div class=ts-pagebuttonPage 1button div class=ts-image amp-img class=ts-thumb alt=Page 1: An Introduction to Astronomy src=https:reader031vdocumentsnetreader031viewer2022020522575067e41a28ab0f07ad9f4dhtml5thumbnails1jpg width=142 height=106 layout=responsive amp-img divp© 1941 Nature Publishing Grouppdiv