View source for Astronomy:W. M. Keck Observatory

{{Short description|Astronomical observatory in Hawaii}}
{{Infobox telescope
| locmapin = USA Hawaii
| location = Waimea, Hawaii County, Hawaii, US
| first_light = {{start date|1990|11|24}}, {{start date|1996|10|23}}
}}

The '''W. M. Keck Observatory''' is an [[Astronomy:Astronomical observatory|astronomical observatory]] with two telescopes at an elevation of 4,145 meters (13,600&nbsp;ft) near the summit of [[Earth:Mauna Kea|Mauna Kea]] in the U.S. state of Hawaii. Both telescopes have {{convert|10|m|ft|abbr=on}} aperture primary mirrors, and when completed in 1993 (Keck 1) and 1996 (Keck 2) were the [[Astronomy:List of largest optical reflecting telescopes|largest optical reflecting telescopes]] in the world.  They are currently the 3rd and 4th largest.

== Overview ==
With a concept first proposed in 1977, telescope designers at the [[Organization:University of California, Berkeley|University of California, Berkeley]] (Terry Mast) and Lawrence Berkeley Laboratory (Jerry Nelson) had been developing the technology necessary to build a large, ground-based telescope.<ref>{{cite web|url=https://news.ucsc.edu/2016/08/mast-in-memoriam.html|title=In Memoriam: Terry Mast (1943 - 2016)|website=UC Santa Cruz News|language=en|access-date=July 28, 2019}}</ref> With a design in hand, a search for the funding began. In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck&nbsp;I telescope, which began in September 1985, with first light occurring on November 24, 1990, using nine of the eventual 36 segments. With construction of the first telescope well advanced, further donations allowed the construction of a second telescope starting in 1991. The Keck&nbsp;I telescope began science observations in May 1993, while first light for Keck II occurred on October 23, 1996.

[[Image:KeckObservatory20071013.jpg|thumb|upright=0.7|left|The Keck II telescope showing the segmented primary mirror]]
The key advance that allowed the construction of the Keck telescopes was the use of [[Astronomy:Active optics|active optics]] to operate smaller mirror segments as a single, contiguous mirror. A mirror of similar size cast of a single piece of glass could not be made rigid enough to hold its shape precisely; it would sag microscopically under its own weight as it was turned to different positions, causing aberrations in the optical path. In the Keck telescopes, each primary mirror is made of 36 hexagonal segments that work together as a unit. Each segment is 1.8 meters wide, 7.5 centimeters thick, and weighs half a ton.<ref>{{cite web |title=Keck Revolution in Telescope Design Pioneered at Lawrence Berkeley Lab |author=Lynn Yarris |date=1992 |url=http://www2.lbl.gov/Science-Articles/Archive/keck-telescope.html |access-date=October 7, 2016}}</ref> The mirrors were made in Lexington, Massachusetts by Itek Optical Systems from [[Chemistry:Zerodur|Zerodur]] [[Chemistry:Glass-ceramic|glass-ceramic]] by the German company Schott AG.<ref name="mast">{{cite journal |last1=Mast |first1=T. S. |last2=Nelson |first2=J. E. |editor1-last=Ulrich |editor1-first=Marie-Helene |title=Keck Telescope Primary Mirror Segments: Fabrication and Support |journal=Very Large Telescopes and their Instrumentation, ESO Conference and Workshop Proceedings, Proceedings of a ESO Conference on Very Large Telescopes and their Instrumentation |date=1988 |page=411 |url=https://ui.adsabs.harvard.edu/abs/1988ESOC...30..411M |publisher=European Southern Observatory (ESO) |location=Garching, Germany}}</ref><ref>{{cite web |url=http://www.schott.com/ft/german/download/zeak13_fb0309.pdf |title=ZERODUR for Large Segmented Telescopes |publisher=SCHOTT Glas|author=Hans F. Morian|author2=Peter Hartmann|author3=Ralf Jedamzik|author4=Hartmut W. Höneß}}</ref> On the telescope, each segment is kept stable by a system of [[Astronomy:Active optics|active optics]], which uses extremely rigid support structures in combination with three actuators under each segment. During observation, the computer-controlled system of sensors and actuators dynamically adjusts each segment's position relative to its neighbors, keeping a surface shape accuracy of four nanometers. As the telescope moves, this twice-per-second adjustment counters the effects of gravity and other environmental and structural effects that can affect mirror shape.

Each Keck telescope sits on an [[Astronomy:Altazimuth mount|altazimuth mount]]. Most current 8–10 m class telescopes use altazimuth designs due to their reduced structural requirements compared to older [[Astronomy:Equatorial mount|equatorial designs]]. Altazimuth mounting provides the greatest strength and stiffness with the least amount of steel, which, for Keck Observatory, totals about 270&nbsp;tons per telescope, bringing each telescope's total weight to more than 300&nbsp;tons. Two [[Astronomy:Thirty Meter Telescope|proposed designs]] for the next generation 30 and 40&nbsp;m telescopes use the same basic technology pioneered at Keck Observatory: a hexagonal mirror array coupled with an altazimuth mounting.

Each of the two telescopes has a primary mirror of 10 meters (32.8&nbsp;ft or 394&nbsp;in), slightly smaller than the [[Astronomy:Gran Telescopio Canarias|Gran Telescopio Canarias]]. However, all of the light collected by the Keck primary mirrors (75.76&nbsp;m<sup>2</sup>) is sent to the secondary mirror and instruments, compared to GTC's primary mirror, which has an effective light-collection area of 73.4&nbsp;m<sup>2</sup>, or {{convert|25.4|sqft|m2|order=flip|abbr=on}} less than each of the Keck primary mirrors. Because of this fundamental design difference, the Keck telescopes arguably remain the largest steerable, optical/infrared telescopes on Earth.

The telescopes are equipped with a suite of [[Physics:Camera|camera]]s and spectrometers that allow observations across much of the visible and near-infrared spectrum.

== Management ==

The Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501(c)(3) organization whose board of directors includes representatives from Caltech and the [[Organization:University of California|University of California]]. Construction of the telescopes was made possible through private grants of over $140 million from the W.M. Keck Foundation. The [[Organization:National Aeronautics and Space Administration|National Aeronautics and Space Administration (NASA)]] joined the partnership in October 1996 when Keck&nbsp;II commenced observations.

Telescope time is allocated by the partner institutions. Caltech, the [[Organization:University of Hawaii|University of Hawaii System]], and the University of California accept proposals from their own researchers; NASA accepts proposals from researchers based in the United States.

Jerry Nelson, Keck Telescope project scientist, contributed to later multi-mirror projects until his death in June 2017. He conceived one of the Kecks's innovations: a reflecting surface of multiple thin segments acting as one mirror.<ref>{{Cite news|url=https://blogs.scientificamerican.com/observations/in-memoriam-jerry-nelson-legendary-telescope-designer/|title=In Memoriam: Jerry Nelson, Legendary Telescope Designer|last=Lewis|first=Hilton|work=Scientific American Blog Network|access-date=June 16, 2017|language=en}}</ref>

== Instruments ==
[[File:Mauna Kea Summit 2021-06-16 35.jpg|thumb|right|Keck Observatory closeup]]
[[File:Keck Instruments.png|thumb|right|Spectroscopic capabilities of Keck Observatory instruments as of late 2019. Instrument modes appear as color-coded boxes with spectral resolution (resolving power) and wavelength coverage. Non-spectroscopic (i.e. imaging-only) instruments are not shown.]]

; MOSFIRE : MOSFIRE (''Multi-Object Spectrometer for Infra-Red Exploration''),<ref>{{cite web|url=https://irlab.astro.ucla.edu/mosfire/|title=MOSFIRE science based capabilities}}</ref> a third-generation instrument, was delivered to Keck Observatory on February 8, 2012; first light was obtained on the Kecks I telescope on April 4, 2012. A [[Astronomy:Multi-Object Spectrometer|multi-object spectrograph]] wide-field camera for the near-infrared (0.97 to 2.41 μm), its special feature is its cryogenic Configurable Slit Unit (CSU) that is reconfigurable by remote control in under six minutes without any thermal cycling. Bars move in from each side to form up to 46 short slits. When the bars are removed, MOSFIRE becomes a wide-field imager. It was developed by teams from the [[Organization:University of California, Los Angeles|University of California, Los Angeles]] (UCLA), the California Institute of Technology (Caltech) and the [[Organization:University of California, Santa Cruz|University of California, Santa Cruz]], (UCSC). Its co-principal investigators are Ian S. McLean (UCLA) and Charles C. Steidel (Caltech), and the project was managed by WMKO Instrument Program Manager Sean Adkins. MOSFIRE was funded in part by the Telescope System Instrumentation Program (TSIP), operated by AURA and funded by the National Science Foundation; and by a private donation to WMKO by Gordon and Betty Moore.<ref>{{cite web|url=http://irlab.astro.ucla.edu/mosfire/84460J.pdf |title=MOSFIRE, the Multi-Object Spectrometer For Infra-Red Exploration at the Keck Observatory |publisher=irlab.astro.ucla.edu |access-date=November 13, 2019}}</ref>
; DEIMOS : The Deep Extragalactic Imaging Multi-Object [[Astronomy:Spectrograph|Spectrograph]] is capable of gathering spectra from 130 galaxies or more in a single exposure. In "Mega Mask" mode, DEIMOS can take spectra of more than 1,200 objects at once, using a special narrow-band filter.
; HIRES : The largest and most mechanically complex of the Keck Observatory's main instruments, the High Resolution Echelle Spectrometer breaks up incoming light into its component colors to measure the precise intensity of each of thousands of color channels. Its spectral capabilities have resulted in many breakthrough discoveries, such as the detection of planets outside our solar system and direct evidence for a model of the [[Astronomy:Big Bang|Big Bang]] theory. The radial velocity precision is up to one meter per second (1.0&nbsp;m/s).<ref>{{cite web |url=http://kepler.nasa.gov/Mission/discoveries/fop/ |archive-url=https://web.archive.org/web/20110721124111/http://kepler.nasa.gov/Mission/discoveries/fop/ |url-status=dead |archive-date=July 21, 2011 |title=Kepler Discoveries - About Follow-up Observations |publisher=[[Organization:NASA|NASA]]|author=NASA}}</ref> The instrument detection limit at 1 [[Astronomy:Astronomical unit|AU]] is {{Jupiter mass|link=y|0.2}}.<ref>{{cite web |url=http://202.127.29.4/bdep_meeting/download/talks/20July/4-AHoward.ppt |title=The NASA-UC Eta-Earth Survey At Keck Observatory |date=October 16, 2010 |publisher=Chinese Academy of Sciences |access-date=February 21, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20110704072607/http://202.127.29.4/bdep_meeting/download/talks/20July/4-AHoward.ppt |archive-date=July 4, 2011 }}</ref>
; KCWI : The Keck Cosmic Web Imager is an [[Astronomy:Integral field spectrograph|integral field spectrograph]] operating at wavelengths between 350 and 560 [[Nanometre|nm]].
; LRIS : The Low Resolution Imaging [[Astronomy:Spectrograph|Spectrograph]] is a faint-light instrument capable of taking spectra and images of the most distant known objects in the universe. The instrument is equipped with a red arm and a blue arm to explore stellar populations of distant galaxies, active galactic nuclei, galactic clusters, and [[Astronomy:Quasar|quasar]]s.
; LWS: The Long Wavelength Spectrometer for the Keck I telescope is and imaging, grating spectrometer working in the wavelength range of 3-25 microns. Like NIRC, the LWS was a forward-CASS instrument, and was used for studying cometary, planetary, and extragalactic objects.  The LWS is now retired from science observations.
; NIRC : The Near Infrared Camera for the Keck I telescope is so sensitive it could detect the equivalent of a single candle flame on the [[Astronomy:Moon|Moon]]. This sensitivity makes it ideal for ultra-deep studies of galactic formation and evolution, the search for [[Astronomy:Galaxy formation and evolution|proto-galaxies]] and images of quasar environments. It has provided ground-breaking studies of the [[Galactic Center]], and is also used to study [[Astronomy:Protoplanetary disk|protoplanetary disk]]s, and high-mass [[Astronomy:Star formation|star-forming regions]]. NIRC was retired from science observations in 2010.
; NIRC-2 : The second generation Near Infrared Camera works with the Keck Adaptive Optics system to produce the highest-resolution ground-based images and spectroscopy in the 1–5 micrometers (µm) range. Typical programs include mapping surface features on [[Astronomy:Solar System|Solar System]] bodies, searching for planets around other stars, and analyzing the morphology of remote galaxies.
; NIRES : The Near-Infrared Echellette Spectrometer is a spectrograph that provides simultaneous coverage of wavelengths from 0.94 to 2.45 microns.
; NIRSPEC : The Near Infrared Spectrometer studies very high redshift [[Astronomy:Radio galaxy|radio galaxies]], the motions and types of stars located near the [[Galactic Center]], the nature of [[Astronomy:Brown dwarf|brown dwarf]]s, the nuclear regions of dusty starburst galaxies, active galactic nuclei, [[Astronomy:Interstellar medium|interstellar]] chemistry, [[Astronomy:Star|stellar]] physics, and Solar System science.
; [[Engineering:OH-Suppressing Infrared Integral Field Spectrograph|OSIRIS]] : The OH-Suppressing Infrared Imaging Spectrograph is a [[Physics:Near-infrared spectroscopy|near-infrared spectrograph]] for use with the Keck&nbsp;I adaptive optics system. OSIRIS takes spectra in a small field of view to provide a series of images at different wavelengths. The instrument allows astronomers to ignore wavelengths where the Earth's atmosphere shines brightly due to emission from OH (hydroxyl) molecules, thus allowing the detection of objects 10 times fainter than previously available. Originally installed on Keck II, in January 2012 OSIRIS was moved to the Keck 1 telescope.
; Keck Interferometer : The Interferometer allowed the light from both Keck telescopes to be combined into an {{convert|85|m|ft|adj=on}} baseline, near infrared, optical interferometer. This long baseline gave the interferometer an effective [[Angular resolution|angular resolution]] of 5 milliarcseconds (mas) at 2.2&nbsp;µm, and 24&nbsp;mas at 10&nbsp;µm. Several back-end instruments allowed the interferometer to operate in a variety of modes, operating in H, K, and L-band near infrared, as well as nulling interferometry. As of mid-2012 the Keck Interferometer has been discontinued for lack of funding.

Both Keck Observatory telescopes are equipped with [[Physics:Laser guide star|laser guide star]] [[Astronomy:Adaptive optics|adaptive optics]], which compensates for the blurring due to [[Astronomy:Astronomical seeing|atmospheric turbulence]]. The first AO system operational on a large telescope, the equipment has been constantly upgraded to expand the capability.

{{multiple image
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 |image1=Kecknasa.jpg
 |image2=Keck laser at night.png
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 |footer=''Left'': The summit of Mauna Kea is considered one of the world's most important astronomical viewing sites. The twin Keck telescopes are among the largest optical/near-infrared instruments currently in use around the world.<br/>''Middle'': The night sky and Keck Observatory laser for adaptive optics. ''Right'': W. M. Keck Observatory at sunset
}}

== See also ==
[[File:Comparison optical telescope primary mirrors.svg|thumb|160px|Size comparison of primary mirrors]]
{{Div col|colwidth=26em}}
* [[Astronomy:Extremely large telescope|Extremely large telescope]]
* Gemini Observatory
* List of astronomical interferometers at visible and infrared wavelengths
* [[Astronomy:List of largest optical reflecting telescopes|List of largest optical reflecting telescopes]]
* [[Astronomy:List of largest optical telescopes historically|List of largest optical telescopes historically]]
* [[Organization:Mauna Kea Observatories|Mauna Kea Observatories]]
* [[Astronomy:Navigator Program|Navigator Program]]
* [[Astronomy:Subaru Telescope|Subaru Telescope]]
* [[Astronomy:Very Large Telescope|Very Large Telescope]]
{{Div col end}}

==References==
{{reflist}}

==External links==
* [http://www.keckobservatory.org/ W. M. Keck Observatory] (official site)
* [http://www.ifa.hawaii.edu/mko/ Mauna Kea Observatories] (official site)
* [http://nexsci.caltech.edu/archives/koa/ Keck Observatory Archive (KOA)]
* [http://www.lbl.gov/Science-Articles/Archive/keck-telescope.html Lawrence Berkeley Lab, ''Revolution in telescope design''] {{Webarchive|url=https://web.archive.org/web/20171222194953/http://www2.lbl.gov/Science-Articles/Archive/keck-telescope.html |date=December 22, 2017 }}
* [https://web.archive.org/web/20070310233855/http://astronomymaunakea.com/photos.html Photos of Keck telescopes and other Mauna Kea observatories from "A Gentle Rain of Starlight: The Story of Astronomy on Mauna Kea"] by Michael J. West. {{ISBN|0-931548-99-3}}.

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