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It is-this is one of Norman Greene's models www.puzzlering.net/astrolabe.html

While more observational instruments would have been used to gather information relating to the motion of the planets, the armillary sphere and astrolabe can both model their motions to a reasonable degree of accuracy. If you haven't already, I would recommend taking a look at this video: ua-cam.com/video/EvBUENmyMBc/v-deo.htmlsi=3BW_TPlWCLYxdOU2 If the ecliptic position of a celestial body is known, the existing ecliptic on the instrument can be used to demonstrate the path and rising/setting time of the moon/planet in question. Because these orbital planes are slightly inclined to the ecliptic, however, this modeling is not perfect. Historically, there are examples of astrolabes with planetary markers for this very purpose. To use this function of the astrolabe yourself, I would recommend taking a look at Alexander Boxer's interactive astrolabe, listed among other astrolabe resources on BCGnomonics.com

The ecliptic is offset from the equator by +/- 23.45 degrees. The width of the ecliptic is mostly a product of its physical construction and does not necessarily bound the orbits of each planet. However, certain armillary spheres do feature separate planetary orbits inclined to the ecliptic that account for this variation, thus making the sphere more precise in its demonstrational capacity.

@@BCGnomonics Hi, thanks for your answer. It seems the ecliptic band touches the tropic of Capricorn armillary at the southern end of its band width, when it should the crossing the tropic of Capricorn armillary in the middle of its band; however the ecliptic band seems to correctly cross the tropic of Cancer armillary in the middle of its band: can you confirm this? If so, is there a way to correct this error? perhaps by removing and putting back the band correctly? Also, do you think it would be possible to add some kind of graded ecliptic line in the middle of the ecliptic band with pen or maker or the like? I am looking at some 18th century French armillary spheres and the ecliptic band is always divided in two along its width: the northern half has zodiacal divisons, while the southern half has months of the year. In the middle is a white line with a graded division (by day) ruler along each side. You can see this if you look for "armillary spheres Jean-Baptiste Fortin" and there are some close-up zooms available on the site Gallica. Thanks!

Thank you for pointing out Gallica-a great site I had not seen before! As for the accuracy of the ecliptic, you are correct about the various tropical offsets of this particular model. While it would be possible to remedy this and add the separation you mention, this model is unfortunately not built to be terribly precise. As you have no doubt noticed, the ecliptic is only marked with the 1st and 30th degrees of each sign, with no way to accurately pinpoint individual degrees. The only truly practical armillary sphere on today's market is made by Norman Greene (normgreene.com/armillary.html) and regrettably exceeded the scope of the grant that started the BC Gnomonics project. Vsevolod of Master Terebrus is working on his own design though, which I am particularly looking forward to seeing.

Yes, that seems to be the correct bearing for your longitude. To be as precise as possible, I would recommend using either this desktop site: networkappers.com/tools/qibla-direction-tool or this mobile one: qiblafinder.withgoogle.com/intl/en/desktop

While there are unfortunately no commercial models currently available, the dialing scale page on BCGnomonics.com features multiple downloadable options that can be printed and used

While I do not personally have access to the appropriate files, these instruments could absolutely be 3-D printed. In fact, NASS offers a selection on their website: sundials.org/index.php/nass-shop2/3-sundials-and-astrolabes Additionally, each instrument page on BCGnomonics.com features a list of recommended contemporary sellers, as well as free crafts if available.

I Would also recommend taking a look at Wymarc's models on Thingiverse. Two astrolabe variants with downloadable files are currently available

The short answer is yes-as long as the correct plate is inserted, the astrolabe is able to model the local sky. Irregular topography may obscure celestial bodies at low altitudes, but their horizontal coordinates can still be accurately pinpointed using the astrolabe. If you haven't already, I would recommend taking a look at my dedicated astrolabe videos. Additionally, virtual models are available on BCGnomonics.com

Take a look at the astrolabe's page on BCGnomonics.com for recommended sellers! www.bcgnomonics.com/

As you indicate, the closer a given star is to the pole (i.e. the closer its declination is to +/- 90), the less variation there is in its altitude and harder accurate readings become. It is therefore not much of a surprise that no star on this particular instrument exceeds +/- 41 degrees of declination. Choosing a star close to the horizon yields the best results. Including such a wide variety of stars allows for an element of choice, gives alternatives in the event of obscuring factors, and perhaps most importantly ensures that for every region of the sky that the sun obscures as it circuits the ecliptic, there is a viable pool of stars to choose from. This seasonal spread of stars is also seen on planispheric astrolabes, though while they are able to include stars with declinations up to +90, they cannot typically include any lower than -23.45, as the projection ends at the tropic of capricorn.

