StarDate

Moon lovers, rejoice! Tonight’s full Moon will be in view longer than any other full Moon of the year – the Long-Night Moon.

The full Moon lines up opposite the Sun, so it does just the opposite of what the Sun does in the daytime sky. The winter solstice – the shortest day of the year – is just a week away, so the Sun is putting in its most feeble appearance` of the year. It rises late, sets early, and scoots low across the south during the day. So the full Moon does just the opposite – it rises around sunset, climbs high across the sky during the night, and sets around sunrise.

The difference is more dramatic as you go farther north. San Antonio, for example, will see about two-and-a-half hours more moonlight than sunlight. But from Seattle, the difference is about seven hours – ten-and-a-half hours of sunlight, followed by seventeen-and-a-half hours of moonlight – a long night to watch the silvery glow of the full Moon.

And as you watch the Moon, look for some bright companions around it. The brilliant planet Jupiter stands to the right of the Moon at nightfall. The star Aldebaran, the bright “eye” of Taurus, the bull, is about the same distance to the right of Jupiter. And the star Elnath, the tip of one of the bull’s horns, is closer to the lower left of the Moon. The Moon will slide especially close to Elnath a few hours later – adding to the beauty of a long night of moonlight.

Script by Damond Benningfield

Friday the 13th brings a bit of bad luck for skywatchers this year. The Geminid meteor shower is at its peak, and it’s generally one of the year’s best, with peak rates of more than a hundred meteors per hour. But the Moon is almost full, so it’ll overpower all but the brightest meteors.

A meteor forms when a bit of debris from a comet or asteroid rams into the atmosphere at tens of thousands of miles per hour. That generates intense heat, so the particle burns up, leaving a streak of light. Most of the streaks vanish in a few seconds. But some of them leave “persistent meteor trains” – glowing trails that can last for a few minutes to more than an hour.

A recent study says that most of these long-lived trains are formed by particles that pass deeper into the atmosphere.

Scientists recorded thousands of meteors above New Mexico. They found that about five percent of meteors left a train that was visible for at least five minutes – a much higher fraction than in earlier studies.

There wasn’t much correlation between the persistence of the train and either the speed or brightness of the meteor. But there was a correlation with the meteor’s altitude. Those that descended to about 55 miles were much more likely to create long-lasting trains.

At that altitude, metals in the chunk of space debris may react with ozone in the atmosphere long after the meteor burns up – creating a glowing trail in the night sky.

Script by Damond Benningfield

Life has a way of adapting when things change. An impact by a giant asteroid wiped out most of the life on Earth about 66 million years ago. Within years, though, life began to rebound – especially plant life. Dense forests developed. And a recent study says that, in the western hemisphere, the winners included grapes and other viny plants.

The asteroid was about six miles in diameter. According to another recent study, it was born in the early solar system, beyond the orbit of Jupiter. An encounter with another body kicked it toward the Sun – and Earth.

When the asteroid hit Earth it created a huge fireball and a shockwave that destroyed everything within hundreds of miles. It also gouged a giant crater, which blasted billions of tons of water and rock into the sky – enough to blot out the Sun for years. It also created acid rain across the globe and caused other major problems. So most life perished.

But research in recent years has shown that new plant life quickly thrived. One example was found by researchers who were studying fossilized grapes in the Americas. They discovered the oldest grape seed ever seen in the western hemisphere – 60 million years old. The researchers suggested that, without giant animals around to knock down trees, forests could have grown taller and thicker. Viny plants that climbed the trees also developed – including grapes.

We’ll have more about space rocks tomorrow.

Script by Damond Benningfield

Antarctica has been a target in a cosmic shooting gallery over the past few million years. At least three big asteroids have exploded above the continent. And two of them were close enough to the ground to cause major damage. In fact, such an explosion over a populated region today could kill millions.

Scientists have found evidence of the explosions in the Antarctic ice.

