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Post by Ron Walker on Sept 6, 2022 12:08:37 GMT -7
Posted by: Tim Mitchell Jul 7 2007, 08:04 PM Hi there folks,
I am an amatuer astronomer from Melbourne, Australia. I am wanting to drill my own planetarium sphere, but I am having some trouble with finding a gore chart for the purpose. Do you have any ideas where I may be able to locate one? What do you use?
I am hoping that you aren't going to say that you all plot the stars by hand... that would be a bit much. ohmy.gif
The size is not too important, Larger would be better, as I can resize any image on my computer to fit the bill.
I looked over the forum and found a conspicuous absence of diagrams or directions to them. It would be nice for there to be plans of different styles of Planetariums on the forum, for those who want to build their own.
I hope you can help.
Also has anyone thought of using an optical fibre with a frosted glass ball on top (1 to 1.5 mm dia) as a pinpoint light source? I would think that it would work rather well for a small dome. A plastic optical fibre could always be melted on the end with a gas flame and rotated while melting, to make a ball on the end.
Also how about little filters of optical gel (plastic filters for spotlights) stuck over the pinholes to give the correct colour for some of the larger stars?
Clear skies and dark rooms, Tim.
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Post by Ron Walker on Sept 6, 2022 12:09:14 GMT -7
Posted by: Ken Miller Jul 7 2007, 08:40 PM Hi Tim
Welcome aboard!
I've been thinking the same thing about an optical fiber with a ball on the end, but I don't know how well it would work. Apparently a micro fisheye lens at the end of an optical fiber is the preferred technique. I want to play around with that concept, but I'm kind of dead in the water right now due to mental overload, burnout, or whatever you want to call it. I've got too many issues that are competing for the few brain cells that I have left. I'm kind of hoping that someone else will pick up the ball and come up with something that we can all use.
Regards, Ken
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Post by Ron Walker on Sept 6, 2022 12:09:38 GMT -7
Posted by: Tim Mitchell Jul 7 2007, 09:11 PM Hi Ken,
I just read the other thread about the fibre optics and it seems that that method would be best. I grabbed an old fibre that was laying around here and made a ball on the end, it seems that the light is concentrated at the end and not dispursed too much. I would say that the fisheye lens would be the only good way of going. The light rays have to go from air to glass and back again to refract the light and scatter it wide enough. It would take a half a ball to work properly and then you have a fish eye lens..... unsure.gif so I think I will go for the fisheye when I am ready.
Any thoughts on the star chart to lay over a sphere?
Regards, Tim.
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Post by Ron Walker on Sept 6, 2022 12:10:30 GMT -7
PPosted by: Ken Miller Jul 8 2007, 07:31 AM OK, if you really want me to activate my remaining brain cells this early in the morning, here goes. I have a book from Edmund Scientific called "The Edmund Scientific Mag 6 Star Atlas". It contains spherical charts of the sky, and it seems like you could manually transfer that to the spherical surface to make a drilling pattern. My other thought is using a Celestial Globe. I have a small one that I use as a reference to locate patterns on my star projectors. There should be larger ones available to make the process more accurate.
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Post by Ron Walker on Sept 6, 2022 12:11:03 GMT -7
Posted by: Tim Mitchell Jul 8 2007, 08:19 AM QUOTE(Ken Miller @ Jul 9 2007, 12:31 AM) * OK, if you really want me to activate my remaining brain cells this early in the morning, here goes. I have a book from Edmund Scientific called "The Edmund Scientific Mag 6 Star Atlas". It contains spherical charts of the sky, and it seems like you could manually transfer that to the spherical surface to make a drilling pattern. My other thought is using a Celestial Globe. I have a small one that I use as a reference to locate patterns on my star projectors. There should be larger ones available to make the process more accurate.
Hey Ken, Are you talking about a spherical projection map like appears in the cambridge star atlas, as opposed to the Mercator projection? I am looking for the segmented map as in tapered segments of longditude from north pole to south pole on a world map that makes up a globe. Most celestial globes are made of cardboard and it would not be too easy to transfer the segments to a globe, hence trying to find a chart.
