Readers ask about dust in space, playgrounds, and COVID-19
Not your bookshelf’s dust Dust may explain why the star Betelgeuse suddenly dimmed in 2019, Lisa Grossman reported in “Betelgeuse is not about to explode” (SN: 4/11/20, p. 6). Reader Steve Ostrom was intrigued by how gas clouds around red giant stars like Betelgeuse condense into dust. “I have read many times about ‘dust’ in space, and have always wondered what that is,” Ostrom wrote. “I doubt it’s the same dust that accumulates on my bookshelves every month. Exactly what is this ‘dust,’ and how does it condense out of gas?” The definition of dust in space depends on where you’re looking and who you’re talking to, Grossman says. “Planetary scientists have a different definition than astrophysicists. But in this case, the dust that red giant stars puff out is gas from the star that has cooled down enough to turn solid,” she says. Below a certain temperature, atoms start to collide and stick...