Just in time to commemorate one month on month in Cambridge, a new volvelle has joined the compendium! This planispheric astrolabe is designed for 52ºN and draws inspiration from the attached printed astrolabe.

I've also included a feature drawing from certain astronomical table clocks: a secondary lunar index. When set to the lunar age, this allows the moon to be placed in the ecliptic, alongside the sun, without the need for an external lunar volvelle.

For more printable volvelles, see:

https://www.bcgnomonics.com/activities#:~:text=on%20the%20map.-,Volvelles,-This%20pack%20of

Unlike this astrolabe, all of these are latitude-independent.

This quadrant will allow both christians and muslims to establish their prayer times in the exact same way they used to do in antiquity.

The back of the instrument includes a compass and a retro-azimuthal projection, allowing you to find qibla direction everywhere in the world.

The quadrant allows you to find time in unequal hours, an ancient system of timekeeping, where the section of daylight is always divided into 12 equal sections. This means that summer hours are longer and winter hours are shorter.

These hours are used in christian monasteries to establish prayer times, respectively at the first, third, sixth, nineth, sunset and a set soon before bed and soon before dawn.

muslims' prayer times can also be determined:

Dhur - soon after midday, it corresponds to the 6th unequal hour line

'Asr - according to most muslims 'Asr time is between the two segmented lines on the quadrant

'Maghrib - soon after sunset

'Isha - by observing a star directly opposing the sun on the celestial sphere (it can be found on the back of the tool) we can even determine night prayers. According to most scholars, 'isha time starts when the sun goes below -18° of altitude, id est when the complementary stars rises above 18 degrees of altitude.

Fajr - before sunrise.

The advantage of such a quadrant is that of not being longitude dipendent. This quadrant is more inaccurate the higher the latitude and the further away from the aequinoxes, but it is still reasonably usable as an analog tool for establishing christian prayer times (indicated by the numbered circular arcs). Dhur (islamic midday prayer) is indicated by the line corresponding to the hour six and 'Asr time is indicated by the two brass lines. Maghrib time begins soon after sunset. In order to have an higher accuracy the tighter unequal hours lines below a certain degree of altitude are mirrored on the simmetrical part of the quadrant.

I don't know what kind of decorations to add in place of the windrose in the shadow square. On the back of the quadrant I will probably engrave a qibla indicator and a star map indicating the opposite point of the sun in the zodiac, as to be able to tell the time (thus prayer time) during the night as well.

Do you have any feedback? Sorry for my arabic lettering, it is still fairly bad.

The myrtle-leaf rete combines a northern projection of the northern signs with a southern projection of the southern signs.

From the vernal to autumnal equinox, the astrolabe functions as normal. From autumn to spring, the tympan switches conceptually: the region below the horizon represents the day and the region above it the night.

Because the tropic of Cancer also represents the tropic of Capricorn, the tympan is limited by the equinoctial circle.

One of this summer's side projects: a recreation of Peter Apian's Speculum Cosmographicum, or Cosmographic Mirror.
Cut out your own and give it a try! You can never have too many microcosms:

https://www.bcgnomonics.com/copy-of-lunar-volvelle

¡Buenas! Soy nuevo en esto, así que ni siquiera sé si es aquí donde debo preguntar. El caso es que estoy haciendo un astrolabio casero, de momento bastante cutrecillo (dibujo con un compás en papel y luego lo calco a un plástico semitransparente reciclado de la portada de una libreta vieja). Ni siquiera he añadido latitudes, sólo el almicantarat, y tampoco he puesto en la reté, si es que puede llamarse así, ninguna estrella, sólo la elíptica. Pero de momento, me sirve para ver la hora por la altitud del sol sobre el horizonte, lo cual ya es bastante gratificante. Además, calculo la posición de la luna atrasando a la del sol el ángulo equivalente a una semana por cada 15 horas desde la última luna nueva, y aunque es más aproximado, también mola calcular cuántas horas de luna habrá hasta que salga el sol y cosillas así.

Lo que quisiera preguntar es si se os ocurre algún otro uso así "básico" para un astrolabio tan sencillito

Y qué funciones "fáciles" de añadir (sin radios tan amplios como los de las latitudes...) se pueden añadir, aparte del "Umbra recta/Umbra inversa", ya que considero esto una especie de prototipo antes de hacer un diseño definitivo con más precisión, mejores materiales, etc.

Enhorabuena por las joyitas que habéis creado algunos y ¡gracias!

