StarDate

The stars on the rim of the galaxy are going for a ride. They’re bobbing up and down like the horses on a merry-go-round. They’re also rippling outward, away from the center of the Milky Way.

The Milky Way consists of a thin disk of stars and gas that spans a hundred thousand light-years or more. For decades, we’ve known that the rim of the disk is warped like the brim of a wide hat. It’s bent upward on one edge, and downward on the opposite edge.

A recent study found that stars on those edges are moving along a big wave. Astronomers looked at the locations and motions of more than 20,000 bright young stars logged by the Gaia space telescope. The stars are as much as 45,000 light-years from the galactic center.

Gaia found that the stars are bobbing up and down as much as a thousand light-years above or below the plane of the galaxy. And they appear to be sliding outward at thousands of miles per hour.

The wave might have been created by a close approach of a smaller galaxy hundreds of millions of years ago. Its gravity disturbed the tranquility of the Milky Way’s outer precincts – sending the stars there for a ride.

Under dark skies, the Milky Way is in good view tonight. In early evening, it extends along the body of Cygnus, the swan, in the west-northwest; through M-shaped Cassiopeia, higher in the sky; then down between Orion and the twins of Gemini, in the east-southeast.

Script by Damond Benningfield

Almost 11 million years ago, a large asteroid slammed into Earth, somewhere around Australia. It could have gouged a crater more than 15 miles wide, and devastated life across tens of thousands of square miles. So far, though, the only traces of it are 14 tiny glass beads. Combined, they weigh just 53 grams – as much as a slice of bread.

The beads are known as tektites. They formed from melted rock and sand that was blasted into the sky. Tiny blobs were shaped into balls by their passage through the air.

Tektites are found all across the planet. Most of them are associated with a few major impacts. The region where a group of related tektites is found is called a strewn field. Five confirmed fields had been identified.

One of them stretches across Australia and Asia. Decades ago, scientists identified eight tektites as members of that field, which was created by an impact about three-quarters of a million years ago.

But a recent analysis found otherwise. Scientists conducted extensive studies of those beads, along with six others. They found that the beads were related to each other – but not to the known strewn field. Instead, they formed a new field, which stretches almost 600 miles across Australia. The beads are all the same age. So they formed in the same impact – 11 million years ago. But no one has yet found a crater – only a tiny handful of beads from a possible cosmic impact.

Script by Damond Benningfield

Farmers in the American breadbasket are used to weather troubles: floods, droughts, hail, and more. But a storm in May of 2024 was something new. It caused machinery to go haywire during the peak of planting season. That caused an estimated 500 million dollars in losses.

What was different about this storm was its source: the Sun. Massive outbursts of particles and energy bombarded Earth. That caused impressive displays of the northern lights. But it also messed with GPS satellites. From the central United States, GPS positions were off by more than 200 feet. That messed with farm equipment, disrupting the planting.

A recent study said that such breaks could be more common in the decades ahead. The Sun goes through an 11-year cycle of storms. Big storms can cause all kinds of problems for modern technology. A couple of recent cycles were unusually quiet. And forecasts had called for the same from the current cycle, which peaked in 2024 and ’25.

But those forecasts were wrong. The current cycle has been much more active than the previous ones, with many more sunspots than expected, and many more big outbursts. The recent study said that upcoming cycles could be even busier. The solar wind has been getting stronger since 2008 – an indication that the Sun is waking up from a “sleepy” period. So farmers – and the rest of us – could see more space weather problems in the decades ahead.

Script by Damond Benningfield

Earth is getting fainter. For proof, just look at the Moon – something that scientists have been doing for decades.

They’ve been looking at earthshine – sunlight reflected off of Earth. We see it lighting up the nighttime portion of the Moon – the part that’s not brightly lit by the Sun. It gives that part of the Moon a ghostly appearance.

Right now, most of the lunar hemisphere that faces our way is in earthshine. The Moon is a thin crescent in the early morning sky. It’s getting thinner by the day as it wanes toward “new.” From the Moon, though, Earth is getting fatter. It’ll be “full” in just a couple of days.