It may be a good idea to have a chart in printable resolution available on the forum for those who want to try their hand at making their own projector.
Sorry for getting you to activate those cells.... I guess it had to happen sooner or later. smile.gif
Kind Regards, Tim.
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Post by Ron Walker on Sept 6, 2022 12:11:40 GMT -7
Posted by: Ken Miller Jul 8 2007, 08:50 AM Tim
Yes, the charts are spherical rather than the distorted Mercator projections, so it should be the same as what's in the Cambridge Star Atlas. I suppose that there is some distortion getting a flat chart onto a spherical surface, but it shouldn't be too much trouble. If you drew the RA and Dec lines onto the sphere, and then eyeballed the stars into their respective sectors for a drilling pattern, you should come out pretty close. Maybe someone else can jump in here with some better suggestions.
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Post by Ron Walker on Sept 6, 2022 12:14:07 GMT -7
Posted by: Ron Walker Jul 8 2007, 11:54 AM Hi Tim and welcome to our little group. I wish there was an easy way to plot stars on a globe but if there is my feeble mind has yet to find a way. I've even experimented with projecting a star chart onto a globe with disappointing results. I'm adding a bunch of 5th magnitude stars to my A3P star globe and the plotting is a pain in the rear. First I laid out grid lines on the outside of the globe. I thought I could do it by just plotting against the existing stars but did not trust it. Since your starting from scratch you will need the grid lines. The nice thing about an Earth globe is that these lines are already plotted thus saving a lot of time. As far as a star chart, I found a great set free at: www.mwvastronomy.com/charts.phpJust remember to take them into Photoshop (or some such program) and flip them as they need to be backwards since your doing your drilling from the outside in. The size of your star ball will be the limiting factor to the magnitude limit of your projector. I would not go any smaller then 10 inches (25 centimeters). Another factor is the size of dome your planning. Maximum dome size for a 10 inch star ball would be probably 16 feet (5 meters). So a few questions come to mind. How big will your projection dome be? How many stars and to what magnitude do you wish to project? As far as the entire projector, what other celestial objects do you wish to project? What automated motions would you like to have? Do you want to be able to project the entire celestial sphere or just basically the southern hemisphere? How much time do you have to devote to this project? Approximate budget? (There will probably be cost overruns) Again welcome and I sincerely hope we can help you get your home planetarium up and running as quickly as possible.
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Post by Ron Walker on Sept 6, 2022 12:14:35 GMT -7
Posted by: charles jones Jul 8 2007, 12:29 PM Hi Tim:
I'll be in Melbourne the end of October - first of November. It would be fun to meet. I have yet to see the planetarium in the heart of the city. Is it a Zeiss? I did see the planetarium in Brisbane two years. They have a wonderful video projection system built into the dome's horizon that is amazing. I am sure you know about. I believe it was an Australian company that created it.
I made three different star globes when I was younger. All were made of clear (thin plastic). I had a celestial globe (12"), put thin globe over it and painted tiny specks over each star. I used different colors representing different drill sizes for different magnitudes. Then I painted the interior of the thin globe flat black and finally started drilling.
What I found was that the celestial globe was not accurate enough because the star magnitudes were represented by various size circles. That coupled with my dots which varied in size, I found I could be off an 1/6 - 1/8 of an inch when I drilled.
The next star globe I made was 16" diameter. I had a metal earth globe that I split in half and used as a template. The metal earth globe already had lines of latitude and longitude. I substituted those for RA and Dec. and began to plot the stars--about 800 or 900 as I recall. This time I drilled right on the mark.
Now it was easy to set this template over the thin plastic and drilled out the plastic globe. Plus I could duplicate it. But to answer the question: I really did plot each star to make it accurate.
I do think your idea of a star chart in 24 sections would be an easier way to do it if you find one.
One thing I remember. Although I set up different drill sizes for different magnitudes, I found I keep adjusting these slightly because sometimes there wasn't enough difference between them. I looked at the individual constellations by projecting light through and many times drilled a bright star a little bigger so get it to look proportionally right. What a pain!
