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A (brief) Visit to Lowell Observatory’s Anderson Mesa and Happy Jack Sites

You may notice that the main site above Flagstaff that I’ve been concentrating on is great for history and outreach but not so much for current professional astronomy. That’s because Lowell’s professional telescopes are all at two dark-sky sites south of Flagstaff, one at Anderson Mesa, the other at Happy Jack.

There’s not that much to see without some kind of backstage pass, just the various domes. So this is just a quick fly-by and description of the telescopes if you’re interested, or are planning on visiting the area and just curious about what you can see. If I am one day lucky enough to get a tour, I’ll obviously update this into a more major article.

Getting There

The older site at Anderson Mesa is accessed from a right turn 12 miles out of Flagstaff along Lake Mary Road. The road begins at a left-hand turn (going south) just out of Flagstaff past the I-40 flyover. The road drives through some urban sprawl before heading out by some largely dry reservoirs. Watch for cyclists along this stretch.

Happy Jack is 42 miles along the same road out of Flagstaff as Anderson Mesa. Chosen for its dark skies, I can see why: it really is miles from anywhere in a very remote spot in the middle of a national forest area.

Even this sign is scarred by buckshot.

What to see

Anderson Mesa Site

It’s not that easy to find and is just signed-posted ‘NPOI’. The road twists up through pine forests, past a rough camping area before reaching some domes on top of the mesa.

The first observatory you come to on the right is a small one for the US Geological Survey. It likely houses a 21” F16, but I can’t find details.

A bit further on is Lowell’s 72" Perkins Telescope in a large dome. The Perkins Telescope is an older long-focal-length (F17.5) Cassegrain with a truss tube on a massive single-arm (‘English’) yoke mount and reminds me a bit of McDonald’s 82”. It was acquired from the Ohio Wesleyan Observatory in the 1960s.

Lowell has partnered with Boston University as a partial divestment of the Perkins, which nonetheless has a number of modern instruments, including multi-object spectroscope and another working in the near infra-red. Of interest if you’re a pro’ with a project in mind is that it’s apparently inviting proposals for research at the absolute bargain price of $800 per night.

Past the Perkin’s dome is a silver one housing the 42” Hall telescope, a fork-mounted F8 truss-tube Ritchey-Chrétien that Lowell describe as their ‘workhorse’. It was inaugurated in 1970 and is used for CCD imaging, spectroscopy and photometry. It got an upgraded lightweight primary mirror in 2004.

Out of sight is a smaller dome that houses the NURO telescope, a yoke-mounted 31” F15 Cassegrain installed in the sixties for the USGS as part of a lunar imaging project for Apollo. The 31” is now used by undergraduates 60% of the time. The Lowell picture shows a piggy-backed orange-tube Celestron SCT!

Also nearby is the signposted NPOI – the Navy Precision Optical Interferometer, the world’s largest optical interferometer - in partnership with the US Naval Observatory (that has a separate site near Flagstaff). You can’t see much of the NPOI from the road.

The NPOI is used to measure exact stellar positions to create a spatial reference system for GPS calibration, among other things.

Happy Jack Site

Location of Lowell’s flagship professional scope, I just drove by to spot the dome from the road. There’s not much you can see if you’re not invited by Lowell.

What’s there?  The 4.3m Lowell Discover Telescope that only became fully operational in 2015 (first light was in 2011) and cost $53 million. The LDT is mainly used as an F6.2 RC, but has other foci too. The LDT has various instruments, including spectrographs and large imagers in the visual and near-IR. It also hosts Yale’s exoplanet radial-velocity instrument. A night on the LDT costs $25,000.

Fun fact: I got chatting to an astronomer doing outreach work on the 24” Clark and he told me that they once attached an eyepiece to the LDT and looked at Mars when it was on the wrong side of the Sun and very small. He said it still showed amazing detail. If true, this might be the largest telescope ever used visually on Mars. Given the specs, the minimum likely magnification was ~500x if they used a custom 100mm eyepiece, double that with a 55mm Plossl (the eyepiece they mostly use on the Clark).

Lowell Discovery Telescope dome poking out of the trees near Happy Jack on Highway 209.


The Anderson Mesa and (especially) the Happy Jack site probably aren’t worth a dedicated trip from Flagstaff. However, they are on the first part of a much more scenic alternative to I-17 if you’re driving down to Phoenix and would be worth a look then.