Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Spanish banking giant Banco Santander (NYSE: STD) shot up as much as 12% in intraday trading, after Portugal conducted a $1.6 billion bond auction.

So what: Optimists exulted that the Portuguese auction proved the country wouldn't be next in line for a eurozone bailout. For Banco Santander, a not-floundering Portugal means that its eurozone sovereign debt holdings may not get crushed, and that its financing costs won't skyrocket. Of course, Santander isn't alone in celebration. Shares of fellow Spanish bank Banco Bilbao Viscaya Argentaria (NYSE: BBVA) also rose significantly; ditto National Bank of Greece (NYSE: NBG).

Now what: This is hardly the end of Europe's sad story. While many hail today's Portugal auction as "successful," some, including PIMCO's Bill Gross, aren't so impressed. Today's news is a step in the right direction, but Portugal and the rest of the PIIGS (Portugal, Ireland, Italy, Greece, and Spain) need to show continued progress toward sound financial footing if they hope to retain whatever shreds of confidence bond investors have left.

Want to keep up to date on Banco Santander? Add it to your watchlist.

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool’s disclosure policy prefers dividends over a sharp stick in the eye.