Are planning on using a metal globe or plastic?
Charles
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Post by Ron Walker on Sept 6, 2022 12:15:15 GMT -7
Posted by: charles jones Jul 8 2007, 06:58 PM Ga'Day Tim:
It was forty years ago that I made my own planetarium. I forgot some details. When I "upgraded" to the 16" globe, I told you I plotted the stars on a metal earth globe. Now I remember what I did. I had some kind of "protractor" that I made from a thin metal strip that ran from the pole of the sky to the equator. I marked off degrees. I would guess I marked only every two degrees or so because I made this myself.
Then I had a circle marked off for 360 degrees. The metal hemisphere sat on the circle and the "protractor" swiveled around the hemisphere. The hemisphere, being an earth globe, still had latitude and longitude for reference. I had a catalog of stars listing them in order of brightness. What was pretty neat was the fact that I could go down the list for all the first magnitude stars and drill those without changing the drill sizes. I had to look up the magnitude for the drill size anyway, so it wasn't that much extra work to get the coordinates, swing the protractor around find the location. I think the whole operation went fairly fast because I didn't have to change the drill bits out often.
I also remember that using this "template" to drill the stars in a plastic globe had problems. I missed some stars, so I finally set up a little section of sky and drilled holes for the stars in that area. The problem was I was always changing drill sizes.
Looking back it may have been just as fast using the protractor device for plotting and drilling the stars in order of magnitude.
I know I used quite a variety of drill sizes. For example, one size for 1 - 1.3 mag. stars, another drill for 1.4 - 1.6 mag., etc. The smallest was the standard number 80 drill.
If you are using a metal sphere and make a mistake, auto body putty and a little sanding will fix the problem.
Ron, if you read this, I don't know if this scheme will work for your A3P globe you want to add stars to because the lens assemblies might get in the way of the "protractor." But you might figure a way to modify it.
I wonder how Spitz made their star globes? I can't imagine they plotted each globe separately, but as I found, the template idea had it's drawbacks.
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Post by Ron Walker on Sept 6, 2022 12:15:45 GMT -7
Posted by: Ken Miller Jul 8 2007, 08:23 PM I realize now that I should have noted that the star charts are in reverse compared to the star globe. The Celestial globe is, however the same as the star globe. As Ron pointed out, you need to reverse the star chart image before using it for a template.
I can tell you that Viewlex used a template for the Apollo globes. The guy I bought mine from was a distributer for the Apollo planetariums, and he toured the factory to see how the projectors were fabricated. He observed the use of the template. If I recall correctly, he said they used a hand drill with different sized bits for the various hole sizes.
Ed Albin is the guy who built the Starland Projector that I have. This is the one that uses a dodecahedron like the Spitz. I dont know for sure how he fabricates those, but there are holes that have been masked in the paint. Inside the masked hole he has punched out the pinhole. Those holes are in fact punched out rather than drilled. I wouldn't have chosen that technique, but it does seem to work well in spite of the somewhat curled-in ragged metal edges.
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Post by Ron Walker on Sept 6, 2022 12:16:25 GMT -7
Posted by: Tim Mitchell Jul 8 2007, 08:26 PM Hi Ron,
Well lets see, I am not planning to build it immediately, I am just getting the stuff together that I will need to have to do it. Probably in a year from now.
Now I have thought that a 20 food dome would be good, but it may end up a bit smaller. I want to be able to project both the northern and southern skies and also I want to be able to switch the constilation pictures on and off. Which means that it will have to be a form of dumbell with some wide angle projectors at the base of the star spheres.
It would be nice to show the precession of the equinoxes which can be done in a couple of ways, and naturally it has to have sun moon and planetary projectors too. I want stars up to at least 4th magnitude. (Yes I know ....... Lots and Lots of drilling)
So all in all I would say it is a small project laugh.gif
I am thinking of using a 20 or 22 inch ball or pair of balls for the star spheres. I would like to use metal as it is much easier to work with, but I would rather not have to have some spun.
