Backazimuth

[cjmiam 10]

Alright, here's a question for all of you orienteering gurus. How do you find a backazimuth? What is a backazimuth? I know someone out there knows this one and good luck teaching me

 

Thanks for your time,

 

cjmiam

[Eagle74 10]

Not knowing your familiarity with compass work, I'll start from the beginning.

 

Azimuth - Measurement in degrees from a north baseline. This could be magnetic north, true north or grid north. Your north baseline is 0 degrees with 360 degrees full circle clockwise. Azimuths are commonly used in the military.

 

Let's say you're standing at point A and want to get to point B. Using magnetic north as the north baseline, 0 degrees on the compass ring should be set at the north end of the needle. The azimuth to point B (direction of travel) is the clockwise deviation in degrees from north. Let's say that point B is in line with 45 degrees. The azimuth is 45 degrees, so if we travel from point A in a direction 45 clockwise degrees from north we will arrive at point B.

 

Back-azimuth - 180 degrees from the azimuth.

 

If you want to return to point A, you need to travel in a direction 180 degrees from the azimuth you traveled at to arrive at point B. 45 degrees plus 180 degrees is 225 degrees. The back-azimuth for your return trip (degrees clockwise from north) is 225 degrees.

 

Simply stated, back-azimuth is 180 degrees (straight opposite) "back" off the azimuth.

 

With 360 degrees total in a circle:

 

If the azimuth is equal to or less than 180 degrees, add 180 degrees to calculate the back-azimuth;

 

If the azimuth is more than 180 degrees, subtract 180 degrees to calculate the back-azimuth. (245 plus 180 would equal 425 degrees and there is no such point on a compass. 245 minus 180 is 65; a valid compass direction and exactly opposite 245)

 

Why use azimuth and back-azimuth? When describing a direction of travel using an azimuth, there is less confusion. There is for instance, only one 25 degree azimuth. If I am giving directions using quadrants however, there are potentially four 25 degree directions; north 25 degrees east, south 25 degrees east, south 25 degrees west, and north 25 degrees west.

 

Using a back-azimuth simply eliminates having to "hold the compass backwards" for a return direction.

 

A lengthy explanation, but I hope it helps. If you draw it out and then use a compass for a trial run you'll find it's not as complex as it sounds.