Go Advanced Search

Subscribe to this:

iTunes Podcast

Podcasts in These Categories

StarDate Podcast

StarDate Podcast


StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

People Who Liked StarDate Podcast Also Liked These Podcasts:
  Cheap Astronomy Podcast
by Steve Nerlich

  Talking Space Podcast
by Gene Mikulka

Reviews & Ratings
User Reviews         Rate this title  

Podcast Episodes

If this Podcast isn't working, please let us know by emailing us and we will try to fix it ASAP:

Podcast Feed URL:

 Podcast Website:


Sun, Mar 26, 2017

M82 is one of the most vigorous galaxies around. It’s classified as a starburst galaxy. That means that, although it’s smaller than our galaxy, the Milky Way, it spawns far more stars. But new research suggests the star-making frenzy could soon come to an end.

A galaxy makes new stars from clouds of gas, which permeate the space between stars. The densest clumps of this gas collapse, heat up, and begin to glow, shining as new stars. Each year, enough gas in M82 comes together to make the equivalent of 13 stars as massive as the Sun — a rate that’s about five times faster than the Milky Way.

But M82’s star-making career can last only as long as its gas supply does. Each year, according to the new research, the galaxy adds just three and a half Sun’s worth of new gas from its surroundings. And each year, the galaxy’s own stars expel a lot more gas through stellar winds and supernova explosions.

As a result, M82’s future looks bleak. When astronomers compare its gas consumption rate with its current supply of gas, they conclude that it’ll run out in just eight million years — the blink of a cosmic eye.

Still, M82 could buy itself some time if additional gas falls onto it. So perhaps this amazing galaxy will keep on churning out bright new stars for a while longer.

And M82 is in Ursa Major, the big bear. It stands to the upper left of the bowl of the Big Dipper as night falls right now, and is visible through a small telescope.


Script by Ken Croswell, Copyright 2016


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Cor Caroli

Sat, Mar 25, 2017

When healthy twins are born, they usually have the same life expectancy. Barring accidents or disease, they should live about the same amount of time.

When twin stars are born, though, it’s a different story. One of them is likely to expire long before its sibling. And it’s pretty easy for astronomers to tell which one will go first.

Consider Cor Caroli, the brightest star of Canes Venatici, the hunting dogs. It’s in the east-northeast at nightfall. It’s the first meagerly bright star to the right of the tip of the Big Dipper’s handle.

Cor Caroli consists of two stars, which probably were born together, from the same cloud of interstellar gas and dust.

One of the stars is about three times the mass of the Sun, while the other is only half that heavy. And when it comes to a star’s life expectancy, it’s all about the mass. Heavier stars consume the nuclear fuel in the cores at a much faster rate than less-massive stars, so they expire much more quickly.

The heavier star of Cor Caroli, for example, will live as a “normal” star for about 350 million years. After that, it’ll puff up to giant proportions, shining hundreds of times brighter than it is now. Then it’ll cast its outer layers into space, leaving only its hot but dead core.

When that happens, its lighter twin will still be going strong. The more leisurely rate of nuclear reactions in its core means that it’ll shine for a couple of billion years after its flashier twin expires.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moving Day

Fri, Mar 24, 2017

Venus is losing its identity. After tonight, it will no longer be the “evening star.” Instead, it’ll be the “morning star,” as it crosses the line between Earth and the Sun.

This crossing is known as inferior conjunction, and it happens every 584 days — about 19 months. During that interval, the planet goes through a series of phases like the phases of the Moon.

At conjunction, Venus is “new” — the entire hemisphere that faces Earth is in the planet’s own shadow, so we’re looking at its nightside.

After conjunction, Venus becomes a thin crescent, which grows fatter as the weeks roll by. It’s during its crescent phase that Venus shines at its brightest. The planet is close to Earth then, so it forms a relatively large target in our sky. That proximity also means that more of the sunlight that Venus reflects into space reaches Earth. The combination makes the planet especially bright.

After that, Venus gets “fuller,” as sunlight illuminates more of its Earth-facing side. But it also moves farther away, so it doesn’t look as bright.

Venus is “full” at superior conjunction, when it lines up behind the Sun. After that, Venus begins to wane again as it once again prepares to cross between Earth and the Sun.

Venus is probably too close to the Sun for most of us to see it this evening. But it could be visible in the east shortly before sunrise tomorrow — and will definitely be putting in a great showing within a few days — as the “morning star.”


