How many physicists could you call “household names”? Newton, Curie, Einstein, Hawking, and Feynman come to mind, but whichever way you split that atom, the answer is “few.” (And notice that they’re almost all dudes.) Now how about astrophysicists, those who gather light from the heavens in a quest to unlock the secret mechanisms of the universe? I guess you could argue the technical definition of astrophysicist, but there might be just two: Carl Sagan and Neil deGrasse Tyson.

Sagan brought the wonders of astronomy into millions of homes through his thoughtful and accessible books and Cosmos, his 1980 exploration of planets, black holes, and billions and billions of stars aboard the “spaceship of the imagination.” In 2014, Tyson presented an updated version of the series to go along with his own collection of bestsellers, including Astrophysics for People in a Hurry.

His latest, Accessory to War: The Unspoken Alliance Between Astrophysics and the Military (co-written with Avis Lang), explores the centuries-old relationship between the two disciplines – complicit, often symbiotic, and sometimes uneasy. Last month, Tyson spared a few minutes of his busy schedule to talk to us on the phone about the new book. (In a moving car while giving directions and eating soup – talk about a polymath!) The following is an edited transcript of our conversation.

Amazon Book Review: Accessory to War is about the relationship between astrophysics and militarism. How far back does that relationship actually go?

Neil deGrasse Tyson: If you think about astronomers, people who care about the night sky, that’s basically the second oldest profession. The night sky offers a mechanism to navigate, not only on land, but especially if you’re seafaring. The earliest empires that were built by dominating the seas were built on intellectual capital–the astronomers who understood the movement of the sun, moon, and stars.

Let me give you an example from the colonial era. In the 1700s, Captain Cook was sent to the South Pacific to conduct a science experiment. The planet Venus would be visible crossing between Earth and the sun, what’s called a transit of Venus. If you looked carefully, you would see this black dot moving across the Sun’s image. If you measure that carefully, you get extra information about the size of the Solar System. Great Britain said This would be really good to know and to have, so why don’t you go on that voyage. But… map every coastline you come across. The British Empire grew as a result of Captain Cook’s voyage to observe a transit of Venus. Within 18 years, Great Britain had taken control of Australia, New Zealand, and other small islands in the South Pacific, and started sending prisoners to Australia….

So not every use was good.

I’ve got one for you. Columbus, on his fourth voyage, was on his way back to Spain but didn’t have enough supplies. On the island of Hispaniola, he goes to the natives and says I need some of your food stores. They didn’t have enough for him, because they only grow exactly as much as they need. They refuse.

He happened to know that there’s a total lunar eclipse one week hence. He said, If you don’t give me the supplies, I will summon divine power and get rid of the moon in the sky. They were skeptical, but sure enough the night comes and the moon begins to disappear – and the natives freak out. They rush and get him supplies. He waits until mid-eclipse and says The divine powers that I summoned are actually benevolent, and just to show you, we will return the moon as a sign of thanks. Of course the moon comes back. So if you wanted a reason to think Columbus was [not nice], in addition to other reasons you might have thought, then that’ll do it.

Your subtitle is The Unspoken Alliance Between Astrophysics and the Military. Does that imply that it’s an uneasy relationship for scientists?

I don’t want to call it uneasy. It may be uneasy to some. We [scientists] don’t make the bombs. What we do is quite humble: Wait around for light to come from the night sky, and then analyze it. But we have such overlapping interests with the military – we’re complicit in what they use of what we invent, and what we use of what they invent. And this relationship exists even though my community is overwhelmingly liberal and anti-war.

Do you think the scientific community has an obligation to speak out on the way that their work is used?

I cut my teeth, my social/cultural teeth, in the Vietnam era. I grew up thinking all war is bad – that was the attitude. The urge to assert that all war is bad, I have found, comes almost exclusively as a result of having grown up with the Vietnam War. But if you grew up in World War II, no one’s saying it was bad. They’re saying it was necessary. They’re saying, yes, we must fight these evil forces. And yes, some will die.

So I’m not going to say that war is bad, but it would take me a decade to figure that out. If there is an enemy that rises up who wants you dead, you’re going to defend against them. And if your scientists have methods and tools that can aid a military in that effort? Are you going to tell them no? This book is an exploration of all the ways this two-way street has manifested. But it’s not an indictment of the relationship. I’m not telling you how to think about this; I’m just telling you it is. You can think about it however you want.

The American tendency is to favor military spending over science, and now the scales seem to be tipping in a way that we haven’t really seen in recent memory. In your opinion, what should the balance be?

Yeah, I don’t tell people what to do. What I can tell you is that if you fund science, you’ll get scientific discoveries. If you fund military, you’ll get military might and you’ll get scientific discoveries. When we went to he moon, that was not a expedition of curiosity. Even though NASA is a civilian agency, we sent military personnel. All but one of the people in the Mercury, Gemini, and Apollo programs were military, a civilian who happened to be a scientist. What mission did they send up a scientist? The last mission.

Astronauts are going to the moon, so heck, Why don’t you take this experiment? Here’s a satchel, why don’t you gather this kind of rock. So science got done in ways it could never have otherwise happened. No one will fund a science mission to just go to the moon – it’s too expensive. But they will fund a geopolitically motivated mission to go to the moon. There’s always money for that.

I loved the original Cosmos series as a kid, as did a lot of other kids. What were your feelings about stepping into Carl Sagan’s shoes for the updated series?

I never thought of it as stepping into his shoes, because I would just fail. All I could do is bring my own shoes to the table and walk in those. I know that I can succeed in being myself, whether or not I could succeed at being Carl. It’s quite a legacy, and I’m honored.