Lunar Corona

The Enchanting Phenomenon of Lunar Corona

Have you ever gazed up at the night sky and noticed a mesmerizing ring of light encircling the moon? This captivating optical phenomenon is known as a lunar corona. While it may resemble a halo, the science behind it is quite different. In this article, we will delve into the intriguing world of lunar coronas, exploring their formation, characteristics, and the factors that contribute to their ethereal beauty.

Understanding the Formation of Lunar Coronas

A lunar corona occurs when the moon's light passes through a layer of thin clouds or mist containing tiny water droplets. These droplets act as miniature prisms, scattering the light in various directions. As a result, an exquisite ring of colors forms around the moon, with the innermost ring appearing bluish and the outer rings exhibiting shades of red and orange. The number of rings visible can vary, depending on the size and uniformity of the water droplets.

A Celestial Sibling: The Telescope Corona

Astrology enthusiasts may find lunar coronas reminiscent of another phenomenon observed through telescopes - the corona surrounding distant stars. When observed through a telescope with sufficient magnification and under steady atmospheric conditions, stars appear as small disks surrounded by shimmering rings. This effect is caused by the same principle of light diffraction that gives rise to lunar coronas.

The Intricacies of Light Diffraction

To understand the formation of a corona, we must explore the concept of light diffraction. When waves of light encounter an obstacle or edge, such as the aperture of a telescope or the periphery of a cloud water droplet, they scatter and interfere with each other. This interference pattern creates the characteristic rings observed in coronas.

The size of the diffraction pattern depends on the size of the scattering body. Larger scattering bodies produce smaller angular sizes for their diffraction wakes. Hence, the minute diffraction pattern generated by the telescope's aperture requires magnification to be visible, while the larger water droplets in a cloud create a more prominent corona.

The Allure of Lunar Corona Photography

Capturing the enchanting beauty of lunar coronas through photography has become a popular pursuit for many sky enthusiasts. These ethereal displays provide a unique opportunity for photographers to showcase their skills and creativity. By experimenting with different camera settings, lenses, and exposure times, photographers can immortalize the delicate hues and intricate patterns of lunar coronas, creating stunning visual masterpieces.

Factors Influencing the Appearance of Lunar Coronas

Various factors contribute to the appearance and visibility of lunar coronas. These include:

  • Cloud Thickness: The thickness of the cloud layer through which the moon's light passes affects the intensity and clarity of the corona. Thicker clouds may obscure the corona, while thinner clouds allow for a more pronounced display.

  • Water Droplet Size: The size of the water droplets within the cloud layer plays a crucial role in determining the number and size of rings in the corona. Uniform droplet sizes result in a well-defined corona with distinct rings.

  • Moon's Altitude: The altitude of the moon above the horizon also impacts the appearance of lunar coronas. When the moon is low on the horizon, its light must pass through a greater thickness of Earth's atmosphere, leading to more pronounced scattering and a larger corona.

The Mystical Allure of Lunar Coronas

Lunar coronas have fascinated sky gazers throughout history, evoking a sense of wonder and mystery. Their ethereal beauty and delicate colors have inspired countless poets, artists, and dreamers. Whether observed with the naked eye or captured through the lens of a camera, these celestial displays remind us of the boundless wonders that exist beyond our earthly realm.

Conclusion

Lunar coronas are a captivating celestial phenomenon that delights and intrigues those fortunate enough to witness them. Understanding the science behind their formation and the factors influencing their appearance adds to the appreciation of their ethereal beauty. So, the next time you find yourself gazing at the moon on a misty night, take a moment to immerse yourself in the enchanting world of lunar coronas and let their celestial magic transport you to a realm of awe and wonder.

Lunar Corona - Taken by Stefano De Rosa (site) at Villefranche, France a few hours after the full moon on on September 5, '09. The moon was 39� high. �Stefano De Rosa, shown with permission.

A magnificent corona with three rings visible testifying to scattering by water droplets of very similar sizes.

A corona should be familiar in another context to telescope observers. A star seen through a steady atmosphere and enough magnification shows a small disk surrounded by shimmering rings.

Stars do not show their real disks except with large telescopes and specialised optics. The apparent disk visible through small telescopes when the air is steady is the 'Airy disk' and is produced by the same light diffraction process as the corona. Waves scattered by the edge of the telescope aperture recombine to form the Airy disk interference pattern. Waves scattered by the periphery of a cloud water droplet produce the same pattern, this time called a corona.

The telescope diffracton pattern is minute and needs magnification to see it because the larger the scattering body, the smaller is the angular size of its diffraction wake.

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Reference Atmospheric Optics

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  • "Lunar Corona". Atmospheric Optics. Accessed on March 1, 2024. https://atoptics.co.uk/blog/lunar-corona-2/.

  • "Lunar Corona". Atmospheric Optics, https://atoptics.co.uk/blog/lunar-corona-2/. Accessed 1 March, 2024

  • Lunar Corona. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/lunar-corona-2/.