A Visit to Sunspot Solar Observatory
Once the National Solar Observatory, Sunspot Observatory near
Alamogordo is still doing active solar science and has a unique solar tower instrument,
the Dunn Solar Telescope.
You can visit the observatory most days, combining it with a
quick look around the domes of next-door Apache Point until 5 pm. There are the
various telescope facilities to explore in a beautiful location and a small but
well thought out museum and visitor centre.
During the week they run tours with the opportunity to view
the Sun.
History
Sunspot started just after WWII with a few Nissen huts and a
dome converted from a grain silo. By the 1950s it housed several proper
observatory domes and various solar telescopes.
Its most important instrument, the Dunn Solar Telescope, was
built between the mid-sixties and 1969 and has done much important solar
research since.
Getting There
If you’re staying in Alamogordo, perhaps after a visit to
nearby White Sands NM, then Sunspot 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.
They’ve put up planet signs all along Highway 130, spaced in
proportion to their relative distances from the Sun.
The Sunspot Highway is a right turn off 130 (between Jupiter
and Mars) and ends at Sunspot Observatory where there is ample parking by the
visitor centre. They warn you not to follow satnav which may take you along an
unnecessary stretch of dirt road.
What to see
The observatory is on the edge of the scarp, in Lincoln
National Forest at 9200 ft, with huge views over the White Sands basin. You can
walk around the domes, visit the museum or take a weekday tour.
Visitor Centre and Museum
The visitor centre has basic facilities and a small museum,
but no café.
You might imagine dusty old displays at such a remote and
quiet spot, but in fact they are lively, very interesting and cover general
astronomy as well as the Sun (I guess it serves Apache Point too, since it
includes a display on the 3.5m telescope there).
I particularly liked the interactive displays explaining refracting
and reflecting telescope optics and the working of a spectrograph’s diffraction
grating.
Walking Tour
There’s a paved half-mile walking route with a brochure to
guide you. It starts at the VC, heads off through a patch of forest and then
runs through the site, taking in the Dunn Solar Tower and various other
facilities. Apart from the Dunn, though, most of the domes you pass (including
the strange conical one at the start and a converted grain silo later on) are
no longer used.
The Dunn Solar Telescope
You can’t miss the 136 ft white concrete spike that houses
the main solar telescope at Sunspot. It’s still a remarkable piece of
engineering and is the most interesting facility at Sunspot, even though it was
built in 1969.
Though the heliostat, that tracks the Sun through a 30 inch quartz window, is at the top of that tower, the
majority of the telescope is below ground in a shaft 227 ft deep. That’s
because the 64 in mirror has a focal length of 180 ft (~F 34) and lies near the
bottom of the shaft.
The entire optical tube weighs about 250 tons, is kept in a
vacuum and hangs from a single mercury float bearing at the top of the tower,
including the 40 ft observing floor which houses adaptive optics and various
instruments. The whole lot rotates to follow the Sun.
Tours sometimes offer the chance to visit the observing floor
and watch the Dunn and its instruments in action, see below.
The now defunct Evans dome once held
a 16” telescope and spectrograph.
The Dunn Solar Telescope is the landmark facility at Sunspot
and is still doing research.
With lots of old and empty buildings and observatories,
Sunspot does feel a little bit like an outdoor museum now.
Viewpoint
Just past the Dunn Solar Tower are some wooden steps up to a
viewpoint over the edge of the scarp. There, the forest drops steeply away to
reveal vast views across the Tularosa Basin to bone-white dune fields and the
distant mountains beyond.
Things to do
Weekday Tours and Solar Viewing
On weekdays apart from Wednesday, they run tours from 10 am
until Noon. Tours start at the visitor centre and may or may not need to be
booked in advance (check the website).
Depending on observing schedules, the tour may include the
chance to visit the observing room of the Dunn Telescope and see sunlight
passing through the various instruments on the optics benches and then
displayed on monitors.
Unfortunately, this wasn’t running during my visit, but I
hope to go back and see it someday.
Summary
You might not make a trip to New Mexico just to visit
Sunspot, but if you’re in the area then combine it with Apache Point and maybe
a forest walk (lots to choose from off Highway 130) to make up a day trip.
Sunspot is worth a visit any day, but go on a weekday (except
Wednesdays when it’s closed) for the tour and a chance to view the Sun.