A view of the sky over downtown Tucson, which supposedly has the darkest night skies of any city its size in the country. (G Vargas/Getty Images/Flickr RF)

Dry heat or not, 109 degrees is a frankly ridiculous temperature.

That’s why, if you find yourself in Tucson in the summer, the best plan is to spend daylight moving quickly from one bubble of air conditioning to the next.

Luckily, when the sun sets and the air cools to a balmy 90 or so, you’ll find that the night was worth waiting for. Thanks to a local ordinance that strictly limits artificial-light pollution, Tucson supposedly has the darkest night skies of any city its size in the country.

If you go, Tucson

The law was first passed in 1972 to conserve energy and to preserve the crystal clarity of the dry desert air, which has drawn professional astronomers for more than a century. Today, astronomy and its spinoff industries are big business in southern Arizona. Many of the state’s dozens of federal and university observatories are within a few hours of Tucson. And the city’s forward-thinking regulations have made it a center of the dark-sky movement, aimed at reducing the creeping tide of light pollution.

According to the Tucson-based International Dark-Sky Association, excess nighttime lighting doesn’t just waste energy. It can disorient migrating birds and sea turtle hatchlings, disrupt frog mating and bat feeding behavior, and upset our own sleep patterns and hormone production.

It also makes the skies over urban areas glow a dull and starless orange, cutting residents off from the beauty of nature’s own light show. (After the 1994 earthquake killed the power in Los Angeles, emergency call centers were inundated with panicked reports of a strange, glowing cloud in the sky. It was the Milky Way.)

Not here. For a city of 500,000, Tucson is an astonishingly good place for stargazing. Best of all, you don’t even have to make the hour-plus drive to the large observatories at Kitt Peak or Mount Lemmon.

On my first evening in town, I climb a curving staircase at the University of Arizona’s Flandrau Science Center to a small circular room with a hemispherical dome split open to the sky. A 1970s-vintage Cassegrain reflector telescope takes up most of the space, which is dimly lit by the glow of computer screens and red lights to help preserve night vision.

Two volunteer docents, using sparkling-green lasers, point out stars and planets to a handful of guests. The air is filled with the futile hum of fans and an occasional deep rumble as one of the docents rotates the dome to point the telescope at something new.

Two young couples from Honduras take turns climbing the two steps to look through the eyepiece.

“Wow,” says one of the women.

“We like ‘wow,’ ” says docent David Acklam with a smile.

When it’s my turn, I see what the woman means. The moon looks so close that only a slice is visible at a time. You can see craters within craters, everything as bright and sharp as glass.

Acklam explains that with telescopes, it’s not about length, it’s about diameter; the larger the mirror inside, the more light it collects and the more detail it reveals. The Cassegrain is a 16-inch (diameter) telescope, which means that its main mirror is just over 200 square inches.

The next afternoon, I’m back at the university, or more accurately, under it. The Steward Observatory Mirror Lab, one of the few facilities that can make mirrors for the world’s largest telescopes, fills most of the space beneath Arizona Stadium, the 50,000-seat home of the Wildcats football team.

A guide leads our tour group down a set of steel stairs to a cavernous space filled with ultra-high technology on an industrial scale. We look down on a round mirror the size of a modest living room. It’s just part of the Large Synoptic Survey Telescope, destined for a mountaintop in northern Chile. Astronomers will stitch together images from its 3,200-megapixel camera to create unparalleled images of the night sky and eventually a 3-D map of the universe.

A spinning machine is slowly polishing the mirror like a Zamboni on the world’s most expensive hockey rink. There’s no room for error: The surface needs to be almost perfectly smooth, no imperfections larger than 20 billionths of a meter.

Another mirror being polished, this one 27 feet across, is one of seven that will make up the Giant Magellan Telescope, also planned for Chile. (The country’s mountainous, bone-dry northern desert is the current hot spot for large-scale astronomy.) When it’s operational in about a decade, the GMT will probably be the most advanced telescope on Earth.

The next room holds the lab’s famous rotating oven, where bricks of borosilicate glass are melted and spun in a circular mold to make the circular mirrors. Casting takes about a week each time, and you can follow the process online through cameras positioned inside the oven.

Climbing back to ground level, I decide to make a daylight trip to the Cat Mountain Lodge on the western edge of the city. The hacienda-style B&B has five rooms around a plant-filled courtyard, but I’m here for the small attached observatory, where guests and visitors can book guided viewings.

Robby Tackett, who runs the observatory, is already here, bent over a small white telescope in the kilnlike heat. The former skydiving instructor and amateur astronomer personally picked out the big guns used for night viewing — a 14-inch Celestron SCT and a 10-inch Meade LX200 SCG — as well as the smaller scope that he’s currently aiming at the sun.

Through unfiltered glass, looking at the sun would have the same effect on an eyeball as a magnifying glass on an ant. But a special hydrogen alpha filter lets through only a fraction of the star’s glare, making it safe to view.

Tackett steps aside so that I can take a look. The burning orb in the sky is reduced to a dark red ball whose surface seethes with convection cells.

“See those wisps along the edge?” Tackett says. “Those are solar flares.”

Each tiny thread is a massive eruption of light and energy, sending a torrent of radiation into space. It’s strange to think that the raw energy prickling my scalp and wilting the hairs on my arms started out somewhere in that roiling mass of hydrogen and plasma and took eight minutes to sail across space and arrive here.

I think I need a drink.

As it happens, Tackett also helps run the Sky Bar in downtown Tucson, where I head after sunset on my last night in town.

At first glance, it looks like any other college bar on funky Fourth Avenue, packed with tank-topped students playing pool and downing pitchers of beer. Then you notice that the photos on the wall and the video screens are all of planets and galaxies and other “Trek”-worthy objects. On the outdoor patio, Tackett is lining up Saturn through a $9,000 motorized telescope taller than he is.

The rings are as clear as tracks on a record, as are four of the planet’s 62 moons, including massive Titan, the only moon in our solar system with its own atmosphere.

The Sky Bar is open until 2 a.m., with free viewing most nights and extra telescopes on Fridays. Tuesday is family night, when Tackett brings camera adapters so that people can shoot photos through the eyepieces.

“Sometimes people cry,” he says as the scope’s automatic tracking system swings it slowly toward the Ring Nebula. “I’ve shown homeless people Saturn. It’s amazing when people see things they’ve never seen before.”

As I look through the eyepiece at the fuzzy halo, the dying gasp of a red giant star before it collapses into a dense white dwarf, I have to agree.

Smith is the author of “Crossing the Heart of Africa: An Odyssey of Love and Adventure.”