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Hello everyone,

A few days ago, I purchased a 1988 SNO-T Russian sextant that was for sale on E-Bay in the country of Latvia. (see picture below)

It arrived in very good condition, so I only had to clean it and add some drops of oil. It came with two telescopes, which one of them has an inverted image and two cross lines. As far as I know, that telescope is only used for collimation.

Over the weekend, I went to the Miami Beach area to calibrate the index error and make a little adjustment to the horizon mirror, so the index error was close to zero.

To check the index error at higher angles I used the star distances method, by taking sights of Saturn and Fomalhaut. These is the data and the results:

Date Sep 22, 2024

Location: Miramar, Florida (north of Miami)

Coordinates: 25 59.5 N / 80 18.5 W

Average time of sights: 04 29 50 UTC

Average measured distance: 21 38.3’

Results:

Calculated distance between bodies using the nautical almanac: 21 39.0’

Measured distance corrected by refraction: 21 39.1

Index error: -0.1 ‘

Based on the excellent accuracy of the sextant, a day later, I did the Lunars distances test between Jupiter and the Moon..Since it was late in the evening and I was inland, I used the A-12 Bubble sextant to take the Hs of Jupiter and the Moon.

These are the data and results.

Date Sep 23, 2024

Location: Miramar, Florida (north of Miami)

Coordinates: 25 59.5 N / 80 18.5 W

Temperature: 22 C

Pressure: 29.92

Jupiter sights:

Average time of sights: 05 15 53 UTC

Average Hs: 19 1.5’

Index error: +1’

Bubble sextant – No dip error

Moon sights:

Average time of sights: 05 15 36 UTC

Average Hs: 29 19.3’

Index error: +1’

Bubble sextant – No dip error

Lunar distances:

Average time of lunar distances: 05 16 45

I used the closer limb for both the Moon and Jupiter.

Average Hs distance: 10 10.3’

Index error: -0.1’

By using Frank’s online calculator, these were the results:

Error in Lunar: 0.3’

Equivalent error in Longitude: 10.1’

Equivalent position error: 9.1 miles

Note: I did not enter the Ho of Jupiter and the Moon in the online calculator, because I took them with a bubble sextant, and the online calculator (I think) only allows either UL or LL sights.

In parallel, I calculated the lunar distances by hand using the direct triangle clearing method, and the results were a little different:

Error in Lunar: 0.2’

Equivalent error in Longitude: 3.8’

Equivalent position error: 3.4 miles

Open question for the group: Should we take into consideration in the lunars calculations Jupiter semi-diameter (which it was 0.22’ at the time of the sights)?  

The Lunars results using the direct triangle clearing method, were better without including Jupiter’s semi-diameter in the lunars calculation.

Thanks !

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