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Storm Impact

Thu, Mar 23, 2017

A major hurricane can cause tens of billions of dollars in direct damages. And it can cause tens of billions more in indirect damages — losses to the economy caused by destroyed businesses, fouled roads, power outages, and other problems.

A major storm on the Sun, however, has the potential to dwarf those losses. A recent study by the American Geophysical Union found that under the right circumstances, a solar storm could trigger economic damages of up to almost 50 billion dollars a day.

The Sun produces storms all the time — big eruptions of charged particles that race outward at millions of miles per hour. Most of the time, these storms miss Earth. But when they do hit, they can knock out satellites, disrupt communications and air travel, and even knock out power grids. In 1989, an especially big storm knocked out power to Quebec.

In recent years, there’s been concern that if a monster solar storm hit Earth, it could knock out power across most of the United States. Not only that, but the currents might fry equipment that could take months to replace. That could leave big chunks of the country powerless for weeks or months.

The recent report looked at the economic impact of such an outage. It found that damages could hit anywhere from a few billion dollars a day, up to 50 billion. About half of that loss comes from a ripple effect that impacts vendors, customers, and others — a major impact from a stormy Sun.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

The Next Generation

Wed, Mar 22, 2017

The next big space telescope, James Webb, is being prepared for launch next year. And the one after that, which will look like a twin of the venerable Hubble telescope, is being developed.

Yet even these instruments will leave many questions unanswered. So NASA is already planning the next generation of space telescopes. They’ll be bigger than anything launched before, and provide capabilities far beyond Hubble or Webb.

A year ago, NASA picked four teams to outline concepts for the next big space telescope. They’ll keep at it for two more years. After that, the National Academy of Sciences will review the ideas and recommend which one to develop.

One telescope would be like a super-sized version of Hubble. It would use a segmented mirror that could be as tall as a five-story building to look at a wide range of wavelengths. That would allow it to detect signs of life on planets in other star systems and watch the evolution of galaxies and black holes.

Another concept would also provide details on other planets. It could photograph planets in Earth-like orbits, and monitor their atmospheres for signs of life.

The other ideas would look only at wavelengths that are invisible to the human eye. That would allow them to study the earliest galaxies, or the disks of superhot gas around black holes.

All of this will take time, though. Whichever concept NASA eventually picks, the telescope won’t launch until at least the 2030s.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Looking Deep

Tue, Mar 21, 2017

Earth and the solar system’s other rocky planets probably grew as smaller blobs of rock and metal slammed together, forming ever larger bodies. As they grew, gravity pulled heavier materials — iron and nickel — toward the middle, forming their cores. Lighter materials floated toward the top, forming the mantle and crust.

We can’t actually see the cores of these worlds. But a new NASA mission may be able to show us the next-best thing: the core of a possible protoplanet, one of the building blocks of planets.

Psyche will orbit an asteroid of the same name. The asteroid is a chunk of metal about 150 miles in diameter — the biggest metallic asteroid in the solar system. It could be the surviving core of a protoplanet. The little object’s outer layers could have been blasted away by collisions with other asteroids, leaving only its dense metallic core.

Observations by ground-based telescopes show that 90 percent of its surface is made of iron. The rest is made of various minerals. A close-up inspection of those minerals could confirm that Psyche is the leftover core of a protoplanet. On the other hand, it could show that the minerals came from impacts with other asteroids, telling us that Psyche never had a mantle or crust.

Either scenario will reveal more about how the inner planets formed and how they grew, and perhaps give us a hint of what their metallic cores look like.

We’ll talk about some other future missions of discovery tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Time Machine

Mon, Mar 20, 2017

Two new NASA missions are solar-system time machines. They’ll visit relics from the early solar system, providing a glimpse into the materials and processes that gave birth to the planets.

Lucy will fly past seven asteroids — big chunks of rock, metal, and ice. One of them is in the asteroid belt, between the orbits of Earth and Mars. But the others share the orbit of Jupiter. Known as Trojans, they’re locked in place ahead of or behind the giant planet by the gravity of Jupiter and the Sun.

Jupiter itself probably moved around a bit when it was young. It slid much closer to the Sun, then back out again. The Trojans might have formed with Jupiter and followed its migrations. On the other hand, they might have been captured by Jupiter as it moved. Studying them may help explain when and where they formed.

In addition, the asteroids contain materials from the birth of the solar system. They probably haven’t changed much over the eons, so they preserve a record of conditions when the solar system was young.

The mission will take advantage of existing technologies. Two of its instruments will be based on those used on New Horizons, which flew past Pluto. And a third will be based on another asteroid mission, Osiris-Rex.

