1 3 Course Aims Radio Astronomy Radio Astronomy This course is intended for graduate and undergraduate students whose major is Physics or Astrophysics. We will discuss various aspects of radio astronomy, such topics as the nature of the Introduction to radio signals, signal processing, designs of receiving systems, atmospheric effects, and observing strategies with modern radio observatories, including single-aperture telescopes and interferometric arrays. The class is aimed at building a solid Radio Astronomy foundation for students to further pursue astrophysical research in the radio waveband.

Fall 2020: offered in English Course website: http://orion.astr.nthu.edu.tw/ra/

2 4 Instructor References Radio Astronomy Radio Astronomy Instructor: Vivien Chen Tools of Radio Astronomy (6ed) by T. L. Wilson, K. Rohlfs & S. Office: 513 Second General Building Hüttemeister, Springer 2013 (ISBN: 9783642399497) eBook Office hour: Wednesday 4-5pm available on campus Phone: (03) 574-2518 Galactic and Extragalactic Radio Astronomy (2ed) by G. L. Verschuur & K. I. Kellermann (editors), Springer-Verlag 1988 Email: [email protected] (ISBN: 0387965750) out of print Synthesis Imaging in Radio Astronomy II edited by G. B. Taylor, C. L. Carilli, & R. A. Perley 1999, ASPC, 180 available on SAO/ NASA ADS Interferometry and Synthesis in Radio Astronomy (2ed) by A. R. Thompson, J. M. Moran, & G. W. Swenson, Wiley 2001 (ISBN: 0471254924) eBook available on campus Observational Astrophysics (3ed) by P. Léna, D. Rouan, F. Lebrun, F. Mignard, & D Pelat, Springer 2012 (ISBN: 9783642218149) eBook available on campus 5 7 Lectures and Grading Policy Course Coverage Radio Astronomy Radio Astronomy

This course will be conducted with lectures of basic knowledges Astrophysical Phenomena in the Radio Waveband and sessions of data reduction projects Continuum emissions Total 16 lectures Thermal emission: dust emission, free-free emission, etc Mid-Autumn Festival holiday on Oct 1 Non-thermal emission: synchrotron emission, curvature radiation, etc Grading policy Spectral line emissions 60% problem sets, 20% project reports, and 20% final exam Recombination line emission Problem sets Atomic line emission Problem sets are due 5PM Tuesday of the following week unless Molecular line emission otherwise instructed. Astronomical masers No late problems will be accepted without a valid excuse approved by Cosmic Microwave Background the instructor prior to the deadline. Quasars and radio galaxies Projects The Cosmic Microwave Background (CMB) Will be announced later in the semester The Sunyaev-Zel’dovich effect

6 8 Course Coverage Course Coverage Radio Astronomy Radio Astronomy

Introduction to Radio Astronomy Signal Processing and Receiving Systems The radio waveband in a nutshell Fundamentals of signal processing and sampling History of radio astronomy Receivers and system designs Radio observatories Atmospheric Effects The Nature of Radio Signals Properties of troposphere Basic definitions and radiative transfer Effects of tropospheric fluctuation Wave propagation fundamentals Calibration strategies Dissipative medium and dispersion measure Single-Dish (Filled Aperture) Antennas Polarization and Faraday rotation Performance of single-dish radio telescopes Spectral Line Fundamentals Observation strategies: calibration and imaging The Einstein coefficients Aperture Synthesis and Interferometers Dipole transition probabilities Fundamentals of radio interferometry Excitation of a two-level system Observation strategies: calibration and imaging Multi-level systems 9 11

Radio waveband

The Radio Waveband in a Nutshell

The radio window Limits set by the terrestrial atmosphere Advantages of the radio waveband

10 12 Observable Window Radio waveband Radio waveband as one observable “window” Radio window

1.2 The Radio Window 3

must be applied to data. These concepts belong to a wide variety of physical fields, from plasma physics to molecular physics. All these concepts are tools, and so we have collected these in a “toolbox” that is consistent and useful.

