StarDate

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