Gary Bernstein

Gary Bernstein head shot
Standing Faculty

Reese W. Flower Professor of Astronomy and Astrophysics


Research Areas: Observational Astrophysics, Cosmology

(215) 573-6252

4N1, David Rittenhouse Laboratory


Professor Bernstein's research centers on extracting gems of astronomical knowledge from large piles of astronomical images.  Currently his group is pursuing two main science projects with the ~100,000 sky exposures of the Dark Energy Survey.

Gravitational lensing is the deflection of light by gravity as predicted by General Relativity. These deflections can cause dramatic distortions of background objects, or subtle changes in shape known as weak lensing. By measuring statistical correlations among the shapes of hundreds of millions of galaxies in the DES, we can measure the properties of dark matter and dark energy, which do not emit or absorb any light of their own.

Professor Bernstein and collaborators are also searching the DES images for solar system members orbiting beyond Neptune, a.k.a. trans-Neptunian objects (TNOs).  These thousands of small icy bodies are remnants of the early phases of the formation of our Solar System and give clues to the dramatic rearrangements of the giant planets that occurred early on.



Ph.D., Physics, University of California, Berkeley (1989)

A.B., Physics, summa cum laude, Princeton University, (1983)

Astrophysics, Gravitational Lensing, Cosmology


Research Interests

Weak Gravitational Lensing: The dark matter in the Universe reveals its presence by its gravitational deflection of passing light rays. This causes very subtle distortions in the appearance of background galaxies, which can be used to unveil the structure of this dark matter. We have used this weak gravitational lensing effect to measure the mass of dark matter halos around typical galaxies, and the power spectrum of matter in the Universe. We have also worked extensively on methods to produce the best possible lensing results from future surveys, which will allow us to track the evolution of dark matter in the Universe. Here's a summary talk (19 MB) about weak lensing presented (not very recently!) at SLAC. The Kuiper Belt: There are many thousands of small icy bodies orbiting the Sun beyond Neptune, remnants of the early phases of the formation of our Solar System. These Kuiper Belt Objects (KBOs) contain many clues to the early steps of planet formation. We have worked from the ground to discover many of these KBOs, confirming that very few exist beyond Pluto's orbit. Using the Hubble Space Telescope we have found the faintest Solar System objects ever discovered - but not enough of them! There are surprisingly few small Kuiper Belt Objects. SNAP: The SuperNova Acceleration Probe is a planned wide-field imaging space telescope for measuring distant supernovae and gravitational lensing. Both measurements will be focussed on measuring the evolution of the dark matter and dark energy components of the Universe, which remain totally unexplained despite being the dominant contents of the Universe. I am a member of the SNAP collaboration, working on calculation and optimization of its imaging and spectroscopic capabilities (e.g. the ETC++ exposure-time calculator). LSST: The Large Synoptic Survey Telescope is a proposed 8-meter ground-based telescope capable of imaging the entire accessible sky every 4 days. It would be extraordinarily capable for locating near-Earth asteroids, Kuiper Belt objects, nearby supernovae, large-scale gravitational lensing, and many other phenomena. I was a member of the Science Working Group for LSST.

Courses Taught

Astronomy 503: Astronomical Methods and Instrumentation

Physics 016: Energy, Oil & Global Warming

Selected Publications


  • Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing, DES Collaboration 2018, PRD, 98, id.043526
  • Trans-Neptunian objects found in the first four years of the Dark Energy Survey, Bernardinelli, P. et al. 2019, arXiv:1909.01478
  • Dark Energy Constraints from the CTIO Lensing Survey
    Jarvis, M., Jain, B., & Bernstein, G. 2006, AJ 644:71-79
  • The Size Distribution of Trans-Neptunian Bodies
    Bernstein, G. M., Trilling, D. E., Allen, R. L., Brown, M. E., Holman, M., & Malhotra, R. 2004, AJ 128 1364-1390
  • The Edge of the Solar System
    Allen, R. L., Bernstein, G., & Malhotra, R. 2001, ApJ Letters 549 L241-244.
  • Big Throughput Camera: The First Year
    Wittman, D. et al. 1998, Proc SPIE 3355 626-634 (3.4 MB). 


CV (file)