Whew, just finished reducing my sight of Venus, shot 40 minutes ago :P Actually it's my first sight reduction done on one of my own sights, and my first star sight! I used an artificial horizon but unfortunately there was quite a breeze running... oh well.

Anyway, since you were mentioning sight reduction the other day I thought I'd share the process I used, transcribed from the front and back of an envelope

I'm thinking I will keep a sort of running fix. I'm starting with a DR of 49°N, 123°W, and will update it whenever I can take a new sight, always shooting from my patio.

Index error was 2.6' on the arc.

Hs at 10:20 pm PDT was 25°40.7'

Index correction of -2.6' gives 26°38.1'

Divide by 2 for artificial horizon, gives

**Ha = 12°49.0'**.

(NB: not sure if that's the right order, but I *think* index error "only applies once" in an artificial horizon measurement)

Correction for refraction (not corrected for temp or pressure since it's probably close enough) is -4.2', which gives 12°44.8'.

Parallax correction for HP = 0.41' is +0.4', which gives

**Ho = 12°45.2'**.

Sight was taken at 0520 on May 10 (GMT). 20m is 1/3 of the hour.

At 0500, GHA was 220°47.6' and

**Dec was 27°41.9**'; d=0.1' so no interpolation is necessary for Dec.

v is 1.9', so GHA correction is 1/3 of 15° + 1/3 of 1.9', or 5°0.6'. This gives a GHA of 225°48.2', and

**LHA = GHA - APLong = 103°** gives an

**AP longitude of 122°48.2' W**.

Page 69 of Pub 249 (87 in the PDF) is for Lat 49° Dec (15°-29°) SAME name as latitude. I look in the 27° column for row 103 and find

Hc = 12°11'

d = 46'

Z = 63° (Zn = 360° - Z = 297°)

The d correction of 46' per degree of declination, combined with 42' of declination, makes for a correction to Hc of +35', so

**Hc = 12°46.0'**.

Hc > Ho gives an intercept of 0.8' away from 297°, which is not great considering where my apartment actually is :P Partially it's the wavy surface of the water I used, and partially I'm not just particularly good at this yet, but I also think there are some uncorrected errors in my sextant. The intercept should have been something like 12 or 13 nm toward.

Maybe tomorrow I'll photocopy a chart from the library and start plotting LOPs on it.