> [!note]
> Below, there is a variety of instruments, observatories, and telescopes used in astronomy and astrophysics.
>
> For different surveys conducted, see [[Catalogs]].
> [!instrumentation] Optical Telescope Comparison
> ![[Comparison_optical_telescope_primary_mirrors.svg.png]]
## Multi-wavelength Surveys
#### SWIFT
*(****Neil Gehrels Swift Observatory****)*
![[swift.gif|align:center|400]]
- [[Electromagnetic Spectrum|X-ray/UV/optical]] space telescope launched in 2004.
- Originally built to search for [[Gamma Ray Burst|GRBs]] and their afterglows.
- Still operational and great for transient follow-up.
- 3 Main Instruments:
- BAT: Burst Alert Telescope ($\sim 15-150\,\pu{keV}$)
- "Coded Mask Aperture" telescope
- XRT: X-Ray Telescope ($\sim 0.3-10\,\pu{keV}$)
- UVOT: UV/Optical Telescope
## Radio Telescopes
#### MWA
*(**Murchison Wide-field Array**)*
![[MWA.jpg|align:center|400]]
- Low frequency $70-230\,\pu{MHz}$ radio interferometer with wide FOV ($\sim 30^\circ$ across).
- GLEAM: survey of extragalactic radio sources measured with MWA
- Precursor to [[#SKA]]
- Jackie Hewitt here at MKI was a founding collaborator.
#### PAPER
*(**Precision Array to Probe the Epoch of Reionization**)*
- [[Spectral Features#21cm line]] observations
#### LOFAR
*(**LOw Frequency ARray**)*
- [[Spectral Features#21cm line]] observations
#### CHIME
*(**Canadian Hydrogen Intensity Mapping Experiment**)*
![[chime.jpg|align:center|400]]
- A radio ($400-800\,\pu{MHz}$) telescope array with a very large FOV ($200\,\pu{deg^2}$) stretching from the northern horizon to the southern horizon
- Consists of four adjacent $20 \; {\rm m} \times 100 \; {\rm m}$ cylindrical reflectors oriented north-south.
- The focal axis of each cylinder is lined with 256 dual-polarization antennas
- "Pointing" takes place in post-processing by examining autocorrelations in the signal.
- Can probe the [[Spectral Features#21cm line]] from redshifts $z\sim 0.8-2.5$ (so $\lambda \simeq 50\,\pu{cm}$)
- An excellent [[Fast Radio Burst|FRB]] finding device, though localization is hard
- Built outrigger stations to assist, will be made better by [[#CHORD]].
- Kiyoshi Masui's group here at MKI is heavily involved
#### ALMA
*(**Atacama Large Millimeter Array**)*
![[ALMA.jpeg|align:center|400]]
#### CHORD
*(**Canadian Hydrogen Observatory and Radio-transient Detector**)*
#### HERA
*(**Hydrogen Epoch of Reionization Array**)*
![[HERA.png]]
- Array of radio dishes in South Africa operating at $120-200\,\pu{MHz}$
- Measure the [[Spectral Features#21cm line]] line heavily [[Redshift|redshifted]] at $z\sim 6-13$ (so $\lambda \simeq 2\,\pu{m}$).
- Precursor to [[#SKA]] (along with [[#MWA]])
- Jackie Hewitt at MKI is PI
#### MeerKAT
*(originally the **Karoo Array Telescope (KAT)**)*
![[meerkat.jpg|align:center|400]]
- A radio telescope consisting of 64 (13-meter) radio dish antennas in the Meerkat National Park (Karoo desert), in the Northern Cape of South Africa (alongside [[#HERA]])
- In 2003, South Africa submitted an expression of interest to host the Square Kilometre Array ([[#SKA]]) Radio Telescope in Africa
- The locally designed and built MeerKAT was incorporated into the first phase of the SKA.
- MeerKAT was launched in 2018.
#### ASKAP
*(**Australian SKA Pathfinder**)*
![[askap.jpg|align:center|400]]
- Radio telescope array located at Murchison Radio-astronomy Observatory (MRO) in the Mid West region of Western Australia.
- Began as a technology demonstrator for the future [[#SKA]] observatory
- Construction commenced in late 2009 and first light was in October 2012
- Consists of 36 (12-meter) parabolic antennas
- Work together as a single astronomical interferometer with a FOV $\sim 4,000 \; {\rm m^{2}}$
- Each antenna is equipped with a phased-array feed (PAF), significantly increasing the field of view. This design provides both fast survey speed and high sensitivity.
#### VLA
*(**Very Large Array**)*
![[VLA.jpeg|align:center|400]]
- A centimeter-wavelength radio astronomy observatory in the southwestern United States.
