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Earth’s Tilt Makes Time Slippery

The Rest Is Science

Hosted by Hannah Fry and Michael Stevens

53m
Transcript

Original podcast

Summary

Written by a model from the transcript; not yet reviewed.

In this episode of The Rest Is Science, the hosts explore the surprising physics behind why traditional sundials fail to match civil timepieces. They explain the equation of time, which accounts for the discrepancies caused by Earth's eccentric elliptical orbit and its axial tilt. A sundial can run up to sixteen minutes ahead in November and fourteen minutes behind in February due to these cumulative variations. The discussion covers how ancient organisms like coral and fish preserve historical records of Earth's rotation, and examines the mechanics of the Sunquest sundial, which automatically corrects for the equation of time using an analemma-shaped slit.

  • Sundials never agree with modern civil clocks because Earth orbits the Sun in an elliptical path at varying speeds and tilts on its axis. 22:14
  • A sundial can run up to sixteen minutes ahead of civil time in November and lag by fourteen minutes in February. 9:52
  • Microscopic analysis of fossilized coral layers reveals that ancient years contained more days because Earth's rotation is gradually slowing down. 12:50
  • The Sunquest sundial uses a wavy, analemma-shaped gnomon slit to automatically correct for the equation of time and match civil clock time. 28:40

Chapters

  1. 0:01
    Podcast Intro and Sundial Debate

    The hosts introduce the episode, joke about sundials, and set up a comedic debate about their reliability.

  2. 1:37
    Equation of Time and Solar Day Variability

    The hosts discuss how Earth's tilt and orbit cause the solar day to vary, leading to sundial inaccuracies.

  3. 3:11
    Wise Sponsored Segment

    A commercial for Wise, explaining its currency transfer services.

  4. 4:58
    Subsolar Point and Solar Noon Explained

    Michael and Hannah delve into what a subsolar point is and how it defines solar noon.

  5. 27:02
    Sundial Mechanics and the Schmoyer Design

    They introduce the Schmoyer sundial, its wavy gnomon, and how it automatically corrects for the equation of time.

  6. 36:13
    Subsolar Point in Practice: Lahaina Noon

    The conversation turns to the phenomenon of the sun being directly overhead in Hawaii, known as Lahaina Noon, and its implications for sundials.

  7. 38:53
    Moon Overhead and Lunar Noon

    They explore the rare event of the moon being directly overhead, discussing Hawaiian terminology and the rarity in the UK.

  8. 48:42
    Antipodes and the Pacific Ocean

    The hosts share interesting facts about antipodal points in the Pacific and the concept of an oceanic antipode.

  9. 52:14
    Sundial Debate Resumes

    Michael revisits his earlier skepticism about sundials, acknowledging their potential usefulness.

  10. 52:54
    Living by Intuition

    They reflect on relying on personal intuition versus external time cues and the role of society’s timekeeping.

  11. 53:31
    Ad: Bose Music

    A brief advertisement for Bose audio equipment is aired.

  12. 54:17
    Ad: Simplisafe Home Security

    Simplisafe advertises its home security system and monitoring plans.

Highlights

  • 9:52

    Sundials Never Match Civil Timedata

    The guest explains that sundials run up to 16 minutes ahead in November and 14 minutes behind in February because solar days vary in length throughout the year.

  • 12:50

    Fossilized Coral Records Earth's Slowdowninsight

    Microscopic layers in fossilized coral show that ancient years had more days, proving that Earth's rotation has been gradually slowing down over millions of years.

  • 14:13

    Dating the Chicxulub Impactstory

    Scientists determined that the meteor which drove dinosaur extinction struck in the spring by examining seasonal bone growth in ancient fish.

  • 27:18

    The Sunquest Sundial Designstrategy

    Invented in 1958, the Sunquest sundial uses an S-shaped slit in the gnomon to cast a ray of light that automatically corrects for the equation of time.

  • 33:27

    Massive Sundial Production Recorddata

    The hosts note that their team became the largest single maker of sundials in human history by producing over 20,000 licensed units.

  • 38:53

    Lahaina Noon in Hawaiiinsight

    Hawaii is the only US state where the sun passes directly overhead at solar noon, creating an event where vertical objects cast no visible side shadows.

  • 48:42

    The Pacific Ocean's Antipodeinsight

    The Pacific Ocean is so vast that its antipode lies entirely within itself, connecting a point off the coast of South America directly to the Gulf of Tonkin.

Quotes

  • “Sundials are set around solar time.”
    Michael Stevens · 7:14
  • “The sun is at the zenith, which is the point of the sky directly above your head, meaning the sun is right above you.”
    Michael Stevens · 36:30
  • “The Pacific Ocean is so big, it contains its own antipode, meaning there are two points in the Atlantic Ocean that are on opposite sides of the earth and they're still the same ocean.”
    Michael Stevens · 48:42
  • “one other problem we haven't discussed, and that is clouds.”
    Michael Stevens · 52:30
  • “aren't clouds in the sky. And the moon is up, right?”
    Michael Stevens · 52:47
  • “What time does it feel like? You know? Don't let other people tell you what time it is.”
    Michael Stevens · 52:53
  • “You can't rely on yourself.”
    Michael Stevens · 53:04
  • “This is, it's all nonsense. It's all, everything is nonsense apart from this podcast.”
    Hannah Fry · 53:08
  • Cancer Research UK 2:01–3:03
  • Wise 3:11–4:35
  • Michelob Ultra 34:34–36:00
  • SimpliSafe 54:17–54:46

About this episode

A sundial can be almost 16 minutes fast in November and 14 minutes slow in February, yet there's nothing wrong with it. So why does the Sun, our oldest timekeeper, disagree with the clock on your wrist? In this episode, Professor Hannah Fry and Michael Stevens (Vsauce) explore the equation of time - the strange relationship between Earth's tilt, its orbit around the Sun and the way we measure our days. Why does a day last 24 hours? Has it always been that way? And how can a piece of ancient coral reveal that time itself has changed? To find out, Hannah and Michael investigate an ingenious sundial that appears to correct its own mistakes, and discover the extraordinary places on Earth where shadows disappear completely. Along the way, they explore why sailors relied on the stars, the Moon's remarkable journey across London's sky, and the curious fact that the Pacific Ocean is so enormous it meets itself on the other side of the world. Michael's references:https://rl.se/subsolarpoint https://www.curiositybox.com/pages/closest-approach-to-uranus-------------------For more information about Cancer Research UK, their research, breakthroughs and how you can support them, visit https://cancerresearchuk.org/restisscience Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666), the Isle of Man (1103) and Jersey (247). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: 2 Redman Place, London, E20 1JQ. ------------------- Find The Rest Is Science all over the internet by ⁠⁠clicking here.⁠⁠ ------------------- Video Producer: Adam Thornton + Oli Oakley + Jack MeekAnimator: Sam BensonVideo & Social: Bex TyrrellProducer: Simona Rata + Lucy LipscombeSenior Producer: Lauren Armstrong-CarterChief Digital Officer: Samuel OakleyExec Producer: Neil Fearn Learn more about your ad choices. Visit podcastchoices.com/adchoices

Transcript

0:00
53:20

9,441 words · 8 speakers

Speaker names marked are inferred from speaking time and the show’s known hosts — they are not voice-verified.

Topics

  • Lahaina Noon
  • Uranus
  • Hawaii
  • Pacific Ocean
  • Lahaina Moon
  • Bose
  • Curiosity Box
  • North American Sundial Society
  • Sunquest sundial
  • Skygate

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