The United States is packed with astronomical observatories — located on high mountain tops or splayed across a desolate desert. Beyond their beautiful terrestrial settings, many of these observatories have fueled the most important astronomical discoveries of the last century.

The world’s largest on-land optical telescope is at the W. M. Keck Observatory atop Hawaii’s nearly 14,000-foot Mauna Kea peak. However, this US observatory is neither open to visitors nor easy to work into a continental road trip. Rather, this road trip begins in California — where the Big Bang Theory was developed — and takes you across several western states, where a dry climate and tall elevations provide the best observing conditions.

The road trip also includes a handful of eastern observatories. These can be part of your cross-country astro road trip, or you can split your travel into a western and eastern US observatory tour. However you choose to explore, these are the best US observatories you can visit on a trip across the country.

The best observatories in California

Chabot Space & Science Center — Oakland, California

The Chabot Space & Science Center is a museum dedicated to space, which also houses three telescopes — so it’s the perfect place to learn about observatories to begin your road trip. You can look through its telescopes for free on clear Friday or Saturday nights between 7:30 and 10:30 PM. The most modern of these, the research-grade 36-inch telescope, offers tremendous night sky views. For its part, the eight-inch Alvan Clark refractor telescope dates to 1883, so it lets you look at the stars as astronomers did 140 years ago.

You can also take in the views of the San Francisco Bay and San Francisco beyond that. Inside the museum you can pilot a rover spacecraft and see an actual Russian Soyuz descent module. While the weekend night telescope viewing is free, the museum costs $20 for adults and $19 for youth and seniors.

Where: 10000 Skyline Blvd., Oakland, California 94619

Lick observatory, Mt Hamilton, California

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The Lick Observatory is located in the San Jose mountains on a site chosen by James Lick, a wealthy businessman who donated to educational causes throughout California. He’s buried under the telescope, which began operations in 1988, a year after his death. Shortly after that Jupiter’s moon Amalthea was discovered here.

Owned and operated by the University of California, one of the observatory’s missions is teaching the public about astronomy — so admission is free (donations are gladly accepted). The outdoor public areas and the Shane Telescope Visitors Gallery are open daily from 10:00 AM to 5:00 PM. The main visitor area is open weekends from noon to 5:00 PM. While there, catch one of the hourly free presentations offered inside the dome of the 36-inch Great Refractor.

Where: 7281 Mount Hamilton Rd., Mount Hamilton, CA 95140

Mount Wilson Observatory — Los Angeles, California

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For over a century, the Mount Wilson Observatory, at 5,715 feet above sea level, was the world’s most significant observatory. Its first telescope, installed in 1908, was the world’s largest operational telescope. Later, world records were again broken with a 100-inch telescope, which Edwin Hubble began using in 1919. Discovering distant galaxies, combined with data from Arizona’s Lowell Telescope, Hubble was first to postulate the idea of an expanding universe.

The Observatory was also home to the first solar telescope (1905) and, more recently, its largest optical interferometer (2004). Unsurprisingly, one of closest institutions to Mount Wilson Observatory is the NASA-owned Jet Propulsion Laboratory, headquarters of Mars missions of the Perseverance and Curiosity rovers. From JPL it’s a short hop along Foothill Blvd. to Highway 2, which wends up 20 miles to the observatory.

You’ll emerge in cooler, pine-scented air, taking in sweeping views of Pasadena and downtown Los Angeles. You can visit a small Astronomical Museum and look at the famed 100-inch telescope from the Visitors’ Gallery daily from 10:00 AM to 5:00 PM. To see the telescope up close, reserve tickets for two-hour guided tours — offered weekends at 11:30 AM and 1:00 PM. Tickets are $15 for adults and $12 for seniors and kids 12 and under.

Where: Mount Wilson, Los Angeles, CA

The best observatories in Arizona

Lowell Observatory — Flagstaff, Arizona

The Lowell Observatory in Flagstaff, Arizona, is one of the best US observatories

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The Lowell Observatory was as important as the Mount Wilson Observatory for Edwin Hubble. Here, Vesto Slipher noticed the redshift in light that indicated that galaxies were moving away from us. Hubble put Slipher’s data together with his own to arrive at his idea of an expanding universe — now known as the Big Bang Theory.

Established in 1894 and now a National Historic Landmark, the Lowell Observatory lies on Mars Hill overlooking Flagstaff, Arizona. At 6,900 feet, Flagstaff is much cooler and more wooded than other Arizonian cities. In fact, Olympic athletes train here to take advantage of the high altitude yet mostly mild weather. That said, bring warm clothing when you head up to the Observatory — which is at 7,800 feet and can have snow on the ground.

