Be amazed at the magnificence of the universe at United States Naval Observatory. There's so much to be discovered beyond our pale blue dot, from black holes and stars to planets light-years away.
You'll be spoiled for sightseeing choice when visiting Northwest. United States Naval Observatory is a good place to kick off here, but there are plenty of other fine places to appreciate. White House, Arlington National Cemetery, and Lincoln Memorial are not far from the out-of-this-world attraction and will top off your day nicely.