1.2 The Radio Window

From the surface of the earth, the atmosphere is transparent to radio waves as long as none of its constituents is able to absorb this radiation to a noticeable extent. This earth-bound radio window extends roughly from a lower frequency limit of ν ∼= 15 MHz (λ ∼= 20 m) to a high frequency cut-off at ν ∼= 1.5 THz (λ ∼= 0.2 mm). These limits are not sharp (Fig. 1.1) since there are variations both with altitude, geographical position and with time. The high-frequency cut-off occurs because the resonant absorption of the lowest rotation bands of molecules in the troposphere fall into this frequency range. Two molecules are mostly responsible for this: water vapor, H2O and O2. Water vapor has bands at ν = 22.2 GHz (λ = 1.35 cm) and 183 GHz (1.63 mm), while O2 has an 13 15 exceedingly strong band at 60 GHz (5 mm). Lines of O2 consist of closely spaced rotational levels of the ground electronic state, resulting in two interleaved series of Radioabsorption lines Waveband near 60 GHz (5 mm) and a single line near 119 GHz (2.52 mm). The Stratified Atmosphere Radio waveband Radio waveband

The terrestrial atmosphere turns opaque at lowest frequencies EM signals absorbed by free electrons in the ionosphere

In this course

R&W Fig. 1.1 Fig. 1.1 The transmission of the earth’s atmosphere for electromagnetic radiation. The diagram gives the height in the atmosphere at which the radiation is attenuated by a factor 1/2 14 16 Why Radio Waveband? Reflection by Ionosphere Radio waveband Radio waveband The ionosphere is comprised of plasma, which sets a lower cuto↵ fre- Atmosphere transparent through a large span of frequency quency for the terrestrial radio observations. An E↵ective permittivity Lower frequency cutoff set by the plasma frequency of the ionosphere can be defined for a uniform plasma medium Upper frequency margin set by increasing occupation of many 2 !p absorption lines due to water, N2, etc. " = " 1 2 , ! ! More penetrating through ISM Continuum less affected by absorption and scattering where the plasma frequency is Critical detection of molecular species (neutral, ions) n e2 Rotational transitions, rovibrational transitions ! = e 9pn 8 MHz. p 4⇡2" m ' e ⇠ Chemical inventory s 0 Mature technology Amplification available, signal path well known, high spectral resolution possible 17 19

Variable Ionosphere ANRV385-AA47-11Rich ARI Molecular 25 July 2009 0:2 Inventory Radio waveband Radio waveband 556 PROPAGATION EFFECTS

1000' I I llllll~ 1 I IIIIIII Example of massive star-forming cores - - - Orion KL, the nearestANRV385-AA47-11 hot molecular ARI 25 July core 2009 0:2 IONOSPHERIC ELECTRON DENSITY - AT SUNSPOT MAXIMUM - 2 2 2 2 2 2 2 2 2 CN OH OH OD SO SO SO SO SO SO SO SO SO 5 3 3 600 a 3

- H U Ghost Ghost Ghost 2 CH CH 60 CH - CH CN 5 H OH 2 400- 40 3 CH CH Ghost Ghost OH - 3 (K)

E CH

x MB - T 30 - 20 I- I

'3 2 2 2 2 2 2 2 2 2 CN OH OH W OD SO SO SO SO SO SO SO SO SO 5 3 3 a 0 3

I 200- H U Ghost Ghost Ghost 200 2 CH CH 863.5 864.0 864.5 60 865.0 CH Night: ωp ~ 4.5 Rest frequency (GHz) CH 20 - Transmission (%) CN MHz when ne ~ 5 H OH 2 3

(K) 40 CH CH

5 -3 Ghost Ghost

2.5×10 cm MB T OH 3

100 (K) CH

- MB 10 Daytime: ωp ~ T 30 80 - 20 11 MHz when - 6 - ne ~ 1.5×10 1 I 1 I I Ill I I I111111 I I I111111 I I IIIIIII -3 cm Io8 lo9 10'0 loll loi2 0 0 0 200 ELECTRON DENSITY (m-3) 800 850863.5 900 864.0 864.5 865.0 TMS Fig. 13.18 Rest frequency (GHz) Herbst & van Dishoeck 2009, ARA&A,Rest 47, frequency 427 (GHz) 20 Transmission (%) Figure 13.18 Idealized electron density distribution in the earth's ionosphere. The curves

indicate the densities to be expected at sunspot maximum in temperate latitudes. Peak sunspot 1014 b NGC 63341 177 ± 9 K

activity occurs at 1 I-year intervals, most recently in 1989 and 2000. From Evans and Hagfors (K) CH OH (1 18 3 MB 20

