Is the earth a sphere?
Executive summary
Scientists and centuries of observations show Earth is not a perfect sphere but an oblate spheroid — slightly flattened at the poles and bulging at the equator — with additional irregularities from mountains, trenches and changing mass distributions (NOAA) [1]. Multiple educational and scientific outlets lay out independent, repeatable evidence: lunar eclipse geometry, changing star visibility with latitude, satellite imagery and pendulum experiments demonstrating curvature and rotation (UNLV, NASA, StarWalk) [2] [3] [4].
1. Ancient measurement to modern confirmation — the throughline of evidence
Arguments that Earth is round began in antiquity and matured into empirical science; Aristotle and later Hellenistic and medieval scholars offered observations that supported a globe, and those methods evolved into modern measurements like satellites and seismology that confirm a roughly spheroidal planet (Wikipedia) [5]. NASA recounts the same historical thread — shadow and star motions led early observers to conclude Earth is round, a conclusion extended by mariners and later by spaceflight [3]. These are independent lines of evidence across eras and technologies.
2. What “not a perfect sphere” means in practice
Earth’s shape is best described as an oblate spheroid — a sphere flattened at the poles and bulging at the equator — and even that idealized shape misses real surface irregularities: mountains, ocean trenches and variable sea level make the planet’s true surface highly uneven; small gravity variations create permanent ocean-surface “hills and valleys” of hundreds of feet (NOAA) [1]. Popular summaries and science reporting repeat this precise point: round but irregular is the correct summary (Marca) [6] [1].
3. The core experimental clues that rule out a flat disk
Multiple, simple observations rule out a flat-Earth model: during lunar eclipses Earth’s shadow on the Moon is always circular, which is what a sphere produces from any orientation (UNLV) [2]; different constellations appear from different hemispheres because a curved surface hides parts of the sky (StarWalk) [4]; and long-baseline physics experiments such as Foucault’s pendulum demonstrate rotation consistent with a globe (UNLV) [2]. NASA also highlights shadow and stellar-motion arguments used since antiquity [3].
4. Spacecraft and satellites: not the only evidence, but decisive
Satellites and orbited spacecraft provide direct images and measurements of Earth’s curvature and gravitational field; space agencies and commercial observers consistently record the planet as round or oblate in shape (NASA, Space reporting) [3] [7]. While some critics question specific images (a recurring topic in blog posts and skeptical sites), mainstream science points to independent, instrumented measurements — not single photographs — as the robust basis for the shape model [8] [7].
5. Why flat‑Earth belief persists despite abundant evidence
Reporting on how to debate flat‑Earthers notes that the belief is often less about empirical gaps and more about distrust of institutions or emotional and social drivers; evidence alone may not change committed adherents because their conclusions can stem from distrust of scientists and authorities rather than lack of data (Universe Today, Space) [9] [7]. Coverage of flat‑Earth communities shows these views circulate in conferences and online, underscoring a social as much as a factual phenomenon (ABC News) [10].
6. Disagreements and limits in the sources
Sources are unanimous that Earth is not flat; disagreements are about nuance — the exact language used (sphere vs. oblate spheroid vs. “not perfectly spherical”) and about how to communicate those facts to skeptics (Marca, NOAA, UNLV, Space) [6] [1] [2] [7]. Scientific papers (for example on inner‑core shape changes) show the planet has dynamic internal structure and changing boundaries at depth, but available sources do not mention any credible scientific challenge to the globe/oblate‑spheroid description as a whole (NYT) [11].
7. What a balanced takeaway looks like
The evidence for a round, oblate Earth is multi-modal: historical astronomical observations, terrestrial experiments (pendulums, star surveys), satellite imagery and geophysical measurements all converge on the same picture (UNLV, NASA, NOAA, StarWalk) [2] [3] [1] [4]. Flat‑Earth narratives persist for social and epistemic reasons, not because of gaps in the physical evidence (Universe Today, Space) [9] [7]. If your question is whether Earth is a perfect sphere — the answer is no; if the question is whether Earth is globally curved and globe‑shaped — the evidence says yes.
Limitations: this summary relies on the cited news, educational and science‑outreach sources provided; detailed geodetic data and primary scientific papers are not included among the supplied documents, and are therefore not cited here (available sources do not mention full geodetic datasets).