Sacramento Peak Observatory

This week, NSO staff will pack the remaining materials from the photographic archive and some other locations at (former) NSO at Sac Peak Observatory. This represents the end of golden era of solar research at the Sacramento Peak Observatory. The observatory is closed, and the site would be restored to its original (national forest) state. The events that led to this outcome include mercury leak discovered inside the Dunn Solar Telescope (DST) on Jan. 5, 2026.

Here is a very brief history of Sac Peak observatory. The reader can find more details in the following publications: (Bushnell, 1962; DeVorkin, 1983; Zirker, 1998; Ramsey, 2002; Liebowitz, 2002; CH2M HILL Inc., 2017 – see Solar Phys (2021) 296:3; https://doi.org/10.1007/s11207-020-01746-5 for complete references).

 

The need for a dedicated solar observatory was realized during World War II, when solar observations were used for predicting the impact of solar activity on radio communications.  

1947: 

• Menzel and Marcus O’Day of the Air Force team up to promote the idea of a second observatory to complement Climax and increase coverage. Same year, the US Air Force awards Harvard a contract for a site survey to select a location for a solar observatory. Subcontract is issued to the newly formed High Altitude Observatory in Boulder CO. Don Menzel of Harvard and Walt Roberts of HAO spearhead the Survey. As part of the Survey, Menzel and Roberts fly over many southwest mountains looking for a site and note Sacramento Peak.
• September: two resident observers begin data collection of observing conditions at Sacrament Peak 
• December: Menzel and Roberts tentatively recommend Sac Peak as site for new solar observatory

1948, April: 

• US Department of Defense (DOD) Research and Development board approves Sac Peak as final site, and Harvard/HAO awarded contract to develop the observatory.  

1949: 

• Harvard/HAO team starts observations with 11 cm (4.5 “) coronagraph on 2.4 m (8’) spar in a sliding roof observatory (Photo 1). Its primary function is a coronal activity monitor. Later same year, a Sears and Robuck grain bin was purchased and made into a rotating dome, named the Grain Bin Dome. 
• 3 m (10’) spar was added; a 15 cm (6”) prominence telescope is mounted on the 3 m spar
• Construction of a 40 cm (16”) coronagraph and 8 m (26’) spar begins in Boulder by Jack Evans and Walt Roberts (Lyot consulting on optics)
• Daily radio observations of the Sun begin (Cornell University). 

1950:  

• Sac Peak became known as the Sacramento Peak Station of the High Altitude Observatory jointly operated by Harvard University and the University of Colorado under contract from the Air Force (Photo 2).

1951:

• March: 6 cm (2.5”) Hydrogen Alpha Flare Patrol camera mounted on the 3 m spar in the Grain Bin and daily observations are started.  
• April: Sac Peak is established as the Upper Air Research Activity under the Air Forces Geophysics Research Division (later to become the Air Force Cambridge Research Laboratory). At that time, the observatory was  operated by a combination of military and civilian US Air Force employees.     

1952:    

• Jack Evans appointed superintendent of Sac Peak. 
• Renamed the Upper Air Research Observatory. 
• Evans hires Richard (Dick) Dunn
•  Construction of a new facility to house the 8 m spar and 40 cm coronagraph begins
• 15 cm white light telescope installed on the 3 m grain bin spar 
• Staff: Dunn, Evans (sup), J. Warwick, C. Warwick
• 10 Redwood houses built along the ridge to house staff, Main Lab office building completed and apartments to house visiting scientist

1953:

• New Facility (Big Dome) completed at Sac Peak and 8 m (26’) spar installed (Spar so well balanced only 2.5 mouse power required to drive right ascension, 1 mouse power = 1/10,000 horse power)
• 40 cm coronagraph installed on 8 m spar, used for both coronal and on disk measurements, used for the next 60+ years with some modifications.

1954:

• Cornell radio observations cease due to interference from Holloman AF Base    

1955:

• 13 m (43’) Littrow spectrograph installed in the Big Dome fed by the 40 cm coronagraph
• Helicopter landing strip built
• 38 cm (15”) chromospheric and prominence camera installed on the 8 m spar

1956

• Upper Air Research Observatory name changed to Sacramento Peak Observatory (SPO) and Jack Evans becomes its first director
• 1956 Staff: Dennison, Dunn, Evans (dir), Orrall, H. Smith,E. Smith, Zirker
• Dick Thomas, Grant Athay, John Jefferies were frequent visitors providing theoretical support

1957:

• Patrol coronagraph installed on Grain Bin Spar
• Universal Spectrograph installed in Big Dome
• Evans designs a telescope for Project Stratoscope, a balloon borne telescope flown my Martin Schwarzchild to measure solar granulation

1958:    

