StarDate

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