The Belt of Venus and the Earth’s Shadow

On clear mornings and evenings, an enchanting phenomenon known as the antitwilight arch, or the “Belt of Venus,” and the “Earth’s shadow” are two atmospheric wonders that create a mesmerizing color gradient in our skies. As dusk or dawn approaches, you can witness a breathtaking transformation above the horizon opposite the Sun, where light and shadow conjure a canvas of soft, pastel colors.

The Truchas Peaks with fresh snow and the Belt of Venus and Earh's shadow.

The pinkish glow above the Truchas Peaks in Northern New Mexico is the antitwilight arch, or the “Belt of Venus.” This glow is caused by the backscattering1 of reddened light caused by Rayleigh scattering2 of light from air molecules as sunlight traverses long paths through the atmosphere. The bluish shade below the pink band of the Belt of Venus is the shadow of the Earth, as seen on the outer layers of the atmosphere. In this photograph, there are no clouds. The reflected light is due to backscattering from air molecules.  Earlier, when the setting Sun was still above the horizon, the snowcapped peaks in this photo were lit up with strong hues of red and orange3. Above the rightmost snowy peak, one can barely see what looks like a planet in the upper left part of the Belt of Venus.  Could this be the planet Venus4

The Belt of Venus occurs due to the backscatter of reddened sunlight5 by fine particulates high in the atmosphere.  Directly beneath this pink band, you’ll notice the Earth’s shadow, a dark blue band, casting its silhouette against the sky. This shadow is the Earth itself, blocking the direct sunlight.

The juxtaposition of the Earth’s shadow and the Belt of Venus creates a stunning gradient from a deep, celestial blue to a soft, dreamy pink. This natural display is a poetic reminder of the Earth’s presence in the vast universe, visible in a delicate play of light and shadow.   When I see the Belt of Venus, it offers a calm feeling.  Perhaps due to the subtle pastel hues.

What is scattering?

In the vast theater of the sky, the colors we witness are a fascinating play of light orchestrated by a phenomenon known as scattering.

At its core, scattering is the redirection of light by atmospheric particles, and it takes different forms, painting the sky with a spectrum of colors.

Read More

We Can See the Shadow the Earth Casts on the Upper Atmosphere

Below the Belt of Venus, we see areas of our atmosphere that are not illuminated by sunlight since the Earth casts a shadow on the atmosphere.

These phenomena show that the atmosphere acts like a projection screen.  It reflects light back to our eyes from the backscattering from air molecules and other small particulates and aerosols.  It also allows us to see the shadow cast by the Earth.

Beyond our atmosphere, no air molecules or particulates exist in the vacuum of outer space, and we would not see these optical effects.

Seeing twilight fall should be prescribed by doctors.

                                                          — Marlene Dietrich

The full moon sets in the Belt of Venus over the Eastern Sierra Crest above Bishop, California.

The Earth’s Shadow is visible over the Eastern Sierra Crest during sunrise with a full moon.  A layer of cirrostratus clouds enhances the amount of reflected reddened light in this scene — without any clouds, the Belt of Venus would still be seen from the backscattering of light from air molecules.

How the Belt of Venus and Earth’s Shadow Change with the Elevation of the Sun

Just Before Sunset

When the Sun is low in the sky, but before it sets, the Earth’s Shadow and Belt of Venus start to come into view, as long as you have a clear view of the horizon that is not blocked by mountains.  In this case, the shadow we see above the horizon is the shadow of the atmosphere itself on itself.  The gradient in the atmospheric density results in more sunlight being attenuated in the lower part of the atmosphere.

Diagram showing the light rays before sunset of the Belt of Venus and the Earth's Shadow.

At Sunset

At sunset, the Earth’s true shadow is visible, with the Belt of Venus appearing bright pink and sharply separated from the Earth’s Shadow. The colors are most intense at sunset due to the backscattering of sunlight from the denser lower atmosphere.

