The bull's-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would repeat every 1,500 years.
The bull's-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would repeat every 1,500 years.
这个牛眼样的图案出现在行星式星云四周让天文学家很吃惊，他们不可能期待1500年，在他们有生之年只能看到片断。