By that time I will have a machine shop that is more complete, so the making it won't be a problem.
So as far as time goes, well I will be working on it in my spare time, I will be building a house sometime around then so that will be not much. I plan on making the northern hemisphere first and then adding everything else as I go. So starting simple which won't take long but also having it as an element of the final projector.
Budget will be scattered over the several years that it takes to make it, so I think that it won't be too noticeable, a few hundred here and there will surely build up. I plan on making it with as many scrounged parts as possible, we will see how that plan goes. dry.gif
I think that an accurate chart glued to the globe would be a real help and after each hole is drilled it can be marked off. A coloured chart would be best with different colours for each magnitude of star.
Thanks very much for your suggestions. I appreciate them.
Unfortunately those charts are in PDF format and I can't extract the graphics from them. I have e-mailed the guy who made them in 2005 and asked him if he is willing to make a mercator projection one and then pass it through a gore map making utility that is on the web. We will see what he has to say. It would be nice to have one even if it is showing less stars. It would be nice to have some good resources available on this forum, plans or diagrams etc. and some good how-to information. I will pass on what ever I come up with. It is good to share information.
Regards, Tim.
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Post by Ron Walker on Sept 6, 2022 12:16:50 GMT -7
Posted by: Tim Mitchell Jul 8 2007, 08:47 PM G'day Charles, I may be here during your visit, I alternate between Melbourne and Sydney. Drop me a line a few weeks before and we may be able to organize a visit to the Planetarium. I think that I went to it once a loooong time ago. Say 17 to 20 years ago. It may be a Zeiss but I can't be sure. I went to the one in Nashville several times while I was living over there. I think that one was a Zeiss it sure looked like it. I have just started to get interested in Planetariums and I have only been back here in Australia for 2 years so I don't know anything about the one up in Brisbane, sorry.
Thanks for your tips about your projector making experience, I am wondering if you still have one of the projectors that you can measure the hole size for the different magnitudes. That would make things a bit less hit and miss when I get around to doing the drilling. I know that it changes with the diameter of sphere but I can calculate it from that to whatever the size is that I end up using. Or perhaps one of the others here can check the hole size on their projectors and make a small list for that diameter of sphere.
With the clear plastic spheres can you paint the outside black and then scribe the constellation lines on it and have them project onto the dome? It is a long shot and I don't think that it would work but I am just curious.
Finding a metal sphere or two would be a bit difficult, I may be able to find one, we will have to see.
Thankyou for sharing your experiences.
Kind Regards, Tim.
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Post by Ron Walker on Sept 6, 2022 12:17:11 GMT -7
Posted by: charles jones Jul 9 2007, 12:43 AM G'Day Tim:
I think if you use a "thick" acraylic plastic globe (these are easy to find on the internet), paint the INSIDE flat black and scribe the the outlines of the constellations INSIDE it, it will work fine. This of course is in conjunction to your main star globe.
The star globe must be of thin material (metal or plastic) and may have to be made custom for your purpose. Spun metal or vacu formed plastic plastic material. This would cost a few dollars, but be worth the expense. If you are lucky, you may find a "metal" earth globe in an antique store which would be purfect to use as I did for my template globe. Remember, for the star globe the material should be as thin as possible. And it will be easily to work with if you can split it in half (two hemispheres).
Yes, I still have one of the two projectors I built. I bring it down from the attic occasionally. I do not have the "template" or the codes for the drill sizes any longer. But the deal with the drill sizes is simply this: You start with the smallest drill easily obtainable - a number 80 drill. I am told it is only 4 times the size of a human hair. For promotional promotional purposes, this sounds great! Find out the diameter. Look at the largest size hole you want to drill. Maybe it is a number 50 or 55. (After a point, the larger holes drilled become to large and do not look like pinpoint stars anymore.) Figure what magnitude stars you want to show. 3rd or 4th or more. Then make a chart of the magnitudes from 1 to 4 using the 30 or so drill sizes (50 to 80). This is an example.
