Earth’s trees outnumber the Milky Way’s stars
Earth may have roughly 3 trillion trees, compared with an estimated 100 billion to 400 billion stars in the Milky Way. The comparison is striking, but neither total comes from counting every object one by one. Both are estimates built from observations and models—and the number of trees is especially difficult to pin down.
How can anyone count trees from space?
Satellites can map forests across huge areas, but they do not simply photograph and tally each tree. Researchers combine satellite images with measurements taken on the ground, where forest plots reveal how many trees grow in a given area. They use those samples to estimate totals across different landscapes, including remote regions that are hard to survey directly.
The result depends on what counts as a tree and on how densely different kinds of land are covered. A crowded tropical forest, a sparse woodland, and a city park cannot be extrapolated from the same sample. Better observations can also revise the estimate, so the total is not a precise, permanent census.
The comparison has limits
Astronomers likewise estimate the Milky Way’s stars rather than counting them individually. Many are too faint or obscured by dust for direct observation, so estimates draw on observations of the galaxy and models of its structure. The commonly cited range is broad because the galaxy’s full population is hard to see from within it.
Still, the scale comparison holds across those estimates: Earth’s trees are thought to outnumber the stars in our galaxy by several times. It is a reminder that a familiar living thing, spread across one planet, can exceed the population of objects in an entire star system on a galactic scale.
