StarDate

A Japanese spacecraft is scheduled to pay a call on an asteroid this weekend. The encounter won’t last long – the craft will buzz by at about 12,000 miles per hour.

This is the second asteroid encounter for Hayabusa2, which launched in 2014. Its main mission was a detailed study of the asteroid Ryugu. It orbited the asteroid for a year and a half. It gathered a few grams of dust and pebbles and dropped them off at Earth in late 2020. Studies have shown that the samples contain all the key ingredients of DNA – the building blocks of life.

Hayabusa then continued its trek. And this weekend, it’ll pass by the asteroid Torifune – a chunk of rock about a quarter of a mile in diameter.

Torifune’s average distance from the Sun is just a fraction farther than Earth’s distance. But its path is lopsided, so it regularly crosses Earth’s orbit. It’s not currently a threat to hit our planet. But it could be sometime in the distant future.

Right now, the asteroid is at its closest point to the Sun, and about 60 million miles from Earth. Hayabusa will scan it with several instruments as it swings by. But the high speed makes that tough. The entire spacecraft has to turn to keep the asteroid in view. And it can’t turn fast enough to keep an eye on it through the entire encounter. So it’ll have to settle for a quick glimpse as it blazes by this potentially hazardous asteroid.

Script by Damond Benningfield

The bright star that marks the tail of the swan is big, bright, and heavy. If you want to know how big, bright, and heavy, well, the most precise answer we can give you is “very.”

We know for sure that Deneb is one of the more imposing stars around. But the details are a little hazy because the star’s distance is hazy. In part, that’s because of Deneb’s impressiveness.

The most accurate stellar distances come from Gaia, a space telescope. But Deneb is so bright that Gaia can’t look at it directly. Instead, it has to study the star indirectly – sort of like checking something out through the corner of its eye. It takes a lot of work to translate those glimpses into solid numbers.

In addition, the star’s outer layers are puffy and unstable, so it’s hard to know just where its surface is. And you need a good idea of the surface to measure the star’s location.

The best estimates say that Deneb is about 1500 light-years away – one of the most remote stars that’s visible to the eye alone. But other estimates say it’s almost twice that far. So based on that range, Deneb is about 15 to 20 times the mass of the Sun, 100 to 200 times the Sun’s diameter, and 50 thousand to 200 thousand times its brightness – impressive numbers for a very impressive star.

Deneb is a third of the way up the northeastern sky at nightfall, and soars high overhead during the night.

Script by Damond Benningfield

When the Moon covers the Sun during a total eclipse, a couple of rare sights greet viewers. One is the corona – the Sun’s hot but thin outer atmosphere, which looks like a silvery halo. The other is the short red or pink tendrils known as prominences – eruptions of gas into the corona. They’re actually there all the time, but they’re impossible to see against the brilliance of the Sun’s disk.

Prominences can span many thousands of miles; the largest are about half the size of the Sun itself. They’re actually thousands of degrees cooler than the surface of the Sun. They look bright only when they’re seen against the dark background of space. When they’re seen against the Sun, they form dark streaks.

Prominences are powered by the Sun’s magnetic field. Strands of the field can levitate above the surface. The strands can be filled with plasma – hot gas that has an electric charge.

Some prominences are common around magnetically active regions. They can erupt in minutes, loop into the corona, then collapse within hours.
Others form in regions that are fairly quiet. They can take days to bloom into the corona, then remain visible for weeks or months.

Some prominences don’t stop at the corona. They can send huge clouds of plasma into the solar system. If they hit Earth, these outbursts can trigger brilliant auroras and disrupt technology – prominent impacts from the Sun.

Script by Damond Benningfield

To predict the lifespan of a star, you don’t need a crystal ball – a bathroom scale will do just fine. Heavier stars age faster, so if you know the star’s mass, you have a good idea of its future.

Consider Tarazed, the second-brightest star of the eagle. It’s only about six percent the age of the Sun. But because it’s about three and a half times the Sun’s mass, it’s already completed the “prime” phase of life. Now, it’s well into the next phase – as a red giant.

Mass is critical because, as the star’s mass increases, so does its gravity. Stronger gravity squeezes the star’s core more tightly, increasing its temperature. That revs up the rate of nuclear reactions in the core.

When a star is born, its core is mostly hydrogen. In the prime phase of life, the star “fuses” the hydrogen atoms to make helium. When the hydrogen is gone, the core shrinks, so it gets even hotter. That causes the star’s outer layers to puff up, which is what’s happened to Tarazed – it’s more than 90 times the Sun’s diameter.

Higher core temperatures trigger the next round of reactions. So today, Tarazed is fusing the helium to make heavier elements. Eventually, that will end as well. Tarazed will shed its outer layers, leaving only its tiny, dead core – ending the star’s fairly short but bright life.

Tarazed is low in the east at nightfall. It’s close above even brighter Altair, at the southern point of the Summer Triangle.

Script by Damond Benningfield

Altair is one of the highlights of summer. It’s at one point of the Summer Triangle, and it’s the twelfth-brightest star in the night sky. And it’s just 16.7 light-years away.

Because Altair is so close and bright, we know quite a bit about it. And we’re learning more all the time. A study a couple of years ago, for example, refined the likely age of the star – 88 million years, give or take 10 million. That’s just two percent the age of the Sun.

Altair is about twice the size and mass of the Sun. And because it’s so young, it spins in a hurry – one turn every eight hours or so, versus 25 days for the Sun. That whirling rotation makes the star look squished – it’s about 25 percent wider through the equator than the poles.

In 2022, astronomers “listened” to the star with a space telescope. It measured vibrations on the surface of the star. Combined with observations from the ground, that revealed a total of 34 vibration modes – like 34 different musical notes.

The vibrations travel deep into the star. Each “note” reveals details about Altair’s interior. Piecing together the whole symphony, the astronomers found that the core of Altair contains more than 97 percent of the hydrogen it was born with. As a star ages, it converts its hydrogen to helium. So the amount of hydrogen reveals that Altair is just starting out.

Script by Damond Benningfield