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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.

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by Steve Nerlich

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A ĎProximateí Orbit

Tue, Apr 25, 2017

Our closest neighboring star was discovered a century ago. Ever since then, astronomers have suspected that itís a member of a triple star system. And some recent research provides confirmation of that idea.

Despite its nearness, Proxima Centauri is so feeble that itís invisible to the unaided eye. Thatís why astronomers didnít spot it until 1915. Today, we know that itís just four-and-a-quarter light-years from Earth.

At the time of its discovery, astronomers noticed that Proxima Centauri was at nearly the same distance as a much brighter star ó actually a pair of stars whose light blends together to make it the third-brightest star in the night sky.

This brilliant double star is Alpha Centauri. Itís only about a tenth of a light-year farther than Proxima, and it moves through space at nearly the same velocity as Proxima. So from the beginning, astronomers have suspected that Proxima Centauri is part of the Alpha Centauri system.

But Proxima is a long way from the other two stars. If it is bound to them, it must have almost exactly the same speed through space. Otherwise, the little star would escape Alpha Centauriís gravitational grip.

Recent measurements of Proxima Centauriís motion have shown that the star is indeed bound to the binary. It orbits its bright partners once every 550,000 years.

So the nearest star system to the Sun is triple, harboring two bright stars plus dim little Proxima.

Script by Ken Croswell, Copyright 2016

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Soyuz 1

Mon, Apr 24, 2017

In the spring of 1967, the Soviet Union was getting ready to celebrate May Day, one of its most important holidays. And the celebration would be preceded by a spectacular mission in space: Two Soyuz spacecraft would rendezvous and dock, and two cosmonauts would walk in space.

Soyuz was designed to carry cosmonauts to the Moon. But three unmanned tests had all resulted in failure. Even so, there was pressure to get on with the first manned flights. So 40-year-old cosmonaut Vladimir Komarov launched aboard Soyuz 1 on April 23rd, 1967.

But the craft was a dud, rushed into space before it was ready. After launch, one of its solar panels failed to open, and systems designed to aim and maneuver the Soyuz failed as well.

The launch of Soyuz 2 was canceled, and controllers set about trying to get Komarov back home. More problems delayed retro-fire by two orbits. Finally, after a day in space, Komarov fired his rockets and headed home.

After reentry, though, the main parachute got stuck. A backup deployed, but got tangled with a smaller chute and never opened. Soyuz 1 hit the ground at 90 miles per hour, killing Komarov. Moments later, braking rockets fired, engulfing the capsule in flames.

It took 18 months to redesign the Soyuz and get it back into space ó a delay that scuttled any chances of winning the Moon race. Today, though, the Soyuz continues to fly ó carrying Russians, Americans, and others to the International Space Station.

Script by Damond Benningfield

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Last Glance

Sun, Apr 23, 2017

This time of year is pretty inviting for a little evening skywatching. The evening hours are warm but not usually too hot, and thunderstorm activity generally hasnít reached its peak ó perfect conditions for watching the stars.

Unfortunately, though, one of the most beautiful star patterns is dropping from view about now, so there arenít many more days to enjoy it.

Orion, the hunter, is low in the west as night falls. Its three-star belt stands almost parallel to the horizon. And its two brightest stars bracket the belt: orange Betelgeuse above, and blue-white Rigel below.

Orion always climbs into prominence in the evening sky around Thanksgiving and Christmas. At that time of year, in fact, itís in view for most of the night.

As the months roll by, though, so does Orion. The constellation rises earlier each night, so by late February, itís already halfway across the southern sky at nightfall.

And now, itís about to disappear from view. Thereís only about an hour of really good viewing time ó between the end of twilight and the time Orionís stars begin to set. And that viewing window gets shorter by the night. In a couple of weeks, itíll be hard to see the constellation at all.

Fortunately, though, thereís still a lot to look at after Orion passes from view. And the hunter wonít stay gone forever. Heíll begin to climb into the morning sky in August ó and will return to the evening sky during the long, chilly nights at yearís end.

Script by Damond Benningfield

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Moon and Venus

Sat, Apr 22, 2017

The two brightest objects in the night sky team up at dawn the next couple of days: the Moon and the planet Venus. Venus stands close to the left or upper left of the crescent Moon tomorrow, and a little to the upper right of the Moon on Thursday. Venus is the brilliant ďmorning star.Ē

The planet has no moons of its own, although for a couple of centuries it seemed that it might. From the late 1600s to the late 1700s, many astronomers reported seeing a moon close to the bright planet. Some of those astronomers were among the best observers of their time, so others took the sightings seriously.

