The Sun narrowly skirts by the heart of the lion today and tomorrow – the star Regulus. At their closest, they’ll be separated by just a fraction of a degree. After that, the Sun will slide across Leo for almost four weeks before moving into Virgo.

That may surprise those whose astrological sign is Virgo. The Sun is supposed to cross into Virgo tomorrow. That highlights two points: the difference between the “signs” and the constellations, and the Sun’s changing position relative to both.

The constellations of the zodiac were drawn thousands of years ago. They were based on connect-the-dots patterns of stars, not formal boundaries.

The constellations are different sizes, so the Sun spends different amounts of time crossing each one. On average, though, with 12 months and 12 constellations, the Sun spent a month in each. So astrology divided the zodiac into 12 equal slices. That meant the Sun spent an equal amount of time in each sign, regardless of the size of the constellation itself.

But the Sun shifts position relative to the background of the stars. So today, the signs and constellations are out of sync by about a month.

And in the early 20th century, astronomers assigned formal borders to the constellations. So the Sun spends from about a week to more than five weeks crossing each constellation. And the way the borders are set up, it actually crosses 13 of them – including Leo.

Script by Damond Benningfield

The space around our solar system is cloudy. Astronomers have mapped 15 individual clouds within a few hundred light-years. The clouds are moving in different directions, and they have different mixtures of ingredients. Some of those ingredients were forged by exploding stars.

Over the past few years, scientists have used one of those ingredients to trace the solar system’s path through the Local Interstellar Cloud. It’s about 30 light-years across, and we’re close to its edge – perhaps in the transition zone with the next cloud.

The scientists have looked at a radioactive form of iron that’s produced when a massive star explodes as a supernova. The explosion scatters the atoms, creating clouds of debris – including iron-rich dust grains.

As Earth flies through a cloud, it sweeps up some of the dust, which falls to the surface. The scientists have found the iron in sediments on the bottom of the ocean, and in fresh snow in Antarctica. And recently, they found it in layers of ice deposited 40,000 to 80,000 years ago, also in the Antarctic.

Those samples fell to Earth before the others did. And they have lower amounts of the radioactive iron. That could mean that Earth was just entering the Local Cloud during that period. The amount of iron went up as we passed deeper into the cloud. Now, the amount is going down again – perhaps heralding the solar system’s exit from the Local Cloud.

Script by Damond Benningfield

Antares is a class M star. That means its surface is thousands of degrees cooler than the surface of the Sun. The lower temperature makes it look reddish orange – a color that’s easy to see with the eye alone.

Every dark orange or red star you can see in the night sky falls into class M. But none of those stars is anything like the Sun. They’re all giants or supergiants – stars that are much bigger than the Sun. And Antares is one of the biggest of them all – hundreds of times wider than the Sun, and tens of thousands of times brighter.

Such stars have completed the prime phase of life, so they’ve puffed up to many times their original size. As they got bigger, their surfaces got cooler and redder.

But these big guys aren’t even the tip of the class-M iceberg – they’re more like a small patch of snow on top of the iceberg. Class M may incorporate half or more of all the stars in the galaxy. That includes the Sun’s closest neighbor, Proxima Centauri, which is just four-and-a-quarter light-years away. But almost all of these “red dwarfs” are much smaller and fainter than the Sun. In fact, they’re so faint that not even one of them is visible to the unaided eye. So any time you see a red star, you’re seeing a monster – one of the bigger stars in the galaxy.

Look for Antares quite near the Moon this evening – a supergiant star at the head of its class.

Tomorrow: going dark.

Script by Damond Benningfield

All is not well with the universe – or at least our understanding of it. There’s growing evidence, for example, that “dark energy” might not behave the way scientists had thought. And that behavior might control the universe’s fate.

Dark energy was discovered three decades ago. It may account for two-thirds of all the matter and energy in the universe. And it appears to cause the universe to expand faster as it ages.

