On 12 June your 1945 DR position is LAT...

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Question 1 of 2066636eea28f7522a1c51aa62

On 12 June your 1945 DR position is LAT 21°47.0'N, LONG 46°52.0'W when you observe a faint unidentifiable star through a break in the clouds. The star bears 130°T at a sextant altitude (hs) of 45°21.2'. The index error is 0.5' on the arc, and the height of eye is 45 feet. The chronometer reads 10h 43m 27s, and the chronometer error is 1m 46s slow. What star did you observe?

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🔍 Key Concepts

• Sextant altitude corrections: Apply index error, dip (height of eye), and main altitude corrections to get the observed altitude (Ho). • Time and GHA/Dec: Correct the chronometer time using the chronometer error, convert to GMT, and then determine the approximate Local Hour Angle (LHA) for the assumed longitude. • Star identification by position: Compare the calculated geographic position (GP) of the star (its declination and GHA) with your Dead Reckoning (DR) position and bearing to see which catalog star fits.

💭 Think About

• First, think through each correction to turn the sextant altitude (hs) into a true observed altitude (Ho). Which corrections increase the altitude and which decrease it? • After correcting the time, consider where the Local Hour Angle (LHA) should roughly place the star relative to your DR longitude. Does a star at that azimuth (130°T) make more sense in the eastern or western sky from your position? • Look at each choice’s approximate declination (north or south, and roughly how many degrees) and compare it to your latitude and the observed altitude. Which declinations could produce an altitude of about 45° from LAT 21°N on that bearing?

✅ Before You Answer

• Double-check the sign of the index error ("on the arc") and apply it correctly to hs. • Verify that you converted the chronometer error properly (slow vs. fast) when finding the correct GMT. • Confirm that the declination sign (N/S) and approximate value of the candidate stars are consistent with both your latitude and the observed azimuth (130°T).

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