StarDate

A cosmic ornament decorates the night at this time of year. NGC 1300 is too faint to see with the eye alone. But images reveal one of the most beautiful galaxies in the universe. A long “bar” of stars crosses its middle, with ribbons of stars trailing away from the bar’s ends. Barred spirals are becoming more common as the universe ages. About seven billion years ago, only 20 percent of spiral galaxies had bars. But in the modern universe, the fraction goes up to about 65 percent. That includes our home galaxy, the Milky Way. So bars may develop naturally as the galaxies age. The bar funnels gas toward the center of NGC 1300. There, it forms a spiral within a spiral – a disk more than 3,000 light-years across. Some of the gas from the bar pours into a black hole that’s about 75 million times the mass of the Sun – many times the weight of the Milky Way’s black hole. The bar in NGC 1300 is one of the most impressive yet seen. It spans most of the galaxy’s diameter – about a hundred thousand light-years. That’s about the same size as the Milky Way. The stars in the bar are mostly old and yellow. The stars in the spiral arms are younger and bluer. And more stars are being born there – adding to the beauty of this impressive galaxy. NGC 1300 is low in the southeast at nightfall, in the constellation Eridanus, the river. But you need a telescope to see it. Script by Damond Benningfield

Despite its appearance, the Moon is dark. On average, its surface reflects only about a tenth of the sunlight that strikes it. But some regions are much brighter than their surroundings. They contain loops and squiggles that can stretch for dozens of miles. Some are big enough to see through small telescopes. And planetary scientists are still trying to figure out what causes them. These features are known as lunar swirls. Many of them look like ribbons of cream poured into a cup of hot coffee. The most famous, Reiner Gamma, looks like a tadpole. It has an oval “head,” with a wiggly tail that extends far across the dark plains around it. All of the swirls have especially strong magnetic fields. The Moon itself doesn’t generate a magnetic field. But pockets of magnetic force might have been “frozen” in place in the rocks. The magnetic field forms a protective dome. It deflects the solar wind – a flow of charged particles from the Sun. The particles are diverted away from the swirl. They may darken the surrounding area, but leave the swirl fairly bright. The magnetic pockets could be created by impacts by iron-rich meteorites, below-ground flows of molten rock, or some other process. NASA plans to land a rover in Reiner Gamma as early as next year – perhaps revealing the origins of these bright features on the dark lunar surface. Look for the Moon in the wee hours of tomorrow morning. The bright star Spica stands close by. Script by Damond Benningfield

Like the Sun, Rho Cassiopeia is a class G2 star. That means their surface temperature is the same, so they both look yellow. But that’s just about the only thing they have in common. Rho Cass is one of the most impressive stars in the galaxy. And it faces a much more dramatic fate than the Sun does. Rho Cass is a yellow hypergiant. If it took the Sun’s place in our own solar system, it would engulf the four innermost planets, including Earth. It’s about 40 times more massive than the Sun, and hundreds of thousands of times brighter. So even though it’s more than 8,000 light-years away, it’s visible to the eye alone – one of the most-distant stars we can see without help. Rho Cass is nearing the end of its life. That’s made it unstable, so its outer layers puff in and out. The star produces a massive eruption every 50 years or so, and smaller outbursts every 20 years or so. During the last one, Rho Cass blew out enough material to make about 10,000 Earths. And it may be building up to a huge outburst – a supernova. That would blast away its outer layers, with its dead core collapsing to form a black hole. On the other hand, Rho Cass might be massive enough for the entire star to become a black hole – and vanish from sight. For now, though, it’s in good view. It’s high in the north at nightfall, to the upper left of the letter M or W outlined by Cassiopeia. Script by Damond Benningfield

The winter solstice is the shortest day of the year – the shortest gap between sunrise and sunset. After the solstice, the days gradually get longer, all the way until summer solstice, in June. But the weather doesn’t begin to warm up right after the solstice. On average, in fact, the coldest days of the year in the United States come in February. The weather doesn’t immediately respond to the extra sunlight for several reasons. For one thing, there’s still more darkness than daylight. And for another, the Sun is still hovering at a low angle in the sky. That means the atmosphere blocks more of the Sun’s energy than at other times of the year. Perhaps the biggest factor, though, is the response of the land and oceans. They absorb the Sun’s energy during the longer, warmer times of the year, then release it back into space quite slowly. It’s like putting a roast in the oven. Even after you turn off the heat, the roast continues to get hotter for a while. And when you take it out of the oven, it doesn’t immediately cool off to room temperature – it slowly radiates its heat into the kitchen. The land cools off more quickly than the oceans. But both of them continue to “cook” the atmosphere for a while as they gradually radiate their heat – a process that continues for weeks. And just the opposite happens after the summer solstice – it takes extra weeks to crank up the heat, creating the oven-like conditions of summer. Script by Damond Benningfield