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Author
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Topic: Star Finder 2102-D (e.g. Star Finder Book p. 8, Fig. 2-4
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Donald
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posted May 16, 2006 06:38 AM
I found out, that I am not the only one to complain on the 2102-Ds design providing an appearance of the sky not as one would already expect from the natural relation between man and space - from the inside, but the outside of the celestial sphere. This is felt highly confusing because of the considerable lack of clearly illustrating how things really are. Similar applies to the mirrored image set of azimuth and declination templates for north and south, where a two colour solution would do better by far.
So two questions remain: 1. Were there and if so, which - advantages to make Gilbert T. Rude choose this design or was it only some sort of theory tradition astrolabe design and celestial globes provide sight from outside? 2. What other and more convenient solutions exist, or are there plans to issue a revised version of the starfinder? Even simple cardboard star disks out of the educative field and not thought for navigation purposes show the better and less misleading approach mentioned above.
Thank you
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Capt Steve Miller
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posted May 16, 2006 06:56 AM
This is the first time I have ever heard that there are complaints about how the Star Finder is set up. To me when navigating and using charts - that looking at the Star Finder and relating the Star positions to your DR position on the chart seems quite logical. I personally have never had a problem with using the Star Finder in this context. From an astronomers point of view you are not trying to relate the position of stars to a position on a chart you are trying to find a given star in the sky among thousands of stars - for that operation the Star Finder is not the tool to use - there are planispheres for that purpose. This brings up the fact that the stars on the Star Finder would be the only ones visible during twilight and can be found without much difficulty. The Star Finder is a tool for finding which stars will be available for sights and is not generally used in 'real time' under the stars.
From: Starpath
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David Burch
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posted May 16, 2006 11:13 AM
Yes, you are right. Every student we have is sad to learn that the device presents the stars upside down and backwards. But the device is not meant to be a "picture of the sky." It is meant to give you actual bearings and heights of the bodies and to do so using templates that the reader can install to customize to their latitude. It is this last requirement that forces this awkward presentation.
Once one accepts what it does and how it does it, however, the device is completely functional and has been used that way since the early 1940s.... though no longer produced by the US Government, the version that is now made and sold is identical to the original device.
So the answer to your question 1 is, the requirement for latitude templates and actual degrees of bearing and height force the design. It is not a tradition, and we would all prefer something different.
Question 2 brings up more points. First, no, there are no plans from any agency or company we know of to remake a star finder in any other design. In fact, our bigger challenge is to encourage those already printing them to keep on doing so... although there is some encouragement there. Weems and Plath have just reduced their price on the device recently as they compete with another two companies that were also reproducing the original Pub 2102-D design. At one point these were selling as high as $39 each and they are now down to $34 each. There are several versions of the same device now being sold and the ones from Weems and Plath are at present the lowest cost and highest overall quality.
As for alternatives. There are many free options online. Over head in the center, East to the right, north to the top. with range rings to represent altitude... zero on the circumference, 90° is in the center. Then just push another button and it will start finding for you the best triads of star-planet combinations for a fix.
You can find an online version of this type of sky presentation at the Tecepe link in our inet connections section. The cel nav plugin for openCPN has this function as well.
Another option for getting computations of the full sky in any conditions is the first link in our cel nav inet connections to the AA dept of the USNO. that will compute Hc and Zn for all nav bodies for any lat/lon time/date.
But when it comes to a portable, non-electronic device to find actual Hc and Zn for cel bodies, there is no substitute for the 2102D star finder that we know of. the maps and wheels and sight tubes that show a nice sort of Mercator projection of the sky give reasonably approximate relative bearings and heights at latitude 42° North (their usual design value), but much away from that they are very misleading, and could never be used to choose the best stars for a fix, and of course they do not include the planets.
From: Starpath, Seattle, WA
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Donald
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posted May 29, 2006 02:24 AM
Thank you for the detailed informations. Hoping you do not mind me obstinately continuing to spin this thread another turn round by one more question: Am I correct understanding, that the main purpose of the starfinder - to provide Zn and Ho of a heavenly body in relation to LHA aries - only can be satisfactorily fulfilled by the present "Upside-down/backwards"-design and not by a different construction, showing the sky how it really appears?
Thank you again
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David Burch
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posted May 29, 2006 11:36 AM
I will double check some of this, but for now i think that is correct. I say this because i have seen about 4 different starfinder designs and they all to my recollection had this same basic layout. I need to check on one of them from Czechoslovakia referenced in an early Bowditch, i think 1977 edition--as i recall it was described as the author's favorite among existing models.
the problem in a sense is hiding in the phrase "how the sky really looks." If you note from the nautical almanac's presentation of star maps, they choose polar azimuthal projections for the regions looking toward the poles of the sky, but choose a mercator projection for looking at stars along the celestial equator.
Also if you play with some of the online or PC star map programs, you will see that the projections get quite distorted in some configurations. So it is not clear that one can come up with a solution that is worldwide and full view of the sky that can be realistic looking.
perhaps by playing with one of those programs (we have links to the free downloads) printing out several screens one might be able to come up with something that works for a limited latitude range, but i am afraid that looking right and providing correct numerical values may not be broadly consistent.
Note that the computer programs can tell us the right Hc and Zn with a mouse over the object, without it having to be on any simple curve or grid that is universal to other settings.
The other factor is how big do you allow the device to be. My guess is if we are allowed to have a filing cabinet full of templates and base plates to choose from, we could maybe do it from a more realistic view of the sky.
From: Starpath, Seattle, WA
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Donald
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posted May 31, 2006 05:16 AM
The problem did not let me out yet. Continuing to pursue it further, I found out, that it should be possible to get, what I hope we and not only me, are looking for, without too much difficulties or work.
A. To check my proposal:
1. Copy both sides of the white disk on translucent template material. The small pole in the disks middle prevents the 100 % plain contact with the glass of the copy machine, but the result is good enough to find out, whether the assumptions satisfactorily work or not.
2. Reverse resulting templates and recopy them onto normal white cardboard to so get a mirrored view of what the sides of the white disk originally look like.
3. For north latitudes now use the mirrored north side of white disk (И) and the south latitude sides of the original blue templates together with the backwards azimuth-scales of the latter and vice versa.
4. The example on page 8 of the handbook brings exactly the same results, except for Vega, which differs slightly, but I think that the device precision anyway decreases rapidly, as heights approach 90°.
B. For manufacturing:
1. Mirror both sides of the white disk and remirror scale for LHA Ү
2. Rename blue templates by interchanging S and N
3. Mirror azimuth scales of blue templates
C.
In case my approach, to develop the character of the starfinder, is supported as being desirable, the above should give an easy to follow procedure for combining the universal applicability and the map projection type advantages of the 2102-D with a natural appearance of the sky as seen by the observer, instead of the present way of portraying it upside down with the azimuths backwards.
Production is valued as being not more expensive in relation to present design and, to my opinion, easily can be adjusted by applying the necessary modifications to the printing plates or master copies.
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