Editing European Southern Observatory (section)

=== Llano de Chajnantor ===
{{Main|Llano de Chajnantor Observatory}}
{{multiple image
 |direction = vertical
 |align = right
 |width = 225
 |image1=Three ALMA antennas close together on Chajnantor.jpg
 |caption1=Three [[Atacama Large Millimeter Array|ALMA]] antennas on Chajnantor
 |alt1=Three large parabolic-dish telescopes, seen from behind
 |image2=ALMA antenna en route.jpg
 |caption2=ALMA antenna on route to Chajnantor plateau
 |alt2=Large white parabolic-dish antenna on yellow, multi-wheeled vehicle
}}

The Llano de Chajnantor is a {{convert|5100|m|ft|adj=mid|-high}} plateau in the Atacama Desert, about {{convert|50|km}} east of [[San Pedro de Atacama]]. The site is {{convert|750|m}} higher than the [[Mauna Kea Observatory]] and {{convert|2400|m}} higher than the [[Very Large Telescope]] on [[Cerro Paranal]]. It is dry and inhospitable to humans, but a good site for [[submillimetre astronomy]]; because [[water vapour]] molecules in [[Earth's atmosphere]] absorb and attenuate [[submillimetre radiation]], a dry site is required for this type of [[radio astronomy]].<ref>{{cite web
|url=http://www.alma.nrao.edu/projectbk/construction/chap14/chap14.html
|title=ALMA Site Characterization and Monitoring
|access-date=2011-10-05
|archive-date=2012-04-25
|archive-url=https://web.archive.org/web/20120425050101/http://www.alma.nrao.edu/projectbk/construction/chap14/chap14.html
|url-status=live
}}</ref> The telescopes are:
* [[Atacama Cosmology Telescope]] (ACT; not operated by ESO)
* [[Atacama Pathfinder Experiment]] (Operated on behalf of the Max Planck Institute for Radio Astronomy (MPIfR))
* [[Atacama Large Millimeter Array]]
* [[QUIET|Q/U Imaging Experiment]] (QUIET; not operated by ESO) <!-- Though the Wikipedia article is horribly outdated -->
* [[POLARBEAR]] (on the Huan Tran Telescope; not operated by ESO)

ALMA is a telescope designed for millimetre and submillimetre astronomy. This type of astronomy is a relatively unexplored frontier, revealing a universe which cannot be seen in more-familiar visible or infrared light and ideal for studying the "cold universe"; light at these wavelengths shines from vast cold clouds in interstellar space at temperatures only a few tens of degrees above [[absolute zero]]. Astronomers use this light to study the chemical and physical conditions in these [[molecular cloud]]s, the dense regions of gas and cosmic dust where new stars are being born. Seen in visible light, these regions of the universe are often dark and obscure due to dust; however, they shine brightly in the millimetre and submillimetre portions of the [[electromagnetic spectrum]]. This wavelength range is also ideal for studying some of the earliest (and most distant) galaxies in the universe, whose light has been [[redshift]]ed into longer wavelengths from the expansion of the universe.<ref>{{cite web |url=http://www.eso.org/public/teles-instr/apex.html |title=ESO APEX |access-date=2011-05-03 |archive-date=2011-06-22 |archive-url=https://web.archive.org/web/20110622023612/http://www.eso.org/public/teles-instr/apex.html |url-status=live }}</ref><ref>{{cite web |url=https://almascience.nrao.edu/about-alma/alma-site |title=ALMA Site – ALMA Science Portal |access-date=2011-05-04 |archive-date=2020-05-17 |archive-url=https://web.archive.org/web/20200517003409/https://almascience.nrao.edu/about-alma/alma-site |url-status=live }}</ref>

==== Atacama Pathfinder Experiment ====

ESO hosts the Atacama Pathfinder Experiment, APEX, and operates it on behalf of the [[Max Planck Institute for Radio Astronomy]] (MPIfR). APEX is a {{convert|12|m|adj=on}} diameter telescope, operating at millimetre and submillimetre wavelengths—between infrared light and radio waves.

==== Atacama Large Millimeter/submillimeter Array ====
{{Main|Atacama Large Millimeter Array}}

ALMA is an astronomical interferometer initially composed of 66 high-precision antennas and operating at wavelengths of 0.3 to 3.6&nbsp;mm. Its main array will have 50 {{convert|12|m|adj=on}} antennas acting as a single [[interferometer]]. An additional compact array of four 12-metre and twelve {{convert|7|m|adj=on}} antennas, known as the Morita array is also available.<ref>{{Cite web |last=information@eso.org |date=2013-05-07 |title=ALMA Compact Array Completed and Named After Japanese Astronomer |url=https://www.eso.org/public/announcements/ann13040/ |access-date=2023-05-14 |website=www.eso.org |language=en}}</ref> The antennas can be arranged across the desert plateau over distances from 150 metres to {{convert|16|km}}, which will give ALMA a variable "zoom". The array will be able to probe the universe at millimetre and submillimeter wavelengths with unprecedented sensitivity and resolution, with vision up to ten times sharper than the [[Hubble Space Telescope]]. These images will complement those made with the [[VLT Interferometer]].<ref>{{cite web |url=http://www.eso.org/public/teles-instr/alma.html |title=ESO ALMA |access-date=2011-05-04 |archive-date=2013-08-10 |archive-url=https://web.archive.org/web/20130810124241/http://www.eso.org/public/teles-instr/alma.html |url-status=live }}</ref> ALMA is a collaboration between East Asia (Japan and [[Taiwan]]), Europe (ESO), North America (US and Canada) and Chile.

The scientific goals of ALMA include studying the origin and formation of stars, galaxies, and planets with observations of molecular gas and dust, studying distant galaxies towards the edge of the observable universe and studying [[Cosmic microwave background radiation|relic radiation]] from the [[Big Bang]].<ref>{{cite web |url=https://almascience.nrao.edu/alma-science |title=ALMA Science—ALMA Science Portal |access-date=2011-05-04 |archive-date=2020-05-17 |archive-url=https://web.archive.org/web/20200517003426/https://almascience.nrao.edu/alma-science |url-status=live }}</ref> A call for ALMA science proposals was issued on 31 March 2011,<ref>{{cite web |url=https://almascience.nrao.edu/call-for-proposals |title=Call for Proposals—ALMA Science Portal |access-date=2011-05-04 |url-status=dead |archive-url=https://web.archive.org/web/20111114071735/https://almascience.nrao.edu/call-for-proposals |archive-date=2011-11-14 }}</ref> and early observations began on 3 October.<ref>{{cite news |title=ALMA Early Science Cycle 0 Call for Proposals |url=https://science.nrao.edu/facilities/alma |publisher=NRAO |access-date=2011-05-04 |archive-date=2011-07-25 |archive-url=https://web.archive.org/web/20110725223434/https://science.nrao.edu/facilities/alma |url-status=live }}</ref><ref>{{cite web|url=http://www.eso.org/public/news/eso1137/|title=ALMA Opens its Eyes|access-date=2011-10-05|archive-date=2011-10-05|archive-url=https://web.archive.org/web/20111005095244/http://www.eso.org/public/news/eso1137/|url-status=live}}</ref>