It sounds like a toddler’s attempt to say “Friday” or, even better, a day to gorge on apple crumb or coconut cream. Alas, “Pi Day” is something completely different. It’s a commemoration of a mathematical constant that’s represented by the Greek letter pi – one of the most important quantities in science. Pi is the ratio of a circle’s diameter to its circumference. When it’s rounded off to two digits, it’s 3.14 – the numerical equivalent of March 14th. Astronomers use pi to calculate the volume and density of a star or planet, the details of an orbit, and much more. Other scientists use it as well. But pi is an “irrational” number. That means that no matter how long you calculate its exact value, you never reach the end – whether you go to a thousand decimal places, a million, or rbrm eleventy-jillion. There’s never a conclusion, and no group of numbers ever repeats. Mathematicians have used various techniques to try to calculate the exact value, without success. The record so far is more than a hundred trillion places to the right of the decimal. Trying to calculate an exact value has been an important plot point in science fiction. Any time a computer is getting too uppity, it’s commanded to calculate pi to the last digit. That impossible task overloads the computer, allowing the heroes to regain control. Whether we’ll need it to rein in A-I – well, have a slice of pie – the tasty variety – while you ponder it. Script by Damond Benningfield

To the eye alone, the brightest star in the night sky is Sirius, the leading light of Canis Major, the big dog. It’s well up in the south at nightfall – a brilliant beacon less than nine light-years away. If we could shift the sensitivity of our eyes to shorter wavelengths, the brightest star would appear a little below Sirius. Adhara is already the second-brightest star in the constellation. But it produces most of its energy in the extreme ultraviolet – wavelengths that are far too short to see with the human eye. At those wavelengths, Adhara would be the brightest object in the entire night sky. The star is an ultraviolet powerhouse because it’s tens of thousands of degrees hotter than the Sun. The hotter an object, the more U-V it produces. And Adhara is huge – more than 10 times the Sun’s diameter. So there’s a lot of real estate for beaming its radiation into space. The U-V zaps molecules of gas and dust anywhere close to the star, splitting them apart and making them glow. But the star has been around long enough that it’s already cleared out most of the space around it. More than four million years ago, Adhara was much closer to the Sun than it is today. That made it the brightest star at visible wavelengths as well. It shined as brightly as Venus, the morning or evening star. But Adhara’s motion through the galaxy has carried the star much farther from us – allowing Sirius to outshine this sizzling star. Script by Damond Benningfield

For Charles Messier, star clusters were a nuisance. The French astronomer was mainly interested in comets. In the 18th century, finding a comet could bring fame and fortune – kings sometimes awarded medals and fat stipends for their discovery. Through a telescope, star clusters could resemble comets. Messier and others might spend time following a cluster, only to find out that it wasn’t the prize. So Messier compiled a catalog of clusters and similar nuisances – a list of objects to ignore. Four of the clusters follow a narrow path near Canis Major, the big dog: M46, 47, 48, and 50 – a Messier “highway.” Although they’re close together in our sky, the clusters are not close together in space. Their distances range from about 1600 light-years to more than five thousand. So there’s no relationship among them. They appear close together because they all lie along the Milky Way – the glowing outline of the disk of the Milky Way Galaxy. In that direction, we’re looking into the most densely populated region of the galaxy, so we see many more stars and star clusters – including the “pesky” clusters cataloged by Charles Messier. The clusters are in the southeastern quadrant of the sky as night falls. Look for Sirius, the brightest star in the night sky, due south. The clusters spread out to the left and upper left of Sirius. All of them are easy targets for binoculars. Script by Damond Benningfield

Winter brings out the big dogs – some of the most prominent constellations of all. And one of those really is a dog: Canis Major, the big dog. It’s best known for Sirius, the Dog Star – the brightest star in the night sky. It’s a third of the way up the southern sky at nightfall. But there’s much more to Canis Major than just Sirius. It includes several bright stars, most of which are below or to the right of Sirius. When you link them up, they do form the outline of a dog. Like all constellations, Canis Major consists of more than just a connect-the-dots pattern of stars, though. It covers a patch of sky that includes everything within its borders. And in that area, you can find several deep-sky objects – objects like star clusters, which are far beyond most of the individual stars visible in Canis Major. Perhaps the best known is Messier 41. It’s not far below Sirius, and it’s an easy target for binoculars. It’s about 2300 light-years away, and includes a hundred or more stars. The cluster probably is about 200 million years old. At that age, its biggest, heaviest stars have expired. They’ve left behind small, dense corpses known as white dwarfs. The next-heaviest stars soon will follow the same path. Those stars have puffed up to become red giants. They’re easily visible through binoculars – sparkling red and orange jewels along the “collar” of the big dog. More about Canis Major tomorrow. Script by Damond Benningfield

A magazine that first hit newsstands 100 years ago today was unlike anything readers had seen before. Its cover featured a brightly-colored painting of people ice-skating on a comet as it zoomed past Saturn. Its founding editor, Hugo Gernsback, called it “a new sort of magazine” – “a magazine of ‘scientifiction'” – a genre known today as science fiction. Amazing Stories was the first magazine dedicated solely to the genre. Its debut issue, which was dated April 1926, carried reprints of stories by Jules Verne, H.G. Wells, Edgar Allen Poe, and others. The story titles included “The Man from the Atom” and “The Thing from – Beyond.” The magazine was an instant hit. Within a year, monthly circulation was at 150,000. Other publishers quickly caught on, and began publishing many more sci-fi magazines. Over the decades, they included such titles as Fantastic, Astonishing, and Astounding. They featured many of the major figures of science fiction’s “golden age.” Their inventive stories and eye-catching covers caught the attention of lots of youngsters. The magazines inspired many of them to pursue careers in astronomy, physics, engineering, and related fields. They also inspired future filmmakers, who expanded “scientifiction” far beyond the printed page. Few science-fiction magazines have survived. But their influence is still felt today – on Earth – and beyond. Script by Damond Benningfield

A future super-giant “onion” perches close to the Moon at dawn tomorrow. It’s the star Antares, the bright heart of the scorpion – one of the most impressive stars in the galaxy. Antares is a supergiant. It’s roughly a dozen times as massive as the Sun, and hundreds of times wider. Because it’s so heavy, gravity squeezes its core tightly. That revs up the nuclear fusion in the core. Like all stars, those reactions initially fused hydrogen to make helium. In the Sun, hydrogen fusion will last about 10 billion years. In Antares, though, it lasted a little more than 10 million years. When the hydrogen in the core was gone, the core shrank, making it hotter – hot enough for the helium to fuse to make carbon and oxygen. That process will last about one million years. Then the carbon will fuse to make heavier elements, and so on. Each step takes less time than the one before. In the final step, silicon will fuse to make iron – a step that takes just a few days. The lighter elements won’t all go away, though. Instead, the “ash” from each step will form layers around the core – like an onion. But that structure won’t last. The core can’t get hot enough to fuse the iron. Gravity will win out, and the core will collapse – forming an ultra-dense neutron star. Everything outside the core will blast outward at a few percent of the speed of light. Supergiant Antares will explode as a supernova – an impressive end for an impressive star. Script by Damond Benningfield

Canopus would be a terrible neighbor. The star is big, bright, and hot, so it might blow away any planet-making materials around nearby stars. Even worse, it may be destined to explode. That would zap any existing planets with radiation – perhaps endangering any life in nearby star systems. Canopus is the second-brightest star in the night sky. At this time of year, it’s visible from the southern third of the United States in early evening. It’s low in the south, well below Sirius, the brightest star. Canopus is at least eight times the mass of the Sun. So even though it’s billions of years younger than the Sun, it’s already completed the main phase of life. Within a few million years, its core will collapse, perhaps forming an ultra-dense neutron star. If so, then its outer layers will blast into space as a supernova. Such an outburst would produce enormous amounts of X-rays and gamma rays – the most powerful forms of energy. That could strip away the ozone layer of any planet within a few dozen light-years, subjecting the surface to high levels of radiation. So far, we know of only one planet within that range where conditions are most suitable for life. The planet itself isn’t likely to host life. But any big moons might be more comfortable homes – at least until the demise of Canopus. Luckily for us, Canopus is 300 light-years away. So Earth is well outside the “danger zone” of this not-so-neighborly neighbor. Script by Damond Benningfield

The tale of Jason and the Argonauts is one of the biggest and boldest stories in Greek mythology. And it involves some of the greatest heroes, many of whom are depicted in the stars – from the twins of Gemini to mighty Hercules. The boat itself was placed in the stars as well. But even it was too big. Astronomers eventually split it apart. The original constellation was Argo Navis. It was first drawn almost 3,000 years ago. It was far larger than any of the other ancient western constellations. And for a long time, that was just fine. But as astronomers began studying the stars with telescopes, the Argo was just too big – there were too many stars and other objects within its borders to catalog. In 1756, French astronomer Nicolas Louis de Lacaille decided to do something about it. He split the Argo apart. He kept the references to the boat, though. So his new constellations were Carina, the keel; Vela, the sail; and Puppis, the poop deck – the deck at the back of the boat. And those constellations are still in use today. Carina is best known for its brightest star, Canopus. It’s the second-brightest star in the night sky. And from the southern latitudes of the United States, it crawls low across the south in early evening at this time of year. As night falls, it’s just above the horizon, almost directly below Sirius, the brightest nighttime star. We’ll have more about Canopus tomorrow. Script by Damond Benningfield

The first ship in a solar-system armada reached its target 40 years ago today. Over the following week, four others joined it. Their target was Comet Halley. It was making its first passage through the inner solar system since 1910. So it was the first chance to study the comet from close range. And space agencies around the world responded. The Soviet Union and Japan each sent two spacecraft, and Europe added one more. The first to arrive was Vega 1, one of the Soviet missions. It and a companion, Vega 2, had first flown past Venus. They scanned the planet and dropped probes into its atmosphere. Both of them flew just a few thousand miles from Halley’s nucleus – its “body” of rock and ice. Europe’s contribution, Giotto, came even closer – just 370 miles. It snapped by far the best pictures of any comet. It found that most of the nucleus was covered by a “crust” that was darker than charcoal. But “jets” of ice and dust erupted from thin spots in the crust. They wrapped the nucleus in a cloud of debris. Sunlight and the solar wind pushed some of that material away from the comet, forming a tail that was millions of miles long. The United States was a notable no-show. A dedicated mission to Halley was scuttled. NASA did turn some craft that were already in space to face Halley, but they were millions of miles away. The next chance to study the comet up close won’t come until 2061. Script by Damond Benningfield

Visitors sometimes just drop in on us. But a visitor to a home in Georgia took the notion of “dropping in” a bit far. It smashed through the roof, an air duct, and a thick layer of insulation before splatting into the floor, leaving a crater the size of a quarter. It missed smacking into a resident by just 14 feet. The “visitor” was a meteorite – part of a much larger space rock. The rock formed a glowing streak as it raced through the skies of the southeastern United States on June 26th. Hundreds of people saw it, and many more heard it – it produced a sonic boom, plus an explosion before it hit the ground. The bit that smashed into the house was one of more than 200 samples recovered. In all, they totaled about 12 pounds. Collectively, they were called the McDonough meteorite for the small town where they hit. Eyewitness reports, videos, weather radar, and weather satellites helped scientists reconstruct the space rock’s origin. It came from the asteroid belt – a wide band of debris between the orbits of Mars and Jupiter. It probably was a piece from a much larger body that broke apart 470 million years ago. Lab studies revealed the meteorite’s age: 4.56 billion years – about 20 million years older than Earth. That means it was similar to the rocky building blocks that came together to make Earth. So the McDonough meteorite is an ancient visitor that dropped in with a bang. Script by Damond Benningfield