Preview images in old CorelDRAW files

CorelDRAW is a popular vector graphics program. Its native .CDR file format has gone through many different versions. I want to focus on the files written by CorelDRAW version 2. These are the .CDR files that begin with "WLl" or "WLm". Even though it dates from 1989 or so, and has been obsolete for most …

Bismuth became radioactive in 2003

I know this is nitpicking, but the definition of a "stable" vs. a "radioactive" isotope seems a little silly to me. The usual definition of a stable nuclide (or isotope) is one that humans have not observed to decay. A radioactive nuclide is one that humans have observed to decay. A stable element is one …

Hill Spheres and apparent radii

Suppose you are a passenger in a spaceship, you look outside, and you notice that, from your vantage point, the Sun and the Earth appear to be almost exactly the same size. Question: Is it possible that you are currently in orbit around the Earth? Suppose instead that it's the Earth and Moon that appear the …

Comments in WMF files

Windows Metafile (WMF) is a vector graphics format native to Microsoft Windows 3.x. It was succeeded by Enhanced Metafile (EMF) in 32-bit versions of Windows, but it seems to have remained in use, alongside EMF, long after Windows 3.x became obsolete. It was often embedded inside other file formats, such as PowerPoint (.ppt) or Write …