Quote:
Originally Posted by LukeFF
The WWII patrol reports mention the use of what is called a "bubble sextant" for navigation. Many commanders also mention how it was sometimes difficult to use this device. How did this new type of sextant differ from the "old" style sextant, and what made it so more difficult to use?
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When using a standard sextant, the angle to a celestial object is determined by sighting it, then bringing the reflected image of the object down to horizon level by moving the index arm along the semi-circular arc scale at the bottom of the sextant. Obviously, in order to do this, you have to be able to see the horizon. See the following link:
http://www.tpub.com/content/administ.../14220_230.htm
If for some reason you are unable to see the horizon, you would need to find a substitute. In a bubble sextant, the visual horizon is replaced by a regular alcohol bubble level. The reflected image of the celestial object would be brought down to the artificial horizon created by the bubble and the angle read off of the arc scale as normal. See this link:
http://www.users.bigpond.com/bgroble...t/sextant.html
Not being able to see the horizon was usually a problem for aviators flying at night. A shipboard navigator usually takes his sights at morning twilight, when it is still dark enough to see the stars, but when it is light enough to drown out the minor stars, making the major navigational stars easier to distinguish and the horizon visible. Aviators flying night missions may not always have this luxury of choosing the time of their sightings. At night and at altitude it would be very difficult, if not virtually impossible to see the horizon.
I have never used a bubble sextant and therefore can not directly comment on its ease of use. However, it is probably quite difficult to keep the bubble level enough to take an accurate sight on the pitching and rolling bridge of a fleet boat. Why didn't they just use a normal sextant? Well, it would give them the advantage of getting a fix at any time during the night, not just at morning twilight. The more fixes you get, the better your navigational situation will be.