Ch. 9: Invisible Light
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Author:  Chris OConnor [ Thu Oct 12, 2017 2:35 pm ]
Post subject:  Ch. 9: Invisible Light

Astrophysics for People in a Hurry
by Neil deGrasse Tyson

Ch. 9: Invisible Light

Please use this thread to discuss this chapter.

Author:  LevV [ Wed Dec 13, 2017 9:42 am ]
Post subject:  Re: Ch. 9: Invisible Light

I can't say that I completely understand this chapter on invisible light, but after a second reading it is becoming somewhat clearer.

It seems that things heated up (so to speak) in 1800 when William Herschel, the English astronomer, discovered a form of light beyond the visible spectrum. While measuring the temperature of the light in the visible spectrum, he went a step further and measured the temperature of the air beyond the the light spectrum. With this insight he discovered a band of invisible light now known as infrared light.

A few years later Johann Wilhelm Ritter discovered untraviolet rays leading scientists to eventually discover the full spectrum of light. A hundred years or so later these important discoveries would be put to a very practical use with the construction of telescopes capable of seeing light invisible to the naked eye. This would make it possible for astrophysicists to discover a wide variety of previously undiscoverable cosmic objects.

Author:  Harry Marks [ Fri Dec 22, 2017 12:09 pm ]
Post subject:  Re: Ch. 9: Invisible Light

I hope people are generally familiar with the idea that other frequencies of radiation, such as X-rays, infrared, UV and radio are still the same phenomenon as light. They are transmitted by photons which follow the same rules as at other frequencies.

What is different is the degree to which we are "tuned" to respond to the frequency. Visible light seems to be the main way that creatures sense the world, though perhaps chemical signals (e.g. smells) should be considered more important, and sound waves are not drastically less important. But some creatures sense higher or lower frequencies than we are tuned to, in much the same way dogs sense notes of a higher frequency of sound than we can detect.

I can't help thinking NDT threw this in partly to suggest that the mysteries of dark matter and dark energy may have something to do with ease of detection, but maybe not since the full spectrum is pretty important to astrophysics. Gamma rays, for example, have revealed black hole phenomena that we might not have suspected for a long time otherwise.

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