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 LensingLight is bent by gravity, so if we had some wallpaper behind a big pile of mass, our view of this wall paper is be distorted – just like looking through a bumpy sheet of glass. Faraway galaxies can serve as this wallpaper. By careful examination of the shapes of many of these galaxies, we can make a map of all the matter between us and the distant galaxies. This even includes the dark matter which greatly outweighs all the normal atomic matter in the Universe, but is otherwise invisible!

Highlights of many years of work in this field with my students and collaborators include the first and the most accurate measurements of the dark matter “lumpiness” in the Universe using this weak gravitational lensing method.

Trans-Neptunian Objects: Pluto is now known to be just one of thousands of icy bodies orbiting the Sun beyond Neptune. But finding them isn’t easy – they are very faint, and they hide among the billions of faint stars and galaxies on the sky. These TNOs can be found by looking for the faint dots that move slowly across the sky, roughly 1 degree per year or less. The orbital arrangements and sizes of these TNOs reveal much about the history of the Solar System. In particular, that the early Solar System must have been much different than the present ones, with the giant planets in different locations, and maybe even some additional large planets that are hiding very far away or have escaped entirely.

Our TNO searches have yielded the first definitive evidence of a sharp decrease in the number of TNOs beyond 50 AU from the Sun, the discovery of the faintest TNO ever found, and the detection of over 300 TNOs using the Dark Energy Survey.

Courses Taught

Astronomy 001: Survey of the Universe

Astronomy 007: The Big Bang & Beyond

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)