From: Bob Goethe
Sent: November 10, 2017 6:36 AM
To: Bill and Carly
Subject: NASA: Bowditch, Budlong, and Compass Bearings
Good morning, friends.
I made the singularly bad choice last night of a) having a late supper, and b) going to bed early. To be Bob Goethe and to do both these things in the same evening is to wake up at 4 AM the following morning with indigestion.
As is my wont, I checked my cell for email, and found yours, Bill. You got me thinking, and now here I am, totally awake. Maybe I can pull my thoughts together, settle my mind back into sleep mode, and get an hour or two of dozing on the couch before it is time to get up.
This week, I have begun curriculum development in earnest...creating hypothetical sights of the sun for January 2 from Edmonton. I have become acutely aware of how tiny the numbers are in columns that one needs to read.
I am completely committed to you both succeeding in celestial navigation. In your case, Bill, part of what this means is that I want you to tell me quickly if you find it hard to get the numbers out of the Almanac/Pub. 249. If you can’t “see” them, then I think I want to cut to the chase and involve you in getting those numbers from your computer rather than from the books.
You know me, I like doing navigation with “no batteries required”. But my commitment to you as a person/student/friend outweighs my navigational preferences. Succeeding is the big thing.
This goes for you too, Carly. If there is some aspect of the celestial task that seems insurmountable, talk to me quickly. Now, some of this is simply that celestial nav, for 100% of the people that learn it, has a steep initial learning curve. That we must all simply power through. But if there is something beyond that which hinders you, I will see if I can modify our approach such that you can succeed.
Compass Bearings and the Night Sky
Part of the fun/challenge in this class for me is that we have three different locations for taking sights. So it will be my job as instructor to take into account the amount of compass variation in your location, and also your topography. Bill, your view of the night sky is to the southeast. The bulk of Vanc Island will keep you from ever seeing a sunset over the ocean.
Carly, you are going to be in great shape for seeing the sky from south through to a bit north of west. But you will never see the dawn sun rise above the ocean the way Bill will.
I live just south of the West Edmonton Mall, maybe 2 miles. I can’t see the Mall, but my view of the northern sky is completely washed out from the parking lot lights. But I get terrific views of the sky from east-northeast through west-northwest. One consequence of this is that I am strong at star-identification of stars that appear to the south of me. Not so much stars in the north.
But to come back to the main point, once you each give me your preferred location for taking sextant sights, I will be using astronomical data plus my imagination to “see” what you are seeing in the sky at any given time of the day. And I will be using that knowledge to develop curriculum that will be localized for each of you.
For the last week or two, I have been following the weather for both Ucluelet and Crofton. If we get clear skies in January/February, you will do most of your learning from actual sextant observations you take. But if you are clouded in, you will learn CNav all the same...it just won’t be quite as much fun. I am preparing a full cloudy-winter curriculum that will give you all of the pencil and paper experience you need to learn CNav with only sporadic views of the sky.
I will have cloudy-day curriculum exercises for Edmonton, Crofton, and Ucluelet. So we will each get to work with all three locations.
Oh Hey! I just figured a good place to hang a tennis ball in my office so I can take sights of a “sun” indoors even when the real sun is obscured. I will definitely teach you both to do the same thing. We are all three going to use our sextants, clear sky or not!!
I am already set up to see your general view of the night sky, from www.Heavens-Above.com. You can create an account for yourself, and then create favorite locations. From this, you can ultimately get the true bearing and altitude of any given star/planet. Then, once I work out your local compass variation, I can come up with a compass bearing for using to locate a given star/planet. Bill, the website you list for variation is the one I always use. I also have an app on my phone that is quick and easy to use.
And I can do all of this prep now for evenings in January/February.
As for the sun and moon, I have a free app for Android loaded called “LunaSolCal” that gives me the observed altitude and bearing (also called azimuth) of the sun/moon at any given time, from any given location.
Once I know where you plan to take your sights from, Carly, I can determine to the minute just when the sun will become viewable for you. And for you, Bill, I can determine just when your “horizon” between you and Saltspring Island will become unusable as the sun continues its movement toward noon.
And also for you, Bill, if you are taking your sights from anywhere near the ferry terminal, I will work out – or better yet, have YOU work out – your short horizon measurements for celestial objects with bearings between X° and Y°.
Once you work out that, then for some exercises we do, Carly and I will use short horizon measurements as from your location. Living on the ACTUAL west coast, Carly gets an unobstructed view of the ocean horizon to the west. But being able to do short horizon shots will be a useful skill to add to her celestial toolkit.
This is terrific what you have done, Bill...getting these inexpensive volumes. Thank you!!
Why don’t you do this: skim both Budlong (1st edition vs. 2nd edition) and Bowditch (Vol. 1: 1962 vs. 1975) to see if there are obvious differences. I expect the 1962 edition of Bowditch will be a terrific resource for Carly. The big break-point in navigation-book history was 1992 when GPS became operational. It was at that point that sextant instruction became a somewhat esoteric add-on rather than a matter of life-and-death.
Volume 2 (1975) is a book of tables of various sorts. It will pair up nicely with almost any edition of Bowditch vol. 1.
Some things may not have changed at all. I have looked in detail at the 2017 edition of Bowditch and compared it to the 1977 edition of Bowditch. The chapter on Navigational Astronomy is word-for-word identical. Even the drawings are the same...except in the 1977 published edition, those drawings are of top quality. In the 2017 edition, they use the exact same drawings, but look like they scanned them at 125 dpi or something like that – like a fax scanner – rather than creating their own drawings afresh. So it is irritating to use the available-by-PDF-download-only 2017 edition if you have a 1977 at hand. The regular printed volume is more satisfying to read.