But the sightings were sporadic. And it was impossible to combine them all to calculate an orbit for the possible moon, so the subject fizzled out for a while.

Then, in 1884, another astronomer thought he had a solution. The sightings werenít a moon, he decided, but a small planet. Its orbit was synchronized with Venusís in such a way that they appeared close together once every three years. He named this rarely seen world Neith, after an Egyptian war and sky goddess who was sometimes known as the veiled goddess.

A few years later, though, the veil was lifted for good. A thorough analysis of all the sightings found that there was neither moon nor planet. Instead, they were all sightings of stars that just happened to line up close to Venus ó simple coincidences. The subject was closed ó and our closest neighbor world remained moonless.

Script by Damond Benningfield

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Through the Gap

Fri, Apr 21, 2017

An amazing mission of discovery is scheduled to enter its final phase tomorrow. Cassini, which has been orbiting the giant planet Saturn since 2004, will change its flight path. The new course will take the craft between Saturnís cloudtops and the inner edge of its beautiful rings.

Cassini has studied the rings in great detail during its journey. Itís found that the system consists of hundreds or thousands of individual rings. Most of the particles in the rings are made of ice, with a smattering of rock and dust.

Cassini has also discovered many small ďmoonletsĒ in the gaps between rings. These bodies are like shepherds tending their flocks; their gravity keeps the ring particles in their proper place.

The innermost ring is fairly thin and faint. Its inner edge reaches to within just a few thousand miles of Saturn itself. Bits of material from this ring probably drop into Saturnís atmosphere, where they burn up as meteors.

To protect itself against possible impact, Cassini will use its large radio dish as a shield as it plunges through the plane of the rings. That should keep its instruments and electronics safe.

Tomorrow, Cassini will fly close to Titan, Saturnís biggest moon. Thatíll change Cassiniís path, setting up its first loop inside the rings next week. Itíll make 21 more passages over the next five months, leading up to its final act in September: a fatal dive into Saturnís atmosphere, bringing its mission to an end.

Script by Damond Benningfield

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Last Visit

Thu, Apr 20, 2017

The Cassini spacecraft has been orbiting Saturn for almost 13 years. During that time, itís made many visits to the giant planetís moons. Itís paid special attention to the biggest moon, Titan, passing less than a thousand miles from it dozens of times. And on Saturday, itíll make one final pass by the big moon ó its final close encounter with any of Saturnís moons.

Titan is veiled by smog ó an orange haze that makes it impossible to see the surface. But Cassini has viewed the moon at wavelengths that are invisible to the eye. Those wavelengths pass through the haze, allowing Cassini to study the surface in detail.

Among other things, those observations have revealed sand dunes that can be hundreds of miles long, and lakes and seas that are filled with liquid hydrocarbons. The largest is bigger than Lake Superior. Occasional rains may fill rivers, which then flow into the lakes and seas.

Cassini has also given us hints of even more liquid far below Titanís surface ó an ocean of water mixed with ammonia. It could be many miles thick, and contain far more water than in all of Earthís oceans.

Cassini will fly about 600 miles above Titan on Saturday, giving scientists a farewell look at the intriguing moon. As a bonus, Titanís gravity will reshape Cassiniís orbit, placing it on a course thatíll carry the craft between Saturn and the inner edge of its rings ó beginning the final phase of its lifetime of discovery. More about that tomorrow.

Script by Damond Benningfield

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Wed, Apr 19, 2017

For sheer grandeur, no astronomical object beats a spiral galaxy. And one of the grandest of them all climbs high across the sky on spring nights: Messier 100. We see it face-on, providing an amazing view of its delicate spiral arms.

The galaxy is one of the leading members of the Virgo Cluster ó a couple of thousand galaxies that travel through the universe together.

M100 is bigger and more massive than our home galaxy, the Milky Way. But like the Milky Way, itís a wide, flat disk. Waves ripple through the disk, squeezing clouds of gas and dust and causing them to give birth to new stars. Many of the newborn stars are especially hot and bright, so they outline the waves, forming the spiral arms.

M100 has another thing in common with the Milky Way: It has a couple of smaller companion galaxies. The gravity of these galaxies is tugging on M100. That may be responsible for a slight offset in one side of the spiral, making at least one of the spiral arms look a bit deformed.

A couple of decades ago, Hubble Space Telescope discovered some stars in the galaxy that are good mile markers. That allowed astronomers to make a good measurement of M100ís distance: about 56 million light-years.

