Interesting idea, poorly executed. Author Neil Comins is an astronomy professor at the University of Maine. The premise of What If the Moon Didn’t Exist? is alternative solar system astronomy; Comins presents a series of scenarios for alternate Earths, giving each a cute little name: Solon, where the Moon never formed; Lunholm, where the Moon is much closer; Petiel, where the Earth has less mass; Urania, where the Earth’s axis is tilted 90° to the plane of the ecliptic like Uranus; Granstar, where the Sun is more massive; Antar, where a supernova goes off near the solar system; Cerberon, where another star passes through the solar system; Diablo, where a black hole passes through Earth; and two versions of Earth, one where our eyes are sensitive to other wavelengths and one where the ozone layer is depleted (the book dates from 1993, where ozone depletion rather than climate change was the man-made disaster du jour.)

The ideas are interesting enough; the main problem is there are no illustrations, no physics and mathematics to speak of, and Comins often strays outside of astronomy into biology and human behavior. The “no illustrations” problem comes to the fore when Comins discusses his hypothetical Urania; he has to explain seasonality on the extant Earth and seasonality on Urania solely with text, leading to extremely awkward constructions like asking the reader to imagine holding a pen over paper at a 23 ½° angle and then drawing circles while keeping the wrist stiff; his description of the seasons on the imaginary Urania has to go through even more convolutions.

Somewhat more unsettling, since Comins is an astronomer, is his explanation of oceans tides (which figure on the moonless Solon and the “supermoon” Lunholm). This is Comin’s explanation of why there are high tides on opposite sides of the Earth:

“The reason there is a second high tide on the opposite side of the Earth is the Moon pulls the bulk of the Earth away from the oceans on the far side.”

This is just plain wrong (or, at best, extremely misleading); the reason there are tides on opposite sides of the Earth is tides are raised by the horizontal component of solar and lunar gravitational attraction, not the vertical component. There’s a good explanation on the NOAA web site; see Section 4, “The Tractive Force”.

Comins gets into similar trouble when he strays into biology; in his chapter on the potential effects of a nearby supernova (his hypothetical one is 50 light years away) he devotes a couple of paragraphs to the mutations that will be caused by supernova gamma rays and X-rays, hypothesizing such things as mutant mice with poisonous fur, mutant wheat that poisons competing strains, and even mutant humans. This is the “mutation as magic” realm of comic book superheroes; in anything more complicated than bacteria, recombination is a – well, astronomically – more powerful force for genetic change than point mutations.

All that being said, some of the ideas presented are intriguing. I’d like to have a solar system simulation program that would allow me to try out some of the ideas; cursory googling doesn’t reveal anything that allows me to start out with the extant solar system and play around with solar evolution and planetary parameters, but I’m sure something will turn up. ( )

A fun series of essays that teaches a bit of astronomy and physics by hypothesizing different scenarios for the origin of the earth-moon system. ( )

I love this presentation of astronomical information. Changing variables helps me understand how something works. ( )

I feel that the author, an astronomer or astrophysicist, doesn't realize how flexible life is. Assuming that there is life, if the earth is warmer, we'd evolve proteins that could stand the heat. However, it's interesting as he goes through various scenarios about what the Earth would be like if the solar system were slightly different.

This is an interesting book but kind of wordy. I think that the author probably writes as he thinks, in well-connected but fairly convoluted sentences, and hasn't realized the need to smooth them out for readers. ( )