Not sure I understand fully what you’re talking about…
First, the “astronimical clock”, you are referring to, has no thumbnails. A thumbnails is generated for a gallery, beeing defined at the “Options/Media” page.
What you seem talking about is the article image which defined by the width of the column.
There is a golden rule for posting: NO “Also….” 😉 Just open another thread with a new topic.
But to answer your question: the box is the standard viewer for images. When you click on the “astronimical clock” image in the post, the same viewer will open.
Cheers,
Alexander @ http://www.mouseclick.com