For radio astronomers, there’s some good news and some bad news. On the good side, a pilot project with SpaceX has devised a way to reduce the radio interference produced by satellites. On the bad side, the satellites can produce accidental interference. Radio telescopes tell us things about the universe that we can’t get any other way. But the telescopes are extremely sensitive. Transmissions from an orbiting satellite are like bright headlights – they overpower the subtle signals of astronomical objects. There are more than 15,000 satellites in orbit today – a five-fold increase in just six years. And the total could balloon to a hundred thousand by the next decade. Astronomers worked with SpaceX to reduce interference from its Starlink satellites. The groups combined the observing schedule of a telescope with the Starlink control system. Satellites passing over the telescope were instructed to turn away – aiming the headlights in a different direction. And there are plans to extend the scheme to other telescopes. On the other hand, a recent study found that tiny radio signals emitted by a satellite’s electronics can also be a problem. Scientists looked at 76 million radio images made by a telescope in Australia. They found that Starlink satellites interfered with up to 30 percent of the pictures. So future satellites may need extra shielding to keep them from blinding astronomy’s radio eyes. Script by Damond Benningfield

Most of the stars are so small and far away that they’re nothing more than pinpoints even in the largest telescopes. That makes it impossible to measure the size of a star. But astronomers can measure the sizes of some stars – not with a giant telescope, but with a collection of smaller ones. The technique is called interferometry. It links up several telescopes. The combo provides an especially sharp view of the heavens. If the telescopes are, say, 300 feet apart, then the combined view is as clear as that of a single telescope 300 feet in diameter. The array’s view isn’t as deep as that of a giant telescope, only as sharp. Interferometers have allowed astronomers to measure the apparent sizes of hundreds of stars. Combining that with a star’s distance provides its true size. One example is Elnath, the second-brightest star of Taurus. It’s about 134 light-years away. It’s five times the mass of the Sun. So even though it’s much younger than the Sun, it’s already passed through the prime phase of life. That’s caused it to puff up – to almost five times the Sun’s diameter. At that size, it shines more than 800 times brighter than the Sun – a big beacon for the bull. Elnath is close to the lower left of the Moon this evening. The Moon will move toward the star during the night. They’ll be closest at dawn. The gap will be smaller for skywatchers on the West Coast, and smallest for those in Alaska and Hawaii. Script by Damond Benningfield

[3, 2, 1, ignition, and liftoff of SOHO and the Atlas vehicle on an international mission of solar physics.] Generally speaking, staring at the Sun non-stop for decades is a bad idea. But a spacecraft launched 30 years ago this week has done just that. It’s told us about the Sun’s interior, its surface, and its extended outer atmosphere. That’s helped scientists develop better forecasts of space weather – interactions between Sun and Earth that can have a big effect on our technology. The craft is called SOHO – Solar and Heliospheric Observatory. It was launched into an orbit around a point in space where the gravity of Earth and the Sun are balanced. From there, its view of the Sun is never blocked. SOHO watches the Sun in many different ways. It keeps a close eye on the Sun’s magnetic field, which produces outbursts of energy and particles that can have an impact on Earth. That’s revealed shockwaves and “tornadoes” rippling across the Sun’s surface. It’s also revealed the source of the solar wind – a steady flow of charged particles that blows through the solar system. Some of SOHO’s observations block out the Sun itself, showing the space around the Sun. That’s allowed SOHO to discover more than 5,000 comets as they passed close to the Sun – many of which didn’t survive. SOHO’s mission is scheduled to end soon – closing this long-working eye on the Sun. Script by Damond Benningfield