Remember, from the first magnitude to the sixth, there is a hundred times difference in brightness. You will not be able to demonstrate this with 30 drill sizes. To do this accurately, the largest drill size would be so large it would probably look like the sun or moon in the sky. So you have to cheat. That's why Spitz, 50 years ago, came up with separate lens to increase the brightness of the "bright stars" without increasing the diamater of the hole drilled. And Zeiss, even early on, had separate projectors for the really bright stars. That's hard for us to do in a home built planetarium. So you need to cheat a bit. When you look at a constellation and want to show a brighter star in the area, you may want to drill a larger hole to constrast with the other stars in the area, even though your "chart" may determine a smaller diameter hole for that star.
But you really can come up with a chart of your own determining drill sizes to magnitudes. This is half the fun!!! Ha Ha!
And thinking back on my history now and how I did it, the "protractor" idea of plotting is simple and really was very fast considering. It saved all the time of changing drill sizes. Theoretocally, you don't even need to mark a line on the star globe if you do this. i know there are catalogs available listing the stars by magnitudes and their coordinates.
If you like, I can photograph the mechanics of my simple projector (I called it a Classroom Planetarium) for you to evaluate.
Charles
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Post by Ron Walker on Sept 6, 2022 12:17:36 GMT -7
Posted by: charles jones Jul 9 2007, 12:55 AM Hi Tim again -
Thinking more about the constellation outlines:
Painting the interior and then scribing the outlines may not work because you may cause the light to be diffused when it projects through the scribed lines. But try it. Try it on a flat sheet of plastic, painted black, and scribe a line. Put a concentrated incandescant lamp near it and see what happens!
If it doesn't work, I would think that you could create a "transparency" of each constellation outline, and "paste" these in some way to the interior of a plastic globe. I am sure you understand what I mean. Take a drawing of the constellation outline, photograph it, have a photo shop make a negative for you which will be all black, except for the constellation outline. Cut this negative and fit it into the globe. the only trick will be getting it the correct size, but you can figure that by trial and error.
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Post by Ron Walker on Sept 6, 2022 12:18:48 GMT -7
Posted by: charles jones Jul 9 2007, 02:03 AM G'Day (again) Tim:
I wanted to add a couple of notes:
If you paint the interior of a plastic globe black and can remove bit of the paint (the constellation outline), it will project if you remove only the paint and do not scratch the plastic. If you scratch the plastic (with the scribbing procedure) it probably will diffuse the light and as a projector will not work. It would be interesting to look at as a globe. So, if you can figure a way to remove the paint without scratching the plastic interior, you can do it.
Also, I think I remember that each star's magnitudes is something like 2.5 times from 1 to 2 to 3 etc. This goes up exponentially making the difference from the brightest star to the 6th magnitude about 100.
Am I right??? Someone help here!!! I can't remember my basic 101 Astronomy classes.
If this is as I think I remember, you can see immediately how impossible it is to show a sky in a planetarium from 6th magnitude to 1 mag. by drilling holes 100 times difference in diameter. This is why the planetarium doesn't want to really show the sky from the sky all the way down to the 6th mag.-- the theoretical limit of what the human eye can see an a clear night in the middle of nowhere!!!
Finally, we all want to know if the stars rise and set the same way in Australia as they do here in America. Maybe they rise in the West and set in t he East!!
Come on, you drive on the opposite side of the road, the water goes down the drain in a different direction, and you don't have a "north" star to navigate with. But I guess we don't have a southern cross to look at in America.
Te He!
Charles
Ps: I am in Sydney about the third week of October.
The planetarium in Brisbane is a small Zeiss (1980's vintage). But they have an amazing video projector system that involves something like 8 + projectors around the dome that projects the sky, and a computerized storyboard that fills the dome. Talking with the folks there, I remember hearing that it was an Aussie company that developed the techniuqe and it is used in planetariums as well as domed theaters. It was amazing because each video projector avoided images that would be blocked by the Zeiss projector. Apparantly another video projector took over avoiding the projector, so the overall impression was a full dome, without any shadows of the planetarium projector.
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