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Why Does the Moon Reflect Red Sometimes?

The question of why the moon sometimes reflects red creates a learning opportunity for exploring the features of atmosphere and refraction. Gaining basic information about the moon and some key ways it differs from the sun gives you the background to understand how the moon looks from earth and the reason it sometimes seems to change color. An understanding of light and its properties and how it affects the colors we perceive equips you to better appreciate the earth's lunar neighbor. You'll also be equipped to answer questions about the moon from kids, or to use this knowledge in a project.

Background
- Unlike the earth, the moon lacks an atmosphere. The earth's atmosphere surrounds the earth in a spherical shape, insulating the planet and maintaining the oxygen necessary for the survival of people, animals and plants. Without its atmosphere, the earth would lose heat and become uninhabitable. Temperatures on the moon become hot enough to boil water when the sun shines on the lunar surface, and drop to far below freezing when the sun sets. Light changes when it passes through the earth's atmosphere, and that affects how we perceive color.
The Moon
- The moon's craters stand out as prominent features. Asteroids, boulders and comets pelted the moon, leaving huge round depressions in the lunar surface where they collided with its surface. The moon's vast plains bear the name "Maria," or mare, singular, the Latin word for seas. The moon's cratered surface resulted from the impact of large debris from the formation of the solar system, according to the New Mexico State University website.
Light and the Atmosphere
- Just as the color of light changes when it passes through a prism, crystal, or faceted diamond, light changes as it passes through the earth's atmosphere. Light arrives from the moon as packets called photons, according to astronomer Kristine Spekkens at the Cornell University website. These photons scatter off of particles in the atmosphere. Because the particles scatter more blue light than red light more red light reaches the earth when the light from the moon passes through more of its atmosphere. The photons that look more blue have shorter wavelengths and photons that appear red have longer wavelengths. More red photons pass through the atmosphere because they aren't scattered as much as the blue photons.
Red Moon
- A setting moon, sun and clouds can appear red at sunset.
  
  When the moon rises or sets and you see it near the horizon, the light from the moon reaches you through more of the earth's atmosphere than when the moon is higher in the sky. If you visualize the atmosphere as a clear round ball surrounding the earth, you can see that the light passes through much more of the atmosphere than when the moon's light passes through the atmosphere from a higher angle. The same effect causes the rising and setting sun to appear red or orange and for clouds near the sun or moon close the horizon to share shades of pink, red or orange. The colors of the sun and moon tend to become even redder when there's a high level of air pollution, including smoke, because of the increased particles in the atmosphere.

Astronomy