Hi birminghambloke

You just found a massive flare, i.e. the reflection of the sunlight on a bright surface.
You might do a search for "flare" and you'll get hundreds of them all over the world. That spiky shape is quite typical and flares usually face south (I said "usually", not always

).
Here is a tech explanation by AZTraveller: LINK.

Have fun and keep searching.
Bye
b