Apache Point Observatory

ARCSAT and SDSS telescope buildings at the Apache Point Observatory.
Alternative names	APO
Organization	Astrophysical Research Consortium
Observatory code	705, 645
Location	Sunspot, New Mexico
Coordinates	32°46′49″N 105°49′13″W / 32.78028°N 105.82028°W / 32.78028; -105.82028
Altitude	2,788 meters (9,147 ft)
Weather	65% clear nights
Established	1985 (1985)
Website	www.apo.nmsu.edu
Telescopes
Astrophysical Research Consortium telescope 3.5 m reflector Sloan Digital Sky Survey telescope 2.5 m reflector New Mexico State University telescope 1.0 m reflector ARCSAT 0.5 m reflector
Location of Apache Point Observatory
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The Apache Point Observatory (APO; obs. code: 705) is an astronomical observatory located in the Sacramento Mountains in Sunspot, New Mexico, United States, approximately 18 miles (29 km) south of Cloudcroft. The observatory is operated by New Mexico State University (NMSU) and owned by the Astrophysical Research Consortium (ARC). Access to the telescopes and buildings is private and restricted.^[1]

The ARC was formed in 1984 with the goal of building the 3.5 m telescope. It originally consisted of five institutions: New Mexico State University, University of Washington, University of Chicago, Princeton University, and Washington State University, some of which have since withdrawn.^{[citation needed]}

Several additional organizations have joined over time: Johns Hopkins University, University of Colorado, University of Virginia, Georgia State University, University of Oklahoma, University of Wyoming, and Brigham Young University. Funding for the 3.5 m and 0.5 m telescopes comes from the consortium members, but funds for the 2.5 m telescope come from a much wider array of sources. The 1.0 m telescope is supported exclusively by NMSU.^[2]

The ARC 3.5 m (140 in) telescope is a Ritchey-Chretien reflector on an alt-azimuth mount with instruments attached at several focal points. Construction of the building began in 1985, but full operations of the telescope were delayed until November 1994 due to problems with fabricating the primary mirror.^[3] From 1991 until early 1993, the telescope was fitted with a 1.8 m mirror, now located at Rothney Astrophysical Observatory under a cost-sharing agreement.^[4][5]

There are a variety of optical and near-infrared instruments available for the 3.5 m telescope, including:

• The ARC echelle spectrometer (ARCES) uses a 2048 × 2048 pixel CCD and has a resolution of .^[6]
• The Double Imaging Spectrometer (DIS) is a low-resolution optical spectrometer.^[7]
• KOSMOS, on long-term loan from NOIRLab, is a low-resolution optical spectrometer.
• The Near Infrared Camera/Fabry–Pérot Spectrometer (NICFPS) was developed at the University of Colorado. It uses a 1024 × 1024 H1RG HgCdTe infrared detector and a near-infrared Fabry–Pérot interferometer. It has many narrow band filters, including H2, [Fe II], and [SiVI]. It is unique among astronomical Fabry-Pérot devices in that it is cooled with liquid nitrogen.^[8]
• The Astrophysical Research Consortium Telescope Imaging Camera (ARCTIC) is an optical imaging instrument with a 4096 × 4096 pixel CCD.^[9]
• TripleSpec (Tspec) is a near infrared spectrograph which provides continuous wavelength coverage over the range 0.94–2.46 μm at moderate resolution (, depending on the choice of slit).^[10]
• Agile is a high-speed imager with a 1024 x 1024 frame transfer CCD.^{[citation needed]}

The 3.5 m telescope is also used by the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) lunar-ranging project. The APOLLO laser has been operational since October 2005, and routinely accomplishes millimeter-level range accuracy between the Earth and the Moon.^[11][12]

Observations using the 3.5 m telescope can be carried out remotely by observers using TUI, the Telescope User Interface, via the internet.^[13]

The SDSS 2.5 m (98 in) telescope is used for the Sloan Digital Sky Survey, and began operating in 2000. It is a Ritchey-Chretien reflector on an alt-azimuth mount housed under a roll-off enclosure. It was designed with an unusually large 3° field of view to better support its primary task of surveying the entire sky.^[14]

The NMSU 1.0 m (39 in) telescope is a Ritchey-Chretien reflector set on an alt-azimuth mount, and was completed in 1994.^[15][16] A 2048 × 2048 CCD mounted at the Nasmyth focus provides at 15.7 arcminute view of the sky.^[17]

The ARC Small Aperture Telescope (ARCSAT) was previously called the Photometric Telescope (PT) when it was part of the SDSS project. It is a 0.5 m (20 in) reflecting telescope on an equatorial mount, with a single CCD camera cooled by a CryoTiger unit.^[18] It was built in 1991, moved from its previous location in 1998, and used by the SDSS until 2005.^[19] It is currently used for small research projects.

• A 0.6 m (24 in) reflecting telescope was built in 1993 to monitor sky conditions for the SDSS project. It never operated in a satisfactory manner, and was replaced with the 0.5 m PT.^[19]

The Minor Planet Center credits the discovery of the following minor planets directly to the Apache Point Observatory:^[20]

• List of astronomical observatories
• List of largest optical reflecting telescopes
• List of minor planet discoverers § Discovering dedicated institutions
• Sunspot Solar Observatory

• Astronomy Department at NMSU
• Sloan Digital Sky Survey homepage
• Apache Point Clear Sky Clock Forecasts of observing conditions.