Tumble Science Podcast for Kids · Tumble Media

How Big is the Universe?

August 8, 2025·24 min·2 clips

Henrietta Leavitt discovered a simple pattern in variable stars that let astronomers measure distances in space for the first time.

This episode of Tumble explores how astronomer Henrietta Leavitt discovered a method to measure the universe's vast distances. Hosts Lindsay and Marshall are joined by astronomer Karen Masters, who uses Leavitt's work in her own research on galaxies. Henrietta Leavitt worked as a "computer" at the Harvard College Observatory in the early 1900s, meticulously analyzing photographic plates of stars for 30 cents an hour. Her job involved cataloging the positions and brightness of stars from these glass plate images. Leavitt became particularly fascinated by variable stars, which change their brightness in regular cycles. She discovered 25 variable stars in a nearby cloud and charted their periods of brightening and dimming. Leavitt identified a clear relationship: brighter variable stars had longer periods of variation. This relationship, later named the Leavitt Law, provided astronomers with a crucial "measuring stick" for space. Before this, astronomers could not accurately measure distances to stars or other objects in space. Leavitt's boss published her findings under his own name in an astronomy journal. Her work later enabled Edwin Hubble to make a monumental discovery about the universe's scale. A key insight is that Leavitt made her discovery while performing a low-paid, repetitive data-entry job not meant for original research. Her story demonstrates how profound scientific breakthroughs can come from persistent curiosity within routine work. At the time, many astronomers believed our Milky Way galaxy constituted the entire universe. Edwin Hubble used the Leavitt Law to measure the distance to the Andromeda spiral nebula. He proved Andromeda was far outside the Milky Way, revealing the existence of other galaxies. Astronomer Karen Masters admits the universe's immense size can be paralyzing, requiring her to actively avoid thinking about it during daily tasks. Our galaxy is 100,000 light-years wide, and estimates suggest there are about 200 billion galaxies in the observable universe. Hubble, using Leavitt's foundation, also discovered the universe is expanding. The tone is educational and conversational, breaking down complex astronomical concepts with relatable analogies like car headlights. The style is narrative, telling the historical story of Leavitt's life and work with enthusiastic and playful commentary from the hosts. Young science enthusiasts and students interested in space history or unsung heroes of science would love this episode. Listeners seeking a highly technical, physics-heavy discussion of cosmology might find it too introductory.

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