@@BCGnomonics Interesting stuff, I've always been curious why northern hemisphere astrolabes end at the tropic of capricorn too. Granted the south pole would be out at infinity with a stereographic projection, but do you know why they ALL end at the tropic like that?

I would speculate that it's mostly a matter of spatial efficiency. Since all computations rely on the ecliptic-which only requires the space between the tropics-engraving beyond the tropic of capricorn would require every element of the instrument to be enlarged while not adding much meaningful functionality. That being said, I would not be surprised if some exceptionally large, perhaps mounted astrolabe existed somewhere, with stars continuing past the tropic of capricorn. There is a precedent for altering the conventional limits of the projection, as seen in this astrolabe that ends at the equator: www.mhs.ox.ac.uk/astrolabe/catalogue/browseReport/Astrolabe_ID=111.html Additionally, here is an astrolabe with a projection that continues slightly past the tropic of capricorn: adler-ais.axiellhosting.com/Details/collect/930

Unfortunately yes, there aren't too many quality models on today's market. Though, if you haven't already seen them, I list recommended sellers on BCGnomonics.com. While I don't have access to blueprints per se, here are a few resources that may be of use when constructing an astrolabe: James E. Morrison's The Astrolabe - archive.org/details/ilmetauqeet_gmail_659/mode/1up?view=theater Chirag Devani's videos on astrolabe construction - www.youtube.com/@chiragdevani6164/videos Astrolabe Generator - www.eso.org/~ohainaut/bin/astrolabe.cgi The Astrolabe Project - www.astrolabeproject.com/the-astrolabe-generator/

@@BCGnomonics awesome thanks a bunch!

Thank you for your question! Yes, that is a shadow square. It can be used to determine the heights of objects and accomplish other distance-related surveying tasks. Until I can record a demonstration, hopefully this will be helpful: in-the-sky.org/astrolabe/shadow_scale.php

Are you referring to the astronomical ring dial as a whole? If so, Master Terebrus (www.etsy.com/shop/MasterTerebrus) is the only current seller. If you're interested in universal horizon plate astrolabes though, there are a few other options. I would suggest Laserdeko's equatorium astrolabe or Norman Green's astrolabe with interchangeable plates.

Indeed, the reading does drift with respect to the "true" seasonal hour as one approaches the solstices, becoming most extreme during the 2nd and 9th hour. The error is certainly mathematically notable because of the dial's imperfect celestial modeling, though in practice wouldn't be noticable, never accumulating above 8 minutes. Very impressive work, by the way. I watched your modernized antikythera video the other week and loved your additions. I always appreciate seeing instruments designed with thought to modern practicality.

In terms of precision, I would recommend Master Terebrus, Helios Sundials, and Kala Pocket Instruments. These makers produce the highest quality sundials on the market

Thank you! Glad you enjoyed. To make this dial work in the Southern Hemisphere, all you'll need to do is reverse the date scales

@@BCGnomonics Awesome - thanks so much!!

Conceptualizing the armillary sphere more like a heliodon, it doesn't seem like there's much need for the earth in the center. It makes a bit more sense when you consider that the celestial equator and tropics represented on the sphere are outward projections of those same circles on the earth. While maintaining a geocentric perspective, the armillary sphere zooms out to capture the greater celestial sphere, including aspects of it that are fundamentally grounded on the globe. I believe including the earth makes this relationship a bit easier to model (also remember that the armillary sphere is most fundamentally a demonstrational, educational tool)

@@BCGnomonics the armillary sphere shows you the part of the sky YOU can see. It's a personal reference frame. Where one is at the center, immovable, observing the heavenly sphere move above you in a clock like manner and precision. As you well know, the entirety of history saw the earth as only geocentric. The idea of heliocentrism and the earth as a globe didn't even come into play until 600 bc. And it was a baseless assumption at that. Geocentrism with a stationary earth was obvious until a few hundred years ago.

I got it from Master Terebrus on Etsy (www.etsy.com/listing/1381835493/french-baroque-analemmatic-sundial?click_key=ec9b94636cbc1ed716a502ef7f5317fdf7936a2d%3A1381835493&click_sum=dd1da5c0&ref=shop_home_active_20&crt=1&sts=1). If the item you're looking for is not available, he's always very responsive and open to special orders

I got this one from Punto Vernal (puntovernal.co.uk/p/armillary-sphere-tycho-de-brahe/)

This one is from Punto Vernal (puntovernal.co.uk/p/armillary-sphere-tycho-de-brahe/). Unfortunately, there are hardly any quality armillaries on the market aside from simple decorative ones. This one does a decent job, though is still missing details that would make it truly precise as an educational model (e.g. the lack of a true ecliptic scale). The very best modern armillary seems to be this one by Norman Greene normgreene.com/armillary.html

Sorry for the confusion. In this example, yes-the sun should be set to the horizon projected for your local latitude, in this case the 45º one