The book title and premise/promise is a revelation of things in the sky that we cannot see with our eyes—the visible part of the electromagnetic spectrum being but a thin sliver of its entire span. As Dr. Bothwell helpfully explains, that is akin to hearing music from only one octave of a giant piano that actually contains sixty five octaves—a novel and memorable analogy that is based on current commonly detected photon wavelength spans (from Gamma to Radio waves). But this by itself should not be news to most: medical diagnosis uses every variety of signal from X-rays to ultrasound to study ourselves. So it should be no surprise that our understanding of our universe comes from using every possible means available to study it—signals we can perceive with our senses and those we cannot. 

Dr. Bothwell uses this ‘all the light we cannot see but our instruments can’ construct to illuminate (pun intended) various exotic cosmic objects and phenomena. These include the usual cosmological celebrities and superstars (see what I did there?) —black holes, neutron stars, pulsars, magnetars, galactic dust, nascent planetary systems, CMB etc. He also goes on to describe discoveries made through the use of non electromagnetic signals such as gravitational waves. And of course, no cosmological tour would be complete without the mention of the two big mysteries: dark matter and dark energy, which are also covered expertly. 

Dr. Bothwell examines each topic with the right mix of history, anecdote, analogy, science and implications, making for engaging and non strenuous reading. I particularly enjoyed his coverage of dark matter, a subject whose gravitational reach draws in almost all modern popular astronomy writing. The analogy with “is this a sign of an as yet undiscovered Uranus or the non existent planet Vulcan”, is novel and perfectly captures the razor’s edge that the question of dark matter rested on for a long time: there is unseen matter vs. we need to rethink gravity; until more recent discoveries (the bullet cluster) seem to have tipped it to the side of “there must be some unseen matter out there”.

He has clearly taken the Stephen Hawking maxim to heart: “every equation reduces book sales by half”, as he himself confesses, and in keeping with the trend in this genre, has omitted all math, but not at the expense of substance.