Lucy will launch in 2021, with arrival at Jupiter’s orbit six years later. By then, the second mission should be well on the way to its destination — the possible core of a would-be planet. More about that tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Vernal Equinox

Sun, Mar 19, 2017

Those of us in the United States will wake up to a new season tomorrow. Spring begins at 5:29 a.m. Central Daylight Time — the moment of the vernal equinox. It occurs when the Sun crosses Earth’s equator from south to north. It ushers in longer, warmer days here in the northern hemisphere, and shorter, cooler days in the southern hemisphere.

Over the course of a year, the Sun moves north and south across the sky. That’s only an apparent motion, though. The Sun itself isn’t moving. Instead, that motion is caused by Earth’s tilt on its axis.

As seen from the Sun, Earth doesn’t stand straight up and down. Instead, it slouches — by about 23 degrees. As Earth moves around the Sun, that causes the north and south poles to nod toward and away from the Sun. In June, the north pole aims toward the Sun. That brings longer days to the northern hemisphere. And in December, it’s the south pole that nods sunward, bringing less daylight to northern climes.

The equinoxes come halfway between these extremes. Neither pole dips sunward, so both hemispheres experience roughly equal amounts of daylight and darkness. In fact, that’s where the name “equinox” comes from — it means “equal nights.”

The equinoxes are also the only times of year when the Sun rises due east and sets due west. Unless you’re on the equator, it rises north or south of those points for the rest of the year.

So enjoy the first day of spring — the start of a new season under the Sun.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moon, Antares, Saturn

Sat, Mar 18, 2017

Many of the gods and goddesses of the ancient world weren’t very nice. They lied, they cheated, they stole, and they even killed. And many of these actions were aimed at their own families.

Consider the Greek god Kronos, who in Rome was known as Saturn. He was the father of an entire race of gods — the gods of Olympus. But to protect himself from his offspring, he swallowed them whole as soon as they were born — except for one.

According to the story, Kronos was the ruler of the gods known as the Titans. His parents had foretold that one of his children would defeat him. So each time his wife, Rhea, gave birth to a new baby, Kronos swallowed it.

Rhea wasn’t happy with that arrangement, though, so she tricked him. She hid her son Zeus in a cave. And — perhaps showing why you shouldn’t gobble your food — she gave Kronos a stone wrapped in a blanket.

When Zeus grew up, he drugged his father, forcing him to regurgitate his now-grown-up children. They ganged up and waged war against the Titans. They won, and imprisoned the Titans in a pit at the edge of the world. With Zeus as their leader, these brothers and sisters then ruled the world from Olympus.

The planet Saturn was named in honor of the god. And it’s in good view early tomorrow. It looks like a bright star to the lower left of the Moon at first light. And the bright star Antares is about the same distance to the lower right of the Moon.

Tomorrow: springtime.

Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Venus and Mercury

Fri, Mar 17, 2017

The Sun’s two closest planets are staging a switcheroo this month. Mercury is climbing higher into the evening sky, while Venus is dropping out of the evening sky. And if you look at just the right time, you can see them standing almost side by side the next few evenings.

Mercury is the closest planet to the Sun. Since Earth is the third planet out, Mercury has a limited range of motion across our sky, so the little planet rarely climbs into really good view. At best, it’s visible for a little while before sunrise or after sunset, quite low above the horizon.

Mercury passed behind the Sun earlier this month. Now, it’s moving away from the Sun, so it’s climbing into the evening sky. In fact, this is its best evening appearance for the entire year. It’ll climb higher over the next few nights, making it easier to see.

Venus is the second planet from the Sun. It’s getting ready to cross between Earth and Sun, so it’s dropping lower in the sky each evening — ready to move into the morning sky in about a week.

For now, though, look for Venus quite low in the west beginning about 15 minutes after sunset. It’s the “evening star,” so if you have a clear horizon, you can’t miss it. Tonight, much fainter Mercury is close to its lower left, but you probably need binoculars to pluck it from the twilight glow. The two worlds will stand side by side tomorrow night, with Mercury climbing away from Venus — and into better view — on succeeding nights.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Giant Cannibal

Thu, Mar 16, 2017

Given the chance, a star can easily become a cannibal — a bigger star can swallow a smaller one. The star that gets eaten can leave its mark on the surviving star, though. Among other things, it can trigger an eruption or change the way the star rotates.

An example of that just may be found in Betelgeuse, the bright orange shoulder of Orion. It’s high in the south-southwest as night falls, above the hunter’s three-star belt.

