StarDate

More than five decades ago, astronomers at the University of California at Berkeley were using radio telescopes to study the Orion Nebula, a giant stellar nursery. They found an especially strong signal at an unexpected wavelength. The astronomers thought the signal might come from a mysterious molecule that no one had ever seen on Earth. So they gave it an appropriate name: mysterium.

They soon learned that it was a common molecule made of one oxygen atom and one hydrogen atom. The radio signal was especially strong because the molecules were being pumped up by infrared energy from gas clouds. That created a maser — the radio equivalent of a laser. It was the first maser ever discovered.

The Berkeley team was led by Harold Weaver, who was born 100 years ago this week.

In high school, Weaver built his own telescopes. He worked on military programs during World War II, then joined the Berkeley faculty in the early ’50s.

Radio astronomy was a young field, but it provided information that couldn’t be obtained with other techniques. Among other things, it revealed the presence of atoms and molecules in interstellar space. That allowed astronomers to trace where stars were being born.

Weaver established a radio astronomy lab and a big radio telescope. The telescope operated for three decades. Its accomplishments included discovering and mapping other masers in space.

Weaver died earlier this year — a pioneer at exploring the “mysteries” of the cosmos.

Script by Damond Benningfield

A pleasant autumn evening is a good time for a little jaunt — on foot, in your car, or in your personal spaceship. You might be tempted, for example, to cruise to a pair of bright objects that are in the southwest this evening: the Moon and the planet Saturn.

So you power up your ship and head toward the Moon, which is about a quarter of a million miles away. At escape velocity — about 25,000 miles an hour — it would take you 10 hours to get there. But that’s only if you could ignore the effects of gravity. As you move away from Earth, the old home planet is reluctant to let you go — it tugs at your spaceship, trying to pull it back. So that slows you down — until you get close to the Moon. Then its gravity takes over and starts making you go faster. So the total travel time is close to three days.

If you’ve packed enough supplies, you might want to go on to Saturn, which looks like a bright star below the Moon this evening. At that steady speed of 25,000 miles per hour, it would take you more than four years to get to where Saturn is tonight.

By the time you arrive, though, Saturn would be nowhere around. That’s because its orbit around the Sun would have carried it hundreds of millions of miles from its current position.

So when you take off for astronomical adventures, it helps to know about gravity and orbits and other essential details for exploring the cosmos.

Script by Damond Benningfield

 

Stars are all glowing balls of gas that “fuse” lighter elements to make heavier ones. Within that broad description, though, there’s a huge diversity of size, mass, brightness, and temperature.

A star at the top end of the scale is in good view tonight. Antares is the heart of the scorpion. It’s below the Moon as night falls, shining bright orange.

The least-impressive stars are only about one-tenth as massive as the Sun, and just one ten-thousandth as bright. But they make up for their puniness with longevity — they’ll live for a trillion years or longer — a hundred times the current age of the universe.

Stars like Antares, on the other hand, burn through their nuclear fuel in a hurry. Antares is about 15 to 18 times as massive as the Sun — one of the heaviest stars around. Because of that great mass, though, gravity squeezes its core tightly, greatly revving up the rate of nuclear reactions. So Antares will live only about 20 million years — the blink of an eye on the astronomical time scale.

Antares is more than half way through that lifetime, so its surface layers have puffed up to enormous proportions — the star is almost a thousand times wider than the Sun. And it produces tens of thousands of times more energy than the Sun — a true standout among the stars.

Again, look for Antares below the Moon this evening. Brighter Saturn is about the same distance to the left of the Moon. More about the Moon and Saturn tomorrow.

Script by Damond Benningfield

A small, faint “shield” of stars scoots across the southwestern sky on these early autumn nights. It represents the coat of arms on the shield of John Sobieski, a 17th-century king of Poland and one of the country’s great national heroes.

The shield is the constellation Scutum. Johannes Hevelius first drew it around 1687, using a few stars from a relatively barren region of the sky. He originally named it Scutum Sobiescianum — the shield of Sobieski. But in more recent times, the last part of the name has been dropped.

