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Sailing in the bay towards the Bay Bridge and San Francisco

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ASA 117
Basic Celestial Endorsement

This basic celestial navigation class teaches the theory and practice to determine latitude and longitude at sea using the noon sun and the star Polaris (a.k.a. the North Star) with just a small eleven-page booklet, a sextant, a watch and simple arithmetic. Experienced celestial navigators and beginners alike will enjoy this simple alternative to the intercept method-one that doesn’t depend on sight reduction tables and yields latitude and longitude directly without plotting. Naval History buffs will thrill to the romance and adventure of determining their latitude in the tradition of the Vikings and ancient Hawaiians. This course is a great introduction to the joys of navigating “celestially” without the rigors of ASA 107, and the skills learned make a nice backup in case you lose your GPS while on a voyage out of site of land.

Printed textbook included.

1 Eveneing and 1 full day

Member: $455

Non member: $545

What's Included

Find a date that works for you

Need a different date? Give us a call (510) 535-1954

Before the Course

Text used: Latitude & Longitude from the Noon Sun by John Karl

What to expect

Schedule and Details:

  • Meet at Afterguard Sailing Academy, 1285 Embarcadero (Oakland CA 94606)

  • This is four day or two weekend Course spent in the classroom. 

  • The written exam is at the end the of the class.

Additional info:

There are bathrooms at our facility and on the boats. Please make sure to check in with your teacher about how to use the 'head 'on the boat, before leaving the docks!

ASA 117 - Course Description

Able to apply celestial navigation theory and practices for safe navigation of a sailing vessel in offshore waters —

Find a date that works for you

Great course for an introduction into sailing in the bay!

This was the perfect way to become comfortable with sailing. By the end of the course I was confident in all the terminology and functions of the boat and understood how to make adjustments to the sail. I look forward to more time on the water with Afterguard!

Hannah R. (ASA 101 course July 2023) 

What's covered in the ASA 101?


1. Convert longitude into time.
2. Convert standard time and zone time to GMT and vice versa.
3. Calculate the zone time given longitude.
4. Calculate the chronometer (or watch) error given a previous error and the daily rate.
5. Apply corrections for index error, dip of the horizon, and total correction to convert sextant altitudes of the sun, stars, planets, and moon to true altitudes.
6. Calculate the time of meridian passage of the sun and calculate the boat’s latitude from the observed meridian altitude of the sun.
7. Determine the latitude at twilight by means of the Pole Star.
8. Solve the navigational triangle using a navigation table and show all appropriate work.
9. Plot celestial lines of position on a Mercator projection or on a universal plotting sheet.
10. Calculate the times (ship’s and GMT) of sunrise, sunset, and twilight.
11. Determine the approximate azimuths and altitudes of the navigational stars and planets at twilight.
12. Calculate and plot the lines of position obtained from observations of several celestial bodies at twilight to find the boat’s position.
13. Advance the LOP obtained from a sun sight to another LOP obtained from the sun at a later time and find the boat’s position using a running fix (sun-run-sun).
14. Calculate the true bearing of a low altitude celestial body to determine the error and deviation of the compass.


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