, if you hold the chart so that magnetic north on the chart lines up with magnetic north on a compass, then the other directions are correct and do not need to be compensated for magnetic deviation (at least not around here). I am not sure what other method would be as easy for an amateur out in the field.

Tim MacSweeney said...

Back in the days before digital watches, the Boy Scout manual showed how to use the sun and a watch to get approximate bearings.
It also showed how to tell approximate time with the shadows of two sticks if you didn't have a watch and were lost in the woods, so you could figure out approximate compass bearings. The Stupid Sheet (which is a misnomer by the way) shows the bearings of many events - as seen on a flat horizon. At various locales, the apparent equinox sunset might set over two standing stones exactly as it appears to touch a spot on a distant hillside that is not at exactly 285 degrees by a magnetic compass, but it's still the equinox sunset sunset at that particular place at that particular time. See:

Anonymous said...

The degree heading of the sun or moon rising or setting on the horizon is affected by the elevation above true horizon. The degree heading can shift by as much as 3 degrees when the alignment is being viewed from a low spot over a high horizon like a hill. Charts like this are useful for calling attention to the potential of an alignment at a particular location. Confirming an alignment requires a higher standard of evidence and more precise measurements.

James Gage

pwax said...

You miss the point of the stupid sheet. It is so you can use a magnetic based compass to get a sense of the directions.

I know it is not accurate enough, given local deviations in the magnetic field, variations in the height of the horizon, and variations in latitude.