Philadelphia can be wonderful to look at when lit up at night. The numerous skyscrapers between the Schuylkill and Delaware rivers really shine during a beautiful spring evening. However, for those interested in looking a bit higher, say to the heavens, that wonderful architectural luminescence does not help.
Fortunately, the urban expanse subsides in a number of locations. I have included those below that fall within a reasonable drive from the city. Each location I describe is one that I have been able to enjoy the celestial scene. They're all accessible from main highways.
Valley Forge National Park is only about an hour from Philadelphia by car ride. It is full of historical sites. Although the town of Valley Forge and the King of Prussia Mall border the park, on a clear night, one can enjoy the stars. Due to the proximity to the development adjacent to the park, a telescope would enhance the experience. The park is only minutes from the Pennsylvania Turnpike, the Schuylkill Expressway and Route 202.
Marsh Creek Park sits in Northern Chester County just over an hour's drive from Philadelphia. The park is smaller and usually not very crowded later in the day. The viewing is enhanced by the relatively high elevation of the park. Conveniently the park is only minutes away from the Downingtown exit of the Pennsylvania Turnpike.
Brandywine Battlefield sits along Route 1 (Baltimore Pike) close to Pennsylvania's border with Delaware. It provides an excellent setting for viewing celestial bodies as the level of light pollution is extremely low as it is surrounded by countryside.
Hibernia Park is close to an hour and half from Philadelphia and sits in western Chester County between Philadelphia and Lancaster. It is only about a ten minutes drive from the Pennsylvania Turnpike and Route 30. It is a hidden gem in the area as the nights are dark and the park is rarely ever crowded.
French Creek State Park is a little bit further of a drive from Philadelphia but is easily accessible as it is located close to the Morgantown Exit of the Pennsylvania Turn Pike. The extra half-hour drive is worth the time as it provides excellent night sky sites with minimal light.