• Six Redwood Houses built on Sac Peak (previous housing was Quonset buildings)
• A concept for an evacuated solar tower telescope (VTT) is put forward to the Air Force

1959: 

• Spectroheliograph installed at the Big Dome 
• Development work on VTT begins

1960:    

• Coelostat and secondary mirror installed at the Big Dome feeding a 30 cm horizontal telescope providing a solar image to all instruments
• The road to Sac Peak is finally paved

1961:    

• SPO staff: Dunn, Dennison, Evans (director), Orall, H and E Smith, White, Zirker

1962:    

• 40 cm (16”) magnetograph telescope installed on the 8 m spar in the Big Dome along with a Doppler Zeeman Analyzer (DZA), Photo 3
• By 1962 there are 70 personnel working at SPO, 10 military, 28 civil service (7 PhDs) and 32 contractors. In addition, there are 12 visiting scientists

 

  

 

1963:

• Hilltop Dome constructed and a 3.6 m (12’) spar installed
• Grain Bin instruments (flare patrol and white light telescope) transferred to Hilltop
• Beckers and Simon join the SPO staff, H. and E. Smith leave

1964:

• Dick Dunn begins final design work begins on VTT
• Additional space for offices and film processing added to Big Dome

1965:

• Dunn designs a photoelectric flare spectrograph to measure flare emissions in 40 spectral lines

1966, Spring: 

• Construction starts on the VTT (Photo 4)
• 10 additional houses completed at Sac Peak, mainlab addition finished
• Photoelectric flare spectrograph install in Hilltop Lab and fed by innovative Gregorian heliostat, used by NASA for Skylab support

 

1967:    

• Dunn designs two photographic flare spectrographs, one for Hilltop and one for the 40 cm Coronagraph to make rapid measurements of flares
• Mainlab computing center developed (XDS Sigma 5) for data reduction

1969:

• VTT Completed with evacuated light path to remove internal telescope seeing, mercury bearings used to support telescope and separate mercury bearing to support the entrance coelestat.
• All SPO contractor personnel converted to civil service

1971:

• Photographic Eschelle Spectrograph installed in VTT

1973:

• Diode Array installed on the eschelle spectrograph
• Jacques Beckers designs a Universal Birefringent Filter which is installed at VTT, the UBF was tunable from 420 to 700 nm angstroms with a variable bandpass of 4 to 13 pm.

1974:

• Air Force notifies SPO of its intention to discontinue funding as a result of the Mansfield amendment in Congress
• AF contracts SPO to build the Solar Optical Observing Network (SOON) telescopes for the Air Force Weather Service
• Daily coronal patrol ceases operation
• 38 cm (15”) prominence telescope removed from Big Dome 8 m spar
• HAO closes Climax Observatory and begins construction of Stokes polarimeter and coronal emission-line photometer for installation at the Big Dome.

1975:

• First SOON telescope completed and installed in Hawaii
• Jack Evans steps down, Dick Dunn appointed director
• Nov 9: Goldberg informs the Association of Universities for Research in Astronomy (AURA) Executive Committee that the AF is divesting SPO
• NSF forms a blue-ribbon panel to determine fate of SPO chair by Martin Schwarzchild, the committee recommended positively, recognizing SPO as the premier solar facility both in the US and internationally

1976:

• July: NSF accepts responsibility for SPO on July 1st
• AURA agrees to serve as interim contractor for SPO operations
• Jack Zirker appointed acting director, AURA management begins
• Joint SPO and KPNO-Solar staffs discuss future directions of the observatories (Oscillations, Stokes Polarimetry, and Solar-Stellar connection seen as rewarding areas)
• Franz Deubner, using the NSF Dunn Solar Telescope at Sacramento Peak, demonstrates how solar five-minute oscillations are trapped inside the sun, leading to helioseismology

1976, November:

• start of Sac Peak K-line, sun-as-a-star observations in Ca II K-line on daily basis

1977:

• Stokes Polarimeter (STOKES I) installed in Big Dome (joint HAO/NSO project), uses the 40 cm coronagraph to measure on disk vector fields, single point detector. 
• K Coronagraph Emission Line Photometer (KELP) installed in Big Dome (joint HAO/NSO project), measures coronal fields in the plane of the sky
• Special Advisory committee to NSF with Art Walker chair, recommend that NSF continue SPO as a national observatory with visitor support and strong staff research.
• NSF solicits proposal to operate SPO
• Ray Smartt begins development of One-Shot coronagraph

1978:

