Written by Los Altos Town Crier Staff Barnard College professor and best-selling author Janna Levin is scheduled to deliver a free, illustrated, nontechnical talk on her new book, “Black Hole Survival Guide,” 7 p.m. April 28. The virtual event is part of the Silicon Valley Astronomy Lecture Series through Foothill College, now in its 21st year. Levin’s lecture will center on mankind’s fascination with black holes, considered some of the most opaque theoretical constructs ever imagined by physicists. Viewers can learn about the dangers of being “spaghettified” by black holes’ enormous tidal forces. Levin also will discuss the influence of black holes on the universe at large, including their mergers and the way their presence can sculpt entire galaxies.