Just to show you what a smarty-pants I am, this photo will be added to the Multiple Sclerosis Companion as my profile. A work-buddy and I finally zeroed in on the meaning and illustration of the term ms companion.
Coincidentally, the closest mscompanion system is Sirius, the Dog Star. A fact that was totally lost on Ellie, but rather enchanted me.
The simplest explanation I can give is that a Main Sequence COMPANION is a star that revolves around another, and is as bright as, or brighter than our sun, rather like an humongous nuclear reactor. This is what I call a "Stephen Hawkins moment." Whenever I peruse A Brief History of Time, I clearly understand what he writes. As soon as the book is closed, my brain totally reverts back to not really understanding what I supposedly just learned. People talk about how we stand on the shoulders of giants; I usually lose my balance and tumble down pretty quickly.
Now, for anyone who thinks I spend too much time with my little doggie, I should point out that I am typing while perched on the edge of my seat. Miss Patches Snowboots is asleep behind my behind, and DeeDee, the crybaby, is running back and forth, from my lap to the desktop (though thankfully not on the keyboard). Scroll down if you aren't already heartily sick of kitty photos.
Enough astro-physics. My head hurts.