DAVIS Mark 15, 25 Sextant - Manual (Page 15)

Page 13
To find Polaris:
1. Locate the pointers of the Big Dipper (Fig. 15).
2. Find a point in line with the pointers and five times the distance between
them.
Polaris is the star shining above.
Note: The Big Dipper revolves around Polaris so be prepared to see the star
cluster in any position.
The Complete Sight: An Example
Let us assume for this example that your ship is sailing from San Francisco to
Hawaii and you have been using the sun to find your position each day. To
allow plenty of time to follow the sun up to its highest point, make sure that
you have completed all your preparations by 10:00 a.m. local time. Your chart
shows yesterday’s position. From this position, draw a line in the direction you
are traveling equal in length to the estimated number of miles to be traveled
by noon today. This is your “dead reckoning position” (D.R.), which will be com-
pared with your “noon sight.”
Note: You will be standing on deck in such a manner that your eye is ten feet
above the water (for Dip correction) and the index error of your sextant is + 5'.
At about 11:20 a.m., you begin taking sights. At 11:23:30, your first sextant
reading is 82° 56'. You continue recording the sun’s altitude approximately
every three minutes until the sun seems to “hang” in the sky, dropping to a
lower altitude at your next sight. The maximum altitude of the sun, 84° 56', is
the altitude of the sun at meridian passage. You continue taking sights until
12:03:30, when the sun has dropped to your original reading of 82° 56'. You
now know that the sun reached its meridian at 11:43:30 (exactly half the time
between 11:23:30 and 12:03:30).
Figure 15