So far, no one knows for sure what dark energy really is. One idea is that it’s “constant” – perhaps a property of space itself. As the universe expands, it creates more space, so there’s more dark energy. But no more matter is created. The existing matter spreads out, so the effect of its gravity gets weaker.

Dark energy then becomes even more dominant, making the universe expand faster and faster.

But some recent studies suggest that dark energy might not be constant – it might change over time. If so, then the universe might not expand forever.

One study says the universe could end in 20 billion years. Over the final few billion, gravity would take control, pulling everything into a Big Crunch. All the stars and galaxies would smash together. Finally, everything would merge to form a single black hole.

After that, perhaps the universe could rebound in another sort of Big Bang. But that universe would be quite different – a universe that we can’t even begin to understand.

Script by Damond Benningfield

In the mythology of ancient Egypt, the universe began when a great god emerged from the void. He created the air and the divine order of the world. And they gave birth to the land and sky.

That’s one of countless creation stories – attempts to explain the birth of the universe. To modern science, the best explanation is the Big Bang, an instant of creation 13.8 billion years ago.

Several pieces of evidence support the Big Bang. For one, on the largest scales, galaxies are all racing away from each other. If you trace the motion back in time, everything comes together in a single point.

For another, the Big Bang left its “fingerprints” on the universe – an afterglow known as the cosmic microwave background. It was created when the early universe had cooled enough for light to travel freely. As the universe expanded, the afterglow shifted to radio wavelengths, which we see in every direction.

One more bit of evidence is the way elements are created. According to the theory, the Big Bang itself created hydrogen and helium, the simplest elements.

Later, the first stars “fused” those elements together to make heavier ones. Over time, the percentage of heavy elements has increased as stars make more of them and release them into space. And that’s just what astronomers observe when they look into the universe – a steady build-up of heavier elements, dating to the beginning of time.

More tomorrow.

Script by Damond Benningfield

The universe consists of everything we can see, plus a whole lot more – all matter and energy, space and time. It was born 13.8 billion years ago, in the Big Bang. It’s been expanding and changing ever since. We don’t know how big it is – it might be infinite. We’re not sure how it will end. And we don’t even know what most of it is made of.

Universe comes from a Latin word that means “combined into one.” It’s been described as everything that is, that ever has been, and that ever will be.

When the universe was born, it consisted almost entirely of hydrogen and helium, the simplest chemical elements. Some of those elements came together to make the first stars, which clumped together to form galaxies. As the first stars aged, they created heavier elements, which were incorporated into later stars. Some of those elements formed planets, and even the life on Earth.

But most of the universe is hidden. About two-thirds of everything in the universe consists of dark energy. We don’t know what it is – only that it’s making the universe expand faster. About a quarter of the universe consists of dark matter. We don’t know what it is, either – perhaps some type of exotic particle.

Everything else – all the stars and galaxies and energy that we can see and experience – makes up just five percent of the universe – the bare tip of the cosmic iceberg.

More tomorrow.

Script by Damond Benningfield

The Artemis II astronauts got to see something that only 24 other people have seen with their own eyes: the far side of the Moon. As they looped behind the Moon, the astronauts could see almost the entire hemisphere that remains hidden from those of us on Earth.

The Moon is “locked” so that one hemisphere always faces our planet – a result of the same process that creates ocean tides. We didn’t get our first glimpse of the farside until 1959, when a Soviet probe snapped a picture.

The two lunar hemispheres look different. While dark volcanic plains cover about a third of the nearside, they cover just one percent of the farside. The farside is more heavily cratered. And the crust on the farside is thicker. That could be the result of a gentle “splat” by a smaller moon when the Moon was young.

The farside often is called the dark side of the Moon – “dark” as in unknown or unseen. It actually receives just as much sunlight as the nearside does. But the nights are darker there. From the nearside, Earth is in view most of the time, brightening the nights. But Earth is never seen from the farside. So the nights are illuminated only by the stars – making the dark side of the Moon a really good spot for stargazing.

