The international date line runs from the North to the south pole, but it isn't straight. It just so happens to pass right between the Diomedes Islands, in the Bering Sea, making it possible to travel through time just by crossing only 3.8 km.

Not only are these two islands apart in two different countries but also that they are 21 hours apart in time. When it's noon on a Thursday in the American Little Diomede, it's 9 a.m. on Friday in Big Diomede.

这是描述国际日期变更线文章中的摘抄段落，请教老师怎么翻译，特别是黑体文字部分。另外，第二段里的That词汇是副词的作用吗？怎么理解？谢谢老师！