Google will start redirecting searches through a secured, encrypted HTTPS connection for logged in users, starting today. (If it's not happening to you right away, it likely will in the next week or so.)
You've been able to manually point your browser toward https://google.com for quite some time now, but the move is intended to keep your browsing behaviour more secure. For more foundation, check out our explainer on why you should care about HTTPS on the web.
Making search more secure [Official Google Blog]