Star witness: why would you find this ANU astrophysicist in court?

As an astrophysicist, Dr Brad Tucker is frequently asked for expert commentary.

You might have caught him on the TV talking about how to observe an eclipse, or heard him on the radio speculating about UFO sightings.

But Tucker can also be found sharing his expertise somewhere you don’t expect: in court.

“I think at ANU there would be a plenty of academics who are expert witnesses,” Tucker says. “Especially in medicine and psychology. But astrophysicists? Not so much.”

Over the past eight years, Tucker, from the Research School of Astronomy and Astrophysics at The Australian National University (ANU),  has been asked to submit astronomical evidence for cases located all over Australia.

He provides statements for about six to ten cases a month, with about one fifth of these requiring him to also appear in court to give testimony under cross-examination.

“It’s the sort of thing you don’t often need an expert for, but when you do… you do,” Tucker comments. “If they need me, it is either a critical point for what is happening or it is a very serious matter, the kind of thing you see on the news, so they want as much detail as possible.”

There are four main types of incident requiring Tucker’s expertise, he says.

“The first is: the sun was in my eyes and I couldn’t see, so I got in a car accident. How do you attest that the sun was going to be in your line of sight on that particular day, at that time, at that location? You need someone to say where the sun was to that precision.

“That’s what we do in astronomy all the time. We map the positions of objects, and we do that really well.

“There’s always a limit to what you can say, of course, because I don’t know about the car windows; I don’t know about the trees; I don’t know about the clouds. But I do know where the sun was, and what it could be doing in that instance. It’s up to the other parts of the legal system to try to work out what that actually means for the case.”

The second type of case, Tucker says, concerns eyewitness testimony from an event which occurred at dawn or dusk.

“The question then is: can you actually visibly see that thing that you said you saw? Dusk and dawn have very clear definitions in terms of the sun’s position and the lighting levels so it actually becomes quite an important thing. And if the event happens two minutes before or after, what does that interpretation mean?”

The third category relates to the moon, including how much a witness can see by moonlight and also cold cases.

“When it’s going back to a historical thing, if a witness says that something happened and they remember it was a full moon, then you can say: it could have been on this day or that day. What constitutes a full moon, technically, is a very specific definition, but to the layperson it might look full for longer than that, so you need some room to move.”

The final type of case is “more of a random one,” Tucker says, but is coming up for him more and more.

“And that’s using satellites to help track things as they happen. There are satellites constantly imaging the Earth, so you just have to know a little bit about where they are, how they work, and how to access the data. Then I usually set it up so they can do a special request to get that information.”

It’s rare for Tucker to know any details about a case he’s working on. “I try to stay as removed as I possibly can,” he says. All he needs to know is what information to plug into the tools, called ephemeris, which astronomers use to map positions of the sun, celestial bodies, and stars.

It’s a regular part of his daily work, and, he says, the “kind of thing I do for fun”. Plus, the average statement doesn’t take too long to turn around, which is one reason Tucker doesn’t ask for any payment as an expert witness.

“The other reason is that in science, we are all about trying to encourage people to go to sources of truthful information, especially now in the era of misinformation. And if the legal system is going to these lengths, engaging people like me and I’m sure from other obscure fields, to work out what has happened based on evidence, then we should support it as scientists.”

It’s also, he says, personally rewarding.

“It’s one of the few times that astronomy is helpful to people! I can say, clearly this is a serious situation that people are trying to solve, and what I did was useful.”

For anyone who knows Tucker, a Canberran who, no matter the season, dresses like he’s still living in his native California, there’s only one question left to answer.

“Do I wear long pants when I appear in court? Hell, no! Thankfully I do all my court appearances via video link from my office at Mount Stromlo, otherwise that would probably be the hardest part of this job.”

A version of this article first appeared at ANU College of Science.