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KF5JRV > TECH 07.08.16 17:36l 59 Lines 3224 Bytes #-3542 (0) @ WW
BID : 7272_KF5JRV
Read: DK3UZ GUEST OE7FMI
Subj: Star Finder Globe
Path: DB0FHN<OE2XZR<OE5XBL<F1OYP<IZ3LSV<I0OJJ<GB7CIP<N0KFQ<KF5JRV
Sent: 160807/1402Z 7272@KF5JRV.#NWAR.AR.USA.NA BPQ1.4.65
Identifying stars at sea
Many historians claim that terrestrial globes were of little practical use in
navigation due to their lack of detail. This 20th-century celestial globe,
however, was designed to be practically useful. It was intended to aid with
the identification of stars at sea.
Many historians claim that globes can have been of little practical use in
navigation - it is difficult to make accurate measurements on a curved surface
and the scale is too small to plot detail. However, these criticisms pertain
to the terrestrial globe, where the surface of the sphere represents the
surface on which the navigator wishes to travel, and which he must therefore
know in detail. This 'Starfinder' globe, designed by one Lieutenant English
and made by Cary & Co. around 1925, provides a late example of a celestial
globe intended to aid with the identification of stars for use in navigation.
It is not known how widely the Starfinder was used, but it most likely became
redundant in the mid 20th century with the development of new navigational
technologies during the Second World War.
English's Starfinder globe is well adapted for navigational use at sea. Only
the most important navigational stars are depicted on the sphere, and are
shown as individual points as they are seen in the night sky, rather than as
imaginative constellations. The box that holds the globe is about the same
size as a marine chronometer, so it would not have been too bulky
for use onboard a ship. In addition, the mahogany box protected the delicate
plaster sphere from damage in rough seas and provided safe storage space for
the accompanying instruction booklet and the red and blue pencils used to make
the markings required for certain calculations.
An independent instrument
Instructions for the globe suggest that it was designed to be used as a
stand-alone instrument. If a navigator were using the Starfinder he would have
no need for azimuth tables, which the author of the accompanying booklet
considered to be "an immense advantage". Nor would a telescope be needed,
since only those stars visible to the naked human eye were depicted on the
globe.
Practice with the globe
All of the applications of the globe were practical, relating to observation
rather than theoretical speculation on the positions of bodies that were
invisible to the naked eye. If a ship's latitude were known, a navigator could
find the approximate altitude and "true bearing" of any star, or conversely
identify a star by its position even in cloudy weather when no other stars
could be used as references. Discs were provided that could be attached to the
globe to show the position of the Moon and planets on a particular day.
However, discs were only provided for Venus, Mars, Jupiter and Saturn - those
"of use to the ordinary observer".
Most surviving examples of Starfinder globes have a brass meridian circle as
well as a horizon ring that supports the globe in the box. The user would
have rotated the meridian, which was set in a runner in the base of the box,
in a groove in the horizon ring to set the globe for the appropriate latitude.
73, Scott kf5jrv
KF5JRV @ KF5JRV.#NWAR.AR.USA.NA
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