Tour the 24-inch Clark Refractor, with which Slipher made his momentous observations, the state-of-the-art 24-inch Dyer Telescope, and the telescope used to discover Pluto in 1930. Check the calendar for “Meet An Astronomer” nights, on certain Saturday nights between 7:00 and 10:00 PM. The observatory is open daily from 10:00 AM to 11:00 PM (except Tuesday, when it closes at 5:00 PM). If the sky is clear, you can look up using one of the telescopes on the Giovale Open Deck Observatory.

The General Admission ticket accesses all of the above options, including stargazing, at a cost of $25 for adults, $22 for seniors, college students, and those with a AAA discount. Plan ahead with friends and you could book a private 74-minute viewing for up to 10 people with the Dyer Telescope, for $525. Visit the experiences page for more details.

Where: 1400 West Mars Hill Rd., Flagstaff AZ, 86001

Mount Graham International Observatory — Safford, Arizona

Perched atop Mount Graham at 10,400 feet above sea level, this US observatory is the highest one on your road trip, something to consider when visiting. The squarish white object atop the mountain top looks space-agey indeed — or like a bad guy’s lair in a James Bond film. Its construction less than 20 years ago was controversial, as the site is sacred to the San Carlos Apache tribe and environmental groups decried the impact on local red squirrels.

The observatory is operated by the astronomy department of the University of Arizona, which monitors the health of the red squirrel population, which is apparently still thriving. Of the three telescopes, the Large Binocular Telescope (BLT) has the largest single-piece mirror of any telescope, which has been used by astronomers from Italian, German, and US institutions to observe galaxies billions of light years away.

The Heinrich Hertz Submillimeter Telescope measures not visible light waves, but very short radio waves that it captures in its parabolic antenna. The third telescope is operated by the Vatican Observatory — which the Vatican itself calls one of the oldest astronomical research institutions in the world, dating back to 1582. (Tell that to Galileo, who was denounced for heresy in 1633.)

You can take weekend tours of the observatory from mid-May to mid-October, depending on the weather. The tours begin and end at Discovery Park in Safford, Arizona. The day starts at around 9:30 AM, ending at 4:30 PM. Lunch is included in the $40 per person price. Reserve your spot by calling (928) 428-6260 or emailing discoverypark@eac.edu. Your guide will inform you of the area’s human and natural history and then take you to visit each of the three telescopes.

Where: ​​Eastern Arizona College, Discovery Park Campus, 1651 W. Discovery Park Blvd., Safford, AZ 85546

The best observatories in the Southwest

McDonald Observatory — McDonald Observatory, Texas

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The McDonald Observatory is located atop 6,800-foot-high Mt. Locke in West Texas, just north of Big Bend National Park. It holds five telescopes, the most significant of which is the Hobby-Eberly Telescope. With a mirror measuring 36 feet across, it’s one of the world’s largest optical telescopes and is dedicated to spectroscopy, which involves studying light to determine the composition and distance of distant objects.

You can visit the observatory Tuesday through Saturday from 12 to 5:00 PM. General admission is $3. You can take self-guided tours and participate in a $5 solar viewing program, or join $10 guided tours. Also, check the website to see when you can join a Special Viewing Night using its research-grade 36-inch telescope. The price for that one is $100 per person, while viewing through its 82-inch telescope is $150 per person. It’s not cheap, but seeing Saturn and its rings clearly, for example, is a memory that will last a lifetime.

Where: ​​Frank N. Bash Visitors Center, 3640 Dark Sky Drive, McDonald Observatory, TX 79734

Karl G. Jansky Very Large Array — Socorro, New Mexico

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The Karl G. Jansky Very Large Array, or VLA, is a different type of astronomical observatory in two ways: instead of using our human eyes aided by a telescope to observe light waves in the visual spectrum, it uses satellite dishes to capture waves that we cannot see. In this case, it is capturing short radio waves. It’s named for Karl Jansky, who in 1933 discovered radio waves coming from distant stars in the Milky Way.

Moreover, the VLA doesn’t listen for radio waves with just one telescope but in fact twenty-seven of them, each one measuring 82 feet across. The telescopes cover a huge area, lined up in three 13-mile long arms emanating from the center. By looking at one object and working in unison, these radio telescopes in fact function like one huge telescope.

