Simple bearings: bearings to objects

In the last post, I discussed how to take bearings from a map.   This assumes the use of a prepared map with magnetic declination lines, the subject of an earlier post.  The reason for doing the work with magnetic declination lines is for ease of interpretation.   Every bearing is based on local magnetic north and doesn't require a lot of fussing to move between true north and magnetic.   I will discuss how to move between true and magnetic north in a future post however.

In the previous post, I discussed the dilemma that my friend Dan and I had about the identity of two islands.   This is one of the simplest cases of compass-and-chart (or map) usage.   It's important to get this one right, which is why I spend so much time on it - other sightings then come naturally.

There were two islands - Camp Island which lay on a magnetic bearing of 80 degrees, and Russ Island, which lay on a magnetic bearing of 10 degrees.   Having found the bearings from our assumed position, the next step is to actually take sightings with the compass and sort out what we saw.

For a standard backpacker's compass, the recommended way of taking a sighting is to hold it with both of your hands at approximately waist-level.   Keep your elbows bent with a right angle at your waist, and keep your shoulders square so that they are perpendicular with the direction-of-travel/bearing arrow on the compass baseplate.   This is illustrated below.

Orientation of arms, hands and compass in order to take a bearing on an object.  

Note that in this figure the direction-of-travel/bearing arrow should be pointing at the object that you are sighting.   In order to get the sighting, you keep the direction-of-travel/bearing arrow pointing at your target, and rotate the compass housing until the compass needle lines up with the orientation arrow.   In essence, this is similar to the orientation you obtained on the map, except in this case, rather than using the variation lines you drew on the map, the compass needle itself serves this purpose.  

While the figure above shows what you see looking down at the compass, the figure below shows schematically what the actual bearing looks like.   Recall from the previous posting that we were sighting on the left hand shoreline of Camp Island and also the left shoreline of Russ Island. 

Taking a bearing toward the left shoreline of island in the distance.   Note that we now align the magnetic needle in the compass so that it lines up inside the orienting arrow.  

A phrase that is sometimes used for the line-up of the magnetic needle is "red is in the shed".   This means the following - there is an orienting arrow, which is in the middle of the compass housing.   It rotates along with the rest of the housing and the gimbal that allows the needle to swivel is in the middle of it.   Rotate the compass housing until the red part of the magnetic needle is aligned with the orienting arrow - it should be fully contained within the orienting arrow with the red end of the needle pointing north.   The needle is "red" and the orienting arrow is "the shed" - so a proper orientation has "red in the shed."    This is shown below. 

Proper alignment of the compass housing rotated so that the compass needle is fully contained inside the orienting arrow with the red end pointing north.  This is captured by the phrase "red is in the shed". 

As you can see from the above figure, the bearing you have just taken is 80 degrees.   If you recall from the last posting, when we took expected bearings on the map, the left hand shore of Camp Island would be 80 degrees, and the left hand shore of Russ Island would be 10 degrees (magnetic).   So, in this case we've identified this island as Camp.   

Job done- comparing two bearings on a map with bearings made from an assumed position. 

Next up: finding position from back-bearings.