There are a variety of formalized summer-research internships for physics and astronomy students, spread across all disciplines and across the country.

Goucher offers its own summer-research program, to which you can apply by speaking directly with your professors.   

The most well-known off-campus program is the REU (Research Experience for Undergrads), which is sponsored by the National Science Foundation (NSF). These are competitive programs hosted at a variety of labs and institutions, which will provide you a stipend (and sometimes living accommodations) to perform research over 8-10 weeks in the summer.  Applications are typically due in late-December through mid-February.  The list of programs is always growing, but can be found at the link above, or http://www.nsf.gov/crssprgm/reu.

A great resource for the REU and other programs can be found at this blog page, hosted by the University of Illinois.  

Below are a list of some of the more popular programs.

• SULI. Funded by the Department of Energy and to bring students to national laboratories to do summer research at e.g. Brookhaven Lab in New York, Los Alamos Lab in New Mexico, or Fermilab in Illinois.
• "Student Research Participation" program at Argonne National Labs. 
• Fermilab  
• IBM and the American Physical Society sponsor female undergraduates in physics. 
• Los Alamos Lab  
• Brookhaven Lab has undergraduate research, and science communication.  
• Stanford SLAC (linear accelerator).
• Sandia National Laboratory.  
• The National Renewable Energy Laboratory.
• NASA.
• Universities Space Research Association
• IBM Summer Internships for Women & Minorities in Physics
• AT&T Summer Internships for Women & Minorities in Physics
• UNCF/Merck Science Initiative (Minorities)
• APS/IBM Research Internship for Undergraduate Women

Here are some direct links to institutions in the area:

• American Association for the Advancement of Science - Entry Point
• Applied Physics Laboratory
• Ciena
• Federal Bureau of Investigation
• Geophysical Laboratory
• NIST
• Smithsonian Environmental Research Center
• Space Telescope Science Institute
• Goddard Earth Sciences and Technology Center