Currently, the VLA is closed to visitors, but it should soon resume twice monthly tours. In the meantime, it is still worth driving by to see the array of satellites pointed skyward. Old Highway 60 crosses right through the complex.

Where: Socorro, NM 87825

The best observatories in the eastern US

Leander McCormick Observatory — Charlottesville, Virginia

Photo: Leander McCormick Observatory

Photo: Leander McCormick Observatory

The Leander McCormick Observatory is named for the wealthy patron who was determined to have the world’s largest telescope housed in his home state of Virginia. The 26-inch telescope, which began observations in 1882, ended up being only the second-largest telescope by the time it was completed. At least the observatory built to house the telescope was the world’s tallest when it was finished in 1884.

Operating by the University of Virginia, the observatory made ground-breaking observations, such as that of Venus crossing the sun. Its measurements of distances to the hundreds of nearby stars shaped the earliest calculations about the size of our galaxy.

The UVA campus is widely considered one of the country’s loveliest, a worthy visit on its own merits. On either side of its central lawn are the tiny, bare-boned rooms that Thomas Jefferson designed as student accommodations. (One of them remains open as a historic model). Never mind that you have to walk outside to use the bathroom; these are the most coveted student accommodations. From this central lawn it’s just a 30-minute walk uphill to the most historic observatory in the South.

Where: ​​600 McCormick Rd., Charlottesville, VA 22904

Green Bank National Radio Observatory — Green Bank, West Virginia

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Just a couple of hours’ drive up into the forested mountains from Charlottesville lies one of the most unusual towns in the US: Green Bank. Like Arizona’s VLA, the Green Bank National Radio Observatory uses parabolic telescopes to “hear” radio waves. These telescopes are what we use, for example, in the search for intelligent life, or SETI — to which the Green Bank Observatory dedicates part of its telescope hours. The Byrd Green Bank Telescope (GBT) is the largest fully steerable radio telescope on Earth.

While radio observatories benefit from operating 24 hours a day, the radio signals coming from the edge of the universe emit less than a billionth of a billionth a watt. A mobile phone, on the other hand, can emit 10 watts. So that these ancient star signals not be engulfed by modern gadgets, the National Radio Quiet Zone was created. It’s a 13,000-square-mile area that prohibits cell phones, microwaves, and even FM radio.

Seven telescopes dot the fields surrounded by the gently sloped Appalachians. At 2,700 feet above sea level, Green Bank is pleasantly cool, even in mid-summer. You could try hiking around here, but remember that there’s no GPS or cell phone signal if you get lost. Green Bank brings together an unusual mix: the scientists and engineers who work at the observatory and the self-described “electro sensitives.” The latter group have come to the radio quiet zone to avoid electro-magnetic frequencies that they say make them unhealthy.

Vaccinated and pre-registered visitors can tour the Science Center for $5. Better yet, pay $10 and you can include a guided bus tour on your visit. The center is open daily from 10:00 AM to 6:00 PM and bus tours depart on the hour. Note: Since you cannot rely on GPS to arrive at the observatory, please refer to their directions page (and maybe print out a copy) before you go.

Where: 155 Observatory Rd., Green Bank, WV 24944

MIT Haystack Observatory — Westford, Massachusetts

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Many prominent Northeastern universities operate observatories. MIT’s Haystack Observatory, an hour east of Boston, is one of the most interesting. It houses three radio telescopes tucked into the wooded surroundings. The first antenna you’ll notice is the massive Radio Antenna & Radome, a white geodesic dome completed in 1964 that measures 120 feet across.

​​The Millstone Hill Incoherent Scatter Radar, which looks like a giant tripod, is the most powerful Earth-based telescope to measure thermal plasma in our atmosphere, while the Westford Radio Telescope is used to better understand our own planet — its shape and location, among other measurements. The fourth telescope, Haystack VLBI Correlator, provides extremely precise measurements related to both our own planet and its distance to other astronomical objects.

If this is all confusing, then sign up now to participate in one of the Haystack Observatory’s twice yearly open houses — on the third Thursday in May and October. (They have been closed due to the pandemic, but stay tuned for updates). You’ll hear lectures on how radio telescopes can teach us about space. The Haystack grounds are free to explore Monday to Friday during 8:00 AM to 5:00 PM, when the car gate is open. Seeing up close the unusual telescopes operated by one of the world’s most important scientific institutions is fascinating, even if you can’t go inside. Otherwise, Haystack suggests calling (617-715-5400) or emailing (info@haystack.mit.edu) with questions about visiting.

Where: 99 Millstone Rd., Westford, MA 01886