And a small telescope reveals M100 shining from that great distance in the corner of the constellation Coma Berenices, near Virgo. A slightly bigger telescope begins to reveal its great beauty ó a grand spiral galaxy whirling through the cosmos.

Script by Damond Benningfield

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Virgo Cluster

Tue, Apr 18, 2017

Galaxies donít like to be alone. They congregate in clusters ó collections of a few dozen to a few thousand of them, all bound by their mutual gravitational pull. Our own galaxy, the Milky Way, belongs to a small cluster known as the Local Group.

The nearest big cluster is about 50 million light-years away. Itís in the constellation Virgo, so itís known as the Virgo Cluster. It contains a couple of thousand galaxies.

Most of them are puffballs ó dwarf galaxies that are only a fraction the size and mass of the Milky Way. But a few are giants ó theyíre the size of the Milky Way or bigger, and some may contain dozens of times as many stars as the Milky Way.

The Virgo Cluster is at the center of a much larger collection of galaxies: the Virgo Supercluster. It includes several clusters that move through space as a unit, tied together by gravity. Membership includes the Local Group, which is on the superclusterís outskirts. Weíre becoming more tightly integrated into the supercluster, though, as the Local Group is pulled toward the Virgo Cluster.

And itís easy to spot the clusterís location right now. Itís high in the east and southeast at nightfall. Itís roughly between the planet Jupiter, which is the brightest object in the sky at that hour, and the tail of Leo, the lion. Binoculars reveal a few of the galaxies as hazy smudges of light, while a small telescope brings several galaxies into sharper view.

More about the Virgo Cluster tomorrow.

Script by Damond Benningfield

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Mon, Apr 17, 2017

There are lots of ways to think of galaxies. We might look at them as cosmic cities, each with a densely populated ďdowntownĒ and more thinly settled suburbs. More poetically, we might think of them as ďisland universesĒ ó collections of stars, gas, and all the other stuff that makes up the universe, all in one big, bright, beautiful package.

However you look at them, galaxies are the biggest individual objects in the universe. They contain anywhere from a few million stars to trillions. And they span anywhere from a few thousand light-years to a million or more.

These giant agglomerations are dynamic ó they grow and evolve. Their clouds of gas and dust collapse to give birth to stars, for example. That can happen steadily, like the drip of a leaky faucet ó just whatís happening now in our home galaxy, the Milky Way. Or it can happen in a hurry, like the rush of a fire hose ó usually when two galaxies interact with each other ó passing close to each other, or even merging.

In fact, big galaxies like the Milky Way probably got so big through mergers. In the early universe, most galaxies were pretty small. They were packed together so tightly, though, that their gravity pulled them together. Today, big galaxies continue to grow by gobbling up smaller ones; the Milky Way is ingesting several right now.

Gravity also holds together big groups of galaxies, known as clusters. And weíll talk about one of the most impressive clusters tomorrow.

Script by Damond Benningfield

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Sun, Apr 16, 2017

Most stars consist almost entirely of hydrogen and helium, the lightest and simplest chemical elements. But thereís a smattering of other ingredients as well ó everything from oxygen to platinum. These elements can be tough to detect, though. For one thing, thereís not much of them ó they add up to only a fraction of one percent of all of a starís atoms. And for another, theyíre usually concentrated deep inside the star, where theyíre hidden from astronomical instruments.

But one class of stars likes to show off some of those elements. The stars in this class all have about the same surface temperature ó theyíre much hotter than the Sun.

Theyíre known as mercury-manganese stars, because they can show concentrations of these and similar elements that are thousands of times greater than in other stars.

They donít really have more of these elements, though. Instead, more of the elements have been dredged up from deep inside. Radiation from the starís core may push these elements to the surface, where astronomers can see them. On the other hand, gravity pulls other types of elements toward the core, so the stars show unusually low levels of them.

One good example of a mercury-manganese star is known as Gienah. Itís the brightest star of Corvus, the crow. The constellation is in the southeast as night falls, and due south around midnight. Its brightest stars form the outline of a small sail. Gienah is at the top right corner of the sail.

Script by Damond Benningfield

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Moon and Saturn

Sat, Apr 15, 2017

Saturn follows the Moon across the sky late tonight. The planet looks like a bright star, and perches close to the lower left of the Moon at first light tomorrow.

The Moon is in its ďgibbousĒ phase now. That means that sunlight illuminates more than half of the hemisphere that faces our way.

The portion thatís in view offers a good look at the contrast between the two main landforms on the Moon: the dark ďseasĒ and the lighter highlands.

As the name implies, the highlands are generally at a higher elevation than the seas. Theyíre the fractured remains of the Moonís original crust. They consist mainly of a mineral known as anorthosite. Itís not very heavy, so when the Moon formed, it floated to the top. It contains a lot of calcium, which is why it has a lighter color.

Over the eons, impacts by space rocks blasted the crust, churning it up ó like pounding the tiles on your kitchen floor with a hammer. That created a jumbled landscape of hills, mountains, canyons, and other dramatic features.

Some of the biggest impacts blasted holes all the way through the crust, or created deep cracks in the crust. That allowed molten rock to bubble up from below, forming volcanic plains. This rock, known as basalt, contains a higher concentration of dark materials, so the plains look dark. They reminded long-ago skywatchers of bodies of water, so they were called maria, the Latin word for ďseasĒ ó dark seas of rock on the surface of the Moon.

Script by Damond Benningfield

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Rio Scale

Fri, Apr 14, 2017

Weather forecasts tell us the odds that itíll rain tomorrow. Betting lines tell us the odds that one team will beat another. And the Rio Scale tells us the odds that a possible signal from ET is either the real thing or just wishful thinking.

Scientists developed the Rio Scale almost two decades ago, after reports of the discovery of intelligent signals from another star turned out to be a hoax. The scientists wanted an easy way to rate the odds that a possible discovery was the real deal ó not only for themselves, but for the media and public as well.

So during a conference in Rio de Janeiro, Jill Tarter and Ivan Almar devised a rating system. It evaluates two main factors. One is the importance of a possible discovery. A signal from a star a few light-years away ó one we could communicate with over a human lifetime ó rates higher than a signal from a star across the galaxy.

The other factor is the credibility of any reported discovery. A signal thatís been detected several times by reputable institutions would get a higher rating than a signal heard by a guy with a backyard radio dish.

When those two factors are combined, they produce a number from zero to 10. Right now, the only discovery that rates as high as a 3 or 4 is Tabbyís Star ó an odd system in which many objects routinely pass in front of the star, blocking some of its light. That doesnít mean ET is there, only that itís worth doing some more looking ó just in case.

Script by Damond Benningfield

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Three Venuses

Thu, Apr 13, 2017

Venus is just beginning its long reign as the ďmorning star.Ē Itís quite low in the east as dawn begins to color the sky. Itís so bright, though, that if you have a clear horizon, itís easy to pick out. Itíll remain in good view in the morning sky until after Thanksgiving.

Despite its beauty, Venus is a hellish world. Surface temperatures are hot enough to melt lead, and the atmosphere is dense and toxic. Thereís nothing else like it in the solar system. But Venus-like worlds may be common in other star systems. In fact, a recent study found a system that could have two Venuses.

Wolf 1061 is just 14 light-years away ó closer than all but a few dozen other stars. Yet itís only one percent as bright as the Sun ó so faint that you need a telescope to see it.

Three planets are known to orbit the star. All three probably are rocky worlds a bit bigger and heavier than Venus and Earth. One of them is so close to the star that itís almost certainly like Venus. Another follows an orbit thatís so stretched out that the planet is quite hot for part of its year, and quite cold for the rest.

A third planet appears to spend about two-thirds of its year inside the habitable zone ó the distance from the star where temperatures are just right for liquid water. But it spends the rest of the time closer than the habitable zone, where itís hot. That may trigger conditions like those on Venus ó keeping all three worlds of Wolf 1061 too uncomfortable for life.

Script by Damond Benningfield

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Planetary Gems

Wed, Apr 12, 2017

If you love gemstones, scientists have discovered a couple of worlds that might be just right for you. One of them probably has a layer of garnet below its crust. And the other may have clouds composed of the mineral that makes up rubies and sapphires.

Kepler 407b is a dense, rocky world like Earth. Itís about the same size as Earth, but up to three times heavier. It orbits a star thatís almost identical to the Sun.

Astronomers looked at the chemical composition of the star. They then worked with geophysicists to estimate the composition of the planet. Their work suggested that Kepler 407b could have a layer thatís made mainly of garnet.

The other planet is HAT-P-7b. Itís bigger and heavier than Jupiter, the giant of our own solar system. But itís only a few million miles from its star. At that range, the planet is not only extremely hot, but itís locked so that the same hemisphere always faces the star.

Like Jupiter, the planet is probably a big ball of gas, with clouds atop its atmosphere. Although no one has seen the clouds, they have detected bright spots moving across the planet ó cloud banks moving from the nightside, where they form, to the hotter dayside.

