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 senior-housing operator Nationwide Health Properties (NYSE: NHP) climbed as much as 13% in early Monday trading after larger competitor Ventas (NYSE: VTR) said it would purchase the company for about $45 per share.

So what: The all-stock deal values Nationwide at about $5.8 billion and represents a 15% premium to Friday's closing price. The combined company will become the market's largest health-care real estate investment trust, operating about 1,300 assets across the U.S. and parts of Canada.

Now what: The offer seems like a reasonable one for Nationwide. In addition to the decent premium, the proposal gives Nationwide shareholders a chance to benefit from, as CEO Douglas Pasquale put it, "expanded strength, diversification and capabilities." For those who would rather cash out, rivals like HCP (NYSE: HCP) and Healthcare Realty Trust (NYSE: HR), both of which now sport lower forward P/Es than Nationwide, might be cheaper baby-boomer bets going forward.

Interested in more info on Nationwide? Add it to your watchlist.