Diagram showing the light rays at sunset of the Belt of Venus and the Earth's Shadow.

During Evening Twilight, Sun Below the Horizon

As the sun descends below the horizon during evening twilight, the Belt of Venus and the Earth’s Shadow rise in the eastern sky. The line separating the Belt of Venus and the Earth’s Shadow becomes less distinct and blurry. Additionally, the colors of both phenomena become muted. This occurs because the backscattering now happens from the less dense upper part of the atmosphere, and we have to look through the lower part of the Earth’s Shadow to see the Belt of Venus.

Diagram showing the light rays during evening twilight of the Belt of Venus and the Earth's Shadow.

The Belt of Venus Does Not Last Long

The following five photographs depict the progression of the Belt of Venus and Earth’s Shadow. Sunset was at 5:19 PM (Mountain Standard Time) when the sun dipped below the sea-level horizon, and civil twilight (when the Sun is 6 degrees below the horizon) occurred at 5:46 PM.

These are some stunning photos of the Belt of Venus and Earth’s Shadow taken on January 13, 2024, at the Bosque del Apache National Wildlife Refuge in New Mexico. They are reflected from the still water and ice of a large pond at the refuge. The photos were taken at different times, looking east at sunset. You can observe how quickly the Earth’s Shadow rises and how the boundary between the shadow and the Belt of Venus becomes more diffuse over time. The light show only lasted six minutes.  Mountain ranges behind me to the west also cast their shadows, resulting in an unevenness to the Earth’s Shadow.

The exact times, camera settings, and elevation angle of the Sun are listed here: Read More

Is the Belt of Venus related to the Planet Venus?

The pink band in the sky, known as the “Belt of Venus,” has nothing to do with the planet Venus.

You will never be able to see Venus in the Belt of Venus because Venus is an interior planet closer to the Sun than the Earth. As a result, Venus will always be visible on the same side of the sky as the Sun and not on the opposite side of the sky where we see the Belt of Venus.

Historians believe that the name of the pink band is related to a girdle or breast band of the Ancient Greek goddess Aphrodite, who is often identified with the Roman goddess Venus.

A Puzzle

The full "Beaver Moon" in the Belt of Venus over the Sangre de Cristo Mountains in New Mexico.

This photograph shows The full moon rising in the Belt of Venus.  Why is the Moon yellowish instead of pink like the backscattered light of the Belt of Venus?

Crescent Moon and Venus Over Sierra Mosca, 20171018__D2_6192-AU_DF_CR

A (low-quality) photo I took of a moonrise at sunrise with some planets.   Where is the Sun in this photograph?  The Sun is below the Moon, not on the other side of the horizon like when we observe the Belt of Venus.  The planet closest to the crescent moon is Venus, and the larger-looking planet is Mars.  Venus is an interior planet8 along with Mercury.  Venus is not as bright in this image since it is lower in elevation angle than Mars and has less contrast than Mars due to the sky brightness near the sunrise horizon.  If we see the moon in the Belt of Venus, it will be a full moon since, by definition, the full moon occurs directly opposite the Sun — where the Belt of Venus occurs.

The Belt of Venus and the Earth’s Shadow are More Vibrantly Colored in Wintertime

Geese flying in front of the Belt of Venus and the Sangre de Cristo snowy mountains in Colorado.

A flock of Sandhill Cranes fly in front of the Belt of the Venus and the Sangre de Cristo Mountains east of the cold San Luis Valley in Colorado, in March.  I often see richer colors in the Belt of Venus and the Earth’s Shadow in cold weather.  Why could that be?