When Betelgeuse was young, it was probably a few dozen times the diameter of the Sun. As it aged, though, changes in its core caused its outer layers to puff outward. Today, it’s many hundreds of times the Sun’s diameter.

And as Betelgeuse expanded, it just might have swallowed a companion star. That’s the conclusion reached by University of Texas astronomer Craig Wheeler after a team of his students used a computer model to study how Betelgeuse spins on its axis.

Wheeler says its rotation rate is unusually fast for a star of its size. The computer model shows that the star would spin that fast if it swallowed a Sun-sized companion. As the star spiraled in, it transferred its orbital motion to Betelgeuse’s outer layers, making the star spin faster.

A shell of gas surrounds Betelgeuse. It could have been expelled from the star when it swallowed the companion. Judging from the size and motion of the shell, that would have happened about a hundred thousand years ago — when Betelgeuse might have become a cannibal.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)


Wed, Mar 15, 2017

Modern amateur telescopes reveal some amazing sights, from the colorful death throes of stars that are thousands of light-years away, to spiral galaxies millions of light-years away. Perhaps the most amazing sight of all, though, looks like an average star. But it’s really a maelstrom of gas around a supermassive black hole. It’s two and a half billion light-years from Earth, which means we see it as it looked two and a half billion years ago.

3C 273 is a quasar — one of the most powerful objects in the universe. It’s powered by a black hole that’s hundreds of millions of times as massive as the Sun. The black hole’s gravity pulls in gas, dust, and stars from the galaxy around it.

This material swirls around the black hole, forming a disk that’s about as wide as our solar system. Friction heats the material to millions of degrees, so it shines brighter than an entire galaxy of stars.

Magnetic fields direct some of the superhot gas in the disk into jets that shoot into space. The jets produce enormous amounts of radio waves. One of the jets aims at Earth, so we get a powerful blast of energy from it.

Astronomers have cataloged a couple of thousand quasars. Some are even more energetic than 3C 273. But they’re also farther away, so they don’t look as bright. That leaves 3C 273 as the most-distant object visible through most amateur telescopes. Right now, it’s in the east a couple of hours after night falls, well above the bright planet Jupiter.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Active Galaxies

Tue, Mar 14, 2017

The center of our home galaxy, the Milky Way, is pretty quiet. The supermassive black hole that lurks there isn't “feeding,” so it doesn't produce much energy.

That’s not the case for many other large galaxies, though. As many as a billion of them could be classified as active galaxies — their central black holes are generating enormous amounts of energy.

The black holes themselves aren’t actually producing the energy. Nothing comes out of a black hole, so it stays black. Instead, an active galaxy’s black hole — which is millions or billions of times the mass of the Sun — is pulling in big clouds of gas and dust, along with occasional stars.

As this material spirals toward the black hole, it forms a disk that’s heated to millions of degrees. At that temperature, the disk emits a lot of energy. Some of it is in the form of visible light, but much of it is in the ultraviolet and X-ray portions of the electromagnetic spectrum.

Some active galaxies also spew out long jets of gas that are moving at close to the speed of light. The jets produce radio waves, so the galaxy can shine brighter at radio wavelengths than any other form of energy; more about that tomorrow.

An active galaxy doesn’t stay active. Energy from the disk can blow away surrounding clouds of gas and dust. That deprives the black hole of food, so it shuts down. The black hole is still there, though, waiting to grab a passing star or gas cloud — once again turning its host into an active galaxy.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moon and Companions

Mon, Mar 13, 2017

One of the most exotic bodies in the solar system is Io, one of the large moons of Jupiter. It’s covered by hundreds of active volcanoes — more than any other body in the solar system. Their molten rock and volcanic gases make Io look like a scarred apricot.

Io is so active because of a gravitational tug-of-war between Jupiter and its other large moons.

The same side of Io always faces Jupiter, just as the same side of our moon always faces Earth. But as Jupiter’s other moons move past Io, they tug at it, trying to turn it around. That creates tides in Io’s crust. While the highest tides in Earth’s oceans are about 50 feet high, the tides in Io’s solid surface are more than 300 feet high. All of that energy melts some of the rock in Io’s interior, which then pushes its way to the surface.

At the surface, the molten rock bubbles up through cracks in the crust, sometimes building broad volcanic mountains.

Some of the volcanoes produce giant plumes of ash and gas, including the most prominent volcano of them all, known as Pele — a red-and-black bull’s-eye that’s hundreds of miles across. And the plumes extend far into space, creating a fat “doughnut” of gas that encircles Jupiter.

