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.