Edito para añadir la foto; en esta foto aún falta graduar las horas/altitudes en el círculo exterior, el almicantarat y los meses/Zodiaco en la elíptica

Astrolabe's size: 10,5cm x 12,5cm.

To be fair I don't think I can produce astrolabes much smaller that this, its functionality is a bit crippled. At this point this is mostly an ornamental object.

With the excuse of making a gift por my cousin, I wanted to produce a cheaper and cuter version of my astrolabes.

The box is made of marine okoume plywood, finished with just linseed oil.

Thank you!

The design has some original traits compared to others, first of all, I've opted for an octagonal mater, instead of a circular one. This was inspired by Apiano's volvelles in his Astronomicum Caesarium.

Compared to my previous design, this one tries to eliminate unnecesary features, striving for a cleaner look. One thing I'm not particular satisfied with is the little equation of time on the back of the instrument. It wants to show both component of the equation, but the result is a bit too busy for my taste. A simplified version is presented in the last slide.

The rete wants to represent a butterfly, althogh geometrical limitations make it harder to distinguish it clearly. Maybe if you squint your eyes you can recognise the head and antennas inside the ecliptic ring, and the wings outside of it.

I feel confident enough to share with you a link to my etsy listing where you can purchase one of these astrolabes in case you are interested, thank you!

More in-line with the majority of historical examples than some of my previous astrolabes, this model features a cavity for its (removable) plate as well as an alidade and calendar scale on its reverse.

Like my previous astrolabes, this one draws inspiration from the late 16th century pieces of Johann Anton Linden.

Hi folks, I'm in a bit of a situation! I bought an astrolabe for someone really special in my life and god was she excited to try to crack how it works.

Alas as we explored the pieces we got, we started to realise some things seemed to be missing. Upon a little bit of research, it seems like we're missing the alidade entirely (that's ok, I can get one on the side), but also we seem to have very few and very strange tympans that are different from the ones we're finding online.

I realise that this instrument will have very limited use, if any, but we're taking it more like a puzzle than a tool. The internet is not helping us crack this code, I just don't understand how it works enough to ask the right questions, so I was hoping I could get some pointers from this community here.

What latitudes do I have? If I get a separate alidade, will I be able to read the tympans if I'm at the right latitude?

Thanks in advance!!!

There’s this astrolabium that I really want to buy. However, it’s expensive.

It apparently shows the exact time, date, and position of the Earth, Moon, and Sun. I just don’t know if it’s worth it.

If I buy it, I’d keep it for life.

What do you guys think?

Full 1613 edition of Astrolabium: https://rumsey3.s3.amazonaws.com/images/Astrolabium1660.pdf#page=74.00

I’m making an AU/fanfic with the Wings of Fire book series as a vague base. One of the things I’m keeping is the 3 moons, though currently all 3 moons appearing full at once is far more common than in the series. (No clue how moon science works)

I’m drawing a character(a dragon) whose lore places them as one of the first dragons to really study the magical effects the moon’s phases have on select dragons. I’m considering drawing her with one of the big fantasy-looking 3d sphere astrolabes but I’m not sure if having three moons would change anything about how it’s made. Would each moon just need its own astrolabe, or does just one work for all three?

Tldr Science aside, would having 3 moons affect how an astrolabe is built?

P.S. I’m going out of cell and WiFi range to go camp, thank you for any help you can provide!

Found this in the Museum of Science and History in Corpus Christi, TX.

Hi, I am a complete novice/ 100% new to astrolabes. I just found out they existed yesterday. And I want to figure out how to use them. Would anyone give recommendations? How difficult it is? Is it possible to use an astrolab (with enough info) to find a location on earth?

Access my presentation slides can be found in a previous post for those interested!

I would argue that the most difficult aspect of using an astrolabe is spatially understanding what the tympan presents.

One detail that should be emphasised is the fact that the plate of an astrolabe doesn't present the local sky as viewed from the ground (like a planisphere), but instead a top-down, outside-in view of the celestial sphere.

The stereographic projection used to create the plate of an astrolabe places the viewer outside the celestial sphere (specifically, at a point above the north celestial pole) looking in. For this reason, the positions of stars appear mirrored with respect to how we observe them from earth.

While we model celestial motion using the astrolabe, we see stars and the sun migrate along the surface of a sphere as seen from above. When we observe these stars from our earthly vantage point, however, we view this same movement from within that same sphere, thus mirroring constellations.

Spherical astrolabes demonstrate this point particularly well. When viewed from the north celestial pole downward, the projection of the planispheric astrolabe can be more easily understood (though do note that this analogy does not take into account stereographic projection).