Venus Rainbow Is a Glory


 The European Space Agency has a probe known at the Venus Express space probe. This probe has taken a picture of what is known as a glory although this one was not seen in the skies of Earth. The glory appeared on the planet Venus. Although the coloration of a glory is similar to that of a rainbow, this atmospheric pattern of lights from Venus is, in fact, a glory.

A glory differs from a rainbow in a significant way. While both rainbows and glories are distorted images of sunlight reflecting off either water droplets or some other form of aerosol in the atmosphere, the manner in which either a glory or a rainbow is formed differs. It wasn’t until the 1980’s when optical theorists were able to be able to explain how glories work. At that time, physicist Moysés Nussenzveig from Brazil demonstrated that the cause of a glory is from a process known as wave tunneling. Wave tunneling happens when the rays of sunlight do not actually pass through the atmospheric droplets but rather only pass nearby them. Rainbows, on the other hand, are from rays of sunlight that either pass through the droplets and are refracted, or bent, by the passage, or they are reflected off the droplets, basically bouncing off the surface. The Venus rainbow like phenomena was caused by diffraction, or a scattering of the light waves into a ring-shaped pattern, making it a glory and not an actual rainbow.

An additional consideration in differences is the viewing angle from which one may see a glory. Glories always appear at an observer’s anti-solar point, or from the place in which they are directly opposite the sun. To view the glory, a person’s back must be toward the sun so that any reflected rays of light come back across their line of sight. Typically, if a person is viewing a glory from the ground, they will see their shadow in the center of the glory. If the glory is viewed from in the air, usually from within an airplane, the shadow of the airplane will be in the middle. A glory is typically much smaller than a rainbow and viewed as concentric rings centered on a bright core. Furthermore, in order for a glory to appear, the aerosols must not only be spherical in nature, and therefore most likely liquid, but they must also be similarly sized.

Rainbows, on the other hand, arch across the sky in wide ribbons. There are only two requirements for creating a rainbow, water and light. Therefore, rainbows may be seen during rain, fog, or spray as from a garden hose or on the ocean. The droplets act as a prism to refract the light and separate it into its individual color components. When a rainbow occurs from reflection, the sunlight is bent as it hits off the droplet. A double rainbow occurs when the rays of light bounce around inside the droplet and reflects twice. Because there is less energy after the first bounce, the secondary rainbow will appear lighter. The actual brightness of a rainbow is due to the droplet size. Larger drops create brighter rainbows while smaller drops create rainbows with less-defined colors. In addition, the lower in the sky the sun may be, the rainbow top will be correspondingly higher.

venusThe phenomena seen in the Venus atmosphere has been determined to be a glory. The atmosphere of Venus is believed to be populated by sulphuric acid droplets. Scientists positioned the space probe in the hopes of spotting a glory so they would be able to determine cloud droplet characteristics in the atmosphere of the planet. When the glory was observed on July 4, 2011, the variations indicated that the clouds were not made up of only water and sulphuric acid and that other chemicals were present. The images of the glory from ESA’s space probe were released this past week. Further analysis is required before researchers can correctly determine the composition of the droplets but those involved do explain that the array of colors captured from the Venus atmosphere constitute images of a glory and not a rainbow.

By Dee Mueller

Astronomy Magazine

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