Parallel Shadows, Hong Kong

Last updated on September 16, 2023

Parallel Shadows: A Fascinating Phenomenon in Hong Kong

Shadows are not always as simple as they seem. In certain atmospheric conditions, shadows can exhibit a captivating phenomenon known as parallel shadows. Hong Kong, with its unique topography and vibrant cityscape, provides an excellent backdrop for observing this optical phenomenon.

When sunlight passes through openings in clouds or objects, it creates a mesmerizing effect of parallel rays and shadows. These rays appear to diverge from a common point, giving the impression of parallel lines extending across the sky. The rays and shadows can be seen radiating in all directions when viewed from the direction of the sun.

It is important to note that while the rays may appear perfectly parallel, they are not entirely so. The sun's diameter, which measures approximately 0.5° in the sky, causes the dark area of shadows, known as the umbra, to taper slightly. This tapering effect becomes more pronounced when objects with different sizes cast shadows.

To illustrate this point, consider the following examples:

• A small object like a pea casts an umbra approximately 700 mm long.
• The umbra of a towering mountain can extend over an astonishing distance of 300 km when the sun is positioned very low.
• The Earth itself casts an enormous umbra that spans a staggering length of 1,400,000 km – three and a half times the distance between the Earth and the Moon.

The phenomenon of parallel shadows showcases the remarkable nature of light and its behavior in our atmosphere. It serves as a reminder of the intricate interplay between sunlight, objects, and atmospheric conditions.

In Hong Kong, where urban structures intertwine with natural landscapes, parallel shadows create captivating visual spectacles. The city's high-rise buildings, mountains, and expansive skyline provide an ideal canvas for observing this atmospheric phenomenon.

Photographers and enthusiasts in Hong Kong have captured stunning images that showcase the beauty of parallel shadows. These photographs highlight the interplay of light and shadows, creating a sense of depth and dimensionality in the urban landscape.

To fully appreciate the beauty of parallel shadows in Hong Kong, one must observe them during specific atmospheric conditions. When the sun is positioned at a low angle, such as during sunrise or sunset, the elongated shadows cast by buildings and mountains create a dramatic effect. The parallel rays of sunlight pierce through the gaps between structures, resulting in a mesmerizing display of converging and diverging shadows.

The phenomenon of parallel shadows is not limited to Hong Kong alone. It can be observed in various locations around the world, each with its own unique characteristics. From the towering skyscrapers of New York City to the majestic peaks of the Swiss Alps, parallel shadows continue to captivate and inspire awe in those who witness them.

In conclusion, parallel shadows in Hong Kong are a fascinating optical phenomenon that showcases the interplay between sunlight, objects, and atmospheric conditions. The parallel rays and shadows create captivating visual spectacles, adding depth and dimensionality to the city's urban landscape. Whether observed in Hong Kong or other parts of the world, parallel shadows serve as a reminder of the remarkable nature of light and its ability to create mesmerizing effects in our atmosphere.

Parallel Rays

Peter Ross imaged these 'crepuscular' rays and shadows at Tai Mo Shan, Hong Kong. They show, if proof be needed, that the sun's rays are indeed parallel. Looked at in the direction towards the sun they would appear to radiate in all directions

Images ©Peter Ross, shown with permission

Not quite parallel. The sun's 0.5° diameter in the sky causes the dark (umbra) of shadows to taper.

A pea casts an umbra about 700 mm long.

A mountain's umbra can extend over 300km when the sun is very low

Earth's umbra is 1,400,000km long, three and a half times the distance of the moon.

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Reference Atmospheric Optics

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