StarDate Podcast

If you’re looking for a place to settle down, it’s all about the location. And that’s the case whether you’re changing addresses or changing worlds. Colonists on the Moon, for example, would want a spot with a good view of home and easy access to power and raw materials. Two locations probably fill all of those requirements: the north and south poles. In particular, deep craters with tall rims could provide everything a settler would need. The tall rim would offer a non-stop view of the Sun, with no nighttime. So banks of solar arrays could track the Sun across the sky. With no night and no clouds, that would provide non-stop power. The rim would also provide a good line-of-sight to Earth, offering good communications with home. The deep part of the crater would be equally important. Orbiting spacecraft have detected big deposits of frozen water deep inside many craters at the lunar poles. The bottoms of the craters never see sunlight, so the ice stays frozen solid. Not only could the ice provide drinking water, but it could be separated to provide oxygen as well as propellants for rockets and fuel cells. So for that perfect location on the Moon, think the north and south poles. And the Moon puts on a good show tonight with the star Aldebaran. They’re low in the east at nightfall, with Aldebaran — the orange “eye” of Taurus — just to the lower right of the Moon. They stay close as they arc across the south during the night. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Superman first blazed into American comics 75 years ago, bringing Truth, Justice, and the American Way to a world on the brink of war. But a star that blazed into view four years earlier may have helped establish him as a visitor from another world. Brad Ricca, a professor at Case Western University, published a book about Superman’s creators, Jerry Siegel and Joe Shuster. Last year, he said that in an early version of Superman, the Man of Steel was a time traveler from Earth’s future. Publishers didn’t buy the story, though, so the young writers continued to refine the character. And in December of 1934, a “new” star flared into view — a nova in the constellation Hercules that was easily visible to the naked eye. The star is a binary, with a stellar corpse known as a white dwarf in a tight orbit with a faint star known as a red dwarf. The white dwarf steals gas from its companion. And as seen in 1934, that resulted in an explosion on the surface of the white dwarf, causing the star to flare to thousands of times its normal brightness. Ricca says that Siegel and Shuster must have been among the millions who were captivated by the star. So they changed Superman’s origin — making him a refugee from an exploded planet: Krypton. Hercules, by the way, is low in the west at nightfall. Nova Herculis has long since faded. But it could one day flare again — once again reminding us of the origins of a legend. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

In the 1860s, a new meteor shower punctuated the December sky. And for more than a century afterwards, it got better and better. But that trend won’t continue. The shower could begin to wane within a few decades, and by the next century it may fizzle completely. The Geminid meteor shower is at its best tonight. At its peak, it should produce a hundred or so meteors per hour. Unfortunately, the bright Moon will wipe out most of its fireworks. But a few should be bright enough to shine through the glow. The Geminids are bits of dust associated with an asteroid. The dust grains spread out along the asteroid’s orbital path. Earth intersects this path every December, so some of the dust grains slam into the upper atmosphere. They quickly vaporize, forming the glowing streaks of light known as meteors or shooting stars. But the gravitational pull of Earth and the planet Jupiter are shifting the path of the dust grains away from the Sun. Calculations made decades ago show that the path began intersecting Earth’s orbit in the 1800s. But it could move beyond Earth’s orbit by the end of the century — bringing the Geminid meteor shower to an end. For now, though, look for the shower beginning in mid- to late evening. It usually produces a few especially bright meteors, so it’s worth a look even through the moonlight. Some of those bright meteors continue for a night or two after the shower’s peak, providing some extra time to catch the fireworks. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The asteroid 3200 Phaethon is the type of object that doesn’t usually get a lot of attention. It’s a boulder about three miles across that orbits the Sun once every year and a half. It passes so close to the Sun that any ice it might have had has long since vaporized, leaving only bare rock. Yet Phaethon is of special interest because it’s the parent of the Geminid meteor shower, which is at its best the next few nights. Moonlight will overpower most of this year’s fireworks, but a few bright meteors should shine through. Over the last few years, as Phaethon passed closest to the Sun, it behaved much more like a comet than an asteroid — it grew much brighter, and it sprouted a tail. Comets have lots of frozen water and gases. When they get close to the Sun, some of the ice vaporizes, releasing gas and dust into space. This material surrounds the comet, making it much brighter. Sunlight and the solar wind blow some of it away from the comet, forming the tail. Phaethon has long since lost any ice, though. Instead, the intense heat probably cracks its rocky surface, releasing grains of dust into space. This outburst briefly surrounds Phaeton, making it appear brighter. The Sun pushes the dust away, forming a tail. Most of the dust is quickly blown out into space. But some of the larger bits join the cloud of debris that causes the Geminid meteor shower — providing fresh material for a celestial lightshow. More tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Oh, Be A Fine Girl — Kiss Me! For almost a century, astronomy students have been learning that little mnemonic to help them remember how the stars are classified: with the letters O-B-A-F-G-K-M. The system was devised by Annie Jump Cannon, who was born 150 years ago today. Until the development of spectroscopy, about the only way to classify stars was by their brightness or their position in the sky. But spectroscopy changed that. By splitting a star’s light into its individual wavelengths or colors, it revealed the star’s composition, its temperature, its motion, and much more. Since they now knew a lot more about the stars, astronomers needed a way to classify them that would help them better understand how stars work. Harvard College Observatory hired Cannon and other women to pore over hundreds of thousands of spectra. Cannon was particularly good at it. During her 40-year career, she catalogued more than 300,000 of them. Before Cannon, a couple of people had developed ways to categorize the stars based on their spectra. One used the letters of the alphabet up through “N.” But Cannon saw a better way. She kept the letters from the earlier system, but rearranged them based on a star’s color, which corresponds to its temperature. In her system, blue-white stars — the hottest — come first, followed by white, yellow, orange, and red. Cannon’s system remains in use today — giving students an easy way to remember how to classify the stars. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Like most professions in the late 19th century, astronomy wasn’t just male dominated, it was pretty much men-only. In fact, one of the few places where women were contributing to astronomy at all was Harvard College Observatory. They weren’t actual astronomers, though — they spent their time classifying photographic plates. But some of them became astronomers, and made some of the most important scientific contributions of the early 20th century. One of those women was Annie Jump Cannon. She was born 150 years ago tomorrow in Dover, Delaware. Her father was a shipbuilder and state senator. But it was her mother who instilled Annie’s interest in the stars. Despite a childhood bout of scarlet fever that left her almost completely deaf, Cannon earned a degree in physics and astronomy from Wellesley College. In 1892 she traveled to Europe to photograph a solar eclipse, and a few years later she returned to Wellesley to pursue a graduate degree. Shortly after that, Cannon enrolled at Radcliffe Women’s College at Harvard. She learned spectroscopy, which breaks a star’s light into its individual wavelengths or colors, revealing the star’s composition, motion, and much more. Cannon soon put that knowledge to work. Harvard College Observatory hired her as a “computer.” She spent six days a week sorting stars by their spectra — a task that eventually led her to create a new classification scheme for the stars. More about that tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Pioneering isn’t always very comfortable. Consider some of the first women astronomers of the modern age. They worked in a small room at Harvard College Observatory six days a week, hunching over photographic plates to catalog star positions and spectra. They were paid less than campus secretaries. And they weren’t even called astronomers — they were “computers.” Yet the group that came to be known as Pickering’s Harem made immensely important contributions to modern astronomy. And today, many of its members are remembered as pioneers. The group was formed by the observatory’s director, Edward Charles Pickering. In 1881, Harvard was cataloging an enormous collection of photographic plates. It required a lot of time and attention to detail, but Pickering had a limited budget for the project. So he decided to hire women because he could pay them as little as a quarter an hour — more than an unskilled factory worker, but less than a secretary. Much of their work involved detailed computations, so they were known as computers. Many of the women were bright and inquisitive, and quickly expanded their roles. Williamina Fleming, who headed the group, discovered the Horsehead Nebula. Henrietta Leavitt developed a way to measure astronomical distances — a technique that’s still used today. And Annie Jump Cannon developed a system for classifying stars — another contribution that’s still in use. We’ll have more about Cannon tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Most of the stars that look like the Sun are like the Sun. In other words, stars that shine with the same yellowish color as the Sun are about the same size and mass as our home star. But a few oddballs are much bigger and heavier than the Sun, and much later in life. In fact, two of them stand close together in the night sky. They’re the brightest stars of Aquarius, which is where the Moon appears tonight. The stars are to the right of the Moon. As seen from Earth, Alpha and Beta Aquarii aren’t all that impressive. But that’s only because the stars are hundreds of light-years away. In reality, they’re some of the brightest stars in our part of the galaxy. Both stars are yellow supergiants. Estimates of their mass say they’re more than six times as heavy as the Sun. And if you dropped either star in the Sun’s place, it would extend out to the orbit of Mercury. The stars are only about 50 million years old — roughly one percent of the Sun’s age. Yet because they’re so heavy, they’re already nearing the ends of their lives. They’ve burned up the original hydrogen fuel in their cores, and have started to burn the “ashes” of those earlier nuclear reactions. That causes their outer layers to puff outward. Before long — astronomically speaking — Alpha and Beta Aquarii are likely to expel those outer layers into space. That probably will leave only their hot but dead cores — a pair of white dwarfs shining feebly through the long cosmic night. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The starry pictures that decorate the night sky are like a giant mural — a complex canvas that never changes. For most of human history, though, that mural was always in flux. Different cultures connected the starry dots to form their own pictures and their own stories. And even cultures that adopted older pictures frequently rewrote the stories that went with them. Consider Aquarius, one of the constellations of the zodiac. It’s in the south at nightfall, with its most important stars to the left of the Moon. Today, the constellation represents a young man pouring water from a jug. And that’s been the basic depiction for thousands of years. But the story behind it has changed. In ancient Babylon, for example, the picture represented the god Ea, who ruled over a portion of the Sun’s path across the sky. He held an overflowing water jug that was associated with flooding. And in Egypt, the constellation was associated with the annual flooding of the Nile River. The story said the Nile overflowed when a boy dipped the water jug into its waters. The Greeks adopted many of the constellations from the Babylonians and Egyptians, so they kept Aquarius. But they changed the story. One version says the boy was Ganymede, a beautiful young man who was stolen away by Zeus, the king of the gods. Whisked to Olympus, he became the cupbearer to the gods, and was later immortalized in the stars — where he remains today. More about Aquarius tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Sirius — the brightest star in the night sky — is often associated with summer. It rises with the Sun at that time of year, ushering in summer’s “dog days.” But summer is the worst time to watch Sirius. It’s either too close to the Sun to view, or it rises not long before sunrise. Instead, the best time to watch Sirius is during late autumn and into winter, when it’s in the sky for most of the night. Tonight, for example, Sirius rises around 9:30 or 10, and remains visible throughout the night. Sirius looks so bright for a couple of reasons. First, it really is bright — it produces about 30 times more energy than the Sun. And second, Sirius is less than nine light-years away. Only a few stars are closer. Sirius is actually a binary — two stars that move through space together, bound by their mutual gravitational pull. The star that we see with the unaided eye is Sirius A. The other is Sirius B. Since Sirius is known as the Dog Star, Sirius B is nicknamed “the Pup.” Sirius A is a main-sequence star. That means that like the Sun, it’s in the prime of life. Sirius B, on the other hand, is a white dwarf — the burned-out core of a once-normal star. It shines only by releasing the intense heat it built up during its long lifetime. It’s so small, and so close to Sirius A, that you need a telescope to see it. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

ENDEAVOUR: Endeavour has a firm handshake with Mister Hubble’s telescope. CAPCOM: We copy that, Covey, and there are smiles galore down here. ENDEAVOUR: It’s quite a sight. Twenty years ago today, astronauts were hard at work on NASA’s most ambitious mission since the Moon landings — and perhaps the most critical to the agency’s future. They were giving Hubble Space Telescope corrective lenses — a project designed to turn it from a national joke to a national treasure. Hubble had been launched in 1990. As it began looking at the stars, though, scientists realized that its vision was blurred. There was a tiny error in the shape of its main mirror. Engineers quickly came up with a plan to bring its vision up to spec: Astronauts would install new optics that would bring Hubble’s view into sharp focus. Space shuttle Endeavour grabbed the telescope on December 4th, 1993. Over the next few days, its crew, led by Richard Covey, installed the corrective optics and a new camera, as well as better computers, solar panels, and other equipment. They released the telescope on December 10th. ENDEAVOUR: All right. CAPCOM: Endeavour, you’ve got a go for release. PAO: The Hubble Space Telescope has been released from the robot arm. CAPCOM: Through your superb efforts, you’ve really shown that NASA can do all that we promised to do and more. And we very much appreciate it. The mission saved Hubble — and NASA’s reputation. And four other servicing missions extended the orbiting observatory’s lifetime and capabilities — allowing it to continue its mission of discovery even today. ENDEAVOUR: All right... Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Venus is our closest planetary neighbor, and the brightest object in the night sky except the Moon. In fact, you can see them close together tonight. Venus, the “evening star” is close to the upper left of the Moon as night falls. Despite Venus’s dramatic appearance, until spacecraft started visiting it, no one had ever seen its surface, because the entire globe is blanketed by clouds. And without being able to see surface features rotating into and out of view, astronomers couldn’t even measure the length of a Venusian day. One thing they did know is that Venus rotates backwards from the other planets. While the Sun rises in the east and sets in the west here on Earth, it’s just the opposite on Venus. Through telescopes, astronomers could see formations in the planet’s clouds, and from that, they calculated that the clouds move around the planet every four days. Finally, in 1961, they used a giant radio telescope to bounce signals off the surface of Venus. By measuring a small shift in the wavelength of the returning radio waves, they determined that Venus completes one turn on its axis in 225 days. Because of its backward spin, though, the length of a “day” on Venus — the time from one noon to the next — is about 117 Earth days. The length of a day doesn’t have much effect on temperatures on Venus, though. The planet’s dense atmosphere locks in heat, so the surface temperature remains about 850 degrees Fahrenheit — day and night. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

NARRATOR: December 2nd, 1973. Tomorrow, Pioneer will make its closest pass of Jupiter, when this fantastic world will fill one-fifth of the sky. Forty years ago today, Pioneer 10 made history. It became the first spacecraft to fly past Jupiter, the largest planet in the solar system. On December 3rd, 1973, it passed just 81,000 miles above the planet’s colorful cloudtops, gathering a wealth of information about this impressive world. Despite its great heft, much about Jupiter was still unknown. And its entourage of moons was a complete mystery — no one knew almost anything about them other than their size and mass. Pioneer 10 was crude by today’s standards. In fact, its pictures weren’t as good as those taken today by Hubble Space Telescope. Yet they provided the first close-up look at the giant planet, and a peek at a few of the moons. Pioneer’s instruments also measured the amount of dust around the planet, the extent of its magnetic field, and the strength of its powerful radiation belts. And as it departed, it showed us something that not even Hubble can reveal, as this NASA documentary recorded: NARRATOR: Now Pioneer views a sight never before seen by man: the crescent Jupiter. From Earth, we can see only its full phase, like a full Moon. These lighting angles give scientists new information. As it departed, Pioneer 10 got a gravitational “kick” from Jupiter — making it the first spacecraft to leave the realm of the planets and head toward interstellar space. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Like Earth, a world in another star system could fairly be described as “the blue planet.” It’s not a place you’d want to stop by for a quick swim, though. The blue comes not from water, but from bits of glass forged high in the planet’s atmosphere. HD 189733b orbits a star in Vulpecula, the fox, which is low in the west as night falls. The constellation is between the stars Deneb and Altair, the two points that form the left side of the bright Summer Triangle. The planet is too far and too small to see directly. But every couple of days it passes in front of, then behind, its parent star. Carefully studying how that changes the qualities of the star’s light can reveal details about conditions on the planet. The planet is a bit bigger and heavier than Jupiter, the giant of our own solar system. But it’s quite close to its parent star, so its dayside temperature is about 2,000 degrees Fahrenheit. But temperatures on the nightside are hundreds of degrees cooler, which should stir up 4500-mile-an-hour winds. Silicon-rich minerals may condense in the planet’s hot upper atmosphere, forming tiny bits of glass. These beads would reflect blue light while absorbing other colors, giving the planet its deep blue appearance. A couple of years ago, astronomers saw a plume of gas blowing away from the planet, most likely pushed into space by a giant burst of X-rays from the star — eroding some of the atmosphere of this blue-hot planet. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The moons of Mars are scrawny little things — chunks of rock that are only a few miles across. But they’re not the only cosmic flotsam that accompanies the Red Planet. At least seven asteroids share its orbit around the Sun. Collectively, the asteroids are known as “Trojans.” One of them orbits 60 degrees ahead of Mars, while the others form a clump 60 degrees behind the planet. The asteroids are held in place by a gravitational balance between Mars and the Sun. Mars is the only inner planet known to have Trojan companions. The first was discovered in 1990, and was named Eureka. Two others were discovered soon afterwards. The last four were identified as Trojans only recently, by a researcher in Northern Ireland. He combed through records of asteroid orbits and found that four of them matched the orbit of Mars. He also found that all but one of the asteroids in the clump that trails Mars are small, and they’re bunched up around Eureka. That suggests that they’re the remnants of a larger asteroid that was shattered by a collision. The impact wasn’t strong enough to kick them out of position, though — it left them in Mars’s orbit, giving the Red Planet a few small, distant companions. And Mars has a couple of bright companions in our sky right now. The planet looks like a bright orange star well up in the southeast at first light. The star Regulus is to its upper right, with Spica about the same distance to its lower left. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.