Can you see the shadow of the earth?

Where there is light and objects, there is always a shadow. Blocking sunlight also creates a shadow on the earth.

But can you see the shadow of the Earth? Astronomers told Live Science that they can indeed see it gripping some objects. In fact, under the right conditions, you might even be able to spot Earth’s shadow every day.

shadow reflected on the moon

Because the Sun is an extended light source (i.e., not a single point of light), Earth’s shadow has three parts. A dark central umbra, a lighter peripheral penumbra, and a dark shadow that appears in the distance, with overlapping penumbra areas replacing the umbra.

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Earth’s shadow is most noticeable during a total lunar eclipse. During a lunar eclipse, the full moon passes through the Earth’s shadow. The moon enters the Earth’s penumbra, then enters the umbra, and passes through the penumbra again. The moon only dims slightly, making it difficult to discern Earth’s penumbra. In contrast, the umbra is up to 2.7 times the moon’s diameter, making it much easier to see.

However, when the Moon is completely within the Earth’s umbra, it is usually not completely black. Most often pale to dark red in color. That’s because Earth’s atmosphere scatters sunlight and bends the reddish light into the umbra.

“In a sense, we’re seeing sunrise and sunset on Earth reflected off the moon!” Emily Rice, a professor of astronomy at the Macaulay Honors College at the City University of New York, told Live Science in an email.

Shadows also tell us about Earth’s atmosphere. “The cloudier and dustier Earth’s atmosphere is at the time, the redder the moon appears,” she noted.

By comparison, it is possible to see a blackened Moon when it straddles the boundary between Earth’s umbra and penumbra. Astrophysicist Fred Espenak writes in EclipseWise that this is due to a contrast effect, as the moon’s penumbra is 500 times brighter than the umbra.

Earth’s shadow is also visible during a partial lunar eclipse, when only part of the moon passes through the umbra.

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But you don’t have to wait for a solar eclipse to see Earth’s shadow. Just before sunrise and just after sunset, the silhouette of our planet, thrown into space, is visible in the sky near the horizon in the opposite direction from the sun.

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“During the day, clear skies are bright because direct sunlight illuminates gas molecules and particles in the atmosphere, potentially scattering some of the sunlight,” Raymond L. Lee, an adjunct professor in the U.S. Naval Academy’s Department of Mathematics and Science, told Live Science via email. “As the sun sets or rises, [roughly] The spherical shape of the Earth prevents the lowest solar rays from directly illuminating the atmosphere, thereby casting a curved shadow on the corresponding lowest part of the atmosphere on the opposite side of the sun. ”

However, the exact features that make up Earth’s shadow are debated. According to a 2017 study published in the journal Applied Optics, this shadow consists of a dark blue band at the top and a brown band at the bottom. But Giovanni Di Giovanni, an amateur astronomer with a master’s degree in physics from Italy’s University of L’Aquila, says neither is a true shadow. Rather, our planet’s shadow is “a thin, very dark band with very little contrast compared to other bands above it,” he told Live Science via email.

In either case, shadows exist until the sun is directly above the horizon and about 4 degrees below it. The planet’s silhouette will remain for about 15 minutes, then disappear with sunrise or blend into the darkening night sky.

To see Earth’s shadow, you need a clear, dust-free sky at high altitude. “Few observers would notice it…only from the top of a high mountain, and probably not too difficult from an airplane,” di Giovanni said.

Earth’s shadow reflected on other objects

Finding Earth’s shadow on other objects is possible, but more difficult. When the International Space Station passes overhead at dusk on a cloudless day, stargazing binoculars will tell you that it appears dimly as it moves into Earth’s shadow.

Additionally, telescopes can show how geostationary satellites “disappear” in Earth’s shadow. These satellites appear fixed in the sky because they orbit directly above the equator at the same speed as the Earth’s rotation. According to satellite operator Space Norway, most geostationary satellites are bathed in sunlight. But it changes by about 21 days with each equinox. According to the Australian Space Weather Prediction Center, during these “eclipse seasons,” satellites slip into Earth’s shadow for several minutes each night.

Earth’s shadow also appears on passing asteroids. For example, astronomer Gianluca Massi, founder of the Virtual Telescope Project, wrote in a blog post that one of their telescopes recorded 10 minutes and 50 seconds of the house-sized asteroid 2016 VA dimming and disappearing as it passed through Earth’s shadow at a distance of 74,520 miles (120,000 kilometers).

However, there is a limit to the extent to which the Earth’s shadow can spread. ” [Earth’s] “The umbra is a very long cone that extends about 1.4 million kilometers (870,000 miles) from Earth,” Rice said. Therefore, Earth’s shadow will not reach its nearest neighbor, Mars, which is 34 million miles (55 million kilometers) away. Still, with so many objects passing through Earth’s shadow, there are many ways to continue to see and marvel at the silhouette of our planet.

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