If you are signed in to a Google account when you search, Google knows more about where you are and your search patterns and can take that into account in personalizing your search results. Sign out and your results will probably be different.

You may not even be aware you are signed in since this is done using "cookies". If you look at the upper right corner of a Google page, it'll show if you are signed in to a Google account.

Also realize that Google is constantly updating its index and is doing so faster than ever. Don't be surprised if results are different one day than they were the day before or even an hour ago.

Of course this is going to be true for so-called "real-time" search subjects such as current news. But it is still true of more static subjects. The number of pages Google indexes for our own website (FastF.com) changes daily.