968). T

by NATIONAL TSING HUA UNIVERSITY on 02/21/10. For personal use only. 100 1013 10 Penetrating Power RichAnnu. Rev. Astro. Astrophys. 2009.47:427-480. Downloaded from arjournals.annualreviews.org Molecular Inventory electric field, but the protons, because of their greater mass, remain relatively un- Radio waveband Radio waveband perturbed. The index of refraction can be found by calculating either the induced 1012 current or the dipole moment. Either method yields the same result. We use the Rotation Diagram analysis latter method, as we did when considering the index of refraction of water vapor using the bound oscillator model in Section 13.1 under Origin ofRefruction. The Excitation temperature of 0transitions 0 Radio-wave 0 200 400 600 1000 800 850 900 equation of motion of a free electron in the plasma is Eu (K) photons Column density of the species Rest frequency (GHz) Small cross-section

Large mean free path 438 Herbst van Dishoeck 1014 b NGC 63341 Good for probing where m, e, and x are the mass, charge magnitude, and displacement of the elec- · 177 ± 9 K CH OH high column densitytron, and Eo and u are the amplitude and frequency of the electric field E of the 3 regions incident wave. The magnetic field of the plane wave has negligible influence on the electrons as long as the electron velocity is much less than c, and the elec- by NATIONAL TSING HUA UNIVERSITY on 02/21/10. For personal use only. 1013 tric field has negligible influence on the motion of the protons. The steady-state

solution to JZq. (13.124) is Annu. Rev. Astro. Astrophys. 2009.47:427-480. Downloaded from arjournals.annualreviews.org

1012

0 200 400 600 1000

Eu (K) Ryter 1996, Ap&SS, 236, 285 Herbst & van Dishoeck 2009, ARA&A, 47, 427

438 Herbst van Dishoeck · 21 23 Interstellar Chemistry High Sensitivity Radio waveband Radio waveband Receivers of1.2 great Data Acquisition sensitivity 19

Naked eye

−10 Galileo (1610) Crab nebula

3C273 Jansky (1931) (z=0.158) COMPTEL IRAS INTEGRAL Fermi HESS −15 ISO

) Hubble−S

2 Einstein − SOFIA Herschel−I 3C273 (placed at z=4) (Wm

ν Herschel−S

F XMM/AXAF ν VLT−S

log VLT−I Westerbork Hubble−I XEUS −20 JWST ELT VLA ALMA

SKA

−25 5 10 15 20 25 LLM Fig. 1.11 log ν ( Hz ) http://www.cfa.harvard.edu/mmw/mmwlab/ismmolecules_organic.html Fig. 1.11 Sensitivity of various instruments and/or observatories, covering the whole electromag- netic range, with the existing instruments for the period 1980–2010, and some others in the near future. Ordinate:Thequantity!F! , F! being the spectral illumination. Abcissa:Thelog10 of the frequency !,onthewholerangeofcurrentastrophysicalobservations.Theplottedvalueof!F! 22 corresponds to the detectable astronomical signal by the considered instrument with the integration 24 time (minutes, hours, or days) made possible by this instrument. Values are orders of magnitude only. Also plotted for reference are the spectrum of a supernova remnant (Crab nebula in the Galaxy), the quasar 3C273, the same quasar placed at a much larger distance (redshift z 4). S spectrographic mode (resolution R 103 to 104). I wide band imaging mode (resolutionD Large Collecting Area High SpectralD ResolutionD D Radio waveband R 1 to 10). For specific data on the instruments, see the table at the end of the book) Radio waveband D 1.2 Data Acquisition 17 Exceptionally large collection capacity of radiation Good velocity resolution to study kinematics of gaseous phase, 20However, in practice, the ability to obtain the ultimate 1 resolutionAstrophysical also Informationdepends on 1000 including ionizedthe number and of photons neutral available, medium and hence the collecting area and measurement Array ALMA 2009 time, as well as the sensitivity of the detectors being used. In almost every spectral ARECIBO 10 10 range, except for those at very high energies (>1keV),spectrographshaveachieved Velocity resolving powers greater than those required to analyse the relevant emissions. 100 EXTREMELY LARGE resolution Indeed, the proper width of the spectral lines produced by a given object, caused TELESCOPES 1 m s–1 Correlation TMT, E-ELT... 8 by internal motions within the source andtheresultingDopplershift,alsolimit RADIO- 10 spectrometer vers 2015-20 TELESCOPES the useful resolution (velocity scale on the(exoplanets) left of Fig. 1.12). In the end, it is this FAMILY ∆λ Germanium 10 / broadening of the lines when they are actually produced that makes it unnecessary

