量天尺
今天阅读三联时学到了一个新知识：人类测量星际和星系际距离靠的是一类称为造父变星的天体。
由于造父变星具有独特的周光关系，即光变周期与光度之间存在确定的关系,通过观测造父变星的光变周期，天文学家可以推算出它的绝对光度。
结合我们在地球观测到的“视星等”和推算出的“绝对星等”，就可以通过距离模数计算出天体的距离。且造父变星在银河系和许多邻近星系中广泛存在，因此是我们建立统一距离尺度的关键参照物。
在无尽的黑暗中，造父变星即是人类探索太空的灯塔，也是我们衡量宇宙的直尺。
BY 你不知道的冷知识
The S&P 500 slumped 1.8% on Monday and Tuesday, thanks to China Evergrande, the Chinese property company that looks like it is ready to default on its more-than $300 billion in debt. Cries of the next Lehman Brothers—or maybe the next Silverado?—echoed through the canyons of Wall Street as investors prepared for the worst.
Telegram has exploded as a hub for cybercriminals looking to buy, sell and share stolen data and hacking tools, new research shows, as the messaging app emerges as an alternative to the dark web.An investigation by cyber intelligence group Cyberint, together with the Financial Times, found a ballooning network of hackers sharing data leaks on the popular messaging platform, sometimes in channels with tens of thousands of subscribers, lured by its ease of use and light-touch moderation.你不知道的冷知识 from us