07/15/2026
🌟 HELP TEST ONE OF HISTORY’S GREAT MATHEMATICAL MACHINES—RECREATED AS AN ANDROID APP
I’ve released my first Android app, **ORLOJ: Prague Cosmos**, into Google Play closed testing.
This isn’t just another clock app. It is an interactive 3D journey inside one of medieval Europe’s most mathematically sophisticated surviving public machines: the Prague Astronomical Clock.
Built in 1410—before modern calculators, electronics or precision machine tools—the Orloj transformed observations of the sky into geometry, ratios and forged metal.
Its astronomical dial acts like a mechanical map of the heavens. Using astrolabe geometry and stereographic projection, it compresses the apparent sky over Prague onto a flat circular display.
Three enormous forged wheels originally used:
⚙️ 365 teeth for the zodiac and star frame
☀️ 366 teeth for the Sun’s reference motion
🌙 379 teeth for the Moon’s motion
A common pinion drives these wheels together. Their tiny differences create separate celestial rates:
366 ÷ 365 = 1.0027397
That small difference reproduces the approximately four-minute daily separation between solar time and star time.
The Moon wheel moves at another rate, approximating the lunar cycle while a hidden mechanism turns the half-dark, half-light Moon sphere to display its changing phases.
The Orloj also brings several ideas of time together on one instrument:
🕰️ Central European civil time
🌇 Old Czech time beginning at sunset
🌞 Babylonian unequal hours that change length with the seasons
⭐ Sidereal or star time
♈ The Sun’s position through the zodiac
🌙 Lunar position and phase
📅 The calendar, seasons and annual cycle
Why does its mathematics still work?
Because the machine embodies repeatable relationships: day and year, Sun and zodiac, Moon and Sun, horizon and sky. The mechanism has been repaired and adjusted over the centuries, but the underlying geometry and ratios remain meaningful.
Was it ever destroyed?
In 1787, officials considered removing the Orloj and discarding its mechanism as scrap—but it was saved. In May 1945, the Old Town Hall was shelled and burned. The Orloj was severely damaged, its wooden figures burned and its mechanism was removed for restoration. It returned to operation in 1948.
Today, approximately 75% of its mechanical components, gears and steel supports are still considered original.
ORLOJ: Prague Cosmos lets you explore this machine, separate its mechanical layers, move through historical and future dates, study its formulas and experience the astronomy, zodiac, philosophy and symbolism built into its design.
ANDROID TESTERS ARE NEEDED
The test is not limited to 12 people. Twelve is only Google’s minimum—everyone with an Android device is welcome.
HOW TO JOIN:
1. Like this post or comment **“I’ll test it.”**
2. Privately message me the Gmail address connected to your Google Play account. Please don’t post your email publicly.
3. I’ll add you to the approved tester list.
4. After I confirm, open:
https://play.google.com/apps/testing/com.inspectorroofing.orloj
5. Tap **“Become a tester.”**
6. Install the app and explore it.
7. Return here and comment **“Opted in.”**
8. Stay opted in for at least 14 days and send me honest feedback.
Tell me:
• What amazed you?
• What confused you?
• Which formula or mechanism needs a better explanation?
• What should be added to the next version?
• Does the 3D clock feel intuitive and real?
Created and programmed by **Richard Amir Nasser**
ORLOJ Engineering
Please share this with Android users who enjoy astronomy, horology, mechanical watches, history, Prague, mathematics, philosophy or the zodiac.
