StarTalk Explainer: Earth's Motion Across 9 Dimensions

In this StarTalk Explainer, Neil deGrasse Tyson and Chuck take you on a tour of Earths motion, from the speed of rotation at the equator to the Sun's orbit around the galaxy. They explain how the equator moves about 1000 miles per hour while higher latitudes move more slowly, and how the Sun travels about 18 miles per second around the center of the solar system. The conversation then climbs to longer timescales, describing axial precession, a 26 000 year wobble, and the Chandler wobble which cycles roughly every 14 months. They also discuss the Moon Earth system, the Sun's corkscrew path through the Milky Way, and the larger cosmic motion including the Andromeda collision and the Great Attractor. The episode ends with a playful note that Mother Earth is twerking in nine dimensions.

Introduction and Scene

At the Hayden Planetarium, Neil deGrasse Tyson and Chuck begin a journey through motion. They highlight that Earth is not stationary but in constant, multi scale movement. The rotation carries equatorial points at roughly 1000 miles per hour, while near the poles the motion is much less, creating a dynamic picture of our everyday environment.

Daily Motion and Solar Orbit

The discussion then layers in the solar system level, noting that the Earth rotates while also orbiting the Sun at about 18 miles per second. This combination means that at any moment we are moving in at least two major directions simultaneously, a reminder of the complex frame in which we live.

Axial Wobble: Precession and Chandler

The hosts introduce axial motions beyond simple rotation. Precession is the slow wobble of Earth's axis, a cycle of roughly 26 000 years. They compare it to a spinning top that wobbles as it slows, a behavior driven by external torques, notably from the Moon and the Sun. In addition to precession, the Chandler wobble occurs on a much shorter timescale, about 14 months, and shifts our instrument frame slightly over time.

Astrology, Constellations and North Star

The movement of the rotation axis and the wobble influence how the Sun appears to trace through the sky, affecting which constellation the Sun is considered to inhabit at different times. The discussion touches on the fact that there are more constellations than the traditional 12 in the zodiac and how the North Star has shifted over millennia from Thuban to Polaris due to axial motion.

Orbit, Tilt, and the Moon-Earth System

Beyond axial motion, the Earth-Moon system orbits the Sun in an elliptical path. The orbital ellipse is not fixed; the perihelion point slowly migrates, a consequence of orbital precession and the rotating frame of reference. The Moon and Earth revolve around their common center of gravity, which lies about 1000 miles beneath the Earths surface, a gravitational partnership that shapes tides and orbital dynamics.

Galactic Journey: The Sun in the Milky Way

The scale rises again as Tyson describes the solar system corkscrewing through the galaxy. Our solar system moves as a coherent unit in a helical path around the galaxy, tracing a rough 21 galactic orbits over its 4.5 billion year history. The solar systems vertical bobbing in the galactic plane adds another layer to our understanding of motion in the cosmos.

Local Group, Andromeda, and the Cosmic Stage

The conversation broadens to the galaxies surrounding the Milky Way. The Local Group is drawn toward the Great Attractor in the cosmic web, a region of intense gravity thought to be shaped by dark matter and mass concentration. In the near future, the Milky Way is destined to collide with Andromeda, a dramatic event moving at tens of miles per second that will distort spiral patterns and scramble orbital alignments.

Reflection: Feelings of Motion and the Big Picture

The episode closes with a reflection on why we do not feel these motions in everyday life, a consequence of friction and the free motion of space. The hosts celebrate the sheer scale and beauty of motion with a lighthearted line about Earth twerking in nine dimensions, underscoring the dynamic nature of our place in the universe.