How bright Earth looks varies a good bit, depending on the exact distance, the amount of ice and cloud cover, and other factors. Clouds and ice are bright; land and oceans are dark. So as Earth turns on its axis, and different features rotate into view, earthshine goes up and down like a dining room light on a rheostat.

Earthshine varies over longer periods as well, as a result of Earth’s changing climate. If cloud and ice coverage goes down, so does Earth’s overall brightness. And several studies have reported that that’s just what’s happening. Earthshine isn’t as bright as it was decades ago. The difference is small but clear – providing slightly darker nights on the Moon.

Look for the Moon low in the sky before dawn tomorrow. The bright star Antares, the heart of the scorpion, is close by.

Script by Damond Benningfield

Mighty Orion the hunter has a mighty resting spot for his tired feet: Cursa, the second-brightest star of Eridanus, the river. The star’s name comes from a longer Arabic phrase meaning “footstool of the central one” – Orion himself. As night falls, the star stands above Orion’s foot: Rigel, the hunter’s brightest star.

Cursa is about 90 light-years away. It’s easy to see from that distance because it’s a giant. It’s several times the size and mass of the Sun, and 45 times the Sun’s brightness. Its classification as a “giant” tells us much more than just its size, though. It also tells us about its stage in life.

A giant star has puffed up as a result of changes deep in its heart. It’s burned through the hydrogen in its core to make helium, so it’s moved into a new phase. In the case of Cursa, it’s fusing hydrogen in a thin shell around the core. The shell is quite hot, so it produces a lot of radiation. That pushes on the surrounding layers of gas, causing the star to expand. And that makes it brighter.

Today, the surface of Cursa is thousands of degrees hotter than the Sun’s. At that temperature, the star shines almost pure white. As it continues to change, though, Cursa may get even bigger and brighter. But its surface will get cooler. So a bigger Cursa will shine redder – an angry-looking footstool for the hunter.

Tomorrow: from giant to supergiant.

Script by Damond Benningfield

Earth passed by Jupiter yesterday. Now, we’re beginning to leave the giant planet behind. We’ll loop past it again early next year.

That passage is known as opposition – Jupiter lines up opposite the Sun in our sky. It’s closest to us then, so it shines brightest for the year. And it’s in view all night.

Jupiter is much farther from the Sun than Earth is, so it takes about 12 years to complete a single orbit. Earth follows a much shorter path around the Sun, and it moves faster. So it passes Jupiter every 13 months.

As we approach Jupiter, the planet stops its normal eastward motion against the background of stars. For a while, it moves backward – a period known as retrograde.

Jupiter itself doesn’t change direction. Instead, the shift is a result of our changing viewing angle. It’s like passing a car on the highway. For a little bit, the other car looks like it’s moving in reverse compared to the background of buildings and trees. As the gap opens, though, it appears to resume its forward motion. Jupiter will reach that point on March 11th – shifting gears as it circles the Sun.

Jupiter looks like a brilliant star – brighter than any other planet or star in the night sky now. The twin stars of Gemini are close by. Pollux, the brighter twin, is close to the left of Jupiter at nightfall. Castor is farther to the upper left. The whole group soars high across the south during the night.

Script by Damond Benningfield

The closer we look at the worlds of the solar system, the more places we see that could be homes for life. Some of those worlds orbit Jupiter, the largest planet in the solar system.

Jupiter itself isn’t on the list. It’s a big ball of gas with no solid surface. There has been speculation that large organisms could float through its skies. But that’s considered a long shot.

It’s more likely that life could inhabit some of Jupiter’s moons.

The leading candidate is Europa. It’s about the same size as our own moon. A deep ocean of liquid water probably lies below its icy crust. Plumes of hot water may squirt into the bottom of the ocean. The plumes would contain a variety of compounds – perhaps including the chemistry of life. So Europa has the right combination of water, heat, and chemistry to support life – at least microscopic life.

Europa isn’t the only Jovian moon with a deep ocean. The largest moon, Ganymede, may have more liquid water than all Earth’s oceans combined. One other big moon may have an ocean as well. But the crusts of these moons are much thicker than Europa’s. So even if their oceans are inhabited, it’ll be much harder for us to find evidence of life.

