On 11 February your 1832 zone time DR position is LONG 110°52.6'W. At that time you observe Polaris with a sextant altitude (hs) of 26°19.8'. The chronometer time of the sight is 01h 34m 56s, and the chronometer error is 02m 16s fast. The index error is 2.7' off the arc, and the height of eye is 60.2 feet. What is your latitude by Polaris?
• Polaris latitude method: Relationship between observed altitude of Polaris (Ho) and observer’s latitude, including small corrections for Polaris not being exactly at the pole • Correcting sextant altitude (hs) to get observed altitude (Ho) using index correction, dip, and altitude corrections • Using DR longitude and date (11 February) to obtain the correct Polaris corrections from tables
• First, carefully reduce hs to Ho: what signs do you use for index error that is "off the arc" and for dip with 60.2 feet height of eye? • After you have Ho, how do you apply the Polaris corrections that depend on your DR longitude and the date (February 11)? Think about LHA Aries or SHA Polaris as used in the tables. • Once you’ve applied the Polaris corrections, how close is your final latitude likely to be to Ho? Which answer choices are consistent with a Ho around 26° and the direction (N/S) you are in?
• Be sure you apply index correction with the proper sign for "off the arc" (negative correction to hs). • Compute dip from height of eye 60.2 ft and subtract it from hs before applying further altitude corrections. • Confirm you’re using the correct column and line in the Polaris tables for 11 February and your DR longitude (or corresponding LHA), and that the algebra of adding/subtracting the Polaris corrections from Ho is consistent.
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