NASA’s Psyche spacecraft has successfully captured remarkable images of Earth and the Moon from approximately 180 million miles away. This distance is notably closer than the average separation between Earth and Mars, which is around 40 million miles. The images, taken on July 20 and 23, 2023, reveal both celestial bodies as featureless dots of light against the vast backdrop of stars in the constellation Aries.
Launched in October 2023, the Psyche spacecraft is en route to explore the metallic asteroid Psyche, which is believed to be the remnants of a protoplanet’s iron-nickel core. The spacecraft is scheduled to reach its destination in August 2029, where it will spend over two years mapping and studying the asteroid, which measures approximately 175 miles in length. Insights gained from this research could enhance our understanding of Earth’s own metallic core, which remains largely inaccessible thousands of miles beneath the surface.
The images from Psyche serve as a poignant reminder of Earth’s relative size in the universe. When viewed from the Moon, located about 239,000 miles away, Earth appears around four times larger than the Moon or approximately 2 degrees across. Despite its significant size, Earth occupies only a small fraction of the lunar sky, highlighting the vastness of space.
Looking from the Sun, Earth would resemble a star, indistinguishable even through binoculars. Observing through a small telescope would reveal a pea-sized, blue planet, adorned with mottled clouds and hints of land. In contrast, the Moon would appear much smaller and dimmer, akin to a chia seed.
The journey of Psyche and its imagery underscores the enormity of space. In just a single day, Earth and its inhabitants travel approximately 1.6 million miles as the planet orbits the Sun. This immense distance contributes to the perception that the universe is predominantly empty, with most celestial bodies appearing as mere points of light.
While telescopes can magnify planets into recognizable forms, smaller objects such as asteroids and comet cores often look like stars, except when viewed through the largest instruments. Even massive stars like Betelgeuse, a bright red supergiant located in the constellation Orion, remain pinpricks of light unless observed through specialized telescopes.
Space is not devoid of matter, but rather sparsely populated. The average density of visible matter across the cosmos is around 4-5 protons per cubic meter, which is significantly less dense than any artificial vacuum created on Earth. To visualize this, consider a cube measuring 3.2 feet across, containing only a few submicroscopic particles.
As distance from an object increases, its apparent size diminishes. This phenomenon explains why binoculars are necessary to read distant objects, such as the name on a vessel in Lake Superior, before it arrives at port. The same principle applies to Earth when viewed from farther out in space, where its brightness also decreases. From Mars, Earth shines similarly to Jupiter and displays phases like the Moon when observed through a telescope.
At a distance of 888 million miles from the Sun, Earth would appear significantly dimmer, shining only slightly brighter than stars in the Big Dipper. If one were to travel to Alpha Centauri, the nearest star system located about 25 trillion miles away, Earth would be nearly invisible, lost in the glare of the Sun, which would shine similarly to the star Altair.
Astronomy not only expands our understanding of the cosmos but also enhances our appreciation for our planet. Observing the universe’s vastness helps to clear mental clutter and offers a fresh perspective on the significance of Earth, reminding us of how precious our small blue planet truly is.