The astronomical polar night has arrived today for the South Pole. This is a period of continuous night when no astronomical twilight occurs for the inner region of the Antarctic circle over the next 11 weeks. Astronomical twilight happens when the Sun is between twelve and eighteen degrees below the horizon and astronomical night when it is lower than that. Thus, the astronomical polar night is limited to latitudes above 84° 34'. During the astronomical polar night stars of the sixth magnitude, which are the dimmest stars visible to the naked eye, will be visible throughout the entire day.
For us across the upper North Island, cold fronts will become stronger as the Polar vortex strengthens with the darkness. From this week, masses of cold air will periodically stream towards NZ with the assistance of the Polar Jet Stream. This means rain and stormy cold outbreaks will increase as the wet season moves up a gear. Today the Concordia Research Station in Antarctica just outside the polar circle dropped to -76.4c. Here comes winter.
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