A partially completed strip form is available for printing here. Fill in the values on the form, then enter your results in the boxes below. If you do not have a Nautical Almanac, you can view an altitude correction table here.
Enter the Ho for each star here:
Altair 21° 23.3'
Spica 39° 56.4'
Dubhe 41° 28.8'
Using the U.S. Naval Observatory web site, find Hc and Zn for each star. Go to http://aa.usno.navy.mil/data/docs/celnavtable.php to get this information. You’ll need to enter the date and time (17 July 2018, 23:10:25 UT) and the assumed position (32° 23.5' N, 55° 44.3' W).
Enter the computed altitude (Hc) and azimuth (Zn) for each star:
Altair Hc Zn
Spica Hc Zn
Dubhe Hc Zn
Altair Hc 21° 19.8' Zn 92.9°
Spica Hc 39° 45.2' Zn 214.1°
Dubhe Hc 41° 33.9' Zn 326.1°
Next, find the intercept for the line of position of each star based on difference between Ho and Hc. Enter your answers in the boxes below.
For each star, enter the distance and direction to intercept:
Altair 3.5 minutes toward
Spica 11.2 minutes toward
Dubhe 5.1 minutes away
If you did not get these values, you may wish to recheck your work and make sure you understand each step before proceeding. You can compare your completed strip form with the filled-in version (available as pdf).
The differences, and Ho-Mo-To, are used to plot the three lines of position. Print the pdf of the plotting form to work on drawing the corresponding lines of position. When you have finished, continue to the next page to view Chief Sheedy correctly plotting the three-star evening fix.