Thanks to NOAA for the answer:
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 is pudgier at the equator than at the poles by about 70,000 feet. This is 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 relative to an ellipsoid.
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 of the National Oceanic and Atmospheric Administration 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.
Image description: Although 75% of the planet is a relatively unchanging ocean of blue, the remaining 25% of Earth’s surface is a dynamic green. The darkest green areas are the lushest in vegetation, while the pale colors are sparse in vegetation cover either due to snow, drought, rock, or urban areas. Data from the NASA/NOAA Suomi NPP satellite is able to detect these subtle differences in greenness.
View and download more images and video animations of vegetation on Earth.
Image from NASA/NOAA.
Image description: NASA’s Cassini spacecraft captured this image of Earth and the moon from its perch in the Saturn system nearly 900 million miles away.
Pictures of Earth from the outer solar system are rare because from that distance, Earth appears very close to our sun. A camera’s sensitive detectors can be damaged by looking directly at the sun, just as a human being can damage his or her retina by doing the same. Cassini was able to take this image because the sun had temporarily moved behind Saturn from the spacecraft’s point of view and most of the light was blocked.
View more images of Earth from Cassini.
Image from NASA/JPL-Caltech/Space Science Institute.
Image description: This animated gif shows a global composite image showing the glow of natural and human-built phenomena across the planet.
Learn about the technology used to capture these nighttime images of Earth from space on NASA’s website.
Image description: This new global view of Earth’s city lights is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (NPP) satellite. The data was acquired over nine days in April 2012 and 13 days in October 2012. It took 312 orbits to get a clear shot of every parcel of Earth’s land surface and islands. This new data was then mapped over existing Blue Marble imagery of Earth to provide a realistic view of the planet.
View a larger image.
Image from NASA’s Earth Observatory/NOAA/DOD