As I said before: There is no thumbnail for the “astronomical clock”.
The “Home” page shows the attached article image with a width of 322px and is calculated to the width of the column. Therefore it can not be wider than that in the “Home” page.
The “Astronomical Clock” page (http://demo.onedesigns.com/pinboard/?p=212) has the same image attached but this time not as an article image but a standard image. The image width of this page is defined by the cloumn page, which is more or less (depending on the space between the column of the “Home” page”) double the size of the “Home” page, as it includes two columns.
The final picture when clicking on the image on the “Astronomical Clock” page is defined by the size you selected while uploading the image.
Cheers,
Alexander @ http://www.mouseclick.com