VLT, KECK, SUBARU... λ Heterodyne spectrometer to seek even higherdetector spectral resolutions, except in certain very special cases, e.g., 2000 10 6 asteroseismology measurements–1 or the search for exoplanets. JWST 2013 1 km s HST 1989 SPITZER 2003 1 HERSCHEL 2008 10 4 1985 GLAST 2008 XEUS ISO 1995 Diameter or equivalent (m) Diameter or equivalent

COMPTON-GRO 1991 power Resolving IRAS 1983 EINSTEIN 1979 2 EEinsteini 1939 0.1 10 ns XMM-NEWTON 1999 Rosat te SIGMA 1989 GLAST in COS-B Integral COS-B 1975 1 0.01 1 TeV 1 GeV 1 MeV 1 nm1 µm 1 mm 1 m 1 TeV 1 GeV 1 MeV 1 nm1 µm 1 mm 1 m Energy Wavelength LLM Fig. 1.9 Fig.LLM 1.12 Fig.Progress 1.12 in relative spectral resolution. Shaded:Performancelevelsin1985.Dashed: Performance levels in 2005. Dotted:Performancelevelsspecifiedforfuturemissions(2010–2020). Fig. 1.9 Progress in collection capacity of electromagnetic radiation by instruments prior to 2007 (continuous line)orinthefuture(dashed line), on the ground (dark grey)andinspace(light grey), Note the exceptional performance of the spectrometers used in the search for exoplanets (see as a function of operating wavelength. The diameters indicated on the ordinate are those of the Sect. 8.3). Updated from Harwit M. (1981), Cosmic Discovery Harvester, Brighton instruments, or those deduced from the total area in the case of an array. The ranges shown are typical of an instrument or family of instruments, and show the evolution over several decades. Note the empirical dependence D !1=3 below MeV. (See the table at the end of the book for a list of acronyms and space missions)/ Nowadays, progress in spectroscopy increasingly involves the ability to measure simultaneously other characteristics of the radiation:

The received radiation intensity is determined by photometry,notrelativeto •Rapidspectroscopyandphotometry,inwhichsuccessivespectraareobtainedatveryshort intervals, sometimes less than one millisecond (solar flares, eruptive variable stars, accretion reference objects such as standard galaxies or stars, for example, but in an absolute phenomena, X-ray sources). manner and expressed in fundamental physical units. This approach to observation, •Spectroscopyandimaging,inwhichimagesatdifferentwavelengthsareobtainedsimultane- essential but difficult, uses absolute calibration techniques (see Sect. 3.5 ). ously (spectroheliograms of solar activity, X-ray mapping of the solar corona in emission lines The performance of the detector determines both the precision and the ultimate of different excitations, maps of the hydrogen velocity distribution in a galaxy using the Doppler sensitivity which can be attained. This performance depends on the technology shift of the 21 cm line). available, but also on fundamental physical limitations, which impose a limit on possible progress in detector sensitivity. Thus statistical fluctuations in the arrival of photons limit the photometric precision of a given instrument for a given observation Time Variability time. These limitations are considered in detail in Chap. 7 . The astronomical knowledge accumulated in different civilisations — Mediter- ranean, but also Indian, Chinese, and Maya — using observations made exclusively Variable stars, which have a slow time variation, have been known since ancient with the naked eye, with no other instruments than sighting tools, is impressive. The times (Mira Ceti), but the first pulsar,ofperiod1.377ms,wasnotdiscovereduntil accuracy of Tycho Brahe’s visual observations of Mars, which allowed Kepler to 1968. Since then, the study of very rapidly varying phenomena has developed as a assign an elliptical orbit to this planet, is also quite remarkable. Figure 1.10 shows consequence of progress in detector sensitivity. A good example is provided by ” the gain in sensitivity obtained over the past four centuries by the use of refracting ray bursts, discovered in the 1970s and only understood much later. and reflecting telescopes of ever increasing diameter. Observation of such phenomena is a rich source of information, as can be seen from Table 1.3,inwhichthecharacteristictimescalesareintendedasanindication of the order of magnitude. The possibility of observing these phenomena is closely linked to detector sensitivity, since here the measurement time is externally imposed. We shall see in Chaps. 7 and 9 how sensitivity improves with increased measurement time. Figure 1.13 shows the progress in time resolution. 25 27 High Angular Resolution The Father of Radio Astronomy Radio waveband

Good angular1.2 Data Acquisitionresolution for reasonable sensitivity with the 23 Dr. Karl Jansky (1905-1950) interferometer option 1000 Born in Norman Oklahoma, USA

IRAS 1983 Ph.D. of Physics, University of Wisconsin 100 Naked eye limit Built the first steerable array antenna while working

10 in Bell Labs (Jansky’s merry-go-round @ 20.5 MHz ISO 1995 = 14.5 m) SOFIA 2008HERSCHEL 2008 1 Seeing limit First discovery of weak signals repeating every 23 CSO (Hawaii) 1991 hours and 56 minutes

0.1 Concluded the signals came from Sagittarius in the 1 km in space Galactic Center (published in 1933) HUBBLE ST 1991 ALMA (Chile) 2009 0.01 Insignificant noise to interrupt terrestrial Angular resolution (arcsec) VLT, KECK, ... + Adaptive optics 2000 communicaitons JWST VLT interferometer 2003 0.001 Great Depression CHARA, OHANA 2005 VLBI Bell Labs neither continuing or hiring 0.0001 0.1µm 1µm 10µm 100µm 1000µm 1 cm -26 -2 -1 LLM Fig. 1.14 Flux Unit: Jansky = 10 W m Hz Wavelength

Fig. 1.14 Progress in angular resolution in the wavelength range 100 nm to 1 cm. All straight lines of unit slope correspond to the diffraction limit. The atmospheric seeing limit is indicated. Continuous lines:Ground-basedinstruments.Dashed lines:Space-basedinstruments.Seethetable 28 at the end of the book for space missions, acronyms, and websites of ground-based instruments

10 4 1°

10 2 1'

1 1"

-2 Diffuse gamma source 1968 10 X-ray stars 1962 Infrared galaxies 1970 Angular resolution [arc sec] 10 -4 Superluminal sources 1971 Quasars 1963 Size of the Earth 26 10 -6 1 GeV 1 MeV 1 nm1 µm 1 mm 1 m A BriefEnergy History Wavelength of Fig. 1.15 Progress in angular resolution between 1959 and 1990 (heavy to lighter shading). Some important discoveries due to this progress are indicated, the resolution attained making possible an unambiguous identification of the source. From Harwit M. (1981), Cosmic Discovery Harvester, Brighton,Radio completed with a dashed Astronomy line for the period 1985–2000 Jansky’s merry-go-round Ref: http://www.nrao.edu/archives/; http://www.jstor.org/stable/22076 29 31

Radio Signals from Milky Way Short spikes (static) caused by human activities, such as Grote Reber (1911-2002) engines

