Thunderstorms generate what may be nature’s most impressive displays: lightning. And there’s plenty of it; lightning strikes Earth millions of times every day. Although lightning is common, it’s also mysterious. The electric fields inside clouds don’t appear to be strong enough to power lightning. So for the past 90 years, scientists have pondered whether it might have a cosmic origin – cosmic rays – particles that ram into Earth’s atmosphere at almost the speed of light. Many of them come from the Sun. But the most powerful come from exploding stars, the gas around black holes, and other powerful objects in deep space. When a cosmic-ray particle hits an atom or molecule in the upper atmosphere, it creates a shower of other particles. And it’s these particles that might then zip through clouds, creating lightning. A study published earlier this year seems to affirm this idea. Scientists studied a thunderstorm over New Mexico with a sophisticated array of radio antennas. They traced more than 300 strikes from beginning to end, at intervals of less than a thousandth of a second. Among other things, the radio waves revealed that the bolts weren’t moving the way they should if they’d been sparked by the clouds themselves. Instead, the lightning seemed to be triggered by something coming from beyond Earth: cosmic rays. Script by Damond Benningfield

If you throw a rock into a still pond, waves ripple outward. They jiggle the leaves and bugs on the surface, shaking things up a bit. And the same thing happens in the stars. In fact, a giant region of the sky is still feeling some “ripples” today. The Scorpius-Centaurus O-B Association contains many stars of classes O and B – the hottest and brightest stars in the galaxy. It spans hundreds of light-years, and contains thousands of stars. And more stars are being born there today. The association began as a massive cloud of gas and dust. About 20 million years ago, it produced a big “wave” of starbirth. Many of the newborn stars quickly exploded as supernovas. That outburst was the “stone” in the pond. Strong winds and shockwaves from the stars rippled outward. That triggered the birth of more stars in the surrounding cloud. The rate of starbirth peaked about 15 million years ago. But the ripples didn’t stop. They created a smaller outburst about 10 million years ago, and another about five million years ago. Most of the stars in the region are no bigger than the Sun. But a few are big, heavy, and bright – monster stars born from the ripples in a galactic pond. Many of these monsters are in Scorpius, which is low in the south at nightfall, to the right of the Moon. It’s marked by the scorpion’s bright “heart,” the star Antares – the most prominent member of the Scorpius-Centaurus Association. Script by Damond Benningfield

The star that marks the heart of the scorpion is at death’s door. Sometime in the next million years or so, Antares is expected to explode as a supernova. But astronomers don’t know exactly when that’ll happen. There’s no way to see into its core, which is where the fusion reactions that power the star take place. And with current technology, we can’t tell that the end is near by looking at the surface of Antares. The star is many times the mass of the Sun, so when its nuclear engine shuts down, its core will collapse to form a neutron star or black hole. Its outer layers then will blast outward at a good fraction of the speed of light. But the star is so big that the shockwave won’t reach the surface for many hours, so it won’t begin to brighten for hours. The shockwave is powered in part by neutrinos – particles created during the collapse. They almost never interact with other matter, so most of them will zip through the star at almost the speed of light. But there are so many of them that the rare times they do interact will help drive the blast. As the neutrinos race through the galaxy, they’ll reach detectors on Earth hours before the surface of Antares begins to brighten – alerting us to the brilliant demise of a giant star. Antares stands to the upper right of the Moon at nightfall, and leads the Moon down the southwestern sky later on. We’ll have more about the scorpion tomorrow. Script by Damond Benningfield

