Earth's shadow

The Earth makes a big shadow in space.

You can see it in the sky. It looks like a dark blue band. This happens at dawn or dusk.

A pink band sits above the blue shadow. This pink band is called the Belt of Venus. It blends into the blue part.

Sometimes the shadow falls on the Moon. This makes a lunar eclipse. The Moon looks red then.

It is fun to watch the sky change.

Earth casts a shadow into space. This shadow is called an umbra.

You can see part of this shadow in the sky. It looks like a dark blue or purple band. This happens at dawn or dusk. The band stays near the horizon. It is easiest to see when the sky is clear. You can see it better if you are high up. For example, looking over the sea helps.

A pink band often sits above the blue shadow. This is the Belt of Venus. The pink band and the blue shadow blend together. The pink color comes from red light. At sunset, sunlight travels through thick air. The air acts like a filter. It lets red light through to the sky.

Sometimes Earth's shadow falls on the Moon. This causes a lunar eclipse.

During this time, the Moon looks red or copper. This happens because some red light still reaches the Moon. The light bends as it passes through our air. This makes the Moon glow with a soft red color.

Earth casts a huge shadow into outer space. This shadow is called an umbra. You can see part of it during twilight. Twilight is the time at dawn or dusk. The shadow looks like a dark blue or purple band. It stretches across the horizon. This band is most distinct when the sky is clear.

This shadow works in a very specific way. The Sun shines toward the Earth. The Earth blocks some of that light. This creates a dark area behind our planet. This shadow is as curved as the Earth itself. It can even reach all the way to the Moon. The shadow appears to move during the day. It recedes as the Sun rises in the morning. It rises as the Sun sets in the evening.

Scientists can use math to understand this shadow. The Sun and Moon look almost the same size from Earth. Because of this, we can find the shadow's length. The Earth's diameter is 3.7 times the Moon's diameter. The umbra is 3.7 times the average distance to the Moon. This distance is about 384,400 kilometers. The shadow's width at the Moon is about 2.6 lunar diameters.

Sometimes you might see a pink band above the shadow. This is called the Belt of Venus. It is also known as the anti-twilight arch. The pink band sits above the dark blue shadow. The two colors blend together without a hard line. The pink color comes from red sunlight. This light hits small particles in the lower atmosphere. The light then bounces back to your eyes.

Earth's shadow also causes lunar eclipses. This happens when the Sun, Earth, and Moon align. The Earth sits right between the Sun and the Moon. Its shadow then falls onto the Moon's surface. The Moon does not go completely dark. Instead, it turns a reddish or copper color. This happens because Earth's atmosphere bends light. The air filters out most colors. Only the long red light reaches the Moon.

Earth casts a massive shadow through its atmosphere and into outer space. This phenomenon is known as Earth's shadow. It is directed toward the antisolar point, which is the direction exactly opposite the Sun. During the twilight periods of dawn and dusk, we can see a portion of this shadow. This visible part is often called the dark segment or the twilight wedge. It appears as a dark, diffuse band stretching across the horizon.

The shadow's appearance depends heavily on your location and the sky. The dark fringe often looks like a bluish or purplish band. It can stretch over 180 degrees of the horizon. You might see it in the eastern sky at dusk or the western sky at dawn. To see it clearly, you need a clear sky and an unobstructed horizon. Looking out over a low horizon, such as the sea, helps a lot. If you are at a higher elevation, the shadow appears even sharper.

We can use geometry to understand the scale of this shadow. The Sun and the Moon have almost the same angular diameters when viewed from Earth. This means we can use ratios to calculate the shadow's size. Earth's diameter is 3.7 times larger than the Moon's diameter. Because of this, the length of the planet's umbra is 3.7 times the average distance between the Earth and the Moon. The shadow's diameter at the distance of the Moon is about 2.6 lunar diameters. This large size allows Earth to cast a shadow big enough to cover the Moon.

Sometimes, a beautiful pink band appears just above the dark shadow. This is called the Belt of Venus, or the anti-twilight arch. It is named after the planet Venus because that planet is often visible in this region. The pink band and the blue shadow blend together without a sharp dividing line. This is a different phenomenon than the afterglow, which appears in the opposite part of the sky. The color of the Belt of Venus comes from how sunlight interacts with our atmosphere.

Specific physics explain why these colors appear in the sky. When the Sun is near the horizon, its light must pass through a very thick layer of atmosphere. This atmosphere acts like a filter. It scatters most colors but lets the longer, redder wavelengths pass through. This red sunlight hits small particles in the lower atmosphere. The light then undergoes backscattering, where it bounces back toward the observer. This makes the Belt of Venus look pink. As the Sun sinks lower, the boundary between the pink and blue becomes less defined. This happens because the Sun illuminates a thinner part of the upper atmosphere. In those higher areas, there are fewer particles to scatter the red light, so we see the usual blue sky caused by Rayleigh scattering.

Earth's shadow is also responsible for the spectacular sight of a total lunar eclipse. This occurs when the Sun, Earth, and Moon align perfectly. The Earth sits directly between the Sun and the Moon. Consequently, the Earth's shadow falls onto the side of the Moon facing the night side of our planet. This shadow gradually darkens the full Moon. The shadow itself is as curved as the Earth is because it is cast by a spherical planet.

Even during a total eclipse, the Moon does not go completely dark. A small amount of sunlight still reaches the lunar surface. This happens because Earth's atmosphere refracts, or bends, the light as it passes through. The air molecules and particles scatter the shorter wavelengths of light. However, the longer, reddish wavelengths are able to reach the Moon. This indirect light gives the eclipsed Moon a dim, reddish, or copper color. This process is very similar to why the Sun looks red during a sunset.