Last updated: 6 February 2009

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Subject:	Daytime Polar Alignment - another method
Sent:	Sunday, February 1, 2009 04:34:19
From:	Niall J. Saunders (niall@njs101.com)
Hi Mike,

And good to hear that you are making progress towards getting the
observatory up and running out at your Oracle site.

I just thought I would mention an 'alternative' method of creating a
true N-S line. One that still requires the Sun, but which does NOT
require any knowledge of your Location, or of the time of day.

You still need to cast a shadow - but this time you do NOT need a plumb
line - just anything that is vaguely vertical, and which has an
identifiable mark on it's cast shadow. Usually a stick or pole is
sufficient, standing upright on the ground - and in a way such that you
can accurately place a mark on the ground to identify the 'top' of the

Now, the only 'time' you need is 'time' itself - just place marks
denoting the 'top' of the shadow as the day passes. Do this as often as
you want (or, more usually, as often as you remember !!). By the end of
the day you should have a series of dots that should be in a straight

And the nice bit is that this straight line will be perfectly East -
West, with the Eastern end represented by the LAST mark that you placed
(because the Sun sets in the West, AWAY from the last mark placed).

Now, all you need is a long length of string - three times longer than
the line of dots that you have created (or three times longer than any
line that you have projected 'beyond' the original ends of the line)

Tie the string to form a single loop. With an assistant (or by other
means) hold the loop at one point, and find the other point that allows
you to have split the loop into two (joined), equal lengths. Now you
need to fold the two lengths at the 'one-third' and 'two-third' points,
such that each person is holding the original point (when you 'divided
by two') and one of the new 'one-third' points. Between you should be
six equal lengths of string. And then, finally, fold the six lengths
once more, to give you TWELVE EQUAL LENGTHS between you.

If you are still with the program at this point (!!!) and haven't
knotted the whole setup beyond recovery, you have one final 'clever' bit
to achieve. And a THIRD person can help here - if available.

First, one person has to hold the string at TWO points, such that they
are holding THREE of the 'divided-by-twelve' lengths between each hand.
They don't actually have to HOLD the string at these points - you could
just use a marker pen, or a piece of tape, or tie on another piece of
string at these points. Then, from one of the two points already
identified, you need to count off another FOUR of the 1/12th length -
and hold, or mark, that point as well. All things being equal, you
should have EXACTLY five remaining 1/12 lengths from this third marked
point, back to the other of the first marked points.

In other words, you now have a loop of string divided into lengths with
a 3 : 4 : 5 ratio. And that ratio is exactly the ratio of a PERFECTLY
RIGHT-ANGLED TRIANGLE. If three people each hold one of the points, and
then walk apart until all three 'string-sides' are taught, the angle
between the '3' and '4' side will be exactly 90 degrees.

And, I am sure that you are ahead of me now, if you line up the '3' (or
'4') side along your previously marked 'E-W' base-line, then the point
of the loop at the far end of the '4'-'5' sides can now be marked. If
you have the space you can repeat this on the 'other side' of your E-W
base-line, and you can mark the point where the ninety-degree angle was
sitting, ON the E-W base-line. Join these three new points, and you have
a perfect N-S base-line.

Further, if you arrange for the N-S line to run UNDER where you hope to
place a pier or tripod, then you have a N-S base-line aligned with where
your scope will be positioned (although, sometimes, it is more useful to
have a base-line OFFSET to one side of the actual position as well -
from which you can re-create a new N-S line as needed).

If you do this a couple of times, and demonstrate repeatable results, it
can be worthwhile marking the ends of both the E-W and N-S base-lines
permanently. How this is achieved is left to your imagination, given the
plot of land you are working with.

I last used this process, for real, on a semi-submersible drilling rig
off the coast of Nigeria, W. Africa. The rig is all metal - so forget
about a compass. Drilling secrecy meant that the exact location of the
rig could NOT be made available to us. I had to establish the location
of a 24" diameter steel pipe, 10 feet long - such that a 20-foot
diameter, satellite communications link, fibreglass dome could be
attached on top. And the dome could not end up 'hitting' any part of the
superstructure, and the 12-foot parabolic dish inside the dome had to
have a clear line-of-sight to one of the geostationary satellites

I used the position of the SHORTEST shadow, and my wristwatch, to
establish the solar transit time, which at least then allowed me to
figure out, roughly, our longitude. The length of the 'shortest' shadow
suggested that the Sun was almost directly over head - suggesting that
we were so close to the Equator as made no real difference. Given this
'rough' calculation for our lat-Long, I could then calculate the
direction the dish needed to point in order to target the geo-stationary
satellite. Which only left finding a suitable 'bribe' to get the welder
to start working.

Job done. Just a shame that, at the end of the operation, the reason for
all the 'secrecy' became evident. My Nigerian client had, in fact, asked
us to erect the comms link on ENTIRELY THE WRONG VESSEL !!!! We should
have been working on the neighbouring FPSO not the Semi-Sub. Still, I
got paid anyway, so I wasn't caring (and, it was the income of that job
that allowed me to buy my first ETX-105, all those years ago!!)

