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  1. #61
    Join Date
    Apr 2005
    Location
    Bromley,Kent
    Posts
    2,819

    Default Re: Cunliffe's star gazing book

    [QUOTE=Kukri;6978987]I learned using MR Rantzen’s “Little Ship Astronavigation”. It is certainly old fashioned now. Those of us who learned from this book can be identified as we tote round copies of the NP 401 / HO 229 tables.
    QUOTE

    I, too, taught myself from this book and I still have it and the book and tables to which you refer. It took weeks and such a hard laborious slog. I worked through every example and on one of them I simply couldn’t get the solution and so I wrote to the author asking for help. The response was quick and helpful- it turned out that in proof reading an error wasn’t spotted apologies were offered and I was told it would be corrected if a further print run happened

    I really couldn’t see me remembering all the reductions etc, let alone being able to juggle all the paperwork at sea, so in the end I got a copy of Mary Blewitt’s book.

    What a difference that made, I liked it much better

  2. #62
    Join Date
    Jun 2007
    Location
    Home: North West, Boat: The Clyde
    Posts
    3,771

    Default Re: Cunliffe's star gazing book

    Quote Originally Posted by lw395 View Post
    Learning to pass YM-Ocean seemed to me to be largely about memorising funny names for angles.
    Then learning a handle turning process to generate a position line.


    I'm more of a 'understand the big principle and work out the details for yourself' kind of learner.
    Those 2 statements seem incongruous.

    I’m reminded that “there are no bad students, only bad instructors”. Perhaps you’re the exception

  3. #63
    Join Date
    Feb 2007
    Location
    West London
    Posts
    3,560

    Default Re: Cunliffe's star gazing book

    Quote Originally Posted by lw395 View Post
    Learning to pass YM-Ocean seemed to me to be largely about memorising funny names for angles.
    Then learning a handle turning process to generate a position line.
    Breathe in Look something up
    Breathe out add something to it

    IT's possible to pass the course wihout having the faintest idea what any of it means.
    The Cunliffe book is, as I recall good for learning to pass the course and will allow you to turn the handle and produce an answer.
    I think there's very little luggage in, everything in there is on the syllabus.

    Books are much cheaper than courses, so I went for reading/buying a few different books to get different insights.

    Unfortunately, names of little angles and corrections is exactly the kind of thing that I forget if I haven't used it for 6 months, and I did the course ten years ago.
    I'm more of a 'understand the big principle and work out the details for yourself' kind of learner.
    "Its possible to pass the course without having the faintest idea what any of it means"

    Of course, but isn't that often the same as many things these days.
    For example, I use a tablet to post on here, how it works I only have a vague idea, I just use it.
    Mine & most cars, can for many, be a complete mystery certainly under that lid thinghy, so what, they get us from here to there. As with astro, all of these things get you the result you were looking for.

  4. #64
    Join Date
    Nov 2009
    Location
    Somewhere in the Atacama
    Posts
    415

    Default Re: Cunliffe's star gazing book

    What hasn't been mentioned in this 'noon debate' is the relationship between observer and sun.

    Simply noting the time when the altitude starts decreasing will be 'accurate enough' when Lat~Dec is small i.e. when you are in the tropics..... not so much when Lat~Dec is large.... e.g. in the northern North Atlantic in winter.

    Good enough in the middle of the ocean... maybe not so good when making landfall in the Tuamotus.

    'Equal Altitudes' works well anywhere and where it comes in very handy is when L~D is very small ... 'frinstance if you are within 2º or 3º of the equator at the equinox it will be very hard to get a decent mer alt.

    The beauty of Equal Altitudes in that situation is that you can also reduce one or both of your altitudes to get a good longitude at ( pretty much ) the same time as you get a latitude.

    If you take both altitudes within - say - 30 minutes of noon the fact that your yacht is moving will be neither here nor there... and can be allowed for.
    Last edited by Frank Holden; 26-11-19 at 22:23.

  5. #65
    Join Date
    Mar 2007
    Location
    Atlantic
    Posts
    21,851

    Default Re: Cunliffe's star gazing book

    One of the past paper exam questions was about being on the equator at the Equinox. Yeah, yeah, I thought, as if.

