You might not be aware of this, but the Earth actually casts a huge shadow into space, and under the right conditions, this shadow can be seen. While most people associate this with a lunar eclipse, scientists say that Earth’s shadow can be seen far more often, even from the ground just before or after sunrise or sunset.
The shadow itself is caused by the Earth blocking the sun’s rays, which creates dark spots. These spots can be seen on the Moon, other satellites, and even the sky.
The shadow exists in three sections, which include the dark central umbra and the lighter penumbra and the distant antumbra. The full moon enters the penumbra during a total lunar eclipse and then moves into the umbra while it transforms from a faint light to a deep red colour because sunlight scatters through Earth’s atmosphere.
Macaulay Honours College astronomy professor Emily Rice explained that we perceive sunrises and sunsets, which happen on Earth, through their reflection on the Moon.
The partial lunar eclipse reveals the shadow of the Moon, while the black spots on the Moon show where the penumbra and umbra meet. The shadow shows Earth's atmosphere changes because a dustier or cloudier atmosphere makes the moon appear redder.
You don’t need to be waiting for an eclipse to see Earth’s shadow. Before or after a sunrise, Earth’s shadow will appear as a curved shadow on the horizon opposite the sun. Raymond L. Lee, an adjunct professor at the US Naval Academy, says, “The shadow appears when Earth blocks direct sunlight from illuminating the atmosphere. The shadow appears for about 15 minutes before or after sunrise or before or after sunset.”
Other objects that go through Earth’s shadow include satellites and other objects in space. Geostationary satellites go through the umbra for a few minutes near equinox time. Asteroids such as 2016 VA are seen to be dimming as they go through the shadow. The shadow is 1.4 million kilometres (870,000 miles) long from Earth.