2020年1月 - 星空迷

木星的卫星——木卫一、木卫二、木卫三和木卫四 Moons of Jupiter—Io, Europa, Ganymede, and Callisto (© Branko Šimunek/Alamy)

Jupiter and the Galilean Moons

On January 7, 1610, Galileo was the first person to train a telescope on Jupiter—and what he saw surprised him. Strung in a line beside the planet were three tiny stars, one to the left of the planet and two to the right. But when he observed the formation the next night, he saw that now all three were on the same side of Jupiter. Over the following week, he watched as the tiny stars (now joined by a fourth) changed their position relative to the planet while remaining beside it. By January 15, he had it figured out: he was observing four moons orbiting Jupiter.

It was a discovery that would have profound implications on our conception of the cosmos, providing crucial evidence that Earth was not the center of the universe around which everything rotated. Savvy as well as brilliant, Galileo named the four moons 'the Medicean Stars' after his patron, Cosimo Medici. But over the years, as the influence of the Medici family waned and the influence of the genius from Pisa waxed, they became known as the Galilean Moons: Io, Europa, Ganymede, and Calisto.

特拉凯城堡博物馆，立陶宛特拉凯 Trakai Island Castle Museum in Trakai, Lithuania (© Andrius Aleksandravicius/Alamy)

'Have fun storming the castle'

Our headline quote comes from 'The Princess Bride' film, of course, but our homepage castle is found in Lithuania, the largest of the three Baltic states. Construction on this fortress began in the 14th century by the Grand Duke of Lithuania and was completed years later by his son. It served as a strategic and bustling center of the Grand Duchy of Lithuania, a former European state. Like much architecture from so long ago, the castle was damaged and fell into disrepair, only to be reconstructed and reopened as a museum. These days it's known as one of the most charming medieval castles in Europe.

'Field of Light at Sensorio,' by Bruce Munro, Paso Robles, Calif. (© George Rose/Getty Images)

'Field of Light at Sensorio' by Bruce Munro

Artist Bruce Munro was camping at Ayers Rock in Australia with his family in 1992 when he envisioned the art installation on today's homepage. Titled 'Field of Light,' it's currently on display at a venue called Sensorio in Paso Robles, California, the latest stop in a tour of sites around the world. At Sensorio, a new arts center that bills itself as representing 'the intersection of art, technology and nature,' visitors will find 58,800 solar-powered spheres, lit by optical fibers, that change color. When the sun sets, the fibers illuminate, creating a shimmering, interactive landscape in the meadow. The art installation changes a bit at each destination, but Munro tells reporters, 'the one constant is that it does make people smile.'

冬季奥兰卡国家公园Myllykoski风景区中的漩涡，芬兰库萨莫 The whirlpool in Myllykoski scenic area at winter in Oulanka National Park, Kuusamo, Finland (© Lassi Rautiainen/Minden Pictures)

Winter in the Finnish wilds

Don't be fooled by this frozen scene's tranquility. Once the snow melts in northern Finland's Oulanka National Park, the river's gentle swirl will turn to deafening rapids, hosting rafters as well as waterfall-peeping tourists. But there's time to enjoy the winter calm, since the region's wintery cold regularly stretches into April or May.

The partly frozen whirlpool churns near Myllykoski, a defunct mill that's now a resting point along Finland's busiest nature trail, Karhunkierros. The 50-mile route begins more than 500 miles north of Helsinki, with midsummer hikers enjoying treks lit by the midnight sun. For determined skiers and snowshoers, portions of the trail remain open through the frigid winter. Not feeling quite that intrepid? Chill at home with today's ice-themed quiz.