Here's why:

* Torrid Zone: This refers to the region around the equator, characterized by consistently hot temperatures. Sydney is too far south for this.

* Frigid Zone: This refers to the polar regions, characterized by very cold temperatures. Sydney is much closer to the equator and experiences a more moderate climate.

* Temperate Zone: This is the region between the torrid and frigid zones, experiencing a wide range of temperatures throughout the year. Sydney falls within this zone, experiencing warm summers and mild winters.

Therefore, Sydney is in the temperate zone.