Not your bookshelfâ€™s dust
Dust may explain why the star Betelgeuse suddenly dimmed in 2019, Lisa Grossman reported in â€œBetelgeuse is not about to explodeâ€ (SN: 4/11/20, p. 6).
Reader Steve OstromÂ was intrigued by how gas clouds around red giant stars like Betelgeuse condense into dust. â€œI have read many times about â€˜dustâ€™ in space, and have always wondered what that is,â€ OstromÂ wrote. â€œI doubt itâ€™s the same dust that accumulates on my bookshelves every month. Exactly what is this â€˜dust,â€™ and how does it condense out of gas?â€
The definition of dust in space depends on where youâ€™re looking and who youâ€™re talking to, Grossman says. â€œPlanetary 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,â€ she says. Below a certain temperature, atoms start to collide and stick together, but the details are far from understood, says cosmochemist Larry Nittler of the Carnegie Institution for Science in Washington, D.C. The composition of the dust depends on the composition of the star â€” carbon-rich stars make mostly carbon dust, while oxygen-rich stars make mostly silicates.
Playground designs that encourage active imaginative play can make a difference in how much kids move, Emily AnthesÂ reported in â€œBuilding playgrounds that get kids movingâ€ (SN: 4/11/20, p. 20).
Reader Stephen RestainoÂ believes that such playgrounds may have other bÂenefits, like decreasing bÂullying and boosting grades. A pediatrician, RestainoÂ mentioned studies that suggest active recess decreases in-class behavior issues. â€œThis isnâ€™t just about â€¦ getting a childâ€™s heart rate up,â€ he wrote. â€œItâ€™s time for these researchers to go back and talk [with] parents, teachers and [administrators] for a more substantive, broader evaluation of these new playgrounds and the other perks that accrue from money well spent.â€
Science News reportersÂ Tina Hesman Saey, Aimee Cunningham, Jonathan LambertÂ and Erin Garcia de JesusÂ are fÂollowing the latest research to keep you up to date on the coronavirus pandemic. The team is answering reader questions about COVID-19.
Reader Nick R.Â asked if exercising outdoors while practicing social distancing is safe.
Exercising outdoors while keeping at least six feet from others is gÂenerally considered a low-risk activity when it comes to catching COVID-19. But virus-laden droplets can travel farther than six feet (SN: 5/9/20 & 5/23/20, p. 6). Whether six feet is safe enough outside likely depends on the weather, how long the virus remains infectious in those conditions and how little of the virus is needed to kick-start an infection. Scientists are still working to understand the interplay of those factors.
A brief encounter with an infected person outside probably isnâ€™t enough contact to catch the virus, some evidence suggests. But if parks or trails are crowded enough to make it difficult to stay away from others, it might be a good idea to exercise during off-hours or wear a cloth mask.
In â€œRelicâ€™s origins may refute tie to Jesusâ€ (SN: 4/25/20, p. 13), Nazareth is incorrectly identified as the location of Jesusâ€™ tomb. Experts believe the tomb is in Jerusalem.