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 (firstname.lastname@example.org) 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 shadow. 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 line. 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 overhead. 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!!) Cheers, Niall Saunders Clinterty Observatories Aberdeen, SCOTLAND
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? Steve
From: Niall J. Saunders (email@example.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 !! Cheers, Niall
Subject: re: Daytime Polar Alignment - another method Sent: Thursday, February 5, 2009 21:12:57 From: firstname.lastname@example.org (email@example.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. Regards, 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 real'. 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 pier). 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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