NavList:

   

Reply

In post 7981 I said I would investigate the behaviour of sextant frames left 
in the sun. It has taken until today for my free time and the sunshine to 
coincide.

I compared the front and rear temperatures of two alloy-framed sextants and 
the rate of temperature rise in midday sunshine, when the sun's altitude was 
about 38 degrees. I arranged the plane of the frames to be approximately 
normal to the sun's rays. I also compared the rate of temperature rise 
between an alloy and a bronze-framed instrument.

I measured the temperatures using thermocouples held in contact with the 
thickest part of the frames via zinc oxide paste. The thermocouples 
themselves were shaded from direct sun by the plastic clamp used to hold them 
in place. The thermometer readout's resolution was to 0.1 Celsius.

There was no difference in the rate of temperature rise greater than 0.5 
Celsius between a SNO-T, a Tamaya 632D and a Brandis Vernier sextant (the 
latter with a bronze frame). Starting at about 16.5 degrees, all took about 
12 minutes to reach an equilibrium temperature of about 29 degrees. During 
this rise, the temperature difference between front and back never exceeded 
0.9 Celsius.

I think we may conclude that frame flexure due to exposing a sextant to midday 
sunshine in Autumn in 35 degrees S is likely to be negligible. If members 
would like to suggest further experiments about the thermal behavious of 
sextant frames I would be happy to try to carry them out.

Bill Morris
Pukenui
New Zealand




--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply