The study of Astrophysics -- understanding the universe in which we live -- has been an exciting field of exploration for centuries. How big is the Universe?  How did it start and what is its fate?  What's out there in deep space?  What are the stars and galaxies made of?  What makes them shine?  How many planets orbit other starsand what are their properties?  These fundamental questions have occupied peoples' thoughts for generations in an attempt to uncover the mysteries of the Universe.  Remarkable discoveries have been made in astrophysics in recent time ranging from the Big Bang and the early Universeto the Cosmic Microwave Background and its fluctuation spectrumto measurements of the large-scale structure in the Universethe existence of Dark Matter and Dark Energythe discovery of Supermassive Black Holesand the discovery of planets around other stars.  These discoveries have provided some answers to these fundamental questions. Among othersthe data revealed a strange Universe dominated by a yet mysterious Dark Energy (~70% by mass) that causes the expansion rate of the Universe to acceleratefollowed by a yet undetected exotic (non-baryonic) Dark Matter particles (~25%)with only the remaining ~5% of the universe made up by normal baryonic matter (i.e., starsgalaxiesand gas).  New discoveries have also spurred new fundamental questions:  What is the nature of the Dark Matter and the Dark Energy?  How do planets form around stars?  How does life form on planets (the new field of Astro-biology)?  How do supermassive black holes form?

Observations needed to probe the universe and answer these questions are carried out mostly with telescopesnot only the familiar ones sensitive to optical light raysbut also with instruments designed to receive radio wavesX-raysand Gamma-rays. Within the solar systemastronomers use space probes. The vast amount of observational detail obtained with these techniques is then interpreted by means of the basic laws of physics. Especially in recent decadesthe new tools of radio telescopes on the ground and X-rayopticaland ultraviolet telescopes in space have permitted us to make the startling discoveries about the heavens mentioned above. In additionwe now knowfor exampleof dense stars that consist almost entirely of neutronswith the same amount of material as in the Sun compressed into a sphere only a few miles in diameterwith a resultant density of millions of tons packed into each cubic inch.  We find even smallermore massiveobjects -- black holes -- whose gravitational attraction is so great that any light waves from the surface cannot escape but are attracted back.  We find that most galaxies contain a supermassive black holeof many millions or even billions solar massesat their cores.  Gigantic explosions of stars within individual galaxies -- supernovae and gamma-ray bursts -- have been found to radiate as much light as billions of suns.  Such explosions have been detected in systems as far out as nearly the edge of the accessible Universewhere stellar systems are moving away from us at close to the speed of lightand from which the light rays we now see were emitted billions of years ago when the Universe was much younger. The Cosmic Microwave Background radiation -- a 3K degree radiation that is a remnant of the hot Big Bang some 14 billion years ago -- has been measured in detail. This radiation is remarkably uniform. Howeveron top of this highly uniform distributionthe tiny fluctuations that provided the seeds for galaxy and structure formation in the early universe have been detected and carefully mapped, a discovery of great importance for understanding how the structure we see today formed. While such discoveries are fascinating in their own rightthey cast light on the fundamental questions that people have been asking since the dawn of mankind about the hidden nature of our Universe.

We explore these properties of the Universe in our Department of Astrophysical Sciences at Princeton.  We research these topics using both observational and data-analysis toolsas well as extensive theoretical and computational techniques.  The undergraduate program in Astrophysics is relatively small but increasingtypically fifteen to twenty Astrophysics majors annually.  Our program is flexible and is open to a broad range of student interests -- from those interested in continuing their science education in Astrophysics graduate schools to those interested in fields such as science policyscience educationspace scienceastro-biologyas well as students who plan to go into financelawand medicine.  For those who are fascinated by the prospect of contributing to the search for the universe's hidden secretsthe rewards of our Astrophysics program are great.

Our program consists of two componentscourse work and independent research projects under the close supervision of a faculty member. The course work is designed to give a solid background in the relevant areas of physics and math and to survey several of the currently most active areas of astrophysical research. We place a particularly strong emphasis on the independent research componentwhich allows students to carry out cutting-edge original research in astrophysics and to gain a working experience of what it is like to do professional astronomical research. A measure of our success is that a substantial fraction of our graduating seniors have co-authored one or more scientific papers published in the astronomical literature as a result of their junior paper or senior thesis work. Another measure of our program's overall effectiveness andperhaps more importantlyof the quality of the students at Princetonis the remarkable success our students have achieved in their graduate school applications and jobs they follow. Our graduates go to graduate schools such as BerkeleyCal TechChicagoCornellHarvardSanta Cruz and other top schools. While many of our graduates continue in Astrophysics graduate school and a career in academiaour program is very broad; a significant number of our students continue in other directionsincluding science policyscience education (one recent graduate is now the Director of Education at a major Planetarium)space sciencebiology and astro-biologyas well as in financelaw schooland medical school.  Many of our students are winners of honorific fellowships.  Our program is a rigorous oneintended to challenge and serve the first-class students that Princeton regularly attracts. In addition to the scientific excellence of the departmentits relatively small size allows for an informal atmosphere and a highly accessible facultyboth of which are greatly enjoyed by our majors.  Our program provides outstanding personal mentoring to the students and a family-like atmosphereand is flexible and adaptive to the student needs and future plans.

Princeton is part of the Sloan Digital Sky Survey (SDSS)the largest 3-D survey ever carried out of the Universe. The SDSS is a multi-institution collaboration to map the Universe in three-dimensions by obtaining digital images of the entire northern high-latitude sky and redshifts of one million galaxies.  Princeton students and faculty have used the Sloan Survey data to make exciting fundamental discoveries -- such as the discovery of the most distant quasars known in the universe and the coolest known stars. Undergraduate majors are working on the scientific analysis from this unique and most exciting survey and participate in its discoveries.

Princeton has been a leading partner in the Wilkinson Microwave Anisotropy Probe (WMAP) that measured the temperature and polarization of the Cosmic Microwave Background fluctuations across the whole sky and enabled accurate determination of cosmological parameters of the universe.  Princeton is leading the Atacama Cosmology Telescope (ACT) projectwhich measures a patch of the Southern sky with 10 times the resolution of WMAP.   Both the physics and astronomy department are active in research in cosmology.  Princeton is also the lead institution for the Southern Cosmology Survey. Undergraduates who are part of this program will have the opportunity to do research in either South Africa or Chile. 

Princeton joined our Japanese colleagues in carrying out a major new scientific surveydeeper than our previous Sloan Surveyand using the large SUBARU telescope in Hawaii. This deeper survey of the cosmos will study the evolution of galaxiesquasarsand large-scale structure from earlier time to todayand determine the mass distribution in the universe as observed by gravitational lensing measurementsamong many other interesting topics. 

Princeton faculty lead the HAT project to discover extra-solar planets orbiting other stars and investigate their properties.  Many new exoplanets have been discovered by the HAT experimentand many Astrophysics students participate in these discoveries. 

We invite you to further explore our Observational Facilitiesour extensive Computational Astrophysics programand our current Research programs.