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.

Here are some direct links to institutions in the area: