Anticrepuscular rays

Two days ago, just after sunset, we had this view from the balcony:

Anticrepuscular rays over Shinagawa hotel area

The pink beams seem to be emanating from the hotels and corporate headquarters around Shinagawa Station. The sun was not setting behind these buildings, as you might think, but rather in the opposite direction in the sky. What was their origin? Although a great theory, they are not related to any imminent re-emergence of the Japanese Empire, as suggested by Anders.

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Total internal reflection as demonstrated by Engineer Guy

In my recent, very long post on the optics of solar halos, I briefly mentioned the phenomenon of total internal reflection: If a ray of light propagating in a material with a high index of refraction, such as water or ice, encounters an interface with a material of a lower index, like air, it will be completely reflected if it enters with a large angle of incidence (close to parallel with the interface). This explained why the sunlight would not be deflected by ice crystals to form the halo for certain incidence angles.

Total internal reflection is also responsible for the working of optical fibres. This is demonstrated clearly and convincingly in this video by Bill Hammack, aka. Engineer Guy that I found via Make. In the first part of the video he very elegantly shows how a laser beam is reflected multiple times inside a narrow stream of transparent liquid. I recommend you to watch the whole video which covers a lot of science and engineering related to fibre optic cables. But stay focused! There is an impressive amount of information packed into those 5:36 minutes.


Engineer Guy has made many other videos covering different technologies. I will certainly try to watch them all.