Podcast Summary: The Rest Is Science

Episode: "The Device That Maps The Heavens"

Hosts: Professor Hannah Fry & Michael Stevens (Vsauce)
Release Date: December 18, 2025

Overview

In this "Field Notes" edition of The Rest Is Science, Professor Hannah Fry and Michael Stevens immerse listeners in the lore and mechanics behind celestial mapping tools, orbital motion, and the quirky characters of scientific history. The episode unfolds around hands-on exploration with an ellipsograph ("the device that maps the heavens"), planetary orreries, and color-mixing cubes. Along the way, the hosts field listener questions—delving into memorable scientists, debunking the goldfish memory myth, and musing on bizarre deaths in science.

Key Discussion Points & Insights

1. Ellipses, Ellipsographs, and Drawing Devices

• [02:50–05:20]
  Hannah introduces an ellipsograph, a tool that beautifully over-engineers the task of drawing perfect ellipses—shapes fundamentally different from circles.
  • On ellipses vs. circles:
    "A circle is a fixed distance from a single point... An ellipse is way harder. Because instead of having one focus, you have two." —Hannah (03:30)
    Michael admires the device: "Those shuttles are following straight line tracks. And yet we trace out an ellipse from circular motion. Well, from linear motion, we get circular motion. I love that." (04:00)
  • Engineering appreciation:
    Observing the brass construction, Michael remarks, "I've seen them made of wood and plastic, but this is like brass. Look at that." (05:09)

2. Historical Shift: Orbits Aren’t Circular—They’re Elliptical!

• [05:25–07:16]
  The hosts recount the dramatic saga of how planetary motion was re-understood.
  • The Greeks insisted celestial bodies moved in "perfect" circles for millennia, but Tycho Brahe’s diligent observations (“he also had a pet elk… the elk passed away because it got drunk,” jokes Hannah at 06:38) and Kepler’s eventual calculations "swallowed a cartload of dung” to accept ellipses (07:05).
• Memorable quote:
  “He just hated, hated the idea that there might be anything other than circles in the sky.” –Hannah (06:50)

3. The Orrery Calendar and Orbital Motion

• [07:16–10:21]
  Michael presents a flipbook orrery calendar, visualizing planetary positions day-by-day through the year.
  • “It doesn't tell you an inspirational quote... It shows you the relative positions of the planets each day.” —Michael (07:28)
  • The duo marvell at how Mercury whizzes, Earth completes a lap, Jupiter barely moves, and Jupiter's rapid axial rotation (10hr per day! at 09:07) generates its persistent storms.
  • Physics digressions:
    They riff on planetary rotation making us lighter: “On Earth, we are rotating at hundreds of miles per hour... We weigh a few fractions of a gram less because of its rotation.” —Michael (09:58)

4. Centrifugal Experiences—From Jupiter to Theme Parks

• [10:21–11:53]
  Tangents to amusement park rides: Negative G-forces, rollercoaster fears, and personal anecdotes.
  • Michael admits: “As a kid, I actually collected newspaper clippings of deaths on roller coasters. It made me feel like my fear was justified.” (11:22)

5. Color Mixing and the CMY Cube

• [12:08–14:15]
  Michael gifts Hannah’s daughters a CMY color mixing cube, which demonstrates subtractive color theory in a tactile, mesmerizing way.
  • “It is a translucent cube… and the colors that you’ll find are… cyan, magenta and yellow. CMY.” —Michael (12:15)
  • Hannah puns: “Do you know where you send naughty rainbows?... To prism.” (13:49)
  • Michael adds, “Prisms can create rainbows, but they can also destroy them. If you send a prism through a rainbow, it comes out as white light.” (13:56)

6. Science Dinner Party—Who’s Invited?

• [17:22–23:16]
  Listeners’ mailbag: “Invite three people (dead or alive) from science to a dinner party.”
  • Michael’s first pick: Einstein (wants to know his last words);
  • Hannah: Galois, the young French mathematician whose final-night scribblings changed modern math (20:00).
  • They add Archimedes (Michael): “On his gravestone… a sphere, a cylinder and a cone of equal heights. Because he showed the relationships between their volumes.” (22:00)
  • Greek mathematicians: Stories about Pythagoras and bean-phobia (23:23), Archimedes’ death over "not disturbing his circles" (22:40), and the dark humor of hosting a dinner party themed around such “stupid deaths” (22:52).

7. Debunking the Goldfish Memory Myth

• [24:45–25:51]
  Hannah and Michael set the record straight: Goldfish don’t have three-second memories; they can solve mazes and retain information for months (25:01).
  • “I think it’s just snobbery… But also it really does, I think, underline the cruelty of putting a goldfish in a bowl where it’s got nothing to do.” —Hannah (25:05)

Notable Quotes & Moments

• On the love of over-engineering scientific tools:
  “They’re the coolest objects. They are how the planets move.” —Michael & Hannah (05:19–05:26)
• On the stubbornness of scientific tradition:
  “He said it was like a cartload of dung… because he just hated…the idea that there might be anything other than circles in the sky.” —Hannah, about Kepler (06:50)
• Puns and playful moments:
  Hannah: “Do you know where you send naughty rainbows? …To prism.” (13:49)
  Michael: “Prisms can create rainbows, but they can also destroy them.” (13:56)
• Darkly comic anecdote:
  “As a kid, I collected newspaper clippings of deaths on roller coasters… It made me feel like my fear was justified.” —Michael (11:22)

Key Timestamps

• 02:50 – Introduction to the ellipsograph and drawing ellipses
• 05:25 – Planetary motion: Greek circles vs. ellipses and the Tycho–Kepler saga
• 07:16 – Michael’s orrery flip calendar and discussion of orbital speeds
• 10:21 – Gravity, rotation, and why we weigh less on Earth’s equator
• 11:53 – Michael’s childhood rollercoaster anxieties
• 12:08 – The CMY color cube and subtractive color magic
• 13:49 – “Naughty rainbow” prism pun and quirky light facts
• 17:22 – Listener question: Dinner party with historical scientists
• 24:45 – Goldfish memory: myth vs. reality

Tone & Atmosphere

• Conversational, cheeky, and curiosity-driven: The hosts balance deep scientific content with playful banter, personal stories, and historical gossip.
• Accessible explanations: Even complex concepts like orbital mechanics and color theory are made tangible, often with physical gadgets and analogies.
• Enthusiasm for quirks of science history: Good-natured ribbing of both the giants of science and each other.

For First-Time Listeners

This episode is a lively, story-packed journey through the mechanics—and odd characters—behind the mapping of the heavens. The hosts’ approachable style, hands-on demos, and gleeful puns make it as fun as it is informative. Whether you're drawn by the math behind orbits or the lore of madcap mathematicians, there's something in this episode to delight and surprise.