Look for brilliant Jupiter rising below our Moon late this evening, with the bright star Spica close to the lower right of Jupiter. Through binoculars, Io and Jupiter’s three other big moons look like tiny stars arrayed near the giant planet.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Darker Skies

Sun, Mar 12, 2017

A big light pollutes the sky tonight: the full Moon. Its glare blocks faint stars from view. But the Moon is so beautiful that it’s worth a little inconvenience — and besides, there’s not a thing we can do to change it.

But we can change other sources of light pollution — the glow of civilization. The International Dark Sky Association says that because of that glow, 99 percent of the American population lives under light-polluted skies. And new light fixtures have the potential to make the problem worse.

Many cities have been switching to LEDs for their streetlights. They last longer than older technologies, and they use less energy.

The problem, though, is that most LEDs produce a lot of blue light. A recent report by the American Medical Association says that blue light scatters inside the eye, clouding your vision. It can also interfere with sleeping patterns. And, in fact, some cities that installed LED lights have had complaints from the neighbors.

Blue light also scatters more in the sky; that’s why the daytime sky is blue. So blue light shining into the sky makes it harder to see the stars.

Fortunately, though, newer LEDs are available in warmer colors than older models. With less blue light, there are fewer problems for residents. Phoenix decided to install almost a hundred thousand of these fixtures, and a city in California replaced its blue LEDs with the warmer ones.

That makes it easier to sleep, drive — and enjoy a dark night sky.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Daylight Saving Time

Sat, Mar 11, 2017

We generally think of “springing forward” as a good thing. It suggests getting ahead — in a race, in a job, or in the progress of a civilization.

Most of us in the United States will “spring forward” tonight, with the return of Daylight Saving Time. Whether that’s good or bad depends on your perspective. Some enjoy the extra hour of sunlight that’s added between the end of the work day and sunset. Others don’t enjoy having to leave for work or school when it’s still dark outside.

The idea of springing forward during the months of more daylight hours caught on during World War I, with the United States adopting it in 1918.

It lasted less than a year, but was reinstated during World War II. After the war, individual states were free to use Daylight Saving Time or not, for any part of the year they chose. It was standardized in 1966, and since then it’s been extended to take up a greater chunk of the year.

The rationale for the modern version of Daylight Saving Time is that people tend to use less energy during the dark early morning than they do after darkness falls in the evening. So the idea is that extending daylight by an hour in the evening cuts down on energy use. Study results are mixed, but most do show a small savings.

For now, just remember to set your clocks forward at 2 a.m. local time — an hour that you’ll get back when Daylight Saving Time ends and we “fall back” in November.

Tomorrow: making the night sky darker.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moon and Regulus

Fri, Mar 10, 2017

A bright star with a hint of color stands close above the Moon as darkness falls this evening. That subtle color reveals some important facts about the star.

Regulus is the heart of Leo the lion. It’s actually a system of four stars, but only one is bright enough to see with the eye alone — the star we know as Regulus.

If you look at it carefully, you’ll notice that Regulus shines with just a hint of blue. The color tells us that its surface is much hotter than the surface of the Sun. The hottest stars are bright blue, the coolest are orange or red, and stars in the middle, like the Sun, are yellow.

Regulus is so hot because it’s more than three times as massive as the Sun. That great weight squeezes the star tightly. That makes its core extremely hot, which revs up its nuclear reactions. As a result, Regulus’s lifespan will be billions of years shorter than the Sun’s.

The energy from the core heats the surface, making it blue — and bright. If you placed Regulus and the Sun at the same distance, Regulus would look about 130 times brighter. But because the star’s surface is so hot, it produces much of its energy at ultraviolet wavelengths. When you add that to the visible light, Regulus is about 360 times the Sun’s brightness.

So just from its color, we know that Regulus is hot and heavy, that it will live a short life, and that it produces a lot of ultraviolet energy — a blue-white beacon leading the Moon across tonight’s sky.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Making Elements IV

Thu, Mar 9, 2017

When a massive star reaches the end of its life, it blasts itself apart as a supernova. But this moment of death is also a moment of creation. As the star rips itself to bits, it creates new chemical elements at a furious rate. In a matter of seconds, it manufactures most of the elements that are heavier than iron — from iodine and xenon to lead and uranium. The supernova then blasts some of these elements out into space.