- 6GHz is ~an optimal frequency for VLA, and is used to measure [[Gamma Ray Burst|GRBs]] afterglows
- Consist of 28 (25-meter) radio telescopes
- 27 are operational while one is always rotating through maintenance
- Deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer.
- Each of the massive telescopes is mounted on double parallel railroad tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface brightness sensitivity.
- Astronomers using the VLA has observed...
- black holes
- protoplanetary disks around young stars
- magnetic filaments
- complex gas motions at the Milky Way's center
- probed the Universe's cosmological parameters
#### GBT
*(**Green Bank Telescope**)*
![[GBT.jpg|align:center|400]]
#### SKA
*(**Square Kilometre Array**)*
- A low-frequency radio telescope to be built in Australia expected to have first light in 2027
- Will have two components which observe [[Spectral Features#21cm line]] up to $z=3$ and $z\in(3,27)$ respectively
- Percursor Observatories include:
- [[#HERA]] (Hydrogen Epoch of Reionization Array)
- [[#ASKAP]] (Australian SKA Pathfinder) and the Murchison Widefield Array (MWA), the MeerKAT is one of four precursors to the final SKA.
#### EHT
*(**Event Horizon Telescope**)*
![[EHT.jpg|align:center|500]]
- A large telescope array consisting of a global network of 11 radio telescopes
- Combines data from several [[Methods#Long Baseline Interferometry|VLBI]] stations around Earth, which form a combined array with sub-arcsecond angular resolution for $1.3 \; {\rm mm}$ wavelengths (sufficient to observe objects the size of a [[Black Hole#Supermassive Black Hole|SMBH]] event horizon)
- Observed M87* (2019 April 10) - center of the supergiant elliptical galaxy Messier 87
- Observed [[Active Galactic Nuclei#Sagittarius A*|Sag A*]] (2022 May 12) - center of the Milky Way
![[EHT-images.jpg|align:center|450]]
#### ZTF
*(**Zwicky Transient Facility**)*"
#### UTRAO
*(**University of Texas Radio Astronomy Observatory**)*
## Microwave Telescopes
#### SPT
*(**South Pole Telescope**)*
![[SPT.jpg|align:center|400]]
- $10\,\pu{m}$ telescope observing in $\pu{mm/sub-mm}$ ([[Electromagnetic Spectrum|microwave]]) at the South Pole.
- First light in 2007 (still operational)
- Goal is to study [[Cosmic Microwave Background|CMB]], but also locates 1000s of [[Galaxy Cluster|galaxy clusters]] via the [[Cosmic Microwave Background#Sunyaev-Zeldovich Effect|SZ-effect]]
- Sometimes can be followed up with [[#HST|HST]]
#### CMB-S4
*(**CMB - Stage 4**)*
![[CMB_S4.jpg|align:center|400]]
- Next-generation ground-based [[Cosmic Microwave Background|CMB]] experiment.
- Telescopes equipped with highly sensitive superconducting cameras operating at the South Pole, the high Chilean Atacama plateau, and possibly northern hemisphere sites.
- Designed for...
- cross critical thresholds in testing inflation
- determining the number and masses of the neutrinos
- constraining possible new light relic particles
- providing precise constraints on the nature of dark energy
- testing general relativity on large scales
- Has more frequency channels which allow one to discern between the [[Cosmic Microwave Background#Kinetic SZ-effect]] and contaminants like background quasars more easily.
#### BICEP
*(**Background Imaging of Cosmic Extragalactic Polarization**)*
- South Pole mission
- Aimed to measure the polarization of the [[Cosmic Microwave Background|CMB]]; in particular, measuring the B-mode of the CMB.
See [[Question 79]] for dust sadness.
#### ACT
*(**Atacama Cosmology Telescope**)*
- CMB measurements of power spectra
- $\sim 98 -150 \; {\rm GHz}$
#### COBE
*(**Cosmic Background Explorer**)*
![[CMB_COBE.jpg|align:center|400]]
- Space probe launched in 1989 to measure the [[Cosmic Microwave Background|CMB]] (ran until 1993)
- Measured CMB anisotropy at $\Delta T/T \simeq 10^{-5}$ precision
- Essentially measured the low-$l$ (where $l \equiv$ multipole moment) flat part of the [[#CMB Power Spectrum|CMB power spectrum]]
- 2006 Nobel prize
#### WMAP
*(**Wilkinson Microwave Anisotropy Probe**)*
![[CMB_WMAP.jpg|align:center|400]]
- Space probe launched in 2001 to measure the [[Cosmic Microwave Background|CMB]] (ran until 2010)
- Beam sizes ranged from $10'-50'$ ([[Units & Conversions#Arcminute (