It is December 1 in Japan. It's winter already and most households are preparing for Christmas already. Meanwhile, a card came in the mailbox for the Soranos' household.
"Okaa-san, there's a card in the mailbox. It was sent from Australia." Aoi said while bringing in the card. "It must have been sent here by your youngest aunt. Let's see." Her mother said as she took the card and opened the envelope.
"Hai, it is from youngest aunt. Ee, the card shows Santa Claus wearing a hat. Why is he also wearing a shirt and shorts?" Aoi remarked after seeing the postcard's picture.
"That's because Australia is in the Southern Hemisphere, so Christmas is in the summer there."
"That means, in New Zealand, Brazil, South Africa and the other places in the Southern Hemisphere, Christmas is also in the summer there?" she asked her mother.
"Yes. The seasons in the Northern Hemisphere and those in the Southern Hemisphere are opposites to each other."
"Ah, I get it. So, in the North, December is in the winter. But in the South, it's in the summer."
"Yes. Also, in Australia the north is hotter than the south because it's closer to the Equator, the imaginary line that divides the Earth into the Northern and Southern Hemispheres. In Japan, the north is farther from the Equator, which means that it's colder than the south."
"So that's why Hokkaido is cold and Okinawa is hot. No wonder youngest aunt says they'll spend Christmas on the beach." With that, her mother put the card in her desk drawer and began to write a reply postcard.