Other than hydrogen and helium, which were made in the Big Bang, the elements on the lightweight end of the scale were forged by nuclear reactions in the hearts of stars. But that doesn’t work for heavier elements. Even the hottest, most massive stars can’t produce enough energy in their cores to “fuse” together lighter atoms to make anything heavier than iron and nickel.

But when the star explodes, it produces enormous amounts of energy. For a few seconds, temperatures and pressures just outside the star’s core are so extreme that a huge number of atoms fuse together to make much heavier ones.

In recent years, though, research has suggested that not all of the heavy elements come from supernovae. Some of the heaviest may be forged when the dead cores of these exploded stars ram together. In fact, it’s possible that that’s how most of the gold came into existence. So that gold ring you’re wearing could be debris from the collision of two stellar corpses — the remnants of mighty stars that blasted themselves to bits.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Making Elements III

Wed, Mar 8, 2017

Some giant chemical factories arc down the southwestern sky this evening: seven bright stars that outline the constellation Orion. The pattern includes the three stars of Orion’s Belt, which are roughly parallel to the horizon at nightfall, and a four-star rectangle around the belt. Orange Betelgeuse is at the top left corner, with blue-white Rigel at the opposite corner.

All of these stars are supergiants. They’re hundreds of times wider than the Sun, and tens of thousands of times brighter. Most important, they’re many times more massive than the Sun — and that’s what makes them chemical factories.

All stars shine by fusing together elements in their cores to make heavier elements, releasing a lot of energy in the process.

The Sun and similar stars fuse hydrogen to make helium. But supergiants make many other elements as well. Because of their great mass, gravity squeezes them more tightly, making their cores much hotter. That allows them to fuse heavier and heavier elements. In the final stage of life, in fact, such a star is put together like an onion. The core is made of iron, surrounded by layers of silicon, oxygen, neon, carbon, helium, and hydrogen, all mixed with other elements.

It takes too much energy to fuse iron to make heavier elements. So the nuclear reactions come to an end. The core collapses, and the star’s outer layers explode into space — creating even heavier elements as they do. More about that tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Making Elements II

Tue, Mar 7, 2017

The Sun is a big nuclear reactor. Temperatures in its core reach tens of millions of degrees — hot enough for hydrogen atoms to “fuse” together to make helium. In fact, the Sun converts more than 650 million tons of hydrogen to helium every second. A small fraction of the hydrogen is converted to energy, which makes the Sun shine.

That same process powers most of the stars in the universe. And it’s the first step toward creating all the chemical elements on the periodic table.

For the least-massive stars, the process actually stops there. Their cores can’t get hot enough to make anything but helium. For stars that are roughly half the mass of the Sun or heavier, though, the process continues.

When a star that’s as massive as the Sun converts the hydrogen in its core to helium, the core shrinks, which makes it much hotter. When it gets hot enough, the next cycle of nuclear reactions begins. This round makes mainly carbon, nitrogen, and oxygen. Stars that are a bit heavier than the Sun make more of these elements, along with a smattering of a few others.

When the star dies, most of the heavier elements are trapped in its dead core. But a few of them are expelled into space along with the star’s outer layers, which are still made of hydrogen. These elements may then be incorporated into new stars, planets, and perhaps living organisms — creation born in the hearts of stars.

We’ll talk about what happens in the heaviest stars tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Making Elements

Mon, Mar 6, 2017

Every time you take a breath, you’re filling your lungs with elements created in the heart of a star. If you take an iron supplement, you’re ingesting an element forged in the heart of a massive star. And if you put on a silver necklace, you’re wearing an element created in the death of a massive star.

In fact, almost all the elements were created by stars. The main exceptions are the lightest and simplest elements — hydrogen, helium, and a smidgen of lithium.

Hydrogen came first — or at least hydrogen nuclei: single protons created in the first fraction of a second after the Big Bang. After a few minutes, the universe had cooled enough that two protons and two neutrons could stick together to form the nuclei of helium.

After a few hundred thousand years more, the universe cooled enough to allow electrons to stick to the bare nuclei, turning them into complete atoms.

Over time, the hydrogen and helium started clumping together to make stars. The cores of these stars were hot enough to ignite the fires of nuclear fusion, which combine lightweight atoms to make heavier ones — eventually making almost all the elements we see in the universe today.

Yet hydrogen and helium continue to dominate the chemical brew. Hydrogen accounts for about three-quarters of all the mass in the universe, with helium accounting for about a quarter. Everything else makes up less than two percent of the total — forged in the hearts of stars.

More tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Pole Stars

Sun, Mar 5, 2017

The North Star is one of the most important beacons in the sky. It serves as a compass, pointing the way due north. And it also serves as the hub of the sky — all the other stars appear to circle around it as Earth turns on its axis.

More than 4,000 years ago, the architects of ancient Egypt used the North Star to align the pyramids of Giza. And more than four decades ago, Apollo astronauts used it to help guide them to the Moon. But the two groups were guided by different north stars. The Egyptians used a star called Thuban, in the constellation Draco. And the astronauts used Polaris, at the end of the handle of the Little Dipper.

Thuban didn’t explode or fade away — it’s still in plain sight. Instead, Earth’s axis turned away from the star — an effect called precession.

It’s caused by the gravitational tug of the Sun and Moon, which cause our planet to wobble like a spinning top. As it wobbles, the axis points toward different stars. Four millennia ago, it aimed at Thuban. Today, it aims at Polaris.

Over the next century, the pole will actually take slightly better aim at Polaris. Right now, the star is about two-thirds of a degree from where the axis is pointing. Around the year 2100, it’ll be less than half a degree from the pole.

After that, though, the pole will move away from Polaris. By around the year 4100, it’ll take aim at a star that’s one constellation over, in Cepheus — a North Star to guide future generations.


Script by Damond Benningfield


Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moon and Aldebaran

Sat, Mar 4, 2017

The Moon and the bright star Aldebaran continue a game of “peek-a-boo” this evening that they’ve been playing for more than two years. The Moon will pass directly in front of the star, blocking it from view. The entire event will be visible across most of the United States.

This is just one of a series of such disappearing acts, known as occultations, that began in January of 2015. The Moon has passed in front of the star every month since then, although not all of the events have been visible from the U.S.

Over the decades, occultations have helped astronomers learn a lot about quite a few stars, including Aldebaran. The amount of time it takes the star to disappear behind the Moon, for example, helps reveal how big the star is. In the case of Aldebaran, occultations and other techniques show that it’s more than 40 times the diameter of the Sun — a true giant among stars.

Occultations can also reveal companion stars. In those cases, a system’s brightness exhibits a two-step drop as the star disappears behind the Moon, and a two-step rise as it returns to view — one “step” for each star. Aldebaran shows no such profile, indicating that it travels alone.

Look for Aldebaran close above the Moon as darkness falls. It passes behind the nighttime portion of the Moon, then emerges below the illuminated portion of the Moon a bit later. The exact timing depends on your location, as the Moon and Aldebaran once again play peek-a-boo.


Script by Damond Benningfield



Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Counting Starspots

Fri, Mar 3, 2017

The Sun has been pretty quiet the last few years. It’s on the downward slope of its 11-year magnetic cycle, so only a few dark sunspots have marked its surface. The numbers should stay low awhile longer, until the cycle heads toward its peak in the next decade.

Astronomers have measured magnetic cycles in quite a few other stars. And they’ve found one star with a cycle that appears to be a little longer than the Sun’s — more than 11 years. And thanks to an orbiting planet, they’ve even been able to map its starspots, which show a pattern similar to the Sun’s.

HAT-P-11 is a bit smaller, cooler, and redder than the Sun, and it takes about the same amount of time to spin on its axis.

It’s orbited by a planet that’s about the size of Neptune, one of the giants of our own solar system. The planet crosses in front of the star every few days, blocking some of the star’s light. Observations by telescopes on the ground and in space found that the amount of starlight that’s blocked varies by a tiny amount. That’s because the planet sometimes passes in front of the dark starspots, which don’t add much to the star’s overall brightness.

By tracking the planet through 200 crossings, astronomers mapped hundreds of starspots. They found that the star has more spots than the Sun, and many of them are bigger than typical sunspots. But they appear at the same latitudes as the spots on the Sun, giving HAT-P-11 some dark bands on either side of its equator.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Habitable or Not?

Thu, Mar 2, 2017

Our closest planetary neighbor remains in good view early this month. Venus is the “evening star,” shining from about 32 million miles away. Despite its beauty, though, it’s not a friendly place to visit. Its surface is extremely hot, and it has a dense, toxic atmosphere.

The closest planet beyond our solar system could be similar to Venus. Then again, it could be similar to our own Earth.

Proxima Centauri b orbits our closest neighboring star, Proxima Centauri, which is four and a quarter light-years away. The planet is probably dense and rocky, like Earth and Venus. And it lies inside the star’s habitable zone — the distance from the star where temperatures are just right for liquid water.

