A Visit to Apache Point Observatory

Apache Point is a small but important professional observatory high on the edge of the scarp above Alamogordo in New Mexico, founded in 1985 and home to the Sloan Digital Sky Survey. It’s operated by the New Mexico State University, but collaborates with numerous other institutions.

APO doesn’t advertise the fact, but although there’s no outreach program, up to 5 pm they do allow tourists to park up, wander around and see the various domes. I wouldn’t have known this if I hadn’t taken a cheeky detour after visiting the Sunspot Observatory next-door.

Getting There

If you’re staying in Alamogordo, perhaps after a visit to nearby White Sands NM, then Apache Point is about an hour’s drive away – up into the mountains to Cloudcroft and then south along snowy (in winter) and slow but scenic byway 130 through the forest. Just a junction off 85 in Cloudcroft, it’s easy to find. The whole route is paved and fine with a normal car.

The Sunspot Highway is a right turn off 130 and then the sign-posted turn to Apache Point is on the left before Sunspot Observatory (if you see the towering concrete solar tower you’ve gone too far).

From the east, it’s about three hours’ drive from Roswell or the Carlsbad Caverns via Highway 85, but that road is mostly quite fast and empty.

There are visitor parking spaces and paths to walk between the domes, several interpretive displays. When I arrived late on a winter afternoon the domes were whirring with fans to start cooling before night.

What to see

The observatory only covers a small area and it’s a beautiful place, with incredible views over the dune fields of White Sands and deer-filled forests on the drive in. Wandering about and snapping the domes only takes a short time, but if you hang on to the end (i.e. 5 pm) you might be rewarded with more as I was.

Sloan Digital Sky Survey Telescope

This is probably the most famous observatory at Apache Point – it’s even featured in my old OU astronomy text book – producing spectra for millions of objects since 1998 and hosting a huge range of different studies.

The observatory building is unusual. As you walk up to it (it hangs out over the mesa edge), you see a run-off area with tracks and indeed the whole thing is a huge roll-off. Inside is an F5 (wide-field for survey work) 2.5m truss-tube Ritchey-Chrétien which has a honeycomb mirror cast at Mirror Lab in Tucson.

Normally you don’t see the telescope, but as I was about to leave I got lucky. I spotted a guy in shorts (even though it was freezing) walk over to the SDSS, so I went back and realised he was opening it up and cooling the scope. Working with him was a young lady who turned out to be the astrophysicist in charge. She was very friendly, patiently answered my questions and gave me some interesting insights.

The SDSS telescope looks odd because it has to work in the open: the tube is surrounded by a rectangular wind baffle which makes it look very futuristic. Despite spending its working life in the open, it hasn’t been re-aluminised for five years, but they wash the mirror every year and always close for pollution events like smoke.

I won’t go into too much detail, but the SDSS has made continuous important observations and discoveries for decades, latterly only with a spectroscope that employs an optical fibre bundle for each object, embedded in a custom plug plate – you can see an example plate at Apache Point, it’s effectively a star map made of holes (see photo below).

The astrophysicist told me that they were just starting to use a new spectrograph, referring to the fact that they’ve retired the old drilled plates and now move the fibres with robot arms. She said that much of their current observing is in the infra-red and just now they are studying galactic red super-giants.

The SDSS 2.5m F5: the front cover opens like petals.

Honeycomb mirror section at next-door Sunspot visitor centre.

Spectrographic plug plate to align fibre optic bundles with individual objects – look at the size of it, never mind covering medium format!

Astrophysical Research Consortium (ARC) 3.5m Telescope

This is the largest telescope and observatory at APO. It was a pioneer of remote operation, with its internet-operable alt-az mount. It was built from 1985, but wasn’t fully operational until the nineties when its mirror was replaced by another Mirror Lab built honeycomb.

Again, it operates mostly with a spectrograph, but its fast remote-operable mount allows briefs studies of targets of opportunity (compare the SDSS’s fixed fibre plates which could be changed only a few times per session).

One notable and unusual ARC study is called APOLLO. It beams a laser at the Moon in order to map its orbit to a precision of 1mm!

Other APO Observatories

Between the SDSS and ARC 3.5m facilities lies a small, raised dome. This contains the ARCSAT telescope, a 0.5m F8 RC that’s equipped with a CCD. It was once used for photometry but gets assigned to smaller projects these days.

An interesting question – why is it raised like that? The answer is that studies have shown most of the air turbulence that ruins seeing is confined to the boundary layer in the first 10m above the ground.

The other small, raised dome betwixt the SDSS and ARC 3.5m houses a fully robotic 1m RC with a fibre-optic infra-red spectrograph that is used by NMSU.

Summary

It’s a small place and you can’t generally see the telescopes themselves, so APO may not be worth a day trip on its own considering it is quite remote. But combine it with the Sunspot Observatory next-door – which has a museum and an outreach solar viewing program – and it certainly is.

Then there’s the area itself: views from the mesa over White Sands are unique. The forests around are stuffed with viewpoints, wildlife and hiking opportunities.