What is a Brocken Spectre?

By Becca Smithers

One very misty morning I went for a walk with family up Maiden Castle in Dorset. The sun was quite high in the sky, but the mist hung around the bottom of this Iron Age hill fort, creating a very spooky atmosphere!

When we reached the top and were out of the fog we began walking around the ridge that circles the top of the fort, and there we had a bit of a surprise. Looking down at the fog that clung to the base of the hill fort, we could see our shadows projected to look like giants, and we each had a ring of light around our heads. We were standing in a line, but could only see our individual shadows. In the picture below you can see my shadow, but not the shadows of the three people stood to my right!

My Brocken Spectre. All rights reserved.

My Brocken Spectre at the top of misty Maiden Castle! All rights reserved.

This phenomena is called a Brocken Spectre, named after a mountain in Germany, and the legend that these shadows were actually supernatural beings! Luckily for us on this misty morning, we were not being haunted by spectres, just physics!

My Brocken Spectre with a glory around my head. All rights reserved.

My Brocken Spectre with a glory around my head. All rights reserved.

The Brocken Spectre only appears when the sun is directly behind you and your shadow is projected on to mist or a cloud. Your body blocks the light from travelling any further, creating your shadow. The light around your shadow is reflected by the water droplets in the mist. There are so many water droplets that the light is reflected back from lots of different points and depths of the mist. This distorts your shadow and makes it appear giant, and hides the shadows of other people.

The water droplets not only reflect the light, they also refract the light. Refraction is where light bends when it travels between two different mediums, in this case when it travels from air to water. Water bends the angle of the light and acts as a prism, splitting the white light into the individual colours of visible light. The refraction of the sunlight creates the ring of light around my head in the shadow, which is referred to as a glory. At higher altitudes the glories can be seen as clear rings of rainbows.

Next time you are out for a hill top walk on a misty, sunny morning, keep an eye out for your Brocken Spectre and its glory. It is a very surreal thing to see, and it’s all down to reflection and refraction!

 


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Posted in Exploring Science, Physics