That doesn’t mean the planet is actually habitable, though. A lot depends on what happened when it was young.

Proxima Centauri is small, cool, and faint. When the star was born, though, it was much hotter and brighter than it is now. That means a lot could have happened to the young planet.

Researchers looked at many possible early conditions for it — with a thick atmosphere and lots of water on its surface, for example. They found that the young star could have vaporized both of them, leaving the planet dry and airless, or with a Venus-like atmosphere. But many scenarios led to conditions that were more like Earth.

We won’t know what Proxima Centauri b is really like until future telescopes allow us to get a direct look at this neighboring world.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

More Moon, Mars, Venus

Wed, Mar 1, 2017

For the scientists who study volcanoes, Venus would be the equivalent of Disneyworld. About 1600 volcanoes pockmark the planet’s surface. Most of them are extinct, but a few may still be active. And thousands of structures that are related to volcanoes dot the surface as well. They include formations that look like rings, pancakes, and even starbursts.

Perhaps the most intriguing formations are known as arachnoids. They consist of a series of concentric rings with dozens or hundreds of lines radiating away from them. That makes them look like giant spiders clinging to vast webs. Scientists have cataloged more than 250 of them.

How arachnoids form is a bit of a mystery. One study, though, says they most likely are created when blobs of molten rock bubble up from the planet’s mantle, which is the layer below the crust. As it pushes up it spreads outward, splitting the crust. That forms the rings, as well as cracks that radiate outward. Molten rock then fills the cracks, forming dikes that can be more than a hundred miles long.

Over time, the process may continue, forming even bigger features — rings and starbursts that may consume the Venusian spiderwebs.

And Venus is in great view right now. It’s low in the west at nightfall, and shines as the “evening star.” Tonight, the crescent Moon stands well to its upper left. And the fainter planet Mars stands beside the Moon, completing a beautiful alignment in the evening sky.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Moon and Planets

Tue, Feb 28, 2017

The Curiosity rover is climbing through time. As it climbs the central mountain peak in a wide crater on Mars, it sees rock layers that were deposited at different times in the planet’s history. The higher it goes, the more recent the rocks — hence, the rover is climbing through time.

That excursion is reinforcing the idea that early Mars was much warmer and wetter than it is today. In fact, conditions on the planet could have been fairly hospitable for life. Alas, there’s no hint of life itself in the rocks — only hints that if life existed, it could have been comfortable on the young planet.

Recently, for example, Curiosity found minerals containing boron. Here on Earth, such minerals form in a wet environment, in temperatures that are comfortable for life. The rover also found fairly high concentrations of clays and a mineral called hematite — both of which form in water.

Liquid water, energy, and the right chemistry are necessary ingredients for known life forms. And Curiosity is showing that all of those existed on Mars in the distant past — discoveries made by climbing through time on a Martian mountain.

And Mars forms the top point of a skinny triangle in the sky this evening. It’s well above the crescent Moon, and looks like a moderately bright orange star. The much brighter planet Venus, the brilliant “evening star,” stands closer to the upper right of the Moon.

We’ll have more about this evening trio tomorrow.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

Loud Sun

Mon, Feb 27, 2017

In late February of 1942, British anti-aircraft radar stations were bombarded with a “noise” that they couldn’t filter out. Fearing that Germany had found a new way to jam the radar, physicist and army officer Stanley Hey investigated. He discovered that the noise appeared only during the day, and that it tracked the Sun across the sky. He also found that a giant sunspot was moving across the Sun at the time.

Hey concluded that the noise came from the Sun itself — the first confirmed detection of solar radio waves. Thanks to wartime secrecy, though, Hey couldn’t share this discovery until after World War II.

Most of the time, the Sun is fairly quiet at radio wavelengths. It does produce some background radio waves, so it’s the brightest radio object in the sky — but only because it’s a big, close target.

The Sun produces more radio energy when more sunspots darken its surface. And it produces bursts of radio waves like this during solar flares and other outbursts. [SFX: sun audio]

Studying solar radio waves reveals details about the Sun itself, and especially about its atmosphere. The radio waves provide a 3-D view of what’s happening out to distances of millions of miles. They also reveal the magnetic field that permeates the atmosphere, and how the magnetic field may heat the outer atmosphere to millions of degrees — discoveries made possible by bursts of static on British radar 75 years ago.


Script by Damond Benningfield

Download File - 0.1 MB (Click to Play on Mobile Device)
Listen To This Podcast (Streaming Audio)

More Details

  • LearnOutLoud.com Product ID: S089370