Stuff You Should Know – "Keeping Time"

Host: Josh and Chuck
Date: January 20, 2026
Podcast: iHeartPodcasts

Episode Overview

In this engaging and lighthearted episode of "Stuff You Should Know," Josh and Chuck explore the fascinating history of timekeeping. From humanity’s earliest attempts at tracking the passage of time with sticks and shadows to the evolution of mechanical and electronic clocks, the hosts walk listeners through millennia of innovation, mishaps, and clever inventions—sprinkled with characteristic banter and laugh-out-loud moments.

The episode’s purpose is to demystify how humans have measured, divided, and coordinated time over the ages, without delving too deeply into the mechanisms of the devices themselves, focusing instead on cultural and historical contexts.

Key Discussion Points and Insights

1. Earliest Timekeeping: Shadows and the Gnomon

• The Gnomon (stick in the ground): Humanity’s first "clock," using the movement of shadows to track the day.

  "You can actually use it to track time throughout the day. And that is almost certainly the earliest way that humans tracked time. And the stick they put in the ground is widely known as a gnomon...also saw that it was slang in Greek for penis." — Josh (02:05)

• Oldest artifact: A shadow-based timekeeping device from northern China, 2300 BC.
• Early timekeeping was about tracking seasons and astrology rather than hours and minutes.

2. Advancements in Sundials and the Concept of Hours

• Sundials & Greek Innovation:
  • Greeks eventually created sundials marking hours, dating to about 350 BCE.
  • The hemicycle: half-bowl stone sundials introduced around 280 BCE, accommodating seasonal changes.
  • Hours were not standardized—summer "hours" were longer; winter "hours" were shorter.

    "The hour was longer in the summer, the hour was shorter in the winter. And it was essentially their way of what we do for daylight savings time..." — Josh (08:59)

• Portability: Ancient portable bronze sundials included adjustment instructions based on location (latitude).

3. Timekeeping for Society: Planetary Hours, Religion, and Practical Needs

• Ancient Rome:
  • Timekeeping governed not just appointments, but rituals and resource sharing.
  • "Planetary hours" dictated which gods to worship at which time.
• Islamic Innovations:
  • Adopted and improved sundials for scheduling daily prayers.
  • Trigonometry led to even more precise sundials (e.g., conical sundials).
• Uniform Hours:
  • 13th-century Moroccan mathematician Abu Alhazan Al Maraqshi advocated for uniform hours, a pivotal shift in timekeeping.

4. Beyond Sundials: Water, Incense, and Candles

• Water Clocks:
  • Developed independently in cultures such as China, Greece, and Muslim nations.
  • Two main designs: tracking time as water filled up or drained from vessels.
  • Flaws: prone to freezing and inconsistent viscosity based on temperature.

  "You could supplement sundials with these, because on a sundial, if it was really overcast, you had no idea what time it was at night. These things worked as well..." — Josh (16:03)

  • Mercury used as an improvement in 10th-century China due to its constant flow properties.
• Incense Clocks:
  • Burned incense (sometimes in a box maze) would mark time and even signify different hours with distinct scents.

  "You could smell the time. So you knew when a certain smell came up, what time it was. Which I think is super, like, ingenious in its simplicity." — Chuck (19:03)

  • Alarm innovation: burning incense would break a thread, dropping bells to awaken sleepers.
• Candle Clocks:
  • Attributed to Alfred the Great: burning down six candles for roughly 24 hours.

5. Mechanical Clocks—and a Pivot to Accuracy

• Astrolabes:
  • Sophisticated medieval timekeepers, navigational and astronomical devices.
• Hourglass:
  • Arrived surprisingly late, with first documented appearance in Italy, 1338 CE, after mechanical clocks.

6. Early Tower Clocks and Engineering Marvels

• Notable inventions:
  • Tower of Winds in Athens by Andronikos: housed multiple timekeeping methods in one structure.
  • Elaborate medieval Chinese clocks with chimes, gears, and automated mannequins (e.g., Su Sung’s clock tower; Al-Jazari’s Elephant Clock).