Scientists have been searching for dark matter for decades. They haven’t found it – every experiment they’ve devised has come up empty. But they haven’t given up. Among other ideas, they’re thinking about ways to use moons, planets, and stars as detectors. Dark matter appears to make up about 85 percent of all the matter in the universe. We know it’s there because its gravity pulls on the visible stars and galaxies around it. Dark matter may consist of a type of particle that almost never interacts with normal matter. But it should interact just enough to reveal its nature. Experiments here on Earth haven’t seen any such interactions. So some scientists recommend using astronomical objects instead of lab experiments. Blobs of dark matter might enfold a binary star system. The dark matter’s gravity could pull the two stars away from each other. And dark matter might clump together to make a special kind of star. Both of those might be detectable with current telescopes. Smaller blobs might slam into an icy moon, creating a special kind of crater. Such craters could be visible on Ganymede, the largest moon of Jupiter. Two missions on their way to Jupiter might be able to see them. And dark matter might fall into the center of a planet and hang around. If enough builds up, it could heat the planet’s interior. So by studying many planets in other star systems, we might see some that are unusually warm – heated up by encounters with dark matter. Script by Damond Benningfield

Things are heating up for a planet that orbits the brightest star of Aries. The star is expanding to become a giant, so it’s pumping more energy into space. That will make temperatures extremely uncomfortable on the planet. Hamal is at the end of its life. It’s converted the hydrogen in its core to helium. Now, it’s getting ready to fuse the helium to make other elements. That’s made the core hotter. And that’s caused the star’s outer layers to puff up – to more than a dozen times the diameter of the Sun. So Hamal is about 75 times brighter than the Sun. Hamal has one known possible planet. It’s heavier than Jupiter, the giant of our own solar system. On average, the planet is about as far from Hamal as Earth is from the Sun – much closer in than Jupiter is. So every square foot of the planet’s surface receives dozens of times more energy than the same area on Jupiter does. If the planet is a ball of gas like Jupiter, then the extra heat is causing its atmosphere to puff up – and causing a lot of it to stream away into space. Over the next few million years, the planet will get even hotter, because Hamal will get even bigger. The extra energy may erode the planet’s atmosphere completely. On the other hand, the planet may spiral into the star. Either way, things are going to get much hotter for Hamal’s only known planet. Look for Hamal in the east at nightfall, well to the left of the Moon. Script by Damond Benningfield

As most parents can tell you, coming up with names isn’t easy. It sometimes takes a while to settle on something that sounds just right. It wasn’t easy for the people who named the constellations, either. Some of the names sound like they just gave up. They picked a region of the sky with few stars, gave it the name of a nearby bright constellation, then added the word “minor.” All three of these minor constellations are in good view at dawn: Ursa Minor, Canis Minor, and Leo Minor. The most famous of the bunch is Ursa Minor – the little bear. Seven of its stars form the Little Dipper, which is in the north – directly below the Big Dipper, which is part of Ursa Major. The constellation is especially well known because its brightest star is Polaris, the Pole Star. It’s at the tip of the little bear’s tail. Canis Minor is the little dog. It’s about half way up the sky in the west-southwest. It has only a couple of bright stars. The brightest is Procyon – a name that means “before the dog.” That’s because the little dog leads the big dog across the sky. In ancient Greece, in fact, the constellation was known as Procyon. Finally, Leo Minor is high overhead. It’s the little lion, standing on the shoulder of Leo. That region of the sky wasn’t depicted as a separate constellation until 1687. Today, though, it’s one of the 88 official constellations – even if it is a “minor” one. Script by Damond Benningfield

The shortest season on the planet Mars begins today – autumn in the northern hemisphere, and spring in the southern hemisphere. It will last for 142 Mars days – almost eight weeks less than the longest season. Mars has seasons for the same reason that Earth does – it’s tilted on its axis. And the tilt is at almost the same angle as Earth’s. But the seasons on Mars are more exaggerated because the planet’s orbit is more lopsided. A planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest from the Sun. That stretches out some seasons, and compresses others. It also changes the intensity of the seasons. Mars is farthest from the Sun when it’s summer in the northern hemisphere. So northern summers are fairly mild, while southern winters are bitterly cold. On the flip side of that, northern winters are less severe, while southern summers are the warmest time on the whole planet. The start of northern autumn also marks the beginning of dust-storm season. Rising currents of air can carry along grains of dust. Enough dust can be carried aloft to form storms that cover thousands of square miles. And every few Martian years, a storm gets big enough to cover the entire planet. The storms usually peak around the start of southern summer. Mars is about to pass behind the Sun, so it’s hidden in the Sun’s glare. It’ll return to view, in the dawn sky, in early spring – on Earth. Script by Damond Benningfield

