The universe follows a set of rules – the laws of physics. Those laws govern everything from the vibrations of the strings on a cello to the motions of the stars and planets. In fact, for centuries it was thought that the stars and planets must produce their own heavenly music – the music of the spheres.

The idea was first proposed about 2500 years ago, by Pythagoras of Samos. The Greek philosopher studied the music produced by a lyre – a small, handheld harp. Its tones were produced by the vibrations of the strings. He found a mathematical relationship between the tones and the length of the strings.

Since the strings were vibrating, that meant they were moving. Pythagoras then suggested that everything that moves produces its own vibrations – its own music. And that included the heavens.

At the time, the leading view of the universe said it consisted of a series of spheres. The Sun, Moon, and known planets were embedded in their own spheres. The stars were in the outer sphere. As the spheres moved, Pythagoras said they should produce musical notes. The relationships between the spheres determined the specific notes. Taken together, they should produce a beautiful cosmic harmony.

Over the centuries, some thought the music was real. Others thought of it as more symbolic – an indication that the universe was in harmony – a different way to “hear” the music of the spheres.

Script by Damond Benningfield

Many of us have our own muse – someone who’s inspired us in a profound way. Such people can be seen as the descendants of the original Muses – goddesses who inspired great accomplishments in music, dance, poetry – and astronomy.

The Muses were the daughters of Zeus, the king of the gods of Olympus, and Mnemosyne, the goddess of memory. And they were the great grand-daughters of Uranus, one of the Titans – the gods who came before the Olympians.

The Muse of astronomy was Urania – a name that means “heavenly.” She inspired people to look at the stars, to draw maps of them, and to create stories about them. She was also said to be able to see the future by “reading” the stars.

In classical artworks, Urania often is shown looking skyward, and wearing a cloak that’s covered in stars. In some pieces, she also has a halo of stars. Because the stars were important for navigation and mapping in the ancient world, her symbols were a globe and a compass.

In the 16th century, Danish astronomer Tycho Brahe named his observatory “Uraniborg” in her honor. A half-dozen other European observatories have also borne her name. And she’s in the official seals of the U.S. Naval Observatory and the Royal Astronomical Society of Canada. So the mythical Muse who inspired people to watch the sky in ancient Greece is still an inspiration today.

Script by Damond Benningfield

The number of known “exoplanets” that might sustain life keeps going up – it’s in the hundreds. Such a planet is in the “habitable zone” of its parent star – the distance where conditions are most comfortable for life. That zone depends on the type of star. It’s close in for small, faint stars, but a long way out for stars that are big and bright. In fact, such stars might not even have a habitable zone. And if they do, it won’t last long.

One example is Antares, the heart of the scorpion, which huddles close to the Moon tonight.

Antares consists of two stars. The star we see is many times bigger and heavier than the Sun. And it’s probably 50,000 to a hundred thousand times brighter than the Sun or more.

For a planet to receive the same amount of energy that Earth gets from the Sun, it would have to be at least 225 times farther out than Earth is. And at that distance, the second star in the system might make the planet’s orbit unstable. It might even kick the planet out of the system.

Even if a planet did exist in the habitable zone, it wouldn’t last long. Antares is likely to explode in the next million years or so – a bad development for any planet.

So if anything inhabits the Antares system, it’s probably just visiting – perhaps some scientists from another star system watching this impressive but unfriendly pair of stars.

Script by Damond Benningfield

Mars appears to have a shadow this evening – a faint star with one of the more lyrical names in the heavens: Zavijava. Mars looks like a fairly bright orange star, quite low in the west as darkness falls. Zavijava is almost touching it. It’s a good bit fainter than Mars, though, so you might want to use binoculars to enhance the view.

Zavijava is a pretty close neighbor. According to the Gaia space telescope, it’s just 35.88 light-years away. Only a few dozen stars that are visible to the unaided eye are closer.

The star’s name comes from an Arabic phrase that means “corner of the barking dog.” But Zavijava isn’t related to any of the dogs in the night sky. Instead, it’s one of the brighter stars of the constellation Virgo, so it’s also known as Beta Virginis.

Zavijava is a little bit bigger and heavier than the Sun. It’s younger than the Sun by roughly one-and-a-half billion years. But because of its greater heft, it’s already nearing the end of the main phase of life. Before long – on the astronomical timescale – it’ll undergo a series of changes in its core. That will make the star much bigger and brighter. It will remain in that phase for hundreds of millions of years.

Over the past few decades, astronomers have reported the discovery of several possible planets around the star. None of those reports has stood up. But the search continues – for worlds orbiting Zavijava.

Script by Damond Benningfield

For a star, passing too close to a black hole is never a good thing. If the star doesn’t get eaten, it can get kicked into a high-speed jaunt across the cosmos. And astronomers can track the path of such a star back to its birthplace.

One such high-speed star is plowing through the galaxy at more than a million miles per hour. Today, it appears near the twins of Gemini. But it may have been born halfway across the sky, in Pegasus.

When astronomers traced the star’s path, they found that it intersected with the star cluster Messier 15 about 20 million years ago. The star is the same age as the stars in the cluster, and it has the same composition. That suggests the star was born in M15, then booted out – probably by an encounter with a black hole more than a hundred times the mass of the Sun.

Other astronomers had reported the possibility of such a black hole more than 20 years ago. And the high-speed star appears to confirm it.

Originally, the star would have been a member of a binary. But the two stars passed close to the black hole – closer than Earth is from the Sun. In a complex gravitational dance, the binary was ripped apart. One star was gobbled up by the black hole. But the other one got away – beginning a high-speed dash across the galaxy.

Today, the star is more than 37,000 light-years from the cluster – a possible survivor of a close encounter with a black hole.

Script by Damond Benningfield

A small star with a planetary companion appears to be making a high-speed exit from the center of the Milky Way – perhaps fast enough to escape the galaxy entirely.

The system is more than 24,000 light-years away, in Sagittarius. It appears to contain a red-dwarf star – a cool, faint ember about 20 percent the mass of the Sun. It’s accompanied by a “super-Neptune” – a planet about 30 times the mass of Earth. They’re separated by less than the distance from Earth to the Sun.

What makes the system especially interesting is its high speed – at least 1.2 million miles per hour. That’s not fast enough to leave the Milky Way behind. But it could be moving a good bit faster.

The system might have started as a member of a binary – two stars bound by gravity. The stars passed too close to the monster black hole in the galaxy’s heart. The black hole grabbed the other star, and gave the escapee a giant kick. On the other hand, the kick could have come from an encounter with a smaller black hole in the Milky Way’s crowded center.

How the star maintained its grip on the planet is a key question. But the planet must have been in a tight orbit to avoid being yanked away.

Researchers were scheduled to take some follow-up observations this month. That might reveal whether the system really is a star and planet on a high-speed ride through the galaxy.

We’ll talk about another possible escapee tomorrow.

Script by Damond Benningfield

The supermassive black hole at the heart of the Milky Way is never quiet – it’s constantly popping off.

The black hole is more than four million times the mass of the Sun. It grabs passing gas clouds, asteroids, and other objects. It also sponges up gas from the “winds” produced by nearby stars. This forms a swirling disk around the black hole. As material spirals inward, it gets extremely hot.

Astronomers watched the black hole with James Webb Space Telescope. They found that it produces several bright outbursts every day, with each one lasting an hour or longer. Between these outbursts there were fainter flares that usually lasted less than a minute.

The flares may have different causes.

Shorter flares may be caused by turbulence in the disk, which squeezes and heats pockets of gas. Particles bounce around inside these pockets, heating up and producing outbursts of energy. The longer flares may explode when magnetic fields twist together, then snap. That produces big outbursts of particles and energy like the giant flares on the Sun.

The astronomers hope to take an even longer look at the system, helping them learn more about the constant flare-ups from the Milky Way’s monster black hole.

The black hole is in Sagittarius. The constellation is in the south on summer evenings, and forms the outline of a teapot. The black hole is immersed in the “steam” above the spout – 26,000 light-years away.

Script by Damond Benningfield

Sagittarius marks the center of our home galaxy, the Milky Way. So the constellation is packed with stars, star clouds, and star clusters. But one of the clusters doesn’t belong to the Milky Way at all – at least not yet. It’s in a small, puffy galaxy on the far edge of the Milky Way’s disk.

Messier 54 is a globular cluster – a ball-shaped region about 150 light-years across, packed with hundreds of thousands of stars.

Native globulars are among the Milky Way’s oldest residents – they were born with the galaxy itself. But a few of the clusters were born in other galaxies, then absorbed when their home galaxies were absorbed by the Milky Way.

For a long time, astronomers thought that M54 was a charter member of the Milky Way – one of its early globular clusters. A couple of decades ago, though, they found that it’s near the center of a newly discovered galaxy, the Sagittarius Dwarf. That puts it outside the Milky Way’s disk. But the Milky Way is pulling the smaller galaxy in. Eventually, it will incorporate all of the galaxy’s stars. So M54 will become a member of the Milky Way – one of its newest residents – and one of its oldest.

Sagittarius scoots low across the south on summer nights. It looks like the outline of a teapot. M54 is at the lower left corner of the teapot, but you need a telescope to see it.

Script by Damond Benningfield

Mars won’t exactly roll out the red carpet for human explorers. In fact, the Red Planet could be deadly. It’s bitterly cold, the air is too thin to breathe, there’s no ozone layer to block the Sun’s ultraviolet rays, and there’s no magnetic field to deflect solar storms.

And if that’s not enough, there’s one more potential hazard: dust. A recent study said the dust could damage lungs and other organs and cause nasty diseases.

Dust covers much of the planet, giving Mars its orange color. It’s easily lofted by the wind, and dust storms can blanket much or all of the planet.

Researchers studied the dust, along with problems that Apollo astronauts experienced with Moon dust. They found that the Mars dust grains are too small to be filtered out by the lungs. Instead, they’d enter a person’s bloodstream. Not only are the grains abrasive, but the dust contains high levels of some nasty compounds. So the dust could cause everything from thyroid problems to a condition similar to black-lung disease.

Some ailments could be treated on Mars. But any serious problems might require help from Earth – a journey of months. So Mars travelers will need good air filters, self-cleaning spacesuits, and other methods to protect them from the deadly sands of Mars.

Mars stands close to the crescent Moon as darkness falls this evening. It looks like a fairly bright star – a hazardous destination for human explorers.

Script by Damond Benningfield

Astronomers generally don’t play many official practical jokes. But an Italian astronomer played one more than two centuries ago. And the joke is still there for everyone to see. It’s in Delphinus, the dolphin.

The constellation is small and fairly dim. But five of its stars form an outline that really does resemble a dolphin, making it easy to find. It’s a third of the way up the eastern sky at nightfall, with the dolphin’s tail on the right and its snout on the left.

The brightest members of the outline are Beta and Alpha Delphini. Beta is a binary – two stars bound by their mutual gravitational pull. Both are bigger, brighter, and heavier than the Sun. Alpha consists of three stars. All of them are more impressive than the Sun, with the main star almost four times the mass of the Sun.

The stars also have proper names. Beta is known as Rotanev; Alpha is called Sualocin. And that’s where the joke comes in.

The names first appeared in 1814, in an atlas published by the director of the Palermo Observatory. The names caught on, but their origin was a mystery. It was solved by a British astronomer 45 years later.

He realized that the observatory’s assistant director at the time was Niccolo Cacciatori. In English, the name would be Nicholas Hunter; in Latin, Nicolaus Venator. Spell the Latin names backwards, and you come up with Sualocin and Rotanev – a little joke among the stars of the dolphin.

Script by Damond Benningfield