iPhone10 Sextant

In the previous post I examined the iPhone10 Compass. In this post we will look at the iPhone10 Level application used as Sextant. The Level app is located in the Utilities/Measure icon.

On January 8th_2020, I was sitting at my desk and the Moon was clearly in view between two newly constructed condo towers. I opened the iPhone level application and sighted along the top edge directly into the Moon Centre. The level application shifts up/down by 1 degree. So I was able to turn slightly to read the result without changing anything. Fig.1 shows the reading of 22deg taken at 18:25EST = 22:25GMT.

I reduced the sighting using ScicosLab scripts and the Nautical Almanac 2020. Then I checked the sight reduction using the iPhone program iMariner along with the Admiralty NavPac. The difference in altitude increments is 1deg which is 60Nautical Miles, so an intercept of 3.3minutes is a lucky result.

Hs = 22deg
Time = 22:25:00GMT
Dip = 0min
Refraction = 2.4min (Fig.2 ref.sce)
PA = 53.6min (Fig.3 pa.sce)
Ha = Hs +/-InsEr +/-IndexEr – Dip = 22 + 0′ + 0′ + 0′ =22deg
Ho = Ha – R +/-SD + PA = 22deg – 2.4′ + 53.6′ = 22deg 51.2′
IF = 25/60
GHA_22hrs = 354deg 26.5′
GHA_23hrs = 8deg 52.8′
GHA_22:25 = 0deg 27.4′ (Fig.4 interp.sce)
DEC_22hrs = 21deg 58.5′
DEC_23hrs = 22deg 3.0′
DEC_22:25 = 22deg 0.4′ (Fig.4 interp.sce)
Hc = 22deg 47.9′ (Fig.5 gcdb.sce) = 22deg 47.8′ (iMariner)
Intercept = Ho – Hc = 3.3min

Celestial Navigation Basics & Equipment Course: