Cunliffe's star gazing book

Kukri said:
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.
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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
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lw395 said:
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.
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Those 2 statements seem incongruous.

I’m reminded that “there are no bad students, only bad instructors”. Perhaps you’re the exception :)
 
lw395 said:
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.
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"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.
 
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.
 
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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.
 
capnsensible said:
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.
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+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.
 
capnsensible said:
Conversion of arc to time? Simple. Longtitude.
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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"
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And you can do that in your head!! Must have a big hat :):)

Python does it much quicker. :cool:

>>> %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'
 
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.......::D
 
capnsensible said:
Or just spend a few seconds looking at the arc to time page in the almanac.......
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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!
 
Dunno why you think people can't do simple sums in their heads?

Anyway, hope the sun comes out for you, often at its height it can poke through the clouds enough, lightly filtered, for a sight. Where are you, around 8 west? 1200 plus 15 for eot equals 1215. 8 X 4 is 32 so local noon at 8w is 1247. Don't be late! That Portugal time think that's where you are. :encouragement:
 
capnsensible said:
Dunno why you think people can't do simple sums in their heads?

Anyway, hope the sun comes out for you, often at its height it can poke through the clouds enough, lightly filtered, for a sight. Where are you, around 8 west? 1200 plus 15 for eot equals 1215. 8 X 4 is 32 so local noon at 8w is 1247. Don't be late! That Portugal time think that's where you are. :encouragement:
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You can convert 02:54:53 to 43Deg 43.25' in your head??????? Full marks if you can!

8W local noon is 12.19, you're late! You did Eqn of time wrong way! You'll get lost ;)

Eq of Time noon today - 00:12'30"; 12:00':00" - 12'.30 = 11:47:30. Solar noon at Greenwich.
8deg = 8/15 * 60 = 00:32:00
11:47:30 + 00:32:00 = 12:19:30

All UTC, that's what Portugal is.
 
capnsensible said:
See you are trying to make simple into complicated. I got eot from a graph. Plus 8x 4. It's not hard!
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Seems it's hard enough for you to get it wrong! ;)

It's not EqnOfT plus 8deg in time, other way round. Apparent time is mean time plus EoT so postive means apparent time is ahead of mean, local noon is earlier.

EOT is in the almanac daily pages, more accurate than the graph. Since accurate long from a Mer pass is what we're after, why not use the most accurate figure?

Rest is mental arithmetic, just written down to show the steps & less chance of making silly errors ;) .

All in Bowditch. https://thenauticalalmanac.com/2017... 3- Celestial Navigation/Chapter 16- Time.pdf
 
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capnsensible said:
Boogaloo. So now I've looked at the almanac mer pass http://www.nauticalalmanac.net/pdf/almanac2019.pdf 1147.

8x4 is still 32 so local at 1219. How is that hard? :rolleyes:
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Hard enough for you to get it wrong apparently ;)

Who said it was hard anyway? Accurately converting time to degrees long in your head is hard.

And local isn't 12.19, it's rounded up to the nearest minute, better for accuracy to use the EoT which is in seconds. And you were the one banging on about how accurate you could get long from a mer pass. Always things to learn ;)
 
Again I think you miss the order to complete a noon sight. It's starts with an EP. Then you can estimate time of local noon. Then you can take your sight accurately and a quick reduction gives you latitude and a consult with arc to time as I mentioned ages ago gives you longtitude.

It's a common mistake by learners to think they are gonna get the same accuracy as gps especially when anything lass than a whole minute on a plotting sheet is pointless.

Also not realising that their EP is the starting point. Which you are predicting, it's not an assured thing. The difference however between practical and theoretical navigation is easy to iron out though. Fr instance I would never have used a graph I've never seen before to get mer pass but gone straight to the almanac page. Mind you it did give to opportunities to demonstrate how easy the sums are.

How was your noon today? Give it another half hour and you could practice a sun sight and run it back for a noon position!
 
capnsensible said:
How was your noon today? Give it another half hour and you could practice a sun sight and run it back for a noon position!
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Cloud stopped play, but keen now while the super cheap hire car is available for the week (quid a day :cool: ) to go find the horizon.

So cards on the table then, what accuracy in Long do you claim for a Mer pass sight?

Seems over egged from what you've been saying the past few posts...

But willing to be proved wrong and it's fun :cool:
 
Yeah indeed. If one or two others read this thread and Mebbe take an interest then it's been worthwhile.

No doubt some of the salty old sea dogs on here that used Astro as a working tool will be able to nail sights down to a mile or two but for what I do I'm happy if I'm inside ten miles. Reckon that with a bit of practice you can get that from a noon sight.

It's heresay for some on here but turning off the gps for a week or two and really using that EP to predict where you think you are gonna be for a sight is probably what it's all about...known unknowns!
 
Used to do practise sights off the beach on Costa deal sol and in gib driving between two places. Time to reduce the first sight over a cuppa......the cafe on Europa Point was a good spot whilst waiting for noon.

How much is the excess on the rentacar for a quid? Sell it to a Romanian drug dealer and tell Avis it was nicked! ;)
 
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