Those clouds are so hot that they probably are made of solid particles, including the mineral that makes up rubies and sapphires. As the clouds move into daylight, those particles ďrainĒ back into the giant planetís atmosphere ó a shower of gems on a distant world.

Script by Damond Benningfield

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Moon, Jupiter, and Spica

Tue, Apr 11, 2017

The Moon is just past full this evening. Sunlight illuminates all but a sliver of the lunar hemisphere that faces our way, so the Moon is bright and beautiful. And it has a couple of bright, beautiful companions. The star Spica stands to its upper right, with the brilliant planet Jupiter above Spica.

If you look at the Moon, youíll see the same features that are always in view ó dark volcanic plains and lighter-colored highland regions. Theyíre the same features youíll see tomorrow night, and a month from now, and a hundred years from now.

Since the same side of the Moon always faces our way, you might think that the Moon doesnít turn on its axis. But thatís not the case. In fact, if it didnít turn weíd see the entire Moon ó the familiar near side and the hidden far side. Instead, itís the rate at which it turns that keeps it aiming our way.

Over the eons, Earthís gravity created tides in the lunar surface. That slowed the Moonís rotation. Eventually, it slowed enough that the same side always faces our way. So the Moon turns on its axis at the same rate at which it orbits Earth. By the time itís moved a quarter of the way around us, itís also completed a quarter turn on its axis, and so on.

The Moon, of course, creates tides in Earthís oceans, which are slowing its rotation. So if Earth and Moon are around long enough, then just as the same hemisphere of the Moon always faces Earth, the same hemisphere of Earth will always face the Moon.

Script by Damond Benningfield

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Moon and Jupiter

Mon, Apr 10, 2017

How long does it take to give birth to a giant?

If the giant happens to be Jupiter or Saturn, about four million years, according to a recent study. Not only that, but the giant planets passed through their period of youthful wanderlust in that same time, settling pretty much where they are today by the end of it.

Researchers at MIT studied meteorites that are more than 4.6 billion years old, which means they were around during the solar systemís formation. The older of these meteorites preserve traces of a magnetic field that permeated the early solar system. But those that are a bit younger show almost no magnetic field.

According to the researchers, that means the solar nebula ó the cloud of gas and dust that gave birth to the planets ó lasted no more than four million years. By the end of that time, the Sunís magnetic field had weakened, allowing the leftover material to dissipate.

Jupiter and Saturn grew so large in part by sweeping up vast amounts of material in the nebula. When the nebula vanished, they stopped growing.

And the gravity of the nebula had caused the giants to move inward and then back out ó a process that also stopped when the nebula went away. That left Jupiter and Saturn pretty much at their current distances from the Sun.

And Jupiter is in great view tonight. The planet is shining at its brightest for the year. And itís quite close to the full Moon, so you canít miss it.

More about Jupiter and the Moon tomorrow.

Script by Damond Benningfield

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Sun, Apr 9, 2017

Astronomers and friends are gathering at McDonald Observatory in West Texas today to celebrate a major upgrade to the giant Hobby-Eberly Telescope. Over the last few years, much of the telescopeís optics and instruments have been replaced. Thatís providing a wider look at the night sky, and allowing the telescope to use more of its main mirror. All of that enhances HETís scientific capabilities, allowing astronomers to tackle new projects.

One of those projects is HETDEX ó the Hobby-Eberly Telescope Dark Energy Experiment. Itís measuring the properties of a million galaxies that are roughly 11 billion light-years away. That means the telescope is seeing those galaxies as they looked when the universe was quite young.

The projectís goal is to see how the rate at which the universe is expanding has changed over the eons.

All but a few galaxies are moving away from us ó the result of the expansion of the universe itself caused by the Big Bang. A couple of decades ago, astronomers discovered that the universe is expanding faster as it ages. That extra kick has been credited to ďdark energy.Ē But just what dark energy is remains a mystery. It could come from the vacuum of space, or from one of several other possible explanations.

By looking at galaxies in the early universe, HETDEX will show how the rate of expansion has changed over time. That will help theorists narrow down the range of possibilities ó and perhaps solve the mystery of dark energy.

Script by Damond Benningfield

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Dark Energy

Sat, Apr 8, 2017

Itís been almost a century since astronomers discovered that the universe is expanding ó a result of the Big Bang in which it was born. But the details of that expansion are still being uncovered. In particular, astronomers are studying a phenomenon that appears to make the universe expand faster as it ages. Itís known as dark energy, and figuring it out is one of the great challenges of modern-day physics.

Astronomers discovered dark energy by measuring the speeds at which distant galaxies are moving away from us. That allowed them to plot how fast the universe was expanding at different times. They expected to find that the expansion rate was slowing down ó the result of the gravitational pull of all the galaxies and dark matter.

Instead, they found that things are actually speeding up ó the universe expands faster as time goes by.

So far, the cause of that faster expansion is still a mystery. Dark energy could be caused by an energy from the vacuum of space itself. It could also mean that our understanding of gravity is wrong ó or at least incomplete. Or there could be some other explanation.

Several experiments are studying how the universe is expanding to try to solve the mystery. That includes a project at McDonald Observatory. HETDEX ó the Hobby-Eberly Telescope Dark Energy Experiment ó is measuring galaxies that are billions of light-years away, when the universe was young. Weíll have more about that tomorrow.

Script by Damond Benningfield

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Jupiter at Opposition

Fri, Apr 7, 2017

One of the brightest objects in the night sky is especially bright right now. Thatís because Jupiter is at opposition ó itís lining up opposite the Sun. Itís closest to us now, and more of its light is reflected back in our direction, so it shines at its absolute best.

Jupiter is the largest planet in the solar system ó about 11 times the diameter of Earth. And the clouds that top its atmosphere reflect a lot of sunlight. But even at its closest, itís about 400 million miles away. That combination makes Jupiter the third-brightest object in the night sky ó behind the Moon and the planet Venus.

It takes Jupiter more than 12 years to make one orbit around the Sun, which means it also takes it that long to complete one circuit against the background of stars. As a result, it spends an average of about a year in each constellation it crosses.

As Jupiter orbits the Sun, Earth is doing the same thing. Our orbit is much smaller, though, so it takes us much less time to make one turn around the Sun. Itís as if weíre on the inside lane of a race track, with Jupiter on the outside lane. It takes about 13 months for Earth to catch up to Jupiter and move past it, so thatís the gap between oppositions. In other words, the next opposition will be about 13 months from now ó next May.

For now, look for Jupiter quite low in the east as night falls, and climbing across the south later on. It looks like a brilliant star.

Script by Damond Benningfield

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Moon and Regulus

Thu, Apr 6, 2017

Regulus, the bright star that marks the heart of the lion, is a lot older than it looks. Until about a decade ago, astronomers estimated its age at no more than a hundred million years. But the discovery of a dead companion star changed things. Today, the best estimate is a billion years.

In most cases, astronomers determine a starís age by comparing its mass, its temperature, and its total brightness. Regulus is several times as massive as the Sun, thousands of degrees hotter, and hundreds of times brighter. Crunch the numbers, and that indicates a vigorous young star.

In this case, though, the numbers donít tell the whole story. Thatís because Regulus has a close companion ó a tiny stellar corpse known as a white dwarf. Itís so small, faint, and close to Regulus that itís impossible to see directly. Instead, it was discovered with the help of sensitive instruments.

When Regulus and the companion were born, the companion was the heavier of the two stars. That means it aged more quickly. As it aged, it got much bigger, so it began dumping the gas in its outer layers onto the surface of the star we see as Regulus. That made Regulus much bigger and heavier. In turn, that revved up the nuclear reactions in its core, making the star bluer and brighter. That change disguised the starís true age: a billion years or older.

Look for Regulus tonight just a whisker away from the Moon ó a bright star thatís older than it looks.

Script by Damond Benningfield

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Quiet Sun

Wed, Apr 5, 2017

The Sun goes through an 11-year magnetic cycle. At the cycleís peak, the Sun produces large numbers of dark sunspots and powerful explosions known as solar flares. At the cycleís low point, the Sun is quiet, with little activity on its surface.

But no two cycles are alike. Some are especially active, while others are unusually quiet. And some of the quietest yet identified may have happened 7500 years ago.

An international team of scientists found this quiet period by studying tree rings. When the Sun is quiet, it allows more cosmic rays to enter the solar system. These particles come from exploding stars and other powerful sources. When they hit Earthís atmosphere, they trigger showers of other particles. And when those particles reach the ground, they can alter atoms.

In particular, they can change carbon atoms to a radioactive form known as carbon-14. So the ratio of normal carbon to carbon-14 found in tree rings varies based on the amount of solar activity.

The new study found some of the highest levels of carbon-14 yet discovered in the rings of bristlecone pines from the White Mountains of California. The levels were especially high from about 5490 to 5460 BC.

That could mean that the Sun was especially quiet during that period. If thatís the case, then almost no sunspots would have mottled its surface. That would have allowed the cosmic rays to flood into the solar system and hit Earth ó leaving traces in ancient trees.

