NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2012 Apr 30, 14:50 -0700
A better way to look at it is to determine the dip of the horizon as seen from 35,000 feet which is 3° 01' meaning the visible horizon is that far below the true horizontal. The altitude of Venus at the position and time you used was 2° 41.7'. so, if the pilots were judging the altitude of Venus by reference to the visible horizon (as when using a marine sextant) they would have measured an altitude of 5° 42.7' above the visible horizon. . But the sun would not be rising until almost 1100 Z so it was pitch black and the horizon would not have been visible, and the moon was not up either. But, when you fly jets you get used to the visible horizon not representing the horizontal. At low altitudes you use the visible horizon to position the nose of the plane but at high altitude (or in clouds) you must adjust the pitch attitude of the plane by reference to the attitude indicator or flight director and, in cruise at high altitude you usually have the nose about three degrees to five degrees (depends on weight and airspeed, we call this deck angle) above the horizontal, haven't you ever noticed that it is an uphill walk back to your seat from the lav in the tail? So, if the copliot momentarilly forgot about the deck angle and if he noticed Venus on the same spot on the windshield where the horizon would appear to be at lower altitudes, then Venus would appear to him to be at their same altitude. This phenomenon is well known, planes that appear to be at your altitude pass above you, and you have guard against this visual illusion. gl --- On Sun, 4/29/12, Michael Meredith <kc8ttv@gmail.com> wrote:
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