A Ham radio from Chicago Motivated by Jansky’s discovery of extra-terrestrial noise in 1993 but was turned away by Great Depression First Map of the Radio Sky Single-handed and self-funded, built a parabolic Slow variation caused 9.57-meter dish in his own back yard in Wheaton, by solar activities and Illinois radio signals of the Galactic Center Limited by ambient noises, only operated at nighttime In 1938, successfully reconfirmed the singles from the Galactic Center at higher frequency 160 MHz (1.9m) Between 1938-1943, Reber continuously observed Reber 1944, ApJ, 100, 279 the sky to produce the first radio map of the Milky Way Establish the foundation of modern radio astronomy! Grote Reber’s Detection

30 Grote Reber First Radio Map of the Milky Way Telescope by Grote Reber In 1960, Reber donated his backyard Telescope to NRAO. It was then moved to Reber 1949, Sky & Telescope, 8, 6 and preserved in Green Bank, West Virginia. 35 Radio Astronomy — Great Pioneers in 40s and 50s Transforming Science after Dr. Oort & Dr. van de Hulst World War II Dr. Jan Oort (1900-1992) Dr. van de Hulst (1918-2000) Predicted the existence of the Atomic Hydrogen 21cm (1420 MHz) Line (1944) Big Ear Hyperfine transition Hydrogen - the most abundant atom in the 110m parabolic reflector 104m flat reflector Universe

128m focal length e- H e- H

1420 MHz 21 cm

34 36 Great Pioneers in 40s and 50s Great Pioneers in 40s and 50s Dr. John Kraus (1910-2004) Dr. Purcell & Dr. Ewen

Dr. John Kraus Dr. Edward Purcell (1912-1997) Dr. Harold Ewen (1922-) Professor of Ohio State University First detection of the Atomic Hydrogen 21cm Builder of Big Ear (1963-1998) line (1951) http://www.bigear.org Measure the Galactic disk rotation from the 21cm The longest operating SETI telescope line (Muller & Oort, 1951) Build capital USD $250,000 Detected The “Wow!” signal (Possible first single of extraterrestrial life) Published the textbook “Radio Astronomy” in 1966, regarded as the From left to right: Radio Astronomy Bible Ed Purcell, Taffy Bowen, Doc Ewen 37 39

38 40

Short spikes (static) caused by human activities, such as engines

Slow variation caused by solar activities and radio signals of the Galactic Center Reber 1944, ApJ, 100, 279 43 Reber 1949, Sky & Telescope, 8, 6 “”

44

(Big Ear) 104m 110m

128m e- H e- H

1420 MHz 21 cm 45 47

Gregorian dome weighted 900 tons carrying two subreflectors (secondary and tertiary focus) to correct for aberration Spherical primary reflector

305m aperture http://www.naic.edu/ Porto Rico, US 312MHz-10.2GHz Arecibo: The largest aperture

in the World

46 48

Antenna Designs

Single-dish Good sensitivity Surface precision of 2mm Low efficiency Interferometers (arrays) High angular resolution Incomplete sampling (no total flux) Surface of the Primary 49 51

GBT 100m West Virginia, US 290MHz-50GHz http://www.gb.nrao.edu/gbt/ Arecibo Subreflector and Ultra-large Steerable: Tertiary reflector Green Bank Telescope

50 52

JVLA Effelsberg (1972-) > ngVLA 100m 25m x 27 Germany New Mexico, US 395MHz-95.5GHz 73MHz-50GHz http://www.mpifr-bonn.mpg.de/div/effelsberg/index_e.html http://www.vla.nrao.edu/ Ultra-large Steerable: Jansky Very Large Array Effelsberg 100m Telescope 53 55 ALMA Regional Centers (ARCs)

