Miles and Miles? Judging Distance in Space

Marianne Dyson, April 2019

On Apollo 14, Alan Shepard famously hit the first golf ball on the Moon. Because of the stiff space suit, he had to hit one-handed. After several tries, he sent it off camera and claimed it went “Miles and miles and miles.” But did it really go that far?

Judging distance in space is tricky. Studies have shown that even on Earth, people routinely underestimate horizontal distances by ten percent. On the other hand, heights are usually overestimated by as much as 30 percent, especially when looking down or from a distance. (A pyramid appears steeper from a distance than it does up close.)

NASA AS14-67-9367.
Credit: NASA AS14-67-9367.

Does the Apollo 14 lander seem closer than 650 feet (two football fields) or taller than 10’7”? The near horizon, sharp shadows, and a tendency to underestimate distance and overestimate height of objects makes judging distances  difficult on the Moon. 

A study conducted on space station astronauts shows these effects are exaggerated in space. Astronauts underestimated distances by as much as 35 percent, even for objects at close range. Astronauts with long arms perceived targets within reach that were out of range. They also perceived objects to be taller than on Earth. This effect may be in part because people use the height of their eyes above the ground to provide scale—and there is no floor when floating in space. [Reference: Distance and Size Perception in Astronauts during Long-Duration Spaceflight]

On the surface of the Moon, many of the cues used to judge distance, such as trees and trucks, are missing. The lack of air also makes objects appear sharper and thus closer—adding to the tendency to underestimate distance and size of objects. Finally, the Moon is a smaller world than Earth, so the horizon is much closer. From a height of about six feet, the horizon is about 1.5 miles away (compared to about 2.8 miles on Earth). Combining all these effects means that what first appears to be a small nearby rock is actually a distant boulder.

Astronauts also have difficulty predicting the motions of objects in space. During a space shuttle mission, catching balls moving at constant speeds was difficult. People are used to balls accelerating as they fall on Earth. So astronauts think they are moving faster than actual and reach for the balls too soon (and miss the catch!). [Reference: Does the brain model Newton’s laws?]

So did Shepard’s ball go miles and miles and miles? [Watch video.] The record for a golf drive (Mike Austin, 1974) on Earth is 515 yards/0.3 miles. Some people have speculated that because of the Moon’s low gravity and lack of air, a golf ball hit that hard might sail more than two miles. Considering Shepard was likely underestimating the distance by up to a third, I wouldn’t be surprised if the ball went a mile—but not more than 1.5 miles since it didn’t disappear over the horizon.

On a more serious note, distortions in perceived distance, height, and motions could have grave consequences during space missions. A poor sense of closing speed has been cited as a contributing factor in a collision with a docking port on the Mir space station in 1997. [Reference: Shuttle-Mir’s lessons for the ISS]

More studies on how people judge distances and react in space will help us better understand our ingrained biases when it comes to judging distances in space.  Laser range finders and future AI lunar golf advisers may even help us figure out how much of a handicap to give an astronaut in a stiff space suit!

Writing about Space

I’m thrilled to announce my newest space book! Watch my website Book Orders page for Welcome to the Moon ordering information.

A Summer 2019 Release!

My fact article about a practice drill for what to do if an asteroid threatens Earth, In Defense of the Planet, is a finalist in the AnLab Readers’ poll. It is available FREE on the Analog website until the winners are announced at the Nebula Awards in May.

Speaking about Space

I offer programs appropriate for school-aged children up through senior citizens, as well as science workshops for students and teachers. See my list of programs on the Author Visits tab of my website.

Saturday, May 11, Comicpalooza, GRB convention center, Houston. I’m on two panels in the Literary Track (upstairs rooms).  From 3-4 PM, Worldbuilding Tips and Tricks: How to Create Believable Worlds, and from 6-7 PM, Writing Historical Fantasy—Getting the Details Right!

Thursday, May 23, Bay Area Writers League, Clear Lake Park, Houston, 7 pm. “Beyond Self-Publishing: Becoming a Publisher. What are the financial, legal, personnel, quality, quantity, and time considerations of creating books for companies or individuals?

Friday May 31, WriteFest Weekend Festival, Anderson-Clarke Center (6100 S. Main St. Houston, 77005), Rice University. The weekend festival includes panels, presentations, agent pitch sessions, and a book fair. Look for me on panels and at the book fair. Register early for the best price ($95 to $185 one day only & $180-$375 F-Sun).

See my website’s contact page for a complete appearance schedule.