Observational Facilities

Astronomers at Princeton University have a proud tradition of wide-field surveys of the sky, including optical imaging and spectroscopy of stars and galaxies, searches for extrasolar planets, and detailed observations of the cosmic microwave background. Undergraduate and graduate students and postdoctoral researchers are involved in all aspects of this effort. Key faculty members include Robert Lupton, Jenny Greene, Michael Strauss, Peter Melchior, and Jim Gunn on the optical surveys; Jo Dunkley, Lyman Page, Suzanne Staggs, Bill Jones, and David Spergel on the cosmic microwave background; and Gaspar Bakos, Josh Winn, Jill Knapp, Ed Turner, and Robert Vanderbei on searches for extrasolar planets.

The Princeton University Astrophysics Department played a leadership role in the Sloan Digital Sky Survey (SDSS).  In the 20+ years that the survey has been in operation, over 11,000 scientific papers have been written, including over 1000 with co-authors from Princeton. The survey has led to the discovery of the most distant quasars, precise measurements of the properties and clustering of galaxies, and determination of structure in the halo of the Milky Way, among many other discoveries.

The SDSS has been very successful at characterizing galaxies in the low-redshift universe. Doing the equivalent at distant cosmic epochs requires a substantially larger collecting area. As part of the SuMIRe (Subaru Measurements of Images and Redshifts) project, we have collaborated with the Japanese and Taiwanese astronomical communities in a wide-field imaging survey of the sky with the Subaru 8.2 meter telescope. Hyper Suprime-Cam is a 1.77 deg^2 imaging camera, and we carried out a 330-night 1200 deg^2 imaging survey in multiple bands to r~26 (3.5 magnitudes deeper than SDSS), as well as deeper imaging in smaller areas. These data are being used to study the evolution of galaxies, the distribution of dark matter through weak lensing, the most distant stars in our Milky Way, and the most distant quasars in the Universe. 

We are also part of an international collaboration to build a multi-object spectrograph for the Subaru Telescope, which represents the second component of the SuMIRe project. The Prime Focus Spectrograph (PFS) will have 2394 fibers deployable over 1.3 deg^2, with spectral coverage from 0.38 to 1.26 microns.  The instrument is currently under commissioning, and will start a 360-night survey of its own in 2024, targeting objects from the HSC survey, to study galaxy evolution and large-scale structure at high redshifts (focused both at 0.7 < z < 2, and also at higher redshifts) and to study the kinematics and chemical composition of the outer halo of the Milky Way and M31. 

We are also playing a major role in the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST), which will carry out its 10-year survey of 20,000 deg^2 of the Southern skies starting in 2024, with a dedicated 6.7-meter telescope.  HSC is very much a precursor for LSST, and we are laying the scientific groundwork for LSST with our HSC observations.  We are leading the development of the imaging pipelines for both projects, developing state-of-the-art software for measuring the brightnesses, positions, and proper motions of about 20 billion stars, and the brightnesses, positions, and morphologies of a similar number of galaxies.  

The Euclid Telescope of the European Space Agency is currently expected to be launched in 2023 or 2024; it is a 1.2-meter telescope which will survey 15,000 deg2 of high latitude sky in near-infrared bands, to measure the large-scale distribution of galaxies and dark matter, measuring cosmological shear via the the weak lensing of faint galaxies.  Romain Teyssier is the co-lead of the Cosmological Simulation Working Group in Euclid.   

The Nancy Grace Roman Space Telescope will be a 2.4-meter wide-field imaging telescope which will operate in the near-infrared. Expected to launch no later than mid-2027, it will measure the large-scale distribution of galaxies and dark matter, and search for extrasolar planets via gravitational lensing.  Peter Melchior is a member of the Roman Science Interest Group, which advises NASA on the best use of Roman, and a number of Princeton faculty are planning investigations with the project. Melchior is also leading efforts to jointly process Roman and Rubin data at the pixel level. 

An imaging survey to search for planets and debris disk around other stars, the Subaru Strategic Exploration of Exoplanets and Disk Survey (SEEDS), a collaboration between Japanese and Princeton astronomers, used adaptive optics and a coronagraph on the Subaru 8.2-meter telescope. It operated over 120 nights, and produced several Princeton PhD theses. It was succeeded by the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), which did spatially resolved spectroscopy of protoplanetary disks to understand the process by which stars may form.  

Gáspár Bakos has developed a series of small-aperture robotic telescopes that are optimized for high precision wide-field photometry. The Northern-hemisphere Hungarian-made Automated Telescope Network (HATNet) project has been operational since 2001, and has found 73 transiting planets orbiting other stars (exoplanets). Many of these were the first of their kind.  The HATSouth project, also led by Bakos, with stations in Chile, Namibia and Australia has been operational since 2009, and has discovered 74 additional transiting exoplanets. The upcoming  HATPI (HAT over Steradians) takes this to the next level, consisting of 64 4-inch lenses which together image 10,000 deg2 every 30 seconds.  HATPI will start operations from Chile in the Fall of 2022, and will give a comprehensive map of the variable sky brighter than 17th magnitude, sensitive to planetary transits, stellar variability, explosions of all sorts, and asteroids. 

The Transiting Exoplanet Survey Satellite (TESS) is performing precise photometry of millions of stars across the entire sky to search for planetary transits.  More than 1,000 planets are being discovered every year using TESS data..  Josh Winn is one of six Architects of the mission and Gaspar Bakos is a Co-Investigator; many recent student projects have been based on TESS data. 

The Terra Hunting Experiment is a future Doppler survey for exoplanets that aims to be sensitive to truly Earth-like planets for the first time.  Princeton is the only U.S. university that is a member of this collaboration, which is building a new spectrograph called HARPS3 for the refurbished Isaac Newton Telescope in the Canary Islands.  The collaboration will observe several dozen Sun-like stars on every clear night for at least 10 years, thereby collecting enough data to permit the detection of an Earth-mass planet in the habitable zone of a Sun-like star. 

Princeton astronomers played a major role in the building of the Wilkinson Microwave Anisotropy Probe (WMAP) and the analysis of its data. These data measuring fluctuations in the Cosmic Microwave Background have firmly established what is now the standard cosmological model, and allow a determination of the age, composition, structure, and geometry of the Universe to exquisite precision.  We are similarly a key institution in the Atacama Cosmology Telescope (ACT) and its successor, the Simons Observatory, to measure the fluctuations in the CMB on smaller angular scales, which is enabling further cosmological probes and explore the physics of the interaction of CMB photons with matter in the relatively nearby universe.

Princeton astronomers have access to approximately 14 nights per year on the Clay and Baade 6.5-m telescopes of the Magellan Observatory on Las Campanas in the Chilean Andes.  These telescopes have a wide variety of optical and near-infrared instruments, which are used by Princeton astronomers in studies of extrasolar planets, stars, and distant galaxies.  



2.5-m telescope at Apache Point Observatory, used in the Sloan Digital Sky Survey