Each of the three ALMA regional partners (Executives) maintain an ALMA Regional Center (ARC) within its respective region. The ARCs provide the gateway to ALMA Learn More for astronomers, whether for infor- mation, assistance through the Help- The three ARCs can be reached through their web sites: ALMA desk, for submitting proposals and NAASC http://science.nrao.edu/facilities/alma/ Figure 3: Another ALMA science goals12m through x 50 & the OT, or ac- antenna takes its place at quiring data through the archive. EU-ARC http://www.eso.org/sci/facilities/alma/arc.html Chajnantor, carried by one 12m x 4+7m x 12 VLBA of the two ALMA trans- The North (ACA)American ARC is part of EA-ARC http://alma.mtk.nao.ac.jp/e/forresearchers/ea-arc/ porter vehicles. (Photo J. 25m x 10 the North Atacama American Desert, ALMA Science Guarda, © ALMA (ESO/ NAOJ/NRAO) US Center (NAASC)Chile based at NRAO http://www.alma.nrao.edu/ headquarters in Charlottesville, VA, USA, and with the assistance of the National Research Council of 312MHz-90GHz 84-720 GHz http://www.eso.org/sci/facilities/alma/ Canada (NRC), is responsible for supporting the science use of ALMA by the North American and Tai- http://www.nro.nao.ac.jp/alma/E/ http://www.vlba.nrao.edu/ wan astronomical communities, and for research and development activities in support of future up- grades to ALMA. What is ALMA? The Atacama Large Millimeter/submillimeter Array (ALMA) will be a single research instrument com- European researchers are supported byAtacama the EU-ARC, basedLarge at the Millimeter/ ESO headquarters in Garching, Ger- Very Long Baseline Array posed of 66 reconfigurable high-precision anten- many, along with regional nodes based in Germany,submillimeter Italy, Sweden,nas (see France, Array Figures the 7 & Netherlands, 8), located on the ChajnanUnited- Kingdom, and the Czech Republic. tor plain of the Chilean Andes at an elevation of Learn More The East Asian ARC (EA-ARC)a b o u t Click on 5000-m is based at the NAOJ headquar- www.almaobservatory.org/en/alma-virtual-tour 54 56 and at a ters in Tokyo, in collaborationlatitude for a virtual tour the ALMA site and vicinity. with Academia Sinica Instituteof -23°. Atacama Large of Astronomy and AstrophysicsALMA will consist of the 12-m Array, made up of fifty 12-m di-

(ASIAA), and supportsRadio waveband theameter as -antennas, plus the Atacama Compact Array (ACA), made tronomy communities ofup Japan of twelve 7-m antennas packed closely together and four 12- m antennas (the Total Power (TP) Array). Millimeter Array and Taiwan. ALMA will be a complete imaging and spectroscopic instrument Figure 9: ARCs are located in Northfor the millimeter/submillimeter regime, providing scientists with capabilities and wavelength coverage which complement Taiwan has (ALMA) America, Europe, and East Asia. The those of other research facilities of its era, such as the Jansky access ALMA headquarters are located in Santiago, Chile © ALMA (ESO/Very Large Array (JVLA), James Webb Space Telescope (JWST), SMA NAOJ/NRAO). and planned extremely-large-aperture optical telescopes. ALMA Image courtesy: Stephane Guisard will enable transformational research into the physics of the cold 6m x 8 Universe, regions that are optically dark but shine brightly in the millimeter portion of the electromagnetic spectrum. Providing Hawaii, US astronomers a new window on celestial origins, ALMA will probe the first stars and galaxies and directly image the disks in 186-696 GHz which planets are forming. http://sma-www.cfa.harvard.edu/ ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the Euro- pean Organization for Astronomical Research in the Southern Submillimeter Array Hemisphere (ESO), in North America by the U.S. National Sci- ence Foundation (NSF) in cooperation with the National Re- search Council of Canada (NRC) and the National Science Figure 10: Array in the moonlight. Image courtesy of Stéphane Guisard (© 2011, www.astrosurf.com/sguisard) Council of Taiwan (NSC), and in East Asia by the National Insti- Figure 4: Map of Chile, showing tutes of Natural Sciences (NINS) of Japan in cooperation with 11 the location of ALMA (red star). 5 57 59 Atacama Large Millimeter Array Even A Song for ALMA Telescopes Telescopes (ALMA)

58 Atacama Large Millimeter Array

Telescopes (ALMA)

60 Upcoming Radio Observatories in the Next Decant 61 63

The collapse of SKA the 85-ft Australia (1993) http://www.skatelescope.org/

Square Kilometer Array Not Standing Forever

62 85-ft (26m) Single-Dish Antennas in

Early Days 33-ft (10m)

33-foot telescope (1960-198x) 85-foot telescope (1962-1993)

Lava