Peter D. Usher

Professor Emeritus
Department of Astronomy and Astrophysics
Penn State University

Ph.D. in Astronomy, Harvard University, 1966

[TXT]Contact Information:
Mailing Address:
1725 Yorktown Place, Pittsburgh PA 15235
Phone: 412-371-3839

Research Interests: Extragalactic astronomy: faint blue objects, quantification of optical selection effects; quasar variability and statistical properties of complete samples. Perturbation theory. Topics in the history of astronomy and the philosophy of science. RIGHT: NGC 891 is a galaxy with a Hubble class of late Sb; it is seen nearly edge-on and is about 18 million light years away.


SHAKESPEARE AND THE DAWN OF MODERN SCIENCE (Cambria Press, 2010). An enduring puzzle of the Renaissance is why William Shakespeare ignores the astronomical revolutions of the sixteenth and early seventeenth centuries. He deals superficially with celestial phenomena and appears oblivious to the effects that new perceptions in cosmology were having on worldview. This book and HAMLETíS UNIVERSE (Aventine Press 1996-7) discuss the rise of evidence-based inquiry into natural phenomena and argue that Shakespeare's plays are allegories describing the chief cosmological models that vied for acceptance at the turn of the seventeenth century and data acquired telescopically.

[TXT]US Survey for Faint Blue Objects:

The survey for Ultraviolet-excess Starlike ("US") objects is named for its selection effects. It lists 3987 in eight fields in the North and South galactic polar caps. The selection method uses relative instrumental B-V and U-B colors and is thus the first quantified multicolor generalization of the methods of Haro and Luyten and of Jaidee and Lynga. It has provided arguably the best quasar surface densities in 1984 and is still among the top three surveys for bright quasars in 2000 (Mitchell et al ApJL 287, L3, 1984; Usher & Mitchell AJ 120, 1683, 2000). Selection effects are fully accounted for. Astrometric positions have been acquired by a unique method that uses a transparant precision grid with measurements made with the Cuffey astrophotometer in the field mode (PASP 93, 655, 1981.) (Perhaps Prof. Cuffey would have been pleased to learn that his astrophotometer could serve also as a measuring engine!) Positional accuracy of about 2" or better can be achieved most of the time. When a Penn State student, Archie Warnock developed and wrote the reduction routine. The morphological condition manifests itself as a "1.2m Schmidt Telescope Criterion" (Usher, Mitchell, & Huang, ApJ 454, 654, 1995) in the Johnson B band. With the help of former Penn State REU students Fabian and Boos, this criterion has been refined and extended to brighter magnitudes with the help of the PG Survey and the Palomar Observatory Sky Survey (see Fabian and Usher AJ 111, 645, 1996; Boos et al. 1996). Individual objects of interest include: US 943 (now DV UMa): When an undergraduate student at Penn State, Dianne Mattson discovered that this faint blue object had undergone a 5 magnitude outburst (ApJS 48, 51, 1982). Subsequent research by the former Penn State student, Steve Howell, has revealed that it is a 19th mag eclipsing cataclysmic variable at the edge of the period gap (Howell et al. MNRAS 233, 79, 1988; Bailey MNRAS 243, 57, 1990). US 1329 is about the 200th brightest quasar in the sky and has a redshift of 0.25. It was identified by four Penn State graduate students using the 62-inch telescope at Black Moshannon Observatory (Mitchell et al PASP 95, 45, 1983). US 1867 is an absorption-line quasar selected for the Hubble Space Telescope quasar absorption line key project (Gannuzi et al ApJS 118, 1, 1998). US 3215: This somewhat unusual compact galaxy was selected by Professor Ke-Liang Huang while visiting Penn State from Nanjing, China (ApJS 56, 393, 1984). The object is an active Seyfert 1 galaxy of morphological type gE2 with a de Vaucouleurs profile, centered on a cluster of galaxies of Abell Richness Class 0 or more. Its visible extent corresponds to a linear diameter of about 150 thousand light years (Howell et al PASP 109, 1149, 1997). The 1.2m Palomar Schmidt was also instrumental in the discovery of a new asteroid on plate PS25740 (103a-O+GG13, Dec 5/6 1978) taken by Archie Warnock and Peter Usher. The reduction and analysis were done by Archie Warnock and E. Bowels of Lowell Observatory. Archie is an accomplished bluegrass and country musician, so he named the asteroid "Whitley" for a country singer who died at the tender age of 34.


For a list of publications click here.


Favorite saying:

"Some people want everything. But where would they put it?"

Last updated 6 June 2014
Web page by Peter Usher (
Department of Astronomy and Astrophysics
Penn State University