  1. Air Clarity: Cold air tends to hold less moisture than warm air. Lower humidity levels result in clearer skies, as there are fewer water vapor particles to scatter light. This increased clarity enhances the visibility of the Belt of Venus. Water droplets scatter light differently than the Rayleigh scattering we observe in dry air.
  2. Stable Atmosphere: Cold weather often brings more stable atmospheric conditions. In warmer months, the heat can cause more turbulence in the atmosphere, distorting or obscuring delicate optical phenomena. In contrast, the cooler air tends to be more stable, allowing for clearer and sharper visibility of the Belt of Venus.
  3. More Scattering of Light: The scattering that allows us to see the Belt of Venus, known as backscattering, is more effective in a colder, drier atmosphere.
  4. Airborne Particles: Cold weather may be associated with different types or amounts of airborne particles (woodstoves and fireplaces). These particles can affect the scattering of light, sometimes enhancing the visibility of atmospheric optical phenomena.

Look at the horizon in the opposite direction of the sunrise or sunset, during the moments just after the sunrise or sunset. Observe the Belt of Venus and Earth’s Shadow and appreciate nature’s beautiful light display. Understanding these phenomena will allow you to see more and explain what you see.  It is pretty cool that we can see the light reflecting from the upper atmosphere and the shadow the Earth casts on it.

Love prefers twilight to daylight.

                                                                                            —- Oliver Wendell Holmes

Comments

11 replies
  1. liz
    liz says:

    Great explanation with beautiful photos. we are so lucky to live in a place where these skies are a regular occurrence. Creede. is an amazing place to photograph those skies. Thanks for your teaching and inspiration.

    Reply
  2. Laura Gulovsen
    Laura Gulovsen says:

    Don’t know what you want. This lovely man did a wonderful program for our Audubon group many years ago and I still marvel at his work and talks. I am now almost 92 years old-so our friendship goes back some time. Highly recommend Ed for a program.

    Reply
  3. Verne Loose
    Verne Loose says:

    Ed you are a genius . . . Such a wonderful blending of the creative aspects of photography with the physics of planets, light, and shadows. I’m so glad I had the opportunity to work with you and therefore, to know you!

    Reply
    • Ed MacKerrow
      Ed MacKerrow says:

      Thank you, Verne. The feeling is mutual, I really enjoyed working with you. I am working on a study looking at the economics of elk hunting in New Mexico and small town economies. I wish you were doing it with me.

      Reply
  4. Dolores Jacobs
    Dolores Jacobs says:

    Ed,
    I am a member of the Pajarito Astronomers group in Los Alamos. You’ve explained this phenomenon every bit as scientifically as they would. Their singular photos are not quite as beautiful and spectacular as yours are but they are always interesting. I love that you turn what your camera sees into a brilliant lesson. It inspires me to write a poem using the imagery.

    Reply

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Footnotes and References

  1. Backscattering is a special case of scattering when the scattering angle is 180° from the incident direction.
  2. See the discussion below of Rayleigh scattering
  3. The name of this mountain range, Sangre de Cristo (Blood of Christ), is due to their color at sunset.
  4. You will never see the planet Venus in the Belt of Venus since Venus is an interior planet and will be seen nearer to the Sun, not on the horizon opposite the Sun.  The bright object is the star Betelgeuse.
  5. The sunlight is reddened by Rayleigh Scattering of sunlight by air molecules and very fine particulates smaller than the wavelength of light.  Rayleigh scattering is discussed below and in these blog articles.
  6. John William Strutt, 3rd Baron Rayleigh, (1842 – 1919) was a British mathematician and physicist who made significant contributions to science.
  7. Backscatter of light (or backscattering) is the reflection of light back in the direction of the light source. Backscattering results in a diffuse reflection due to scattering, as opposed to specular reflection from a mirror or highly reflective surface. In contrast, forward scattering diffuses light, giving soft light.
  8. Earlier, I had Mars also listed as an “interior planet,” meaning it is closer to the Sun than Earth; however, this was incorrect, and I thank Joe Schillig for catching my error.  Mars is an inner planet.  An “interior planet” and “inner planet” refer to different things.   Mercury and Venus are both “interior (inferior) planets” and “inner planets,” Mercury, Venus, Earth, and Mars are all “inner planets”.  Confusing terminology.