Shadow-band in the total solar eclipse on Aug 21, 2017
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|Date & Time: ||Aug 21 2017 from 10:16:46 to 10:19:48 PDT(-0700)
|Fixed on tripod
|Digital video camera: ||SONY XPERIA Z1f SO-02F (Smartphone)
|Location: ||Salem, Oregon, USA
|Camera Settings: ||Mode...Full-HD (1920×1080) 30fps|
When the diamond ring appears in total solar eclipse, we may see the stripe-shaped shadows move on the ground rapidly like the heat haze.
This phenomenon is called "shadow-band". It's considered that the shadow is the projected image of atmosphere of the sky refracted by density's fluctuations,
which is in focus on the ground with leakage solarlight of the diamond ring as a close to ideal point light source.
The principle is mostly the same with that of the pinhole camera.
Comparison of diamond ring between the second and third contact displayed the zenith direction upward. Arrows indicate positions of dominant leakage lights.
I could observe the total solar eclipse under clear condition without thin clouds, a video movie of a white paper (60cm×42cm) confronting to the sun had succeeded in recording the appearance of shadow-band.
I released an edited version in 85 seconds via the YouTube's server.
In the movie, I inserted the same time solar movie for reference.
You can confirm that the shadow-band appears before the second contact at 10:17:12 until 10:17:22 and right after the third contact at 10:19:18 until 10:19:35.
The latter one looks comparatively clear, it seems the dull stripes on the right diagonal are moving leftward.
According to the recorded results, it can be seen that the shadow-band at the second contact is very indistinct compared with that at the third contact.
A right image shows the comparison of leakage solar lights in diamond ring between at the second and third contacts.
At the second contact, you can see plural leakage lights from lunar edge. On the contrary, only two lights can be detected at the third contact.
Therefore it's conceivable that the solar light after the third contact is close to ideal point light source and the shadow-band was observed clearly.