On 10 June your 2010 zone time DR position is LAT 41° 10.0' N, LONG 61° 15.0' W. At that time, you observe Polaris with a sextant altitude (hs) of 40° 35.8'. The chronometer time of the sight is 00h 08m 18s, and the chronometer error is 01m 54s slow. The index error is 2.0' on the arc, and the height of eye is 40 feet. What is your latitude by Polaris?
• Polaris latitude method – how Polaris’ corrected altitude relates to observer’s latitude • Sextant altitude corrections – index error, dip (height of eye), and altitude corrections to get observed altitude (Ho) • Small corrections for Polaris (a₀, a₁, a₂) taken from the Nautical Almanac for date and LHA Aries
• First, think through how to get from sextant altitude (hs) to observed altitude (Ho). What corrections do you apply, and in what order? • Once you have Ho for Polaris, how is it related to your latitude? Is it exactly equal, or are there small corrections that depend on date and longitude (LHA Aries)? • Consider whether you are north or south of the equator, and how that affects the sign (N/S) of the latitude you obtain from Polaris.
• Be sure you applied index correction with the correct sign ("on the arc" vs "off the arc"). • Confirm you converted height of eye in feet to dip in minutes of arc correctly and subtracted it from the sextant altitude. • Verify you used the right Polaris Corrections (a₀, a₁, a₂) for 10 June and for your approximate LHA Aries before comparing the resulting latitude with the answer choices.
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