FIGURE 3. Deviation of alignments from true north resulting from use of the simultaneous transit method of orientation.

As the chord between the pair of stars moves away from the pole, alignments taken toward the stars when they are in simultaneous transit (actually vertically aligned) may be on either side of the pole depending on which star is at its upper culmination. The size of the deviation from north will be the same at a given date regardless of whether it is east or west of north. Here a much later date is mapped to exaggerate the effect of time on the result of the alignment process. a, Winter and spring alignments with -UMa at upper culmination; resulting alignments are east of north. b, Summer and autumn alignments with -UMi at upper culmination; resulting alignments are west of north. Maps produced on SkyMap Pro 6 (ref. 17).