The Moon will step on the head of the scorpion tonight. It will pass directly in front of one of the stars that outlines the head, blocking it from view – an event called an occultation. Pi Scorpii is actually a system of three stars, about 600 light-years away. The main star in the system is about a dozen times the mass of the Sun, and more than 20,000 times the Sun’s brightness. Because of its great mass, it’s already nearing the end of its life, even though it’s billions of years younger than the Sun. Before long, it will explode as a supernova. The Moon sometimes passes in front of the star because Pi Scorpii lies near the ecliptic – the Sun’s path across the sky. The Moon’s orbit around Earth is tilted a bit, so it roams a few degrees either side of the ecliptic. That allows it to occult quite a few stars that are bright enough to see with the unaided eye. This month alone, in fact, the Moon will stage almost a dozen occultations. But each of them is visible across only a small slice of the globe, so we don’t see all of them from here in the United States. But some of them align just right – allowing us to see the Moon briefly stomp out a star. The occultation of Pi Scorpii will be visible across almost all of the Lower 48 states. The exact time, and how long the star remains blocked, depends on your location. We’ll talk about the Moon and the heart of the scorpion tomorrow. Script by Damond Benningfield

Antimatter may power more than just starships. It might also have helped rev up the BOAT – an exploding star nicknamed “the Brightest Of All Time.” It was seen in October of 2022, in Sagitta, the arrow. Right now, the constellation is in the east at nightfall. The event was a gamma-ray burst – a stellar explosion that aimed “jets” of gamma rays in our direction. It was by far the most powerful cosmic event ever seen. It produced more energy in one second than the Sun will generate in its entire lifetime of more than 10 billion years. It was so powerful, in fact, that it created minor disturbances in Earth’s upper atmosphere – even though it was more than two billion light-years away. The outburst probably happened when a star many times the mass of the Sun died. Its core collapsed to form a black hole, while its outer layers blasted into space as a supernova. As the star died, superheated gas spiraled around the black hole. Magnetic fields directed some of that material into space from the star’s poles. Earth lined up along one of those beams, which is why we saw the outburst of gamma rays. A recent study says that an odd feature recorded during the outburst might have been produced when electrons and their antimatter counterparts rammed together and destroyed each other. That would have added to the energy of the blast – helping make the gamma-ray burst the BOAT – the Brightest of All Time. Script by Damond Benningfield

A giant tarantula creeps through a nearby galaxy. It’s not trying to be stealthy, though – it’s the galaxy’s brightest feature. In fact, it’s the most impressive stellar nursery in the entire Local Group – the cluster of dozens of galaxies that includes the Milky Way. The Tarantula Nebula is in the Large Magellanic Cloud, a companion galaxy to the Milky Way that’s just 160,000 light-years away. Over the last few million years, the nebula has given birth to millions of stars. That’s probably the result of a close encounter with a smaller galaxy. The gravity of the other galaxy caused large clouds of gas and dust to collapse, forming new stars. The Tarantula incorporates several star clusters – groups of stars that all formed at about the same time. The most impressive is R136. It contains a half-million stars, most of which are no more than three million years old. Most of those stars are the mass of the Sun or lighter. But a few are monsters that are many times heavier than the Sun. At least nine of them are more than a hundred times the Sun’s mass. And the biggest of all may be more than two hundred times the Sun’s mass – the heaviest star yet seen in any galaxy, including our own. Within the next few million years, many of these stars are likely to blast themselves to bits as supernovas. In fact, a star on the outskirts of the nebula did just that in 1987 – a brilliant outburst from the tarantula. Script by Damond Benningfield

Fireworks will light up the skies of many cities and towns this week – celebrations of Independence Day. For a real fireworks display, though, you might want to visit one of the Milky Way’s companion galaxies. It’s giving birth to many thousands of new stars, including some of the biggest and brightest yet seen anywhere – a result not of independence, but of a close relationship with another galaxy. The Large Magellanic Cloud is too far south to see from the continental United States. In southern-hemisphere skies, though, it’s quite a sight – a bright cloud that’s several times bigger than the full Moon. The galaxy is much smaller and fainter than the Milky Way. But it’s right next door – just 160,000 light-years away. That’s one of the reasons it looks so bright. Another is that the galaxy contains millions of hot young stars – stars that are thousands of times brighter than the Sun. And it’s giving birth to more. In fact, it contains a stellar nursery that’s far more impressive than anything in the Milky Way. We’ll have more about that tomorrow. The fireworks probably are the result of an interaction with another galaxy, the Small Magellanic Cloud. The smaller galaxy passed close to the bigger one. That encounter squeezed giant clouds of gas and dust. The clouds split into smaller clumps, which gave birth to new stars – creating fireworks in a busy galaxy. Script by Damond Benningfield