Here are some of my responses to the 2017 edition of Bowditch:
Budlong: I expect the first edition will be just fine for Carly to use. Any differences we can cover in our instruction.
Bowditch: Unless you are a navigation junkie like me, you are NEVER going to read this from cover-to-cover. Rather you are going to use it like an encyclopedia...just looking up a certain section when you need it.
Bowditch chapter 21, Comparison of Various Methods of Sight Reduction, is completely missing in 21st century editions...and I think it is among the more interesting chapters in the whole book. It reviews a gazillion methods of sight reduction that have been used over the last century or two. This is not a thing I read in detail, but skimming it was interesting.
P. 610, you learn that one of the CNav methods used by the Japanese Navy in WW2 was an actual, 27 pound spherical model of the earth. They worked their fixes manually, without mathematical calculation, by drawing circles-of-position on the surface of the sphere. Allegedly, they could get fixes accurate to within 1 nm.
Bowditch is completely on side with Budlong in his approach...which is the approach I am going to teach you both. The last sentence of 1977, vol. 1, page 559, section 2103 is “The modern navigator thinks primarily in terms of lines of position, rather than of (separate) latitude and longitude observations.”
And on page 566, “The principal advantage of (the method we will be learning) is that it provides a universal solution that is equally reliable in all latitudes, with all values of declination, and with all values of meridian angle.”
Carly, you will have noticed that Frank and others at NavList speak very positively about noon sights to determine latitude and dawn sights (a.k.a. time sights) to determine longitude. This is a method that was used in 1880, but Bowditch (1977) and I both think it is a waste of time to learn these methods – each of which requires its own separate type of worksheet. These mid-20th c. editions of Bowditch were written at a time when the Navy, merchant ships, and yachts all used sextants each and every day while at sea. This is also true of Budlong (2nd ed: 1978). I think more recently written books tend to follow intellectual rabbit trails a bit more readily (though it can be those rabbit trails that keep CNav interesting for you once you have mastered the basic skillset).
The Use of the Noon Sight
When we get to week 4 or 5 of our course, I will indeed teach you to do both noon sights of the sun, and Polaris/North Star sights at dawn/dusk. If you have a catastrophic failure of onboard electronics, including your electronic watch, and you have let your mechanical watch run down, noon sights and Polaris sights will be sufficient to get you home even without a timepiece. But this is not where we are going to start our instruction.
Preparing for the Unexpected
Another thing I will be teaching you is the proper way to make a Faraday cage to protect at least one digital watch, and also one handheld GPS, while at sea. So even if an electromagnetic pulse from a lightning strike fries every microchip on board, you will still be navigating just fine.
You will often read web pages about putting a GPS unit in a baggie and wrapping it in aluminum foil. I have consulted with a PhD electrical engineer (who wrote his dissertation on WiFi radio signal propagation) and this is the WRONG way to protect your electronics. I will tell you the right way.
Well, it is 6:20 now. I think I can go back to bed for a little bit, and be ready to get up and enjoy the day. Hope you both have a good weekend.
"As I sail, I praise
God, and care not."
Luke Foxe, Arctic Explorer, 1634
I desire no more delight
Than to be under sail and gone tonight.
Gratiano, in Act 2, Scene 6, The Merchant of Venice
By William Shakespeare, 1596
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Good evening Carly and Bob,
Thanks Bob for the note. Of the gear you mention, I have "the whole enchilada" as it is put. It turns out, and this is for Carly's sake perhaps, that now that I know what to look for, I keep stumbling upon the publications in used book stores. Hence today, whilst at the Nanaimo Literacy Centre, I picked up a 1962 Edition of American Practical Navigator Volume 1 and the 1975 edition of Volume 2 and had also picked up a first edition of Sky and Sextant by Budlong a couple of weeks ago. All books were at 50% off for members this week, so the Bowditch volumes came in at a whopping total of $15 - and I thought I got a great deal when I bought mine in Sidney last month! The Sky and Sextant was $4. So, Carly, if you don't have those publications - and if they are close enough to the right editions for Bob, we can figure out how to get them to you, if you would like.
Master Bob, I have a question of you regarding the use of a compass to locate stars, in particular using magnetic North as a reference bearing. If you are looking to the sky and find a star at 96 degrees magnetic in Edmonton, your compass will point about 14 degrees and 19 minutes West of true North whereas for Carly, her compass declination is more like 16 degrees 33 minutes and for me here in Crofton it is 16 degrees 16 minutes. That puts the star about 2 degrees out, does it not? It will also be interesting to consider where the star is at any given "moment", with the three of us in rather different places. http://geomag.nrcan.gc.ca/mag_fld/magdec-en.php
The simple map included with this note is my feeble attempt at trying to recollect how to create a GIS map. I am one of the has beens, I am afraid. I wanted to show the declination data in a conical projection so that True North was a point, but found that the labels didn't want to cooperate unless I used the "GPS" projection known as WGS84.
You might recall Bob mentioning in an earlier note my dyscalculia. When I bandy about numbers like I know what I am talking about, it is only to offset my fear.
Hey, I have to hit the sack.
Blessings on both of you.
PS Bob, your note didn't include a watch- was that part of the test?
You cannot create experience. You must undergo it.