Thirty years ago, for example, teams looking for meteorites atop the ice found a dark streak in the ice. The streak contained a lot of dust. The minerals in the dust grains were like those found in the most common type of meteorite. But they’d been changed by interactions with the ice. Scientists concluded the grains were embedded in the ice when an asteroid exploded above Antarctica about two and a half million years ago. A powerful shockwave slammed into the surface, showering it with dust grains.

Similar groups of dust grains have revealed two other explosions, both within the past half-million years. One of the asteroids weighed about a hundred thousand tons when it plunged into the atmosphere. It exploded so high that the damage was minimal. The other weighed a million tons. It exploded deep in the atmosphere. Heat from the blast vaporized a lot of ice, while a shockwave would have gouged a crater in the ice. Bits of the asteroid slammed into the surface – of the Antarctic shooting gallery.

More about asteroid impacts tomorrow.

Script by Damond Benningfield

Several scientists plan to spend the next few weeks snowmobiling across the ice sheets of Antarctica. It’s not a vacation or an extreme-sports event. Instead, they’ll be hunting for meteorites – bits of space rock sitting atop the ice.

About two-thirds of all the meteorites found on Earth have been recovered from Antarctica. They aren’t more common there, but they are easier to find. There aren’t many Earth rocks on the ice, and meteorites look different. Many of them have been frozen below the surface, then exposed as the ice vaporized. Others are exposed when ice piles up at the base of mountains.

Scientists find about a thousand meteorites every southern summer, during expeditions that last a few weeks. But a recent study says that pace might not hold in the decades ahead – a result of our changing climate.

Under warmer conditions, the dark meteorites could heat and melt the ice below them – then sink into the ice, where they’d be lost from view. Under the temperatures predicted for the rest of the 21st century, about a quarter of the Antarctic meteorites could drop from view by 2050. And three-quarters could be hidden by the end of the century.

Scientists say there may be hundreds of thousands of meteorites sitting atop the ice today. But future expeditions might have to spend more time on their snowmobiles to find them.

We’ll have more about Antarctic meteorites tomorrow.

Script by Damond Benningfield

Making planets is messy. It involves giant clouds of gas and dust, and frequent collisions between planetary building blocks. And it takes tens of millions of years to sort out.

A good example of how it works is seen in the star system Beta Pictoris. The star is only about 20 million years old. It has two known planets, both of which are much more massive than Jupiter, the giant of our own solar system. But the star also is encircled by huge disks of gas and dust – the raw materials for making planets.

And the supply is constantly changing. In one example, Webb Space Telescope revealed a ribbon of dust that looks like a cat’s tail. The tail might be debris from a collision between two big space rocks a century ago as seen from Earth.

And earlier this year, scientists reported evidence of a more recent collision. They compared observations made by Webb to those from another space telescope a couple of decades ago. They found that two clumps of dust had vanished. That suggests there was a collision between two giant space rocks as recently as 20 years ago. The impact blasted out huge clouds of dust, which were seen by the earlier telescope. But the star has blown away most of that dust – part of the messy process of making planets.

From the far-southern U.S., Beta Pictoris just climbs into view around midnight, quite low in the south. It’s to the upper right of Canopus, the second-brightest star in the night sky.

Script by Damond Benningfield

Astronomers were scattered across the globe 150 years ago today to watch a black dot move across the face of the Sun – a transit of the planet Venus. They’d use their observations to measure the distance to the Sun, revealing the scale of the entire solar system.

Astronomers already knew that distance to within a few million miles. But they wanted a more accurate reading. They’d get that by watching the transit from many locations. Venus would cross the Sun at a slightly different angle from each location. Measuring the difference would reveal the distance to both Venus and the Sun.

So the nations of the world mounted dozens of expeditions. They spread out from Cairo to Honolulu, from Cape Town to Tasmania. Each trip required years of planning, plus months of travel. The scientists carried tons of equipment, including prefab observatories and housing. They spent weeks setting up. And they had to calculate the precise longitude of each site, which was a key factor in measuring the angles to Venus and the Sun.

