StarDate

The best sign in the night sky that fall has arrived is the appearance of the “autumn star.” It’s the only bright star that puts in its best showing during the nights of autumn: Fomalhaut, the leading light of Piscis Austrinus, the southern fish.

Fomalhaut is only about 450 million years old — just one-tenth the age of the Sun. It’s also a good bit bigger and heavier than the Sun, which makes it hotter and brighter — one reason that Fomalhaut shines so brightly in our sky. The other reason is that it’s just 25 light-years away, which makes it a close neighbor.

The most interesting thing about Fomalhaut isn’t the star itself, though. Instead, it’s a wide disk of dust that encircles it. The disk seems to be bounded by a giant planet that’s about 15 billion miles from Fomalhaut — more than a hundred times farther than Earth is from the Sun. Hubble Space Telescope has snapped pictures of the possible planet, although it’s so small and far away that it’s nothing more than a tiny dot.

Its orbit is stretched out, so the planet’s distance from Fomalhaut varies by almost 300 billion miles. That odd orbit may suggest that another planet orbits much closer to Fomalhaut, deep within the dust that surrounds the “autumn star.”

Look for Fomalhaut low in the southeast not long after night falls, and due south around midnight. There are no other bright stars or planets anywhere near it, so you can’t miss the signature star of autumn nights.

Script by Damond Benningfield

When it comes to the greenhouse effect, timing is everything. The current warming of our planet is forecast to have dire effects on life. But a greenhouse effect when Earth was young may have been a boon for life.

When Earth was born, the Sun was fainter and cooler than it is today. That means Earth wouldn’t have received enough energy for liquid water to exist on its surface. Instead, any water would have been frozen solid. And without liquid water, it wouldn’t have been possible for life to take hold. Yet the geologic record of that early era suggests there was liquid water.

A recent study by researchers at the Southwest Research Institute proposed a possible solution to the problem: a steady bombardment of asteroids.

By looking at the craters on the Moon and Mercury, we know that the asteroids pounded the worlds of the inner solar system for several hundred million years. On Earth, those impacts vaporized the asteroids, spewing hot gas and rock into the atmosphere. They also created pools of molten rock on the surface.

The recent research says that the bubbling rock released a lot of carbon dioxide and other greenhouse gases into the air. That trapped more of the weak solar energy, warming the planet enough to melt the ice and create lakes and oceans. The impacts also delivered much of the chemistry of life.

So these powerful collisions might have created a powerful greenhouse effect — turning Earth into a comfortable home for life.

Script by Damond Benningfield

The Sun changes hemispheres today. It crosses the equator from north to south. That ushers in autumn here in the northern hemisphere, and spring in the south.

There’s also a division of hemispheres in the evening sky — a division that also marks the changing seasons. The western half of the sky features some of the most prominent stars and constellations of summer, while the eastern sky features the stars of autumn.

As night falls, look low in the south and southwest for two bright markers of summer — the teapot of Sagittarius and the curved body of Scorpius, the scorpion. And off to the left of Sagittarius, in the southeastern sky, look for Capricornus and Aquarius, two denizens of autumn. They’re fainter than the summer stars, though, so they’re tougher to pick out.

Over the next few weeks, Scorpius and then Sagittarius will drop out of the evening sky, but their autumn counterparts will climb higher.

It’s all caused by our changing perspective on the stars. Every star rises and sets four minutes earlier each day. So that gives us new stars to admire with each season — and a season for each star.

One symbol of summer straddles the eastern and western halves of the sky tonight: the Summer Triangle. And that seems fitting, since the name is a bit off. The triangle is in good view in the evening skies of summer, but it remains in the evening through the next change in seasons — when autumn gives way to the cold nights of winter.

Script by Damond Benningfield

We all know what happens when aliens invade Earth. They kill as many people as possible, enslave the rest, and take our planet’s resources for their own. And we have one man to thank for that scenario: Herbert George Wells, author of “War of the Worlds” — the tale of an invasion from Mars.

H.G. Wells was born 150 years ago today in Kent, England. The young Wells was a bit sickly, and he suffered an injury at age seven that kept him in bed for months. He put the time to good use, though, reading every book he could get his hands on.