The Moon slides by Saturn the next couple of nights. The planet looks like a bright star. It’s to the left of the Moon as night falls this evening, and to the lower right of the Moon tomorrow night. Saturn is best known for its rings. They’re almost wide enough to span the distance from Earth to the Moon. Right now, we’re viewing them almost edge-on, so they look like a thin line across the planet’s disk. Saturn isn’t the only world with rings. The solar system’s three other giant outer planets also have them. But they’re dark and thin, so they’re hard to see. Several asteroids and dwarf planets have rings, too. But the biggest set of rings yet seen may encircle a “rogue” planet about 450 light-years away. The possible rings were discovered years ago. Over a period of eight weeks, the light of a star in Centaurus flickered – sometimes dropping to just five percent of its normal level. The most likely cause was the passage of a set of rings in front of the star. And it’s quite a set. The rings are more than a hundred million miles across – greater than the distance from Earth to the Sun. The ringed planet appears to be traveling through the galaxy alone, and it just happened to pass in front of the star. It could be up to six times the mass of Jupiter, the giant of our own solar system. And moons could be orbiting inside the rings – the most impressive rings we’ve seen anywhere in the galaxy. Script by Damond Benningfield

Planets are tough little buggers. They can form and survive in some extreme environments. In fact, the first confirmed planets outside our own solar system orbit the remnant of a dead star – a pulsar. A pulsar is tiny – the size of a small city. But it’s more massive than the Sun. A teaspoon of its matter would weigh as much as a mountain. Yet a pulsar spins rapidly – up to several hundred times per second. It has an extreme magnetic field. The field shoots “jets” of particles out into space. As the pulsar spins, the jets can sweep across Earth like a lighthouse beacon, producing short pulses of energy. The timing of those pulses is extremely precise. That makes pulsars some of the best clocks in the universe. But the timing can be changed by a companion – another star, or even a planet. And that’s how pulsar planets are discovered – through tiny changes in the timing of the pulses. Eight pulsar planets have been confirmed. But they present quite a challenge. A pulsar is the remnant of a titanic explosion – a supernova. It’s hard to see how any planets could survive such a blast. So it’s likely that the planets formed after the blast – perhaps from debris from the explosion’s aftermath. Regardless of how they formed, the planets aren’t friendly places. They’re blasted with charged particles, X-rays, and gamma rays from the pulsar. That may slowly erode the planets – no matter how tough they are. Script by Damond Benningfield

[pulsar audio] This is the rhythm of the stars – the beat of dead stars. It’s the “pulses” of radio waves produced by rapidly spinning stellar corpses. They produce beams of energy that sweep around like the beacon of a lighthouse. Radio telescopes detect the beams when they sweep across Earth. The stars are known as pulsars. They’re some of the most extreme objects in the universe. They’re neutron stars – the dead cores of some of the most massive stars. When a heavy star can no longer produce nuclear reactions in its core, the core collapses. Gravity squeezes the core down to the size of a small city. But that tiny ball is heavier than the Sun. The star is rotating as it dies. As the core collapses, it keeps on spinning. But the smaller it gets, the faster it spins. So newborn neutron stars can spin a few dozen to a few hundred times per second. Particles trapped in the neutron star’s magnetic field produce energy that’s beamed into space – the source of the pulses. The neutron star spins down over time, slowing the pulses. But if it has a close companion, it can be revved up even faster. The neutron star can pull gas from the surface of the companion. As it hits the neutron star, the gas acts like an accelerator – creating some of the fastest pulsars in the universe. These extreme stars can still host planets; more about that tomorrow. Script by Damond Benningfield