Look for Jupiter in the eastern sky in early evening, and arcing high across the sky later on. It looks like a brilliant star. Through binoculars, its big moons look like tiny stars quite close to the planet.

More about Jupiter tomorrow.

Script by Damond Benningfield

Jupiter looks like it’s wearing zebra stripes. Bands of clouds that run parallel to the equator alternate between bright and dark – zebra stripes. Each one is thousands of miles wide.

The stripes are a result of Jupiter’s composition and its rotation. It’s basically a ball of gas – it’s made almost entirely of hydrogen and helium. And even though it’s 11 times the diameter of Earth, it spins on its axis in less than 10 hours. That forces the clouds that top its atmosphere into bands that stretch from east to west.

The bands alternate between belts and zones. The belts are darker – probably because they allow us to see deeper into the atmosphere.

The zones are topped by the highest clouds. The clouds are made of frozen ammonia, which looks bright white. The belts don’t have that layer. Instead, we’re seeing clouds in the next layer down. Those clouds are made of water and other compounds, which are darker.

The stripes are flanked by jet streams that blow in alternating directions. They can roar at hundreds of miles per hour. They keep the belts and zones separated – maintaining the zebra stripes on this giant planet.

Jupiter is at its best this week. It’s in view all night, and it shines brightest for the year. It looks like a brilliant star. It’s low in the eastern sky in early evening, and climbs high across the sky later on. The stripes are easily visible through just about any telescope.

Script by Damond Benningfield

If today is your birthday, then Happy Birthday! The next one is just one year away – 365 sunrises and sunsets. If today is your birthday and you happen to be from Jupiter – well, Happy Birthday, and … we’re sorry. Your next one is almost 12 Earth years away – almost 10,500 sunrises and sunsets.

The Jovian year is so long for a couple of reasons.

First, the planet is more than five times farther from the Sun than Earth is. So its path around the Sun is more than five times longer than Earth’s.

The second reason is the laws of orbital motion. The farther a planet is from the Sun, the slower its orbital speed. At Jupiter’s great range, it moves at less than half the speed of Earth. Ergo, one Jovian year lasts almost 12 Earth years.

But to get all those sunrises and sunsets, you also have to factor in the length of a Jovian day. Although Jupiter is 11 times the diameter of Earth, it spins in a hurry – a day lasts less than 10 hours. Add it all up, multiply, divide, and carry the two, and – well, it’s a lot of days between birthdays on the Sun’s largest planet.

Jupiter is especially vibrant now. It reaches opposition this weekend – it lines up opposite the Sun in our sky. It rises around sunset and is in view all night. The planet is also closest to us, so it shines at its brightest. In fact, in all the night sky right now, only the Moon outshines it.

More about Jupiter tomorrow.

Script by Damond Benningfield

Stars are born when giant clouds of gas and dust break apart and collapse. And if that’s all there was to it, the Milky Way Galaxy would give birth to a couple of hundred stars every year. Instead, thanks to feedback from the stars themselves, it makes only a few.

Feedback is a process that clears away the material for making stars, but can also trigger the birth of more stars.

Young stars, for example, produce winds and jets that blow away the gas and dust around them. Since stars are born in clusters, many youngsters can be sweeping away the star-making material at the same time. That pares back the number of stars that can be born in a cluster.

Mature stars add to the feedback – not only with winds, but also with radiation. Hot stars generate a lot of ultraviolet energy. It vaporizes tiny particles of dust – eliminating possible building blocks for new stars.

The heaviest stars explode as supernovas. These blasts can clear out the space for light-years around, creating big, empty bubbles. And supernovas also accelerate subatomic particles around them to almost the speed of light. These “cosmic rays” help to sweep away the raw material for making more stars.

But supernovas can also enhance the birth rate. Their shock waves can cause distant clouds of gas and dust to collapse to form stars. So feedback is a complex process – one that both aids and hinders the birth of new stars.

Script by Damond Benningfield