    Then a couple of years ago I had the greatest of good luck to be able to take a sight some place near the Galápagos Islands almost right on our horizontal great circle at the Equinox. Hey presto......impossible. Kinda like those Falkland Island penguins that watch the jets flying over and fall over backwards.

  6. #66
    Join Date
    Dec 2007
    Location
    Boat: Falmouth. Work: Cambridge
    Posts
    1,402

    Default Re: Cunliffe's star gazing book

    Quote Originally Posted by capnsensible View Post
    One of the past paper exam questions was about being on the equator at the Equinox. Yeah, yeah, I thought, as if.

    Then a couple of years ago I had the greatest of good luck to be able to take a sight some place near the Galápagos Islands almost right on our horizontal great circle at the Equinox. Hey presto......impossible. Kinda like those Falkland Island penguins that watch the jets flying over and fall over backwards.
    +1!

    I did a sight - for the purpose of falling over backwards I think - with observed altitude = 89 degrees 59'. No damn use at all for nav, but fun. I also have done a midnight sun sight - it had to be done - when in the high arctic. But when I've actually wanted to know where I am it's always been (a) raining, and (b) nearing the English coast in a rising sea.

  7. #67
    Join Date
    Jun 2013
    Location
    Hopefully somewhere warm
    Posts
    9,826

    Default Re: Cunliffe's star gazing book

    Quote Originally Posted by capnsensible View Post
    Conversion of arc to time? Simple. Longtitude.
    Just playing around with some python, Google came up with this, time to degrees >

    Time & Arc Conversion

    1 day = 360° = 24 hours


    15° = 1 hour


    1° = 4 minutes


    15' = 1 minute


    1' = 4 seconds


    To convert time to arc:


    1. Multiply the hours by 15 to obtain degrees of arc.


    2. Divide the minutes of time by four to obtain
    degrees.


    3. Multiply the remainder of step 2 by 15 to obtain
    minutes of arc.


    4. Divide the seconds of time by four to obtain minutes
    of arc


    5. Multiply the remainder by 15 to obtain seconds of arc.


    6. Add the resulting degrees, minutes, and seconds.


    Example 1: Convert 14h21m39s to arc.


    Solution:


    (1) 14h ´ 15 = 210° 00' 00"


    (2) 21m ¸ 4 = 005° 00' 00" (remainder 1)


    (3) 1 ´ 15 = 000° 15' 00"


    (4) 39s ¸ 4 = 000° 09' 00" (remainder 3)


    (5) 3 ´ 15 = 000° 00' 45"


    (6) 14h21m39s = 215° 24' 45"
    And you can do that in your head!! Must have a big hat

    Python does it much quicker.

    >>> %Run inputTime.py
    Input time to convert:2,45,53
    Time input= 1900-01-01 02:45:53
    Decimal hours= 2.7647222222222223
    Decimal degrees= 41.47083333333333
    41Deg 28.25'

  8. #68
    Join Date
    Mar 2007
    Location
    Atlantic
    Posts
    21,851

    Default Re: Cunliffe's star gazing book

    I can see we found the problem. I've no idea what a python is apart from a big snake so that stuff is.....foreign.

    I guess those of us who didn't grow up with calculators find mental arithmetic easy. 15 into 60 is not much of a challenge though.

    I do use shock horror pieces of paper sometimes.......:

  9. #69
    Join Date
    Mar 2007
    Location
    Atlantic
    Posts
    21,851

    Default Re: Cunliffe's star gazing book

    Or just spend a few seconds looking at the arc to time page in the almanac.......

  10. #70
    Join Date
    Jun 2013
    Location
    Hopefully somewhere warm
    Posts
    9,826

    Default Re: Cunliffe's star gazing book

    Quote Originally Posted by capnsensible View Post
    Or just spend a few seconds looking at the arc to time page in the almanac.......
    Ah, not in your head then Add/subtract time is one thing, not too hard but easy to make mistakes - time to angle in your head - yeah right

    Python is a programming language, earns you money - by having something interesting to play with on the boat instead of going to the bar every night
    Playing with some code to graph sextant readings by inputting time/Hs.
    And cloudy this morning for a change!!!! Was hoping to head down the beach for a noon sight or several!

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