    "...there were mannequins that came out and rang gongs...this is from the 11th century. So it's pretty impressive..." — Josh (24:03)

7. European Mechanical Clocks and the Regulation of Time

• Shift to weights and gears: Early European clocks ran on falling weights; accuracy improved with gear innovations.
• The Verge and Foliot Mechanism:
  • Controlled the release of kinetic energy, giving rise to the first clock 'tick-tock' sound.
• Cultural impact:
  • Clocks regulated not only prayer but daily life, marking a departure from seasonal, sun-based time perception:

    "Lewis Mumford...says that that is the birth of the modern era, not steam power...removing people from the natural rhythms of the day and imposing time on them." — Josh (34:31)

8. Pendulum and Portable Clocks: Toward Modern Timekeeping

• Pendulum Clocks:
  • Inspired by Galileo, built by Christian Huygens (1656), further improved by Robert Hooke.
  • William Clement’s "long-case clock" (grandfather clock) added the minute hand (1680).
• Spring Mechanisms:
  • Coiled springs enabled truly portable clocks, paving the way for pocketwatches and wristwatches.
• Grandfather Clock Name Origin:
  • From the 19th-century song "My Grandfather’s Clock" by Henry Clay Work.

9. Watches: From Jewel to Utility

• Initially women’s jewelry (Countess of Hungary, 1868), became military gear (Wilhelm II’s naval officers, 1880).
• Post-WWI, wristwatches gain mass popularity among men.
• Military necessity drove many innovations, including chronographs for timing munitions.
• Modern features: waterproofing (Rolex Oyster, 1926), stopwatch, luminescence.

10. Atomic Precision: From Quartz to the Present

• The leap from pendulums to quartz crystals (20th century) and then atomic clocks, which drive modern timekeeping—from your phone to GPS systems.

Notable Quotes & Memorable Moments

• On earliest timekeeping:

  "And that is almost certainly the earliest way that humans tracked time. And the stick they put in the ground is widely known as a gnomon... also saw that it was slang in Greek for penis." — Josh (02:05)

• On ancient sundials:

  "Seasonal hours... the hour was longer in the summer, the hour was shorter in the winter. And it was essentially their way of what we do for daylight savings time..." — Josh (08:59)

• On incense clocks:

  "...you could smell the time. So you knew when a certain smell came up, what time it was." — Chuck (19:03)

• On the cultural leap of mechanical clocks:

  "All of a sudden it wasn't like, the sky is purple, so I better milk the cows. It was like, oh, it's one in the afternoon, so I better milk the cows." — Josh (34:31)

• On portable timekeeping:

  "Coiled springs meant they became portable, because, of course, humans love to make things portable." — Josh (36:23)

• On shifting societal rhythms:

  "Lewis Mumford...says that...removing people from the rhythms, the natural rhythms of the day and imposing time on them...That is the birth of the modern era, not steam power..." — Josh (34:31)

• On grandfather clocks:

  "...didn't get the name grandfather clock until 1820. I'm sorry, 1876. And that's actually from a song called my grandfather's clock." — Chuck (40:17)

• On atomic clocks:

  "From crystal quartz came atomic clocks. And from atomic clocks came things like GPS is how your iPhone or, you know, Google phone keeps track of the time..." — Josh (41:33)

Timestamps for Key Segments

• 00:28 – 02:46: Origins of timekeeping — gnomon, sundials, ancient China.
• 04:06 – 08:05: Sundials in Egypt & Greece; hemicycle and portable sundials.
• 11:48 – 13:39: Timekeeping in Rome and by Muslims; religious and practical timing.
• 15:24 – 19:33: Water clocks; mercury; incense clocks and alarm innovations.
• 20:13 – 21:43: Candle clocks and astrolabes.
• 23:22 – 25:28: Tower and automaton clocks, Chinese water-powered clocks, and ornate designs.
• 26:00 – 31:34: Mechanical clocks, weights, gears, and verge & foliot mechanism; cultural impact.
• 33:32 – 36:56: Clocks in churches and daily life; shift toward uniform hours.
• 36:56 – 40:52: Pendulum clocks, spring-driven portability, Clement's grandfather clock.
• 42:38 – 45:03: Rise of watches—women’s jewelry to military gear.
• 45:28 – 46:29: Watch features: waterproofing, luminescence, and wristwatches as status and utility.
• 47:33 – 47:48: Etymology—"horoscope" comes from "hour marker."
• 41:33 – 42:13: Atomic clocks and the precision era.

Tone and Style

True to "Stuff You Should Know" tradition, the episode combines a rich, collaborative conversational flow, capable research, and off-the-cuff humor. Josh and Chuck strike a balance between historical detail and everyday relatability, providing both depth and accessibility. Their witty asides, self-deprecating jokes, and occasional pop culture tangents make the history of timekeeping not just educational but thoroughly entertaining.

Conclusion

If you ever wanted to know how humans went from reading the sun to glancing at their lit-up wrist for the time, this episode delivers the essential story—with chronologically relevant laughs, social context, and plenty of sidebars worth quoting. Whether you’re a horology enthusiast or just "watch" curious, you’ll never look at your phone’s clock the same way again.