bubble horizon

bubble horizon

[′bəb·əl hə′rīz·ən]
(navigation)
An artificial horizon parallel to the celestial horizon, established by means of a bubble level on a bubble sextant.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

bubble horizon

i. A circle on the celestial sphere parallel to the celestial horizon formed by the intersection of the sphere with the plane of the sensible horizon as established by the bubble sextant.
ii. The plane established by a bubble sextant, other-wise called a sensible horizon.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved