Astro-Compass MkII

Brooke Clarke, N6GCE
Astro-Compass MkII
Astro-Compass MkII
Astro-Compass MkII
                      Astro Compass Base
      RAF O.2 Compass mount?


The manual Astro-Compass is a device that is pointed to a known star (that includes the Sun) and then will indicate true North.
A typical version is the Astro-Compass MK II, Sperti, Inc., Cincinnati, Ohio.  D500 also shows up on the label.

The manual astro compass was replaced by the periscopic sextant.
An experimental Skylight Compass was built to use the same mounting and carry case.

Sir Francis Chichester - wrote 4 volumes about the use of the astro compass.
CV/Profile -


PG&E - Using the Astro-Compass to Study Solar Access - pdf version -

T.O 05-15-10 Astrocompass, its installation, use & maintenance - Wanted
Have (could make into a CD-ROM):
W.W. Boes Instruction book, 27 pages
Sperti Instruction book, 9 pages
Naval Avation News 15 Dec 1944, 52 pages (<1 on Astro Compass)
Specific Operations Vol 2 15 Mar 1972, 252 pages (7 on Astro Compass)
Stores Reference 6A, 21 pages
PG&E Sun Path Instructions, 7 pages

Aircraft Ref 48: Astro-Compass



The Astro-Compass can not be used by placing it on a flat surface.  The leveling screws will not make any change.  It needs to be mounted in a pipe with an I.D. of about 1.925" and an O.D. of about 2.250".  There should be a 0.325" wide slot extending about 0.85" from the top of the pile to pass the clamp screw.  See photo above for the mount.

The mount may be the same as for the RAF O.2 Compass?

It also works for the Skylight Compass.


1852166 Position Finder, H.B. Kaster (Kaster Spherant Co), Apr 5 1932, 356/147; 33/268; 356/148 -
These may apply to the AN-5851-1 Sextant, aircraft rather than to this astro comapss?
2207656 - Process of Decreasing Reflection of Light from Surfaces, and Articles so Produced, July 9, 1940, assigned to Research Corporation, NY - This is the idea of coating optical surfaces to lower reflection and increase transmission, still used today!
2281474 - Treating Surfaces of Light-Transmitting Articles, and the treated products, April 28, 1942, assigned to Research Corporation, NY - extends the single layer coating to multilayer coatings.
2281475 - Reducing Reflection of Light from Surfaces, and Articles so Produced, April 28, 1942, assigned to Research Corporation, NY - by baking the 1/4 wave coating films they become much harder

2446258 Compass, R.C. Burt (Lockheed Aircraft), Pasadena, California, Aug 3 1948,33/348 ; 33/349; 33/355R - has the look and feel of the astro compass
682585  Dipping Needle Compass, H.D. Cotter & J.W. Gardam, Sep 10 1901, 33/355R ; 324/259 - mine??
1216953 Magnetic Cinoassm F.O. Creagh-Osborne & A.J. Hughes, Feb 20 1917, - gimbled ship's compass
1533683 Compass and Magnetic Dip Indicator, C.G. Abbot (GE), Apr 14 1925, -
1961312 Magnetic Compass for Avaiation, E. Vion, Jun 5 1934, - installs in the upper wing of a biplane just above the pilot
2087086 Magnetic Compass, G.D. Beeson, Jul 1937 - operates a valve for auto pilot
2116103 Compass for Automatic Pilots, G.D. Beeson May 3 1938
2118082 Compass Alarm, J.H. Hammond, Jr. May 24 1938 - off course for ships
2215622 Magnetic Compass, E.A. Spreey, Jr (Sperry Prod), - combined compass, artifical horizon, gyro and inclinometer
Called By:
4110914 Hand compasses Sep 5, 1978
4227313 Compasses Oct 14, 1980
6094830 Inclination-compensating display device for a compass Aug 1, 2000

Celestaire - sells the Astro-Compass MK II & the base
Arctucus, the Missing Hours and Fate A short story by Chuck Ellsworth
Lincoln Tales - Stories of 10 Squadron RAAF in Townsville
B-29 Superfortress Then and Now - The Navigator - by Sandy Amell -
Navigators Celebrate 50 Years Too - But perhaps the greatest improvement was the periscopic sextant, the technological breakthrough that freed navigators from hand-held sextants that necessitated peering through astrodomes atop our aging craft. No longer did we have to add corrections for errors in astrodome refraction or endure the frustrations of scratched and discolored Plexiglas portals distorting our celestial sightings.  With the periscopic sextant we also had the means of quickly and more accurately locating our selected stars for observation. And determining aircraft heading by periscopic sextant became much easier than with the earlier astro-compass.
ASTRO COMPASS MKII. Used in the B-24 Liberator. This unit was manufactured by the W.W. Boes Co. Part No. 94.
TITLE 14 CODE OF FEDERAL REGULATIONS (CFR) - Part 63 Federal Aviation Regulations - (7) Demonstrate or explain a meod of aligning an astro-compass or periscopic sextant. - Astro Compass base -
The Truth Will Out - Whereas the RAF instrument can be used with the Sun, Moon, stars and planets, the Roman astro-compass can be used only with the Sun.
A Third Survey of Domestic Electronic Digital Computing Systems BRL161 - Libraxcope ASN 24 - Automatic inputs of the following form may be accepted. (When utilized with appropriate complementing input-output equipment): Compass heading, Astro compass heading
RAAF - Part III - It was essential, when taking a reading with the Astro Compass, that you used the correct star. The Astro Aid Roller was good for this. However on one night trip, a Navigator complained that he had difficulties. He saw a "red" star to his port side, and took a reading. However the only "red" star was Betelgeuse and it wasn't shown on the Roller or on the Astro Almanacs (for calculating). Eventually the mystery was solved when he mentioned the "red" star kept on moving. There were six aircraft flying on training exercises that evening, and he had taken an Astro reading on the red light of one of the other aircraft.
Antique Aircraft-parts - Swiss source for aircraft related manuals -
Torquetum - the exact same functionatity from 1284
YouTube: Astrocompass Mk.II: Tools for Northern Navigation, 11:05 -

Palm Pilot Software

There is also a program for the Palm Pilot called "astro compass".  This uses the time and location of an observer to calculate some astronomical data.

Back to Brooke's  PRC68Products for Sale, Navigation, Military Autio, Squad Radio, Military Information, Personal Home page

This is the [an error occurred while processing this directive] page created 20 Oct 2001.