Earth’s shadow: When can you see it?

Earth's shadow: Snowy mountain rising from foggy lowland, against blue sky with a horizontal fuzzy pink stripe.
View at EarthSky Community Photos. | Did you miss the lunar eclipse earlier this month, when Earth’s shadow fell on the moon? Like all worlds orbiting a sun, Earth casts a shadow. It extends some 870,000 miles (1.4 million km) into space. And you can see it – easily – twice a day. You’ll want to look eastward after sunset for the shadow (or westward before sunrise). Earth’s shadow is the dark blue line above the horizon. And the Belt of Venus is the name for the pink band above the shadow. Stephanie Longo captured this image at Eleven Mile Canyon State Park in Colorado in 2020. You can just see Earth’s shadow, above the ridgeline to the right of the image. Thank you, Stephanie!

Earth’s shadow is easy to see

Like all worlds orbiting a sun, Earth casts a shadow. It’s easy to see in the sky, just after sunset and before sunrise. In fact, you’ve probably already seen Earth’s shadow, many times, as day changes to night.

That’s because night itself is a shadow. When night falls, you’re standing within the shadow of Earth.

The best time to watch for Earth’s shadow is when it’s creeping up on your part of Earth … Like all shadows, the shadow of Earth is always opposite the sun. So, you’ll want to look eastward after sunset for the shadow (or westward before sunrise).

In the photos above and below, Earth’s shadow is the dark blue line above the horizon. And the pink band above the shadow is the Belt of Venus.

Nearly full moon rising in blue and pink horizontally striped sky over deep blue water.
View at EarthSky Community Photos. | Cissy Beasley captured the moon from Rockport, Texas, in September 2020. She wrote: “As a longtime fan of the original StarDate radio show when I was a student at UT Austin, I have since been intrigued with nature photography. As a professional nature photographer, I eagerly embrace opportunities to capture scenes of sunrises and sunsets, and the moon. Last night, I found a nice spot for documenting the rising moon amid the Belt of Venus. Here is what I saw!” Gorgeous, Cissy. Thank you!

Available now! 2023 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year! Makes a great gift.

What to look for to see Earth’s shadow

The shadow is a deep blue-grey, and it’s darker than the blue of the twilight sky. The pink band above the shadow is the Belt of Venus.

The shadow of the Earth is big. You might have to turn your head this way and that – along the arc of the horizon opposite the sun – to see the whole thing. And, just so you’ll recognize it more easily, remember that the shadow is curved, in exactly the same way that the whole Earth is curved.

And, once you spot it, don’t go back inside just yet. Wait awhile, and watch Earth’s shadow ascending or descending at exactly the same rate that the sun is rising or setting on the opposite horizon.

Earth's dark blue shadow and pink belt of Venus, over clouds with trees in the foreground.
View at EarthSky Community Photos. | Most people picture Iran as mountains and deserts, but there are great forested regions, too. Mohsen Salehi captured this image on October 17, 2019, in the Alimastan jungle in Iran’s Chelav Rural District. Known for its scenery and nicknamed ‘Iran Green Gold,’ the area attracts nature photographers. Mohsen wrote: “Earth’s shadow and Belt of Venus over an ocean of cloud.” Thank you, Mohsen!
Diagram of sun, Earth and moon, with Earth's shadow extending into space, falling on the moon.
A lunar eclipse takes place when the sun, Earth and full moon line up in space. The full moon passes through Earth’s shadow. Image via Wikimedia Commons (CC0 1.0 Universal Public Domain).

Our shadow is why we see lunar eclipses

Earth’s shadow extends so far into space that it can touch the moon. That’s what a lunar eclipse is. It’s the moon within Earth’s shadow.

When the sun, the Earth and the moon align in space (nearly or perfectly), with the Earth between the sun and moon, then Earth’s shadow falls on the moon’s face. That’s when people on Earth see the shadow gradually turn a bright full moon dark in a lunar eclipse.

As seen from Earth’s surface, there are typically two or more lunar eclipses every year. Some are total, some are partial, some are a subtle kind of eclipse known as penumbral.

During a lunar eclipse, a very small amount of light from the sun filters through Earth’s atmosphere onto Earth’s shadow on the moon. It’s why – at the middle part of a total lunar eclipse – the shadow on the moon looks reddish.

Large orange-red moon in dark blue sky over a steep brushy hillside.
Eclipse guru Fred Espenak in Arizona – whose calculations of eclipses have been a mainstay of eclipse observing for decades – wrote of the January 31, 2018, total lunar eclipse: “What a wonderful total lunar eclipse! This was my 30th, and the 1st one I’ve seen where the moon set during totality.” Image via Fred Espenak/ Used with permission.

The view from space

Another way to get an awareness of Earth’s shadow is simply to think about it as seen from space.

The image below provides a beautiful global view of Earth at night. It’s a composite image, assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite over nine days in April 2012 and 13 days in October 2012.

The dark part is, of course, Earth’s shadow.

Full Earth at night with patches of artificial light on dark side.
Global view of Earth at night. Image via NASA..

Bottom line: Look for Earth’s shadow in both the evening and morning sky. It’s a blue-gray darkness in the direction opposite the sun, darker than the twilight sky. The pink band above the shadow – in the east after sunset, or west before dawn – is the Belt of Venus.

November 20, 2022

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