Wells became a teacher, then earned a degree in biology. Afterwards, he turned to writing. In 1895, he published his first novel, “The Time Machine.” It was an instant success. Wells followed up with such classics as “The Invisible Man” and “The First Men in the Moon.”

He moved into other forms of writing in the early 1900s, including comedies about working-class characters, utopian novels, and non-fiction.

His writing often expressed his views about class and society. Wells was a socialist who advocated a single world government. And he traveled the world, meeting with such notables as Vladimir Lenin and Franklin Roosevelt.

The two world wars made Wells much more pessimistic about the future. One of his final works prophesied a bleak end for humanity. But today, he’s best known for his earlier works of science fiction — including one in which humanity almost came to an end at the hands of alien invaders.

Script by Damond Benningfield

For most of its long lifetime, a star like the Sun is pretty stable. It steadily “fuses” the hydrogen in its core to make helium, releasing energy in the process. That keeps it shining steadily for billions of years.

As it uses up the hydrogen, though, things change.

Aldebaran, the bright orange eye of Taurus, is going through the first of those changes right now. The star rises to the lower left of the Moon before midnight, and is closer to the Moon at first light tomorrow.

Aldebaran has already converted the hydrogen in its core to helium. But the core isn’t hot enough for the helium to fuse together to make heavier elements. Instead, fusion probably is taking place in a thin layer of hydrogen around the core. That’s pushed outward on the surrounding layers of gas, causing Aldebaran to puff up to more than 40 times the diameter of the Sun. That’s caused the surface to cool, so it glows reddish-orange.

Over the next few million years, Aldebaran will get even bigger and brighter. At the same time, its core will get smaller and hotter. Eventually, it’ll get so hot that the helium will ignite. That will begin a new round of fusion reactions, which will create carbon and oxygen.

The star will burn through the helium quickly. When it’s gone, fusion will shut down for good. Aldebaran’s outer layers will puff out into space, leaving only its hot but dead core, which will spend many billions of years cooling and fading from sight.

Script by Damond Benningfield

X-rays are far more energetic than most other forms of radiation, so they can cause cancer and other health problems. Fortunately for life on Earth, our atmosphere blocks X-rays from space. Un-fortunately for astronomers, though, that makes it tough to study those X-rays, which come from some of the most extreme objects in the universe.

Still, there are ways to see the X-ray sky — by lofting X-ray telescopes on balloons and rockets. And 50 years ago tomorrow, astronomers used a rocket-borne instrument to discover an exotic source of X-rays in the constellation Vela.

Scientists launched an X-ray detector from a small island southwest of Hawaii. Its rocket pushed it above most of Earth’s atmosphere, where it detected a source of X-rays now known as Vela X-1.

Today, astronomers know that the system is about 6500 light-years away. It consists of two very different stars that are in a tight orbit.

One star is a supergiant — it’s much bigger, brighter, and hotter than the Sun. Its mate is a neutron star. It’s a mere dozen miles across, but it weighs more than the Sun. As a result, its gravity is immense. If you dropped a pebble from a height of a few feet, it would smash into the surface at millions of miles per hour, releasing an enormous amount of X-rays.

And material is falling onto the neutron star: gas from the companion. As the gas plunges in, it gets so hot that it produces X-rays — which astronomers first detected 50 years ago.

Script by Ken Croswell, Copyright 2016

Going to the bottom of the fourth inning of a playoff game between the Pittsburgh Pirates and the Brooklyn Dodgers 75 years ago today, the score was tied at zero. But Pittsburgh first baseman Elbie Fletcher led off with a single, and right fielder Bud Stewart followed with a double. Vince DiMaggio then singled them both home, starting a four-run rally.

For the 6800 fans at Forbes Field in Pittsburgh, it was a bracing 15 minutes or so. For the fans listening on radio station WUR in Brooklyn, though, it was a major aggravation. The station went dark during the inning, leading to thousands of unhappy phone calls.

The reason for the blackout was a magnetic storm on the Sun. It bombarded Earth with radiation and charged particles. Earth’s magnetic field funneled many of those particles toward the surface, where they had a big impact.

The storm not only knocked out the Brooklyn station, for example, it blacked out shortwave radio broadcasts between the U.S. and Europe for most of the day. The storm also triggered a bright display of the northern lights in Chicago and deep into the Midwest. And in Europe, it created northern lights that were bright enough to help British bombers see their targets.

Incidentally, Brooklyn fans weren’t any happier when the playoff game came back on the air. The Dodgers took the lead in the eighth inning, then gave it right back. They lost, 6 to 5.

Script by Damond Benningfield

The starship Enterprise began warping around the galaxy 50 years ago this month, discovering new life and new civilizations on just about every planet. But according to researchers in Australia, the real explorers of the future might not be so lucky. They won’t find a bounty of inhabited planets. Instead, they’ll find a bounty of worlds that were inhabited in the distant past, but that now are dead.

The most likely abodes for life are expected to be Earth-like planets orbiting Sun-like stars in the habitable zone — the distance from the star where temperatures are just right for liquid water.

Earlier this year, Aditya Chopra and Charles Lineweaver wrote that such planets probably are common. They even suggested that life is likely to develop on such worlds. But they argue that unless that life can adapt to rapid changes on such planets, it won’t last long — it’ll die off in less than a billion years. Surviving that early period may be “like trying to ride a wild bull,” they wrote: “Most life falls off.”

But life on Earth held on. Early single-celled organisms altered the climate enough to allow more complex forms of life to develop. And life adapted quickly enough to overcome impacts with comets and asteroids, the loss of water and other key compounds, and other unhealthy events.

If the researchers are right, then Earth is a rarity: a world where life altered the climate enough to keep itself going — a world worth a visit by a starship.

Script by Damond Benningfield

Like most people, many scientists believe there’s some type of life on other planets. It could be as simple as microbes, or as complex as the plant and animal life here on Earth.

But there’s a huge gap between believing that something’s there and actually proving it. And so far, there’s no confirmed evidence of life on any world other than our own. Yet astronomers are already trying to tease out that evidence on exoplanets — worlds that orbit stars other than the Sun.

They’re doing so by taking advantage of the fact that most of the worlds discovered so far pass in front of their stars. Astronomers take a spectrum of the star when no planet is in front of it, revealing the star’s chemistry. Then they take another spectrum when the planet passes in front of the star. If the planet has an atmosphere, then some of the star’s light passes through it. Comparing the spectra can reveal the chemistry of that atmosphere.

Life on Earth produces elements and compounds that are rarely found without life, such as oxygen and methane. So if one of these “biomarkers” turns up in a planet’s atmosphere, it increases the odds that something is living there. And if more than one biomarker is found, especially at high concentrations, then it’s a good bet that it’s a living world.

Astronomers have used this technique to study the atmospheres of several planets. So far, though, they haven’t found any biomarkers — the signature of life on another world.

Script by Damond Benningfield

The giant planets Jupiter and Saturn are unlikely homes for life. They don’t have solid surfaces, and conditions in their atmospheres aren’t good for the kind of life we have here on Earth. Yet both planets have moons that are considered much more likely abodes for life. The moons have liquid water below their icy crusts, along with sources of energy and the right chemistry for life. That’s inspired astronomers to look for moons orbiting planets in other star systems.

They’ve already discovered several giant planets that are in the habitable zone — the distance from the star where temperatures are just right for liquid water. The planets are too much like Jupiter and Saturn for Earth-like life. But if they have big moons, those worlds could be good abodes for life — small, rocky worlds with lots of water.

Recent simulations by researchers at McMasters University found that such “exomoons” could grow to about twice the mass of Mars — bigger than any moon in the solar system. Such a heavy world could hold on to its water and atmosphere for billions of years — providing plenty of time for life to develop.

So far, no one has seen any exomoons. They’re quite hard to detect with current technology. But new telescopes on the ground and in space should have the ability to pluck them from the observations of exoplanets — perhaps revealing some distant homes for life.

We’ll talk about how we might find evidence of life on other worlds tomorrow.

Script by Damond Benningfield