Script by Damond Benningfield

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Event Horizon Telescope

Tue, Apr 4, 2017

Astronomers have cataloged thousands of black holes. Some of them are the remnants of collapsed stars. Others, found in the hearts of galaxies, are millions or billions of times the mass of the Sun. Yet so far, no one has actually seen even a single black hole.

In part, thatís because black holes produce no energy at all. And theyíre also tiny targets; a black hole thatís a hundred times the mass of the Sun is only a few hundred miles in diameter. Supermassive black holes are much bigger, but theyíre so far away that theyíre too small for current telescopes to see.

So astronomers infer the presence of black holes from their effects on the visible matter around them. They discovered the black hole at the center of the Milky Way in part by plotting the orbits of the stars that are close to it. The speeds of those stars mean theyíre being pulled by something thatís heavy, but smaller than our own solar system.

Astronomers are hoping to actually see that black hole soon. Theyíre combining a dozen radio telescopes across the globe to create the Event Horizon Telescope. Itíll look at the center of the galaxy to try to see the event horizon ó the boundary between the black hole and the space around it. That technique could allow them to see the black hole, which would look like a silhouette against the background of stars and gas, with a thin ring of light around it.

The first observations are scheduled for this month ó an attempt to see a black hole.

Script by Damond Benningfield

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Event Horizon

Mon, Apr 3, 2017

A black hole doesnít have a ďsurfaceĒ ó thereís nothing for you to crash into. Instead, it has a boundary ó a point of no return for matter and energy. Anything that crosses the boundary is trapped forever inside the black hole.

That boundary is known as the event horizon. Itís the distance from the center of the black hole at which escape velocity ó the speed you need to get away from it ó equals the speed of light. Since nothing can travel faster than light, nothing within that distance of the black holeís center can get away. So the event horizon looks like a black hole in space.

The size of the event horizon depends entirely on the mass of the black hole. For a black hole as massive as the Sun, the event horizon would span about three and a half miles. At a million times the mass of the Sun, the black hole would be three and a half million miles in diameter, and so on.

If you approached an event horizon, things would get a little weird. As seen by an outside observer, your clock would begin to tick slower and slower. At the event horizon, it would appear to stop. So anyone watching you approach the horizon would never see you cross it. Instead, youíd appear to stand still, with the light from your spaceship shifted to longer and longer wavelengths ó just one of the strange effects around a black hole.

Even though thereís good agreement that black holes exist, no one has ever seen one. But that could change soon. More about that tomorrow.

Script by Damond Benningfield

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Vela Nursery

Sun, Apr 2, 2017

Vela, the sail of the ship that carried Jason and the Argonauts, flutters quite low across the south on these early spring evenings, but only if youíre south of about Dallas or Tucson. And even then, it contains only a couple of moderately bright stars, so thereís not much to see.

If we could view that region in a few million years, though, it would be a different story. Several giant clouds of cold gas and dust appear to be giving birth to new stars. And some of those stars could be big, heavy, and extremely bright.

The biggest of these clouds is known as Vela C. Itís about 2300 light-years away, and more than a hundred light-years wide. In all, itís more than 50,000 times as massive as the Sun.

Most of that mass is still in the form of gas and dust. But the cloud is splitting into smaller clumps of material. Gravity is causing the clumps to collapse. Eventually, some of them will condense enough to become new stars, making Vela C a stellar nursery.

In fact, thereís evidence that itís already given birth to some stars. Theyíre extremely young ó no more than a million years old, and probably a good bit younger. Itís hard to see them because theyíre still embedded in cocoons of dust, which absorb most of their light.

Some of these stars are quite massive ó perhaps 10 or more times the mass of the Sun. So when the dust around them clears away, theyíll shine thousands of times brighter than the Sun ó lighting up the celestial sail.

Script by Damond Benningfield

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Seeing Orange

Sat, Apr 1, 2017

Two colorful stars accompany the Moon down the western sky this evening. Aldebaran, the eye of the bull, is to the lower right of the Moon. And slightly brighter Betelgeuse, the shoulder of Orion, is a little farther to the left of the Moon.

If you look closely, youíll notice that both stars are orange ó two rare specks of color in the night sky. The color is a function of their surface temperatures. Both stars are thousands of degrees cooler than the surface of the Sun. Cool stars shine red or orange, while hot stars shine blue or white. Yellow stars like the Sun are in the middle of the temperature scale.

The surfaces of Aldebaran and Betelgeuse are cool for the same reason: the stars are huge.

Both stars are nearing the ends of their lives. Theyíve undergone dramatic changes in their cores, causing them to puff up. As the stars expanded, the gas at their surfaces got cooler ó and redder.

Aldebaran is more than 40 times the diameter of the Sun, so itís classified as a giant. Betelgeuse, on the other hand, is more massive than Aldebaran, so itís inflated even more ó itís almost a thousand times the Sunís diameter, which makes it a supergiant.

A few billion years from now, the Sun will puff up as it nears the end of its life. Itís not massive enough to reach anywhere close to the proportions of Betelgeuse. But it will resemble present-day Aldebaran ó a giant star shining bright and orange.

Tomorrow: Sailing to a nursery.

Script by Damond Benningfield

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Moon and Aldebaran

Fri, Mar 31, 2017

The Moon goes nose to nose with the bull this evening. It stands just below the V-shaped pattern of stars that outlines the head of Taurus the bull. The brightest member of that pattern is Aldebaran, the bullís orange eye. The other members of the V, including the one at the nose, all belong to the Hyades, one of the most prominent star clusters in the sky.

Aldebaran looks so impressive because itís a stellar giant. Itís at the end of its life, so itís puffed up to many times its original size. Itís dozens of times wider than the Sun, and hundreds of times brighter.

Several of the stars of the Hyades are also giants. They donít look as impressive as Aldebaran, though, in part because theyíre more than twice as far away.

One of those giants is Gamma Tauri, the star that marks the bullís nose. Itís heavier than Aldebaran, but not quite as big or bright. That may be because the two stars are in different phases of their ďgianthood.Ē

Aldebaran has converted the original hydrogen fuel in its core to helium. Now, itís getting ready to burn the helium to make even heavier elements. Changes in the star during this transition have caused it to expand and brighten.

When it starts burning the helium, itíll get a little smaller and fainter ó and thatís the stage that Gamma Tauri is already in. Itís still big and bright, but not as big and bright as it once was. But itíll puff up again when the helium is gone ó giving the bull a big, bright nose.

Script by Damond Benningfield

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Moon and Mars

Thu, Mar 30, 2017

Mars is cold and dry, and its air is a bare wisp compared to Earthís air. Thatís not an especially comfortable environment for life. But itís not an impossible one, either. Life on Earth can survive in conditions that are pretty inhospitable. So itís possible that microscopic organisms could live below the Martian surface, perhaps in underground pools of water.

A recent study found that some of the simplest organisms on Earth could survive Mars-like conditions. That doesnít mean weíll actually find life on Mars ó only that we canít rule it out.

Scientists at the University of Arkansas tested several species of methanogens ó microbes that produce methane. Observations have revealed traces of methane in the Martian atmosphere. They might come from geologic processes, but they could also be produced by life.

The scientists exposed the methanogens to conditions similar to those found below the Martian surface ó similar chemistry and pressure, for example. And they found that the organisms survived the exposure just fine. So now theyíre planning a new round of experiments thatíll factor in the Martian cold ó new tests to see if microscopic life could survive on Mars.

And Mars huddles quite close to the crescent Moon this evening. It looks like a moderately bright orange star, and stands to the lower right of the Moon as they drop down the western sky.

Weíll talk about the Moon and another orange companion tomorrow.

Script by Damond Benningfield

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Moon, Mars, and Mercury

Wed, Mar 29, 2017

Three small, rocky worlds put in an appearance this evening that makes them look more impressive than they really are. Theyíre low in the west as twilight fades away.

The brightest member of the trio is also the smallest: the Moon. Itís a beautiful crescent right now, with sunlight illuminating just five percent of the hemisphere that faces our way.

The Moon is a couple of thousand miles in diameter ó roughly a quarter the size of Earth. It probably consists of a small iron core surrounded by thick layers of lighter rock.

To the lower right of the Moon, look for Mercury, which looks like a bright star.

At about three thousand miles in diameter, Mercury is the smallest planet in the solar system. But its core is massive ó it accounts for more than three-quarters of the little planetís diameter, and more than half its mass. Mercury may have been bigger in the distant past, with a thicker layer of rock around the core. But an impact with another body might have blasted away most of that material, leaving the core undisturbed.

Finally, look farther above the Moon for Mars. Itís the biggest of the three worlds by about a thousand miles. But itís also the farthest, which makes it faint. It looks like a modest orange star.

Mars also has an iron core, although the iron is mixed with lighter elements. So even though Mars is bigger than Mercury, itís less dense ó a rocky planet with a difference.

More about Mars and the Moon tomorrow.

Script by Damond Benningfield

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