Astro compass MkII

#Aviation

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The Astro Compass Mk ii is a celestial analogue. It reconstructs the celestial sphere in three dimensions by means of graduated quadrants and circles. The Astro compass was primarily used to check heading between the period of time (circa 1945) when the astrodome was still in use but before the introduction of the periscopic sextant.

The Astro compass, when required, was fixed firmly across the bottom of the astrodome. The viewing device at the top could be looked through to sight on a distant object in the sky or on the ground, or a bright object, such as the sun, could be aligned by letting its rays to pass through a lens onto a translucent screen. A measurement of the relative bearing of a known object could, for instance, be used to check the aircraft's heading. Conversely, if aircraft heading were known to be correct, the relative bearing of an object could produce a position-line. Accuracy depended on the altitude of the body observed but was usually well within 2 degrees.