For those who haven't heard this before, the Blue Mountain World Heritage Area is just across the street from me and extends a couple of hundred kilometres to the north. They (the Blue Mountains) get their name from eucalyptus oil. On hot summer days, the entire horizon has a blue glow from all the gum tree oil being released into the atmosphere.
Today the mountains were blue. This marks the unofficial start of summer in these parts. After this it just gets bloody hot. Incidentally it also marks the official start of bush fire season due to the same root cause.