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YOU’VE GOT QUESTIONS. WE’VE GOT EXPERTS

Q: Why did James Smithson leave his fortune to the United States and not to institutions in his native England?

— Helen Scott | New York City

THE SMITHSONIAN’S founding donor never even visited the United States. His father was a duke and his mother was a distant relative of King Henry VIII, but because they never married, James Smithson wasn’t treated well by class-obsessed English society. He did manage to amass a fortune, and he left it all to his nephew, Henry James Hungerford, with one caveat: If his nephew died childless (which he did in 1835, six years after Smithson’s own death), the money would go “to the United States of America, to found at Washington, under the name of the Smithsonian Institution, an Establishment for the increase & diffusion of knowledge.” William Bennett, a conservator at the Smithsonian Institution Archives, thinks the bequest was Smithson’s way of establishing his own legacy, one that wouldn’t depend on the conventions of his family or birth nation.

Q: Were the two kinds of World War II cargo ships—Liberty and Victory—used differently?

— Gary N. Miller | Davenport, Florida

LIBERTY SHIPS helped carry cargo and contributed to the Allies’ cause through sheer numbers alone— the United States cranked them out faster than the Germans could attack them, says Paul F. Johnston, curator of maritime history at the National Museum of American History. The slightly larger Victory cargo ships came later and there were fewer of them, but they were faster and harder to catch up with. Together, the two types of ships helped cement a win for the Allies in 1945.

Q: How do we define the position of a spacecraft when it’s traveling between planets? Is there a coordinate system for space?

— Ed Farrell | San Diego

WE USE A FEW DIFFERENT points of reference, says Andrew Johnston, a researcher at the National Air and Space Museum. At the beginning of a mission, when a craft is launched from Earth, we track it in relation to the Earth’s position. Coordinates are defined by lines similar to latitude and longitude, but extending into space from the Earth’s center. For far-out missions, we switch to the Sun as a reference point. And once the craft is approaching its destination, we calculate its position in relation to that destination.

Q: I’ve read that the Earth’s magnetic field is becoming weaker. How do we know about the Earth’s ancient magnetic fields?

— Gary Hurley | Portland, Oregon

IT TAKES SOME SERIOUS sleuthing, says Ben Andrews, a geologist at the National Museum of Natural History. First, scientists gather thousands of rock samples from around the globe, since tectonic plates move over time. The samples are tested in laboratories constructed to cancel out the Earth’s magnetic field—much as the Faraday shield blocks electromagnetic interference. Geologists cross-reference the info they gather about the rocks’ ages, locations and magnetic profiles to piece together a picture of the Earth’s overall magnetic field. This is how scientists figured out that magnetic north, a wandering point more than 250 miles from the North Pole that’s currently shifting from Canada toward Siberia, has at times been as far away as Antarctica, most recently 40,000 years ago. And while the overall magnetism of the Earth has been declining recently, it has also gone through periods of growth and could do so again.