Very interesting tool, indeed! Thanks. 🔭

À la lecture de la thèse de Marc Thomas (2014, Nantes) sur l’histoire des règles à calcul, il semblerait que celle trouvée en brocante à 8€ daterait de 1882-1900, quand la maison Tavernier-Gravet avait pour adresse 19 rue Mayet. #histsci

The hour lines are computed for latitude 42°N (Rome), but if you tilt the sundial you can make it work for higher latitudes. A list of cities with their latitudes is provided. A small graduated arrow helps find the correct angle. 4/6

Used separately, these sundials have to be oriented along north-south, but this one is self-oriented: rotate it until the shadows of both edges tell the same time. This is only possible because the 2 edges have different directions. The sundial then also indicates *true* north. 3/6

The octagon is a horizontal sundial, working with the shadow of the tilted edge of the triangle. The oval is an analemmatic sundial, working with the upright edge of the triangle. The user needs to set the date by sliding the octagon until its edge reaches the current date on the calendar. 2/5

🔭 🧪 #EduSky #astrohistory Don't mind me, I'm just dreaming I was one of Delure's wealthy clients in Paris, commissioning this lovely double #sundial in the early 18th c... 1/5🧵

Wooden grasshopper on a table. Mandibles move with gears under the sculpture.

This exhibition is « Anima (ex) musica ». Created by « Tout/reste/a/faire ». More about their work : www.toutresteafaire.com

Insects made of pieces from music instruments. Muséum d’Histoire Naturelle, Le Havre (France).

🔭 🧪 New meridian #sundial in Paris, at the Université Paris Cité (campus Grands Moulins). More about the project (in french): www.youtube.com/watch?v=t4sH...

2/3 If you compute the right ascension difference between a star and the Sun for a given date, you can guess the time of meridian crossing of this star. My script is adapted from Ronnie Bathoorn (github.com/bathoorn/sta...) This map comes in 2 styles: 'deepblue' or 'vintage'.

🔭 New sky map with ecliptic path. Right ascension increasing towards left, so constellations appear as in the sky. Ecliptic path shows the Sun's position every 5 days. Powered by #Python with the Skyfield ephemeris library. Adapted from R. Bathoorn. 1/3 🧵

🔭 🧪 #EduSky Le n° de juillet/août de L'Astronomie est paru, avec entre autres un article sur les crépuscules. Merci à son autrice Marie-Claude Paskoff de m'avoir laissé une page pour présenter ma maquette en papier servant à déterminer la durée du crépuscule (et de la journée). 1/2

The Sun follows a line from midnight (left) to noon (right) and back, on this day. When a line is above the horizontal diameter, it's daytime. At latitude 90°N, the line is horizontal (the Sun doesn't set). Vertical line: at the equator. Hour circles (dashed), altitude scale around the diagram. 2/3

🔭 AltZero studio sells astronomy-related posters. Among others, the June Solstice poster, a very beautiful diagram showing the Sun's path on the celestial sphere on June 21. Each orange line is for a given latitude, from -90 to 90° every 5°. 1/3 🧵

They asked me to design a very simple paper sundial for their educational kit. institutions.ville-geneve.ch/fr/mhn/votre... Exhibition until April 11th 2027. 3/3

... including a rarissima Venetian navicula (probably only 5-7 extant copies!). 2/3

🔭 🧪 #EduSky At the Musée d'histoire des sciences of Geneva (Switzerland), the exhibition 'À l'ombre des découvertes' deals with scientific discoveries related to shadows. With #sundials inside. This museum hosts a nice collection of them... 1/3

Nice discovery this morning at a vintage sale: the typometer is a kind of slide rule for typesetting. Relates the text width of a page, the font size (6-12pt) and the number of lines on the page. Brand : Graphoplex. #typesetting

En formation impression 3D aujourd’hui. Je glane quelques idées pour le labo, et pour convaincre les collègues d’acheter une imprimante. Je modifierais bien les dés de groupe sanguin pour mon échantillon de décroissance radioactive. 🧪 🎢

🔭 🧪 🎢 #EduSky I finally managed to color countries in my map for the refraction horizontal #sundial Round map with hour lines, to be placed under 5cm acrylic glass. The flower's shadow tells solar time and the place where the Sun is overhead. Here off the coast of west Africa, heading to Cuba. 1/2

Lovely exhibition of astronomical instruments (modern reproductions)! Left to right: A torquetum (converting celestial coordinates) A Rojas astrolabe (time, coordinates) A brass ‘mirror of the world’ (time around the world) Quadrants, nocturnals. 🔭 🧪 #histsci

And its ‘grasshopper’ low friction escapement :

Seen in Nantes, France, this weekend: a reproduction of Harrison’s H1 clock, made by Martial Le Berre for the association ‘Méridienne’. 🧪 #histsci

#canicule

Dans ce n°53, je présente deux instruments astronomiques anciens : - le quadrant de Gunter (1623), un cadran solaire mais pas que. - l'Astronomical Time Keeper de James Ferguson (1770), pour déterminer l'heure de nuit.

🔭 🧪 #sundials #cadransolaire Le n°53 de Cadran Info, revue de la Commission des cadrans solaires de la @safastrofrance.bsky.social, est paru. PDF sur abonnement. Je rappelle que les numéros datant de plus de 5 ans sont en libre accès ici ccs.saf-astronomie.fr/cadran-info/