• AURA discusses their proposal for SPO at the annual meeting
• April: AURA awarded contract for SPO (NSF contract 78-17292), AURA now has separate contracts for KPNO, CTIO and SPO
• Jack Zirker appointed director with a 5 year term
• Oct: First AURA visiting committee visits SPO
• Tim Brown and Jacques Beckers develop concept for a Fourier Tachometer for measuring small (a few m/s) velocities in the solar atmosphere and construction of prototype begins (NSO/HAO)
• SPO assumes operation of 48” AF photoelectric telescope in Cloudcroft, NM and builds a new photometer under contract to the AF
• First rubber mirror image improvement experiments at VTT by U.C. Berkeley group – only for stellar images

1979:

• One-Shot coronagraph mounted on Hilltop spar (simultaneously views the entire corona out to two solar radii – hence One-Shot
• Real Time Atmospheric Compensation (RTAC) developed by Itek Optical Systems tested at VTT – demonstrates feasibility, but only on rare conditions, shows that first order image motion can be removed by fast mirror
• White Light Flare Polarimeter installed in Hilltop, observes white light flares in 4 continuum band passes to study energetics 
• STOKES II (STOKES I upgrade to 2-D detector)
• Deubner and UCLA co-workers produce the first estimate of the internal solar rotation using Sac Peak data

1980    

• First of three oscillation experiment to the South Pole (later, telescope became part of the Sac Peak Visitor Center exhibit)
• SOON Telescope system completed for the Air Force

1981: 

• 12 cm refractor white light flare patrol in Hilltop
• First detection of the mesogranulation on the sun using Sac Peak observations 

1987:

• The Big Dome at Sacramento Peak Observatory was officially rededicated and renamed the John W. Evans Solar Facility on August 18, 1987

1989:

• First reflective coronagraph based on highly polished silicon mirror was developed at NSO and installed at Hilltop facility.

1990-92: 

• The Advanced Stokes Polarimeter was developed as a joint project between NSO and HAO. ASP begun operations at Sac Peak  in 1992.

1993:  

• First successful demonstration of solar adaptive optics system achieved with the Lockheed segmented mirror and a Shack-Harthmann wavefront sensor at Dunn Solar Telescope (DST, NSO/Sac Peak). This work laid a foundation to later development of low-order (1999), high-order (2004) adaptive optics system for NSO telescopes, and future multi-conjugated AO.

1995: 

• The development of the Precision Solar Photometric Telescope (RISE/PSPT) for providing full-disk images to allow detailed study of the total solar irradiance variation in three wavelength bands at various temporal scales. Three instruments were put into operations: the Osservatorio Astronomico di Roma (1996), the Mauna Loa Solar Observatory (1998), and NSO at Sac Peak (2000). 

1996:

• Initial design study for a solar telescope network to replace the existing Solar Observing Optical Network (SOON). The design was completed, and the group proceeded with building a prototype, Improved SOON or ISOON. 

1997: 

• The SOON telescope at Palehua, Hawai’I, was dismantled in April 1997 and shipped to Sacramento Peak for developing ISOON prototype

1998:

• The Vacuum Tower Telescope (VTT) at Sacramento Peak was renamed the Richard B. Dunn Solar Telescope on September 30, 1998.

1999:

• Steve Keil became the director of the National Solar Observatory (NSO) in May 1999. He served in the role until July 2013 

2001: 

• First phase of the Diffraction-Limited Stokes Polarimeter (DLSP) is an upgrade of the Advanced Stokes Polarimeter). DLSP became a prototype of Spectropolarimeter (SP) on board of Japanize satellite Hinode. 

2002: 

• Establishment of the Advanced Technology Solar Telescope (ATST) design effort, which later became the NSF's Inouye Solar Telescope (DKIST) - the world's largest solar telescope.

2015:

• Observatory/scientific  staff begun relocating to new NSO Headquarters in Boulder, CO
• On December 26, 2015, Sac Peak experienced a severe storm with heavy snow and high wind (80+ MPH). Over 30 trees were uprooted, which damaged several houses and power lines. Conditions were severe enough to require an evacuation of personnel from Sacramento Peak to Alamogordo. Electric power, heat, and network services were restored by January 5, 2016.

2021:

•  As part of the divestment, NSF donated relocatable houses to the White Sands Habitat for Humanity. Starting April, 2021, the houses were moved to the Alamogordo, NM (Photo 5). 

 

Photo 6 shows aerial photograph of the National Solar Observatory at Sacramento Peak taken on 16 November 2002. The locations marked by white numbers are (1) the Grain Bin Dome, (2) the Hill Top Dome, (3) the Evans Solar Facility, (4) Dunn Solar Telescope, (5) ISOON, (6) Sunspot Visitor Center, (7) the Main Lab and Machine Shop, (8) platform for site testing of future DKIST, (9) – telescope that was used on the South Pole for solar oscillations measurements. Background photo courtesy of Kit Richards.