The crescent Moon is low in the west in early evening. The planet Venus, the “evening star,” is close to its right. And the star Spica is even closer above the Moon.

Script by Damond Benningfield

The Moon is lumpy. In fact, its gravity is the lumpiest of any body in the solar system. That makes it tricky for spacecraft to maintain the right speed and altitude as they orbit the Moon.

The lumps are known as mass concentrations – “mascons.” They were discovered by Lunar Orbiter 1, which arrived at the Moon 60 years ago. You can’t see them – only feel their gravitational pull.

Lunar Orbiter was designed to survey possible landing sites for Apollo astronauts. But as it circled the Moon, its orbit changed in unexpected ways. As it flew over some parts of the Moon, it sped up a little and dropped closer to the surface. The same effect was seen in the orbits of later missions as well.

The effect could be dramatic. Apollo 16 left a small satellite in orbit in April of 1972. It was supposed to stay in orbit for several months. Instead, it crashed after just one month.

Many of the mascons are associated with giant impact basins. They formed when asteroids slammed into the Moon long ago. Dense molten rock bubbled up below the scars, then cooled and hardened. This rock is denser than the surrounding rock. That makes its gravitational pull a little stronger.

Today, we have good maps of the mascons – allowing satellites to escape their fatal attraction.

The crescent Moon is quite low in the sky as twilight fades the next couple of nights. Venus, the “evening star,” stands close by.

Script by Damond Benningfield

The first of a series of lunar “spy” satellites entered orbit around the Moon 60 years ago today. There wasn’t any secret about it – it was conducted in full public view. But its camera system was adapted from one built for an Air Force spy satellite.

Lunar Orbiter 1 was the first American spacecraft to orbit the Moon – a half-dozen earlier attempts had all failed. Its main goal was to snap high-resolution pictures of possible landing sites for Apollo astronauts. But it would also map a good portion of the lunar surface, and take a close-up look at a few spots on the far side. And it would measure the Moon’s gravitational and magnetic fields.

Its camera system used two lenses – one for close-ups, the other for wider views. The images were recorded on 65-millimeter film, then processed in an on-board lab. Finally, they were scanned and transmitted to Earth.

Eastman Kodak had created the camera system for a spy satellite called SAMOS. But for that craft, the film was dropped back to Earth, where it was grabbed by an airplane as it parachuted toward the surface – something they couldn’t do from a quarter of a million miles away.

Lunar Orbiter 1 took more than 200 pictures. They were combined with the images from four successor missions to produce the most comprehensive atlas of the lunar surface to that time. And scientists continue to study the images today.

Script by Damond Benningfield

A stellar vanishing act led to a revelation about an iceball far from the Sun: It has a thin atmosphere. It’s the smallest object with a known atmosphere in the entire solar system.

The object is 2002 XV93. It’s in the Kuiper Belt – a wide “doughnut” beyond the orbit of Neptune, the Sun’s outermost major planet. The belt contains millions of icy bodies, including Pluto.

XV93 is about 300 miles in diameter – just one-fifth as big as Pluto.

Astronomers in Japan watched the little iceball in January of 2024. They’d calculated that XV93 would pass in front of a star, hiding the star from view. As they watched the star disappear, it didn’t blink out instantly. Instead, it dimmed a bit before it passed behind XV93. And it took a moment to reach full brightness when it returned to view. That meant that something was partially obscuring the star: an atmosphere. It’s only about one percent as thick as Pluto’s atmosphere, which is a bare wisp.

XV93’s gravity is extremely weak, so it can’t hang on to any atmosphere for long. So the gases might vent into space from its interior, which would keep the atmosphere going. Or they might have surrounded the object after it was hit by a small comet. In that case, the atmosphere would start to vanish quickly – eventually leaving XV93 airless.

Script by Damond Benningfield