Clouds blocked the view from many of the sites. Even so, the astronomers still managed to snap thousands of pictures of the event, and take many more measurements visually. Then came years of tedious calculations. And the results were disappointing. The transit didn’t improve the known distance to the Sun at all. So astronomers fanned out once again for the next transit, eight years later.

Script by Damond Benningfield

The Moon barrels toward the planet Saturn tonight. Saturn looks like a prominent star to the upper left of the Moon at nightfall. As they drop lower in the sky, the gap between them will close. From most of the country, they’ll be a couple of degrees apart as they set – the width of a finger held at arm’s length. From Alaska and Hawaii they’ll be even closer – almost touching each other.

Although Saturn is bright, it’s a little fainter than average now. That’s because of our viewing angle on the planet’s rings. Most of the time, the rings are tilted enough to add quite a bit to Saturn’s luster. But right now, we’re seeing them almost edge-on. At that angle, they just about disappear.

The rings will be precisely edge-on early next year. But Saturn will appear so close to the Sun that it’ll be hidden in the Sun’s glare.

Saturn’s rings turn edge-on to Earth roughly every 15 years. It takes almost 30 years for Saturn to orbit the Sun. Because of the planet’s tilt on its axis, its north and south poles take turns dipping toward the Sun – just like Earth’s poles. The changing angle brings a change in seasons – also like Earth. The rings turn edge-on to Earth and the Sun at the equinoxes – the start of spring and fall.

Northern fall arrives next year. So the rings will look like a thin ribbon across the planet for a good bit longer. After that they’ll begin to open up – providing a better view of Saturn’s majestic rings.

Script by Damond Benningfield

Jupiter is like a mini solar system. The Sun’s largest planet has a family of almost a hundred known moons. Most of them are little more than cosmic flotsam – chips of rock and ice no more than a couple of miles wide. But a few rank among the most interesting worlds in the solar system.

The four largest moons are Io, Europa, Ganymede, and Callisto. They account for more than 99.9 percent of the combined mass of all of Jupiter’s moons. They probably formed along with Jupiter itself, from dust and gas that encircled the newborn planet.

Io is the most volcanically active body in the solar system. It’s covered by hundreds of volcanoes, lakes of molten lava, and other features. The other three big moons appear to have oceans of liquid water buried below their icy crusts. And Europa’s ocean is considered one of the most likely homes for life in the solar system.

Some of Jupiter’s little moons could have formed at the same time as the big guys, then perhaps moved into different orbits. But most of them appear to be the remains of asteroids that Jupiter captured when they wandered close. The asteroids were blasted apart in big collisions, leaving small chunks of ice and rock in orbit around the planet.

Jupiter is low in the east-northeast at nightfall, and climbs high overhead during the night. It looks like a brilliant star. Through binoculars, the four big moons look like tiny stars lined up near the planet.

Script by Damond Benningfield

Jupiter is backing up. The planet is in the “retrograde” portion of its trip across the sky. Instead of its usual eastward motion against the background of stars, it’s moving to the west. And right now, it’s about half way through that “reverse” period. That’s because Jupiter is at opposition – it lines up opposite the Sun in our sky.

Some people see a planet’s retrograde period as an omen. What kind of omen depends on the planet and the person making the prognostication.

In reality, retrograde is just an optical illusion. The planet doesn’t move backward at all. It only appears to do so because of the relative motions of Earth and the other planet. Now, for example, Earth is moving past Jupiter in our smaller, faster orbit around the Sun. As we do so, Jupiter appears to stop and back up for a while.

The effect is like passing a slower car on the highway. For a while, the other car appears to move backward against the background of buildings and trees. But when you get far enough away it appears to resume its forward motion. The car itself hasn’t actually changed direction – it only looks that way.

Jupiter entered retrograde in early October. It’ll resume its normal course in early February.

Jupiter is low in the east-northeast as darkness falls, and climbs high across the sky during the night. It looks like a brilliant star, with Aldebaran, the brightest star of Taurus, close by.

More about Jupiter tomorrow.

Script by Damond Benningfield