Niall Saunders
Clinterty Observatories
Aberdeen, SCOTLAND

Start of today's update

06 Feb 09

From: Steve
Sent: 04 February 2009 15:31
Subject: Daytime Polar Alignment

I just read your post on Weasner's site. To be honest, my head started
swimming when I got to the folding of the string. Here is a thought.

You are right that the line formed by the shadow cast throughout the day
will be in a true East/West direction. After connecting the dots with a
straight line, why can't a person then simply draw an intersecting line
exactly 90 degrees through it. A T square could be used for this.
Wouldn't that then give you a true North/South line?



From:	Niall J. Saunders (niall@njs101.com)
Hi Steve,

Yes - but I enjoyed adding it to the plan anyway.

After all, not everyone will have a 'big' and 'accurate' T-square. However,
if you know how to make a 3:4:5 triangle, which will provide the 90 degree
angle you are after, then you can achieve the N-S projection that you need.

I just suggested ONE of the ways to get such a triangle, one that is
reasonably accurate, and very easy to make. And one that is scalable to any
size that might be needed.

You should challenge some of your buddies - it's a great 'party game', "Make
a perfect 90-degree angle from a single piece of rope". I regularly use it
at 'ice-breakers' and 'company motivation exercises'. I have even used it in
the middle of Antarctica, when Jim Lovell (Apollo 8 and 13) and Dr. Owen
Garriot (Skylab-3 and STS-9 Columbia) were down visiting. It's great fun,
and keeps the 'grey matter' active.

But, don't just 'read' the article, go out and 'do' the article - and tell
us whether it worked, or whether I left out some crucial step !!


Subject:	re:  Daytime Polar Alignment - another method
Sent:	Thursday, February 5, 2009 21:12:57
From:	rucc@roadrunner.com (rucc@roadrunner.com)
First time sending a message, use you site often.

The method that Niall Saunders sent was interesting, but complicated at
the end.  Actually, once you get the East-West line, geometry comes into
play.  When you bisect the line, you will end up with a perpendicular
(North-South) line.  To do this, a string that is longer than half the
distance of the East-West line is needed.  Pin the string at one end and
draw a large arc that cuts across the East-West line.  Then pin the
string to the other end and draw another arc.  The two arc will
intersect in to points.  Connecting these two points give you an
North-South Line.


Ron Ugolick


Great Stuff Ron,

That's what I like to see - other people remembering elementary-grade
geometry, and suddenly realising how it can be put into practice 'for

I know I was being over-complicated - but I was enjoying describing how
to 'answer' one of the 'team-building' challenges that I use.

What I really hope is that even ONE person actually goes outside and
'draws a line in the sand'. And that that person realises that their
accomplishment defines East and West just as accurately as the
'ancients' did, back in the time of the Pyramids !!

Sometimes science and technology hasn't really moved that fast at all

I sorted out my N-S reference AFTER I had built my roll-off roof
observatories. I strung a taught line from the South wall to the North
wall (with the roof open, obviously), and then dropped two plumb-lines
from that horizontal, so that they were just off touching the floor. I
then lay down, head to the south, and sighted all three lines against
Polaris in the sky overhead. I had someone adjust the horizontal line -
at both ends such that the two verticals, and the horizontal - when all
aligned, also covered Polaris as well. I marked the two plumb lines on
the floor, translated this N-S line sideways to hit dead centre of my
pier foundation (already poured and set, ready for the attachment of a

Then I shifted the horizontal line and one of the plumb-lines, such that
the whole process could be repeated with the furthest plumb-line
actually hitting the pier centre 'dead on'. I finally marked the two
walls with 'N' and 'S' marks, and threw a pair of 90' projections to the
other two walls to give me 'E' and 'W' as well. The marks are still
there, five years later, but have now been joined by a full set of
direction indicators, right around the open roof space - very handy when
working with a planisphere, or trying to use a pair of binoculars to
find a passing comet, etc.

Have fun.
(and if you want another challenge, try this:- "It is the 21st December
1999. You have just landed in a small plane at the South Geographic
Pole. It is your intention to walk to a distant Antarctic base camp -
say the one I was stationed at, Patriot Hills at 80'W, 80'S). You have a
GPS receiver and a magnetic compass (which you purchased, say, in New
York, from the sport's department at a well-known supermarket). It is
9pm, but you want to be on your way whilst the weather is good. What
direction do you start walking in, and how do you determine that
direction, and how do you maintain that direction?" (Knowing that you
cannot afford to set off in the WRONG direction, because you have
limited supplies, and anyway everyone on the SGP base would be laughing
at you!! And, NO, you CAN'T ask them for directions, after all YOU are
supposed to be the polar explorer !!) [This scenario ACTUALLY HAPPENED -
to one of the leading polar expeditioners, and I had to spend ages over
a satellite phone link trying to explain HOW to navigate in these
circumstances !]

Niall Saunders
Clinterty Observatories
Aberdeen, SCOTLAND

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