Astrophysics for People in a Hurry (Astrophysics for People in a Hurry Series)

by Neil deGrasse Tyson

Herschel inadvertently discovered “infra” red light, a brand-new part of the spectrum found just “below” red,

Sure enough, the pile in the unlit patch darkened more than the pile in the violet patch. What’s beyond violet? “Ultra” violet, better known today as UV.

Filling out the entire electromagnetic spectrum, in order of low-energy and low-frequency to high-energy and high-frequency, we have: radio waves, microwaves, infrared, ROYGBIV, ultraviolet, X-rays, and gamma rays.

Heinrich Hertz had shown that the only real difference among the various kinds of light is the frequency of the waves in each band. In fact, credit Hertz for recognizing that there is such a thing as an electromagnetic spectrum. In his honor, the unit of frequency—in waves per second—for anything that vibrates, including sound, has duly been named the hertz.

The range of wavelengths (or frequencies) that comprise each band of light strongly influences the design of the hardware used to detect it. That’s why no single combination of telescope and detector can simultaneously see every feature of such explosions.

That region of the sky swung by the telescope’s field of view every twenty-three hours and fifty-six minutes: exactly the period of Earth’s rotation in space and thus exactly the time needed to return the galactic center to the same angle and elevation on the sky.

In the microwave band, relatively new to interferometers, we’ve got the sixty-six antennas of ALMA, the Atacama Large Millimeter Array, in the remote Andes Mountains of northern Chile. Tuned for wavelengths that range from fractions of a millimeter to several centimeters, ALMA gives astrophysicists high-resolution access to categories of cosmic action unseen in other bands, such as the structure of collapsing gas clouds as they become nurseries from which stars are born.

Their origin remains a bit of a mystery, but the best explanation holds that in the electrical storm, free electrons accelerate to near the speed of light and then slam into the nuclei of atmospheric atoms, generating gamma rays.

There is no knowledge of the cosmic background, and no real understanding of the big bang, without microwave telescopes. Want to peek at stellar nurseries deep inside galactic gas clouds? Pay attention to what infrared telescopes do. How about emissions from the vicinity of ordinary black holes and supermassive black holes in the center of a galaxy? Ultraviolet and X-ray telescopes do that best. Want to watch the high-energy explosion of a giant star, whose mass is as great as forty suns? Catch the drama via gamma ray telescopes.

But it’s not empty, the space between the planets contains all manner of chunky rocks, pebbles, ice balls, dust, streams of charged particles, and far-flung probes. The space is also permeated by monstrous gravitational and magnetic fields.