Sobieski became king of Poland in 1674. He built alliances with several European neighbors, and fought the Ottoman empire when it tried to expand westward. In 1683, he earned fame across all of Europe by defending Vienna against the invading Ottoman army.

To honor his native country, Hevelius included the new constellation in a beautiful star atlas, which was published in 1690. He depicted several faint stars as the cross on Sobieski’s shield. Scutum Sobiescianum has kept its place in the stars ever since then.

Unfortunately, the stellar shield isn’t all that much to look at. You need fairly dark skies to see any of its stars. Right now, look for it in the southwest as night falls. It’s above the teapot-shaped constellation Sagittarius. The shield of Sobieski drops down the southwestern sky during the evening, and sets after not long after midnight.

Script by Damond Benningfield

 

When spring and autumn arrived in the ancient city of Cahokia, the city’s chief reaffirmed his connection to the cosmos. On the equinoxes, priests watched the sunrise from inside a ring of tall poles that served as a calendar. They saw the Sun climb into view behind Monks Mound, a great pile of earth topped by the chief’s home and court. The Sun was reborn — and so was the chief.

Cahokia stands across the Mississippi River from present-day Saint Louis. The city reached its peak around eight centuries ago. It covered about six square miles, incorporated more than a hundred earthen mounds, and its population swelled to perhaps 20,000 — larger than London.

The focal point for Cahokia was Monks Mound — the largest earthen structure in the early Americas. It covered 14 acres and rose a hundred feet into the sky. Most of it is still standing.

To the west of the mound, inhabitants built a calendar circle. Archaeologists named it Woodhenge because of its resemblance to Stonehenge. The Cahokians actually built five Woodhenge circles. Each consisted of a central Sun-watching station, surrounded by a ring of cedar poles. The Sun aligned with these poles on the equinoxes, solstices, and other important dates.

Archaeologists have rebuilt one of the rings, which spans more than 400 feet. Visitors watch the equinox sunrise from Woodhenge even now — observing an act of nature that was a potent symbol for a long-ago culture.

Script by Damond Benningfield

 

It’s been a scorching summer for much of the country. And while we can’t say whether the scorching is over, we can say that summer is. Autumn arrives in the northern hemisphere today at 3:02 p.m. Central Time — the autumnal equinox.

The season changes when the Sun crosses the equator from north to south. It will continue its southward trek until the winter solstice, in December. As it does so, the days will get ever shorter in the northern hemisphere, while they get longer in the southern hemisphere.

For a few days around the equinox, day and night are about the same length. In fact, that’s where the name “equinox” comes from. It’s a Latin word that means “equal nights.” So at the equinoxes, the interval between sunrise and sunset is roughly 12 hours. And that’s the case across the whole planet.

On the equinox itself, though, the interval is actually a few minutes longer. There are several reasons for that. One is that Earth’s atmosphere acts like a lens, “bending” the Sun’s rays back over the horizon. So when you see the Sun sitting on the horizon, it’s an illusion. The Sun itself is below the horizon, but an image of it is projected back into view.

With the Sun in view for less time each day, and the sunshine coming in at a lower angle, temperatures north of the equator will fall. That will bring more comfortable days after a long, hot summer — and provide more time for watching the stars under the cool nights of autumn.

Script by Damond Benningfield

 

A giant lake sits on the surface of Io, one of the big moons of Jupiter. It’s about 125 miles wide, and it covers an area bigger than Lake Ontario. But that’s where the comparisons to earthly lakes end. That’s because Loki Patera is filled not with water, but with lava.

Io is the most volcanically active body in the solar system. The gravity of Jupiter and its other big moons pull at Io, stretching and squeezing its interior. That melts rock below the surface. Some of the sulfur-rich molten rock punches its way to the surface, forming volcanoes, along with pools of super-hot lava.

There could be more than 400 active volcanic features on Io. And Loki Patera is the biggest of them all. It’s been filled with molten rock since at least 1979, when it was discovered in pictures by Voyager 1. But it doesn’t always look the same. Every year or two, it flares up.

That’s probably because the top of the lake gets cooler, so it forms a solid crust. The solid rock is denser, so it sinks, allowing fresh molten rock to bubble to the surface. This process happens in waves, which take several weeks to ripple across