What Did Graffiti Look Like Before Spray Paint and More Questions From Our Readers

graffiti illustration
One reader wonders what graffiti was like before spray paint. Illustration by Mark T. Smith

Q: What was graffiti like before spray paint was invented?

—James Cloonan | Rochester, New York

Graffiti most certainly predates the spray paint can. The term comes from the Italian word for “scratched.” Ancient Romans, Greeks and Egyptians used to etch writing and pictures onto walls or rocks using sharp objects. Sometimes the markings were applied to a surface using chalk or coal. Graffiti served as a form of expression, often consisting of terms of endearment or quotations. These messages offer valuable insights about culture and identity, both before and after the invention of spray paint.

Rhea L. Combs, director of curatorial affairs, National Portrait Gallery

Q: How did dinosaurs, especially featherless ones, survive and thrive throughout winter seasons and ice ages?

—George Kammerer | Rancho Murieta, California

Dinosaurs lived in vibrant ecosystems in the high Arctic and Antarctica for millions of years. Plant fossils suggest that the climate at the poles was temperate, though dinosaurs may have occasionally encountered snow and ice during the long polar winters. Still, there were no polar ice caps in the hothouse world of the Mesozoic Era. How might dinosaurs have fared in a true ice age? Feathered ones may have done well, and perhaps some giant herbivores could have relied on inertial heat from their enormous bodies. But it’s likely most dinosaurs would have lived in a more limited geographical area. Still, it’s worth pointing out that birds—dinosaurs in their own right—not only survived but thrived during our most recent ice ages. 

Matthew Carrano, dinosaur curator, Department of Paleobiology, National Museum of Natural History 

Q: What stages does a physical object go through as it gets sucked into a black hole?

—Vanessa Wolter | Alameda, California

It depends which type of black hole an asteroid or star encounters. “Stellar mass” black holes are enormously dense—they have masses up to about a hundred times the mass of the Sun but are no more than several hundred miles across. As an object approaches one of these black holes, the difference in gravitational force acting on its near side and its far side increases dramatically. Eventually, it is literally ripped apart, its material subsumed into an orbiting accretion flow that either falls into the black hole or gets shot out as a relativistic jet. On the other hand, “supermassive” black holes, residing in the centers of galaxies, can be larger than our entire solar system, but they’re relatively low in density. The largest black holes are even less dense than the air we breathe. An object is able to approach undisturbed until it passes the “event horizon,” the legendary point of no return that defines the edge of the black hole. No one knows what happens to it after that. 

Dominic Pesce, radio astronomer, Center for Astrophysics, Harvard & Smithsonian

Q: Do cats’ eyes require time to adjust to darkness, like humans’ eyes do?

—Kevin Clark | Yucaipa, California

Cats’ pupils do take time to dilate and constrict as they adjust to light. The difference is that once cats’ eyes adjust, their large corneas and slit pupils use light so efficiently that they have virtual “night vision” goggles on in the dark. 

Craig Saffoe, curator of large carnivores, National Zoo

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