Korean Airlines Flight 902 was shot down by a Soviet fighter in April 1978 after the pilot turned through 150 degrees and entered Russian airspace. The New York Times reported it happened around 8.30 pm Paris time, so this happened during sunset. But if he had kept to the correct course, he should have been flying over the North pole and into the middle of the day.
Given that magnetic compasses are not helpful at this latitude, the aircraft did not have an inertial navigation system, and the Earth's surface (if visible) is presumably similar in both directions, what other clues could the pilot have to his heading?
In other words, for flying at high latitudes in the late 70's, what checks were available to the accuracy of navigation?