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3. Is the Earth round?

**Is the Earth round?**  The Earth is an **irregularly shaped ellipsoid**. Earth from space*This NASA image shows  Earth from  space. The image is a combination of data from two satellites. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s Terra satellite collected the land surface data over 16 days, while NOAA’s Geostationary Operational Environmental Satellite (GOES) produced a snapshot of the Earth’s clouds.* While the Earth appears to be round when viewed from the  vantage point of space, it is actually closer to an ellipsoid. However, even an  ellipsoid does not adequately describe the Earth’s unique and ever-changing shape. Our planet's diameter bulges at the equator due to the centrifugal force created by the earth’s constant rotation. Mountains rising almost 30,000 feet and ocean trenches diving over 36,000 feet(compared  to sea level)  further distort the shape of the Earth. *Sea level* itself is even irregularly  shaped. Slight variations in Earth’s gravity field cause permanent hills and  valleys in the ocean’s surface of over 300 feet. Additionally, the shape of the Earth is always changing.  Sometimes this change is periodic, as is the case with daily tides that affect  both the ocean and the crust; sometimes the change is slow and steady, as with  the drift of tectonic plates or the rebound of the crust after a heavy sheet of ice has melted; and sometimes the shape of the planet changes in violent,  episodic ways during events such as earthquakes, volcanic eruptions, or meteor  strikes. The National Geodetic Survey measures and monitors our  ever-changing planet. Geodesy is the science of measuring and monitoring the  size and shape of the Earth, including its gravity field, and determining the  location of points on the Earth’s surface.
 More **Information** What is the geoid? What is geodesy? NOAA's National Geodetic Survey Geodesy (audio podcast) Building a Better Geoid (audio podcast)   Get **Social** Social
  **Last updated:** 10/04/23 **Author:** NOAA How to cite this article Contact Us


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