StarDate Podcast

BENEDICT: The process of science is messy... Fritz Benedict is a Texas astronomer who’s leading a team that’s studying Gamma Cephei, a system of two stars and one known planet. The goal is to find out whether all three objects orbit in the same plane — an observation that’s important to understanding the formation of all planets. The team has used Hubble Space Telescope to precisely plot the position of one of the stars as it’s pulled by its orbiting planet. That should reveal the mass of the planet — a key bit of intel in plotting the system’s layout. But while the Hubble observations were good, the overall results have been frustrating. BENEDICT: You say, ‘Whoa, that’s a nice result. I like that result. The orbit fits the data very nicely.’ Then you double check things. And the double check is to go to our friends who find out if systems are dynamically stable or not. And they come back instantly — almost within a day. ‘Bad news — this is not a stable system.’ That’s a huge red flag that we have not got the right answer. The problem is with the orbit of the two stars — something that’s crucial to measuring the position of the target star. But the stars take so long to orbit each other that the researchers have had to rely on plots made over many decades. But those plots give results that don’t make sense. So the astronomers will need continued observations of Gamma Cephei to better plot the orbits of the two stars. Only then will they know how the system is laid out — a bit of stellar geometry that’ll help explain the formation of all planetary systems. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Astronomers have discovered hundreds of planets in other star systems. Now they’re trying to use those planets to find out how all planets are born. One thing they want to know is whether all planetary systems are laid out like our own — whether the planets orbit their parent stars in the same plane, as though they were all rolling around a table top. A team led by Texas astronomer Fritz Benedict is using Hubble Space Telescope to study the layout of several systems. One of them is Gamma Cephei. It consists of two stars, plus a planet orbiting the larger star. BENEDICT: All my theoretician friends say, ‘Oh, pooh, Fritz, you shouldn’t even bother because it has to lie on the same tabletop, otherwise this system is unstable — it wouldn’t last for longer than 10,000 years or something.’ Even so, the astronomers observed the system from 2008 to 2010. They were looking for a tiny “wobble” in the position of the larger star, caused by the tug of the planet. But the wobble is tiny, so isolating it is quite a chore. For one thing, Gamma Cephei is moving across the sky as it orbits the center of the galaxy. For another, it’s quite close — only 45 light-years away — so as Earth orbits the Sun, the star shifts position with respect to the background of distant stars. And for yet another, the star also moves as it and its companion star orbit each other. In fact, measuring that orbit has proved to be a big headache. We’ll explain why tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The art and science of astrometry is all about making precise measurements of tiny angles in the sky. Those angles are often described with analogies. Measuring a given angle might be like measuring the size of a quarter held 1500 miles away, or the width of a gnat’s eyelash from opposite shores of Lake Gitche Gumee. But that eyelash can be critical — it can tell us a lot about a star and its environment. Consider Gamma Cephei, which is about 45 light-years away, in the northern constellation Cepheus. It consists of two stars and one known planet. But the technique that was used to discover the planet doesn’t reveal its mass. Nor does it reveal how the system is laid out — whether all three objects move in the same plane, as though they were all on a tabletop. That measurement is important for understanding how all planetary systems were born, including our own. A team led by Texas astronomer Fritz Benedict has been using Hubble Space Telescope to plot the position of the larger of Gamma Cephei’s stars, which is the one with the planet. The star is pulled back and forth a tiny bit by the planet’s gravity. Measuring that shift, along with the orbit of the two stars, will reveal the mass of the planet and the system’s layout. Even with Hubble, though, it’s a tough measurement to make. The researchers have to account for a lot of other motions — some of which aren’t so easy to isolate. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The constellation Cepheus, the king, circles high across the northern sky on September nights. Its brightest stars form a shape that looks like a child’s drawing of a house, with a square topped by a triangle. It’s upside down during the evening, but turns over as it wheels around the sky during the night. The star at the top of the roof is actually a system of two stars, plus at least one planet. Gamma Cephei is 45 light-years away. Its primary star is larger and more massive than the Sun, and farther along in its life cycle. It’s used up the hydrogen in its core, and is now beginning to burn the helium that it created through billions of years of nuclear fusion. As a result, it’s puffing up to form a red giant. Gamma Cephei’s other star is a red dwarf, which is far smaller, cooler, and less massive than the Sun. Because of its low mass, it will continue to shine for billions of years after its heftier companion expires. The planet orbits the larger star once every two-and-a-half years. Astronomers discovered it by measuring a tiny “wobble” in the star’s light, which is caused by the planet’s gravitational pull. This technique shows that the planet is at least twice as massive as Jupiter, the largest planet in our own solar system, and perhaps a good bit larger. Over the last few years, a team has been trying to get a more precise measurement of the planet’s mass, as well as the exact layout of the Gamma Cephei system. They’re using a technique that precisely measures the position of the planet’s parent star in the sky. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The calendar makers of ancient Rome just ran out of gas. They named the first eight months of the year for gods and goddesses, or for emperors with godly ambitions. But after that, all they could come up with were numbers indicating a month’s position in the year. September, for example, means seventh month. Now you’ve no doubt noticed that September is actually the ninth month of the year. But in the original Roman calendar, the year began in March, and lasted only 10 months. January and February were added later. In other cultures, the calendar year began at different times. In ancient Egypt, for example, it started in July, when Sirius returned to view in the morning sky. Sirius is the brightest star in the night sky. And more importantly to the Egyptians, it returned to view about the same time that the Nile began its annual life-giving floods. Using Sirius as a marker, the Egyptians established the first 365-day calendar. Later, they added leap days to keep the calendar in sync with the true seasons. Much later, the Romans were fussing with a calendar that was a great big mess. Its months didn’t add up to a full year, so extra days or months were added at whim. In 46 B.C., Julius Caesar ordered a reform of the calendar. Rome adopted the 365-and-a-quarter-day year of its newly conquered province of Egypt, but kept the Roman names for the months — including September, the seventh month that’s really the ninth. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Certain astronomical events happen just once in a blue moon. We had a couple of those events earlier this year — an annular solar eclipse in May, and a transit of the planet Venus across the face of the Sun in early June. And tomorrow we’ve got another. Appropriately enough, it’s a Blue Moon. There are all kinds of definitions for Blue Moon. It can literally mean that the Moon looks blue, which can happen when certain types of smoke particles enter the upper atmosphere. It can also refer to the fourth full Moon in a three-month period, or to the 13th full Moon in a calendar year. All of these occurrences are rare, hence the phrase “once in a blue moon,” meaning something that happens infrequently. But over the last quarter-century or so, it’s taken on an entirely new meaning — the second full Moon in a calendar month. The Moon was full on the night of August 1st as measured here in the United States, and it’s full again tomorrow, at 8:58 a.m. Central Daylight Time — hence, a Blue Moon. Even though the second-full-Moon-in-a-month definition isn’t old, it certainly maintains the spirit of the older definitions. Full Moons are separated by about 29-and-a-half days, so it’s difficult to squeeze two of them into a single calendar month. On average, that happens just once every 27 months. By just about anybody’s reckoning, that’s rare — something that happens once in a blue moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Two legendary “rivals” are sharing the southwestern quadrant of the evening sky. Although they’re a good distance apart, they’re pretty easy to pick out because they’re both bright orange. The most famous member of the rivalry is the planet Mars. It’s low in the west-southwest as night falls, and it forms a triangle with two other bright objects to its right — the planet Saturn and the star Spica. Mars’s rival is far to its upper left: Antares, the brightest star of Scorpius, the scorpion. It’s almost exactly the same color and brightness as Mars, so the two really do look like a matched set. In fact, the “rivalry” comes from that physical resemblance. Mars reminded ancient skywatchers of the color of blood, so they named the planet for the god of war — Mars in Rome, and Ares in Greece. And since the star in Scorpius looked so much like Mars, it was called Ant-Ares — a name that means “rival of Ares” or, in the Roman version, rival of Mars. It’s a one-sided rivalry, though. Mars is quite small — only about half as big as Earth. It shines by reflecting sunlight, and gets its orange color from iron-rich sand and rock at its surface. Antares, on the other hand, is a supergiant star — one of the largest stars in the galaxy — thousands of times wider than Mars. Mars will move closer to Antares over the next few weeks, making the rivalry even easier to see. We’ll talk about another colorful object — a Blue Moon — tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As you gaze upon the stars in the night sky, it’s tempting to think of them as fixed neighbors — like rows of houses scattered through the galactic suburbs. But that’s not the case at all. The stars all came from somewhere else, and they’re moving at different speeds around us, so the layout of the neighborhood changes. It’s hard to tell just where each star came from, though. Some were born in the broad, thin disk of the Milky Way galaxy, just as the Sun was. Others were born just outside this disk. And still others were born in other galaxies that were swallowed by the Milky Way. One star whose origins have been a bit of a puzzle is Arcturus, the brightest star of Bootes. The bright star is well up in the west at nightfall, and shines yellow-orange. Arcturus is nearing the end of its life, so it’s puffed up to giant proportions. Although it’s about as massive as the Sun, it’s about 25 times wider, which also makes it burn brighter. Some studies have suggested that Arcturus came from another galaxy. But a study released last year came to a different conclusion. The study’s authors plotted the star’s composition, motion, and other characteristics. From that, they concluded there’s a 94 percent chance Arcturus was born in the puffy outer regions of the Milky Way, known as the “thick disk.” Over the eons, it worked its way into our region of the galaxy. As time continues to pass, though, so will Arcturus — away from Earth and out of sight. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

This is one of the best times of year to watch the Big Dipper. It’s in the northwest at nightfall, with its bowl a little below the handle. It looks as though it’s about to scoop up a big bowlful of stars. Using the bowl’s handle, you can use one of skywatching’s most famous directions to find one of the sky’s brightest stars: Arc to Arcturus. In other words, follow the curve of the handle until you come to the brilliant yellow-orange star Arcturus, which is well up in the west as night falls. It’s the brightest true star in the sky on summer evenings, and there are no other bright stars around it, so it’s hard to miss. In skylore, there’s a connection between Arcturus and the dipper. The dipper’s stars are the brightest members of Ursa Major, the great bear. And the name “Arcturus” means “the bear watcher.” As the stars rotate across the night sky, Arcturus always follows Ursa Major, so skywatchers imagined that the star was keeping an eye on the bear. There’s no real association between Arcturus and the bear, though. Arcturus is only 37 light-years away, while the seven bright stars that outline the Dipper are all at least twice that far. And for skywatchers, there’s one other important difference. Arcturus will set not long after midnight tonight. But for much of the northern hemisphere, the dipper never sets. So for awhile, the bear can roam freely — without the watchful eye of the bear watcher. More about Arcturus tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There are lots of reasons to study asteroids. There’s the purely scientific: Asteroids are leftovers from the formation of the planets, so they can tell us a lot about the materials and processes that formed our own Earth. There’s the practical: Asteroids could provide metals, ice, and other resources for future solar system explorers. And there’s the scary: Some asteroids could someday hit Earth, devastating large areas of our planet. All of those are among the motivations behind OSIRIS-Rex, a mission to study an asteroid that comes close to Earth’s orbit around the Sun. It’s scheduled to launch in 2016, and enter orbit around asteroid 1999 RQ36 three years later. At the end of the mission, it’ll scoop up a few ounces of dirt for return to Earth. RQ36 comes close to Earth’s orbit around the Sun, so it’s a potential danger, says Ed Beshore, a mission scientist: BESHORE: It is one of the most threatening of all asteroids right now. It has about, roughly a one-in-a-thousand chance of hitting the Earth late in the 22nd century. It’s about a 500- to 600-meter-wide asteroid, and because of that, if it did hit the Earth, it would actually be a pretty destructive event. It probably wouldn’t be a civilization-threatening event, but it would be catastrophic. Studying the asteroid will help refine its orbit, and help scientists ponder ways to protect Earth from future catastrophes — all while learning about the birth of the planets. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Like a sort of homeworld security force, teams of astronomers are keeping their eyes on the sky for potential deadly invaders from space. They’ve already found most of the really dangerous ones, and now they’re looking for those that are the next threat-level down. The potential invaders are asteroids with orbits that come close to Earth’s orbit around the Sun. These giant boulders could someday hit Earth, causing widespread damage. In the 1990s, Congress instructed NASA to find and plot the orbits of at least 90 percent of all the near-Earth asteroids that are one kilometer in diameter or larger — large enough to cause global damage if they hit us. And the search teams that NASA’s funded think they’ve done just that. They’ve found hundreds of objects in that category, but none on a likely collision course. Now, the search has been expanded to asteroids that are as small as 140 meters in diameter — about 450 feet. That’s big enough to cause major regional damage, but not global. Just last year, searchers found an asteroid of about that size that could hit Earth in 2040. The odds are small, but the possibility can’t be ruled out. Astronomers will look for the asteroid again next year. New measurements of its position will allow them to plot a more accurate orbit — and let us know whether our home planet could face the risk of a deadly invasion in the decades ahead. We’ll talk about a mission to a Near-Earth Asteroid tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Dawn spacecraft isn’t exactly a speedster. With its engines operating at maximum thrust, it would take about four days for the craft to accelerate from zero to 60. But what it lacks in horsepower, it makes up for in stamina — the engines can operate for years at a time, giving Dawn quite a push. They’re about to push the craft away from its first target and toward the second, where it’ll arrive in early 2015. Dawn has been orbiting the asteroid Vesta for the last year. It’s found that although Vesta’s only a few hundred miles in diameter, it’s put together like a planet, with layers of heavier material as you bore toward the center. Dawn also confirmed that several types of meteorites on Earth actually came from Vesta. Now the craft is ready to head for the largest asteroid, Ceres. It’s about twice the diameter of Vesta. And unlike Vesta, which is quite dry, there’s some evidence that liquid water could lurk below the surface of Ceres. One of Dawn’s prime objectives is to look for that water. To reach Ceres, Dawn will rely on three ion thrusters. Electricity from two large solar panels gives an electric charge to the craft’s xenon fuel. The thrusters then shoot out a stream of xenon ions — generating up to a third of an ounce of thrust. If the thrusters do their job correctly, they’ll help put Dawn in the space history books — as the first craft ever to orbit two separate bodies in the solar system other than Earth. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Vesta is one of the largest asteroids — a layered ball of rock and metal more than 300 miles in diameter. It’s also something of a scientific conundrum, notes Carol Raymond, a scientist with a mission called Dawn. RAYMOND: We’ve had pieces of Vesta under study in the laboratory for decades, but are now only getting out to know the parent body. For decades, scientists have suspected that several groups of meteorites came from Vesta — blasted from Vesta’s surface when it was hit by another asteroid. The composition of the meteorites seemed to match what astronomers could see of Vesta through telescopes. Until Dawn entered orbit around Vesta last year, though, there was little way to confirm that idea. But Dawn’s observations strongly support it. In fact, they’ve even narrowed down the likely site of the impact that chipped off the meteorites — a large basin at the asteroid’s south pole. The energy of the impact caused the asteroid’s crust to rebound, building a mountain that towers 13 miles above the basin floor. The combination of the meteorites and Dawn’s observations will help scientists better understand Vesta’s composition, structure, and history. And since Vesta is one of the oldest surviving “leftovers” from the formation of the planets, the combination will also provide new insights into the process that gave birth to the planets — including our own Earth. Dawn’s time at Vesta is almost up, though; more about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There’s quite the little traffic jam in the western sky this evening — a conjunction of the Moon, two planets, and a bright star. The entire group becomes visible as twilight fades from the sky, about 30 to 45 minutes after sunset, and drops from sight a couple of hours later. Spica, the brightest star of Virgo, is the closest of the other three to the Moon. It’s just to the upper right of the Moon, with the planet Saturn above it. The other planet, Mars, is to the upper left of the Moon. The Moon is a pretty thin crescent — sunlight illuminates only about 20 percent of the lunar hemisphere that faces our way. As the sky darkens, though, the rest of the lunar disk is clearly visible — lit up by sunlight reflecting off of Earth. It gives the Moon a ghostly glow. In fact, if you were standing on the Moon and looking back this way, you’d see a big gibbous Earth in the sky. As the hours rolled by, you’d see Earth turning on its axis, with new continents and oceans rotating into view. And as the days rolled by, you’d see the illuminated fraction of Earth grow smaller and smaller. What you wouldn’t see is Earth moving across the sky. Because the same side of the Moon always faces Earth, from any given point on that hemisphere, Earth would remain at the same place in the sky, so you wouldn’t see Earth rise and set. For that, you’d have to travel around to the lunar farside, and watch Earth set as you moved out of view. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

[SFX: voyager01] Sometime in the far distant future, the captain of an alien starship may listen to that sound and wonder about its creators. The sound is encoded in gold-plated phonograph records carried by a pair of American spacecraft. The first of them, Voyager 2, was launched 35 years ago today. Voyager 2 and its twin, Voyager 1, which was launched a couple of weeks later, were designed to explore the outer planets of the solar system. Each of them flew past Jupiter and Saturn, with Voyager 2 continuing to Uranus and Neptune — still the only craft to visit the solar system’s two outermost planets. Yet the journey isn’t over. Both craft are probing the boundary between the Sun’s realm and interstellar space. They should continue to beam back new findings for perhaps another decade, as they cross that boundary and leave the solar system behind. After that, they will cruise silently through the interstellar void, occasionally passing within a light-year or so of another star. And just in case they’re ever found, the Voyagers carry information about the civilization that built them — pictures and sounds from planet Earth, including greetings in several languages — greetings from the people who launched two ambitious voyagers. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.