Zarah Brown/Solar system walk

Ph.D. candidate and project lead Zarah Brown poses for a photo with the first stop of the new solar system walk, the plaque for the sun outside the Kuiper Building, that stretches through the grounds of the University of Arizona on Wednesday. The walk has markers for the system’s main bodies, from the sign for the sun just east of Cherry to Pluto’s sited just east of Euclid.

Remember those textbook diagrams of the solar system or the foam planets that hung in a tidy row from the ceiling of your grade school classroom?

All lies.

A sprawling new installation at the University of Arizona is designed to provide a true picture of our solar system in all its humbling vastness.

The Arizona Scale Model Solar System is a collection of 10 informational signs stretching from the Kuiper Space Sciences Building on the UA Mall to Main Gate at the west edge of campus.

Each sign represents a planet or other celestial object, carefully placed to reflect its relative position in orbit around the sun. Even at 1:5 billion scale, the display covers more than half a mile. It takes about 10 minutes to walk from the sun to Neptune, a real-world (real-space?) distance of almost 2.8 billion miles.

“Astronomical scales can be difficult to grasp,” said project lead Zarah Brown, a doctoral student at the UA’s Lunar and Planetary Laboratory.

The signs provide details on the mass, diameter, surface gravity and temperature of each solar system object. They are illustrated with NASA images and artwork by James Keane, an alumnus of the Lunar and Planetary Laboratory.

The permanent display also doubles as tribute to the university’s out-sized contributions to planetary science. At each stop on the solar system tour, visitors can read about UA research related to that object.

Brown said they had no trouble finding all the Tucson connections they needed. “It was harder to choose which ones to include,” she said.

The installation illustrates the vast distance between planets.

Celestial stroll

The signs went up in late August. The university hosted a ribbon-cutting ceremony for the installation on Friday in front of the Kuiper Building.

That’s where the sun can be found, scaled down to the size of a basketball, along with the rest of the inner solar system — Mercury, Venus, Earth and Mars, all grouped within about 150 feet of each other.

The distances increase as you move west along the UA Mall, out past the asteroid belt. The signs for Uranus and Neptune are two-tenths of a mile apart.

“That gives you a sense of how lonely and vast the outer solar system is and why some of these objects are under-studied. They’re harder to get to,” said Brown, who is wrapping up her Ph.D. dissertation on the upper atmosphere of Saturn.

The solar system walking tour was developed with the help of a multidisciplinary team that included about 10 graduate researchers who helped write and edit the information on the signs. The display was funded through a NASA Space Grant Fellowship that was awarded to Brown in 2020 and later extended.

She said she has been fascinated by the enormity of the solar system since she first learned about it in elementary school.

Once when she was a child, she tried to draw the planets at their proper scale and distance using a calculator and some art supplies, but she had to abandon the effort when she realized that she was going to have to ask her dad for several hundred more sheets of paper.

“It was mind blowing. There’s all of this empty space around us. Everything that feels so big and so important is actually really tiny,” Brown said. “This has been something that I’ve felt compelled by for a very long time.”

The solar system exhibit is designed to serve as an educational tool for UA students and campus visitors alike. As part of the project, Brown is drafting lab exercises to help undergraduates conceptualize large numbers and vast distances by walking the installation and making calculations along the way.

Way out there

Brown said there’s a bit of “environmentalism” included on the sign for Venus, where a “runaway greenhouse effect” has rendered the planet hot enough to melt human-built space probes in a matter of minutes.

“The interplay between the surface and the atmosphere are the same processes that are happening on the Earth,” she said.

A QR code on each sign links to a website that can be used with a screen reader for the visually impaired. Brown hopes the website will be expanded some day to include additional information about the solar system and the UA’s role in exploring it, along with updates as new discoveries are made.

The installation was arranged based on each object’s average orbital distance, although some minor adjustments were made to make sure the signs ended up someplace safe and convenient.

“We did fudge on Neptune,” Brown said. “It would more rightly be placed in the middle of Park Avenue.”

Instead, it can be found just inside the volcanic rock wall of Main Gate at Park and University Boulevard.

Eventually, the installation will extend off campus by about 700 feet to include Pluto. Brown said they plan to place that sign near the corner of University and Euclid Avenue, as soon as they finalize a legal agreement with the Marshall Foundation, which owns much of the Main Gate Square commercial development there.

“We decided to put it in because I think the argument about whether Pluto is a planet is awesome,” Brown said. “It gets people emotionally fired up, which is sometimes hard to do with some of these space topics that people don’t necessarily feel personally invested in. People have definite opinions about Pluto.”

She added that the demoted dwarf planet has such a strange, elongated orbit that its sign actually could be placed as far away as Time Market, another third of a mile farther west on University Boulevard.

And if that isn’t mind-boggling enough, consider this: If you wanted to include Proxima Centauri, the closest star to our sun, Brown said the scale model would have to be expanded by about 5,000 miles, roughly the distance between Tucson and Glasgow, Scotland.

“One of the takeaways that somebody could get from this model is that we are so precious and tiny,” Brown said. “Why don’t we take care of our one and only home? And why don’t we treat each other a little better? All we really have is each other in this huge amount of vast space.”

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Contact reporter Henry Brean at or 573-4283. On Twitter: @RefriedBrean