The Sun is an impressive star. Its mass ranks in the top 10 percent of all the stars in the galaxy. But the bright star that snuggles up to the Moon the next couple of evenings puts the Sun to shame. It’s bigger and heavier, it has a close companion, and it’s shaped a bit like an egg. And it faces a more dramatic fate. Spica is the brightest star of the constellation Virgo. It consists of two stars – the bright star we see, plus a close companion that we can’t see. We know the companion is there because it reveals its presence to special astronomical instruments. The stars are so close together that their gravitational pull on one another makes both of them look more like eggs than balls. The main star is called Spica A. It’s more than 10 times the mass of the Sun. At that great heft, it gulps its nuclear fuel in a big hurry. That makes the star especially hot and bright – more than 20 thousand times brighter than the Sun. Spica A also is about seven and a half times the Sun’s diameter, and more than 400 times its volume. And its fate is king-sized as well. Within a few million years, it will explode as a supernova – briefly shining as the brightest object in the entire galaxy. Look for Spica to the left or upper left of the Moon this evening. The Moon will slide a bit closer to the star before they set, after midnight. Spica will stand closer to the Moon tomorrow night. Script by Damond Benningfield

When it comes to Earth’s orbit around the Sun, the more things change – well, the more things change. Over the course of a year, our distance from the Sun varies by about three million miles. But that’s changing. And we’re farthest from the Sun in early July – but that’s changing, too. The farthest point from the Sun is known as aphelion – from Greek words that mean “far from the Sun.” And we’ll reach that point on Thursday. Earth will receive about seven percent less sunlight than it does when we’re closest to the Sun, in early January. Earth’s orbit around the Sun is elliptical – like a slightly flattened circle. But the exact shape changes over a period of about a hundred thousand years. Right now, the orbit is getting a little more circular, so there’ll be a smaller change in the distance to the Sun. After that, it’ll get a lot more stretched out. That will cause much bigger changes in Earth’s climate between the closest and farthest points. The timing of those points also changes. About 800 years ago, aphelion happened around the time of the summer solstice in the northern hemisphere. Now, it’s shifted a couple of weeks later. And the shift is continuing. So, about 4400 years from now, aphelion will happen at the fall equinox, in September. It’ll return to its current spot on the calendar more than 20,000 years from now. Tomorrow: A bright star that looks like an egg. Script by Damond Benningfield

Lots of star clusters adorn the evening skies of summer. That’s because the glowing path of the Milky Way climbs high into the sky. It’s the combined glow of millions of stars that outline the disk of the Milky Way Galaxy. So not only does it contain lots of individual stars, it hosts many star clusters as well. But a few clusters are far from the path of the Milky Way. One example is Messier 5. It’s in Serpens Caput – the head of the serpent – a region with not much around it. M5 is a globular cluster – a big ball packed with several hundred thousand stars. Such clusters are scattered all across the sky. Some appear in the disk, but they’re not part of the disk – they loop high above and below it. Globular clusters are the oldest members of the galaxy. And M5 is one of the oldest – 12 billion years or older. That means its original stars were born when the universe was only about one-tenth of its present age. Any stars that were more massive than the Sun have burned out. So the remaining original stars are smaller and fainter than the Sun. There’s evidence that a second wave of starbirth rippled through M5 well after the cluster was formed. Some of these stars can still rival the Sun – the “youngsters” of an ancient star cluster. Messier 5 is high in the south at nightfall. Through binoculars, it looks like a fuzzy star. A small telescope reveals some of the cluster’s individual stars. Script by Damond Benningfield