At the beginning of Prisoner of Azkaban, Harry gets a fright when he sees Sirius in dog form on a street near his aunt and uncle’s house. In the letter Harry gets from Sirius on his way back to London at the end of the school year, he writes:
I would also like to apologise for the fright I think I gave you, that night last year when you left your uncle’s house. I had only hoped to get a glimpse of you before starting my journey north, but I think the sight of me alarmed you.
Prisoner of Azkaban, ch. 22: “Owl Post Again”
This description makes it sound like it was sort of a spur-of-the-moment thing to go and see Harry—something he just thought he’d do on the way. He doesn’t make it sound like a major thing he’d spent lots of time on, at any rate.
But how did he know where to look for Harry to get a glimpse of him?
There is an older question on here which asks how Sirius found Harry in Privet Drive when it was supposed to be protected from Voldemort and his supporters, but the answers to that question mostly just point out the flawed premise: Harry wasn’t in Privet Drive when he saw Sirius,note 1 and Sirius wasn’t a Voldemort supporter (even if he was widely believed to be one at the time).
What puzzles me more is how Sirius knew where to look in broader terms. After all, Sirius would have had to know to go to Little Whinging somewhere in Surrey to find him at all.
DVK’s answer to the older question says that “He'd have known Lily extremely well (being James best friend and Harry's Godfather) and would have likely known that Lily's sister got married and to whom”, which seems like an unlikely answer to me. It requires several things to all hold true:
- That Hagrid actually told Sirius that Harry was being sent to live with his mother’s sister before borrowing his motorcycle
- That Lily ever mentioned her sister’s husband’s last name to Sirius, despite not having seen her sister for a long time
- That Sirius remembered this last name (which, at the time it was mentioned, was presumably quite unimportant to him) for however long it was between him hearing it and the Potters dying, and then for twelve more years in Azkaban
- That, once he escaped from Azkaban, he managed to locate the present whereabouts of the Dursleys armed with nothing but a name remembered from at least twelve or thirteen years ago
Even if the first three points held up, which would be unlikely but not unthinkable, Sirius would still have had to locate two specific people in a country of about 58 million people. This was in 1993, before the common availability of the Internet, so he would likely have had to resort to phone directories. As far as I can tell (please correct me if this is wrong), there were no national phone directories for the UK in 1993, only local and regional ones, so it wouldn’t be as easy as just looking under D and finding Dursley, Vernon and Petunia. He’d have had to do that in dozens of different phone books to get lucky (if they were listed at all, that is).
Granted, Dursley isn’t a particularly common name (there are apparently just under 200 of them in the UK), but even so, finding the family that lived on Privet Drive would not have been an easy task for a worn-out wizard who’s never lived among Muggles and likely doesn’t know how to use a phone.
Surmountnig all these practical difficulties seems like a lot of overkill just to “get a glimpse of [Harry] before starting [the] journey north”, which makes me think perhaps there’s some other way he knows where Harry lives.
How did Sirius know where in the country to look for Harry at the Dursleys’ place?
note 1 It is a bit too much of a coincidence for my taste that Harry just happens to drag his suitcase to the exact street and sit down for a breather at the exact place where Sirius is standing at that moment (if Sirius has narrowed it down to the correct neighbourhood of Little Whinging, why isn’t he looking for him on Privet Drive itself, rather than on some other street?), but I’ll let that slide for now.