StarDate

Social media may go wild the next few days – filled with reports of UFOs in the early morning sky. Ignore them. The objects are fully identified. They’re the planets Venus and Jupiter – the brightest objects in the night sky after the Moon. They’re crossing paths, as Jupiter pulls away from the Sun as seen from Earth, and Venus drops toward it. Venus is the brighter of the two.

Venus and Jupiter could have a big influence on our own planet – not astrologically, but gravitationally.

The planets all probably moved around a lot when the solar system was young. Today, their configuration is stable. And it should remain stable for hundreds of millions of years.

But it’s impossible to predict beyond that. Tiny differences in a planet’s current orbit could have a big impact on its position in the far distant future. As a planet moves toward or away from the Sun, its gravity pushes and pulls the other planets, changing their location.

Earth is most influenced by the gravity of Venus – which passes closer to us than any other world – and Jupiter – the most massive planet. They squeeze and stretch Earth’s orbit over a cycle of about 400,000 years. In the distant future, they could destabilize the orbit – dramatically changing Earth’s place in the solar system.

Look for these “influential” planets beginning a couple of hours before sunrise. They remain visible deep into the dawn twilight.

Script by Damond Benningfield

Based on how bright the stars look to our eyes alone, Deneb ranks among the 20 brightest stars in the night sky. Because the stars are at different distances, though, that ranking is a little misleading. If we could arrange them based on their true brightness, Deneb would outshine them all. In fact, it might be the brightest of all the stars that are easily visible to the unaided eye.

Deneb is high in the east-northeast at nightfall, at the lower left corner of the bright Summer Triangle.

Deneb is a blue supergiant – it’s much bigger, heavier, and hotter than the Sun. And it’s much, much brighter. Exactly how much brighter isn’t certain. That’s because there’s disagreement about the star’s distance.

Astronomers have measured the distance with several techniques. Some are more direct, while others are based on models of different types of stars. That’s yielded estimates of about 1400 to 2600 light-years.

And that makes a big difference. At the greater distance, Deneb would be almost four times brighter than at the smaller one. So Deneb’s true luminosity – the value when you add up all wavelengths of light – is somewhere between 50,000 and 200,000 times the Sun’s. If the high end of that range is correct, then Deneb is one of the brighter stars in the entire galaxy – and perhaps the brightest star that’s easily seen with the eye alone.

Script by Damond Benningfield

Altair is a close neighbor – just 16.7 light-years away. Only about 50 star systems are closer. And it’s bigger and brighter than the Sun, so it’s easy to study. Even so, not even the largest individual telescopes can see it as more than a bright dot. Yet astronomers have managed to take a fairly detailed picture of it.

They’ve done so with a technique known as interferometry. It combines the views from several fairly small telescopes that are linked together. That reveals as much detail as a single giant telescope. Just how much detail depends on the number and size of the telescopes, and how far apart they’re spaced. The setup doesn’t necessarily see fainter stars and galaxies, but it does see the universe with greater clarity.

With conventional telescopes, astronomers had found that Altair spins in a hurry – once every eight hours, versus about 25 days for the Sun. That suggested the star was flattened. They measured that flattening with an interferometer; the star is about 25 percent wider through the equator than through the poles.

A few years later, they confirmed that it’s cooler and darker around the equator. And in 2006, they even took a picture of Altair – the first detailed image of any Sun-like star.

Altair is high in the southeast at nightfall, at the lower right corner of the bright Summer Triangle. We’ll talk about another member of the triangle tomorrow.

Script by Damond Benningfield

A bright Moon is a beautiful sight – unless you have your heart set on seeing the stars. In that case, it’s a pest. The Moon’s glare overpowers many of the stars in the sky.

But some manage to shine through even the brightest moonlight. Tonight, for example, even though the Moon is about 95 percent full, three stars are quite easy to find: Vega, Deneb, and Altair – the Summer Triangle. The triangle stands high in the eastern sky at nightfall, and climbs directly overhead later on.

Its brightest member is Vega, at the top of the triangle. It’s about 25 light-years away. That means the light you see from the star tonight began its trek across the galaxy in the year 2000. Vega is bigger and heavier than the Sun, and almost 50 times brighter.

Deneb is to the lower left of Vega. Its distance is uncertain; more about that tomorrow. What is certain is that it’s a supergiant – many times bigger and more massive than the Sun, and tens of thousands of times brighter. And its fate is pretty well known, too: Deneb is likely to explode as a supernova sometime in the next few million years.

Altair is farther to the lower right of Vega. It’s the closest member of the triangle – just 17 light-years away. It’s a lot like Vega, just not quite as impressive. Still, it’s easy to spot through the moonlight – a member of the bright Summer Triangle.

Script by Damond Benningfield

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