NavList:

Last night was a rare good night for star gazing despite the light pollution from our over-generous Council and the nearby air base.  I wanted to follow up my idea that in an ideal World navigational stars should be colour coded.  I recently bought an Ebbco sextant to practice adjustment on.  To renew the dark filters, which had gone funny, I had to buy a full set of differently coloured filters from China in order to get just one Sun filter.  I thought I’d try all the remaining different light shade filters on stars to see if I could change their colour.  Not unexpectedly, the result was a complete failure. However, with my sextant out, and observing through the open spare bedroom window, kneeling against the radiator like ‘Christopher Robin’, I thought I might as well practice checking index error, going progressively from Rigel to Betelgeuse to Sirius.  I found it best to discard my spectacles and focus the telescopes on the Moon before concentrating upon the stars.  I’m convinced now that it’s all a matter of practice, practice, and then more practice.  Eventually I believe that with the 2.5 times telescope, I could check for index error to less than one minute, and probably nearer to half a minute.

Next, I tried using the 5x inverting telescope.  This required more practice, because to aim at all you must get used to moving the sextant up when everything is saying you should move it down and left when it appears you should be moving it right.   Eventually I felt I could measure index error to about a quarter of a minute, which is about the same as I achieve on distant buildings and shorelines in daylight.

Then I turned my attention to measuring the angle between Sirius and Rigel.  With the 5x inverting telescope I found initial aiming though the eyepiece almost impossible.  I found it best to move my head back and hold the sextant in what I thought looked about the correct position.  Then I looked through the eyepiece and the stars were nearly always visible.  This time I was confident I could narrow the angle to between 21°41’ and 21°41.5’.  Bauer’s uncorrected value is 23°40.4’.  Maybe an appointment with lunars is beckoning.  DaveP