Our Home, Earth
Earth is the third planet from the Sun, and the largest of the four rocky planets in our solar system.
It’s also the only planet within the narrow band around the Sun known as the continuously habitable zone (CHZ), which is defined as the region in which liquid water can stay on a planetary surface for long periods of time. While other planets and moons may have frost or oceans of liquid methane, only Earth has oceans and lakes of water. Because of this, Earth is the only object in the solar system on which we know life exists.
The Apollo 8 crew were the first to see Earth from the moon. This photograph, dubbed “Earthrise,” became iconic. (NASA/Apollo 8)
On November 27, 2022, a camera on the Artemis I mission captured the Earth as the spacrecraft traveled in orbit around the moon. (NASA)
Earth is also the only rocky planet that has total solar eclipses. Venus and Mercury don’t have moons, and Mars’s two moons are too small and not at the right distance to completely block out the disk of the Sun. Our solar system’s four giant gas planets (Saturn, Jupiter, Uranus, and Neptune) have moons that are the right size and distance, but because they don’t have a solid surface to stand on, it would be tough to see an eclipse from there!
This animated GIF is made of 13 images of the March 11, 2016, eclipse taken by NASA’s Earth Polychromatic Imaging Camera. (NASA/DSCOVR EPIC team)
The Perseverance Rover captured Mars’s moon Phobos crossing in front of the Sun on April 20, 2022. Phobos is about 16 miles across, so it only covers a small portion of the Sun’s disk. Because the edges of the Sun are still visible, this would be considered an annular eclipse. (NASA/JPL-Caltech/ASU/MSSS/SSI)
Jupiter’s moon Io casts a shadow on the planet in this image taken by the Juno spacecraft on September 11, 2019. Because Jupiter has 92 moons, eclipses are common. Yet viewing them is currently impossible as there are no spacecraft flying close to the surface. The raw image was color-enhanced by citizen scientist Kevin M. Gill. (NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill)
A triple eclipse occurring on Jupiter, captured by the Hubble Space Telescope on March 28, 2004. (NASA/ESA/University of Arizona/E. Karkoschka)
Earth is also unique as the only known planet in the universe that has artificial light. Our ability to illuminate our homes and cities creates patterns of light visible from space. The view of our planet at night is beautiful, but it does have a dark side. Just 100 years ago people all over the world could look up and see a starry sky, but now millions of people are only able to see a few of the brightest stars, due to light pollution. As a result, there is a worldwide movement to create Dark Sky Parks—places where outdoor illumination is strictly regulated. This allows for nocturnal animals to thrive, astronomers to conduct research, Indigenous people all over the world to continue to use the sky as a source of knowledge and traditions, and the public to experience a clear view of stars, planets, and our Milky Way galaxy.
A time-lapse made by combining 710 images taken by European Space Agency astronaut Paolo Nespoli on the International Space Station on September 12, 2017. (ESA/Paolo Nespoli)