Little Thunder was looking at the farm calendar. "Monday, Tuesday, Wednesday... Who named the days?"

"People long ago," said Suzy. "And lots of the names come from the sky."

"Monday is Moon day," said Spike. "Sunday is Sun day."

Little Thunder's eyes went wide. "What about Saturday?"

"Saturn's day," said Suzy. "Named after the planet."

Just then, a parcel arrived from Rome the cow, who was travelling around the world. Inside were postcards, each with a calendar in a different language.

"This one's from Italy," said Spike, reading. "In Italian, Monday is lunedì. That comes from luna, the Moon. And Tuesday is martedì, from Mars."

"Mars is a planet too!" said Little Thunder.

Suzy held up a postcard from Spain. "In Spanish, Wednesday is miércoles, from Mercury. Thursday is jueves, from Jupiter. And Friday is viernes, from Venus."

"So every day is a planet!" said Little Thunder.

"In some languages," said Spike. "But in English, Tuesday, Wednesday, Thursday and Friday are named after old gods from northern Europe. Thursday is Thor's day."

Little Thunder picked up another card. "What about this one?"

"Japanese," said Suzy. "In Japanese, the days are named after the Sun, the Moon and the elements. Fire, water, wood, metal and earth."

"And this one is Portuguese," said Spike. "They just use numbers. Monday is segunda-feira, the second day."

Little Thunder pinned all the postcards to the shed wall in a long row. "Seven days, and so many names."

"But they all come round once a week," said Suzy.

"Then today is Wednesday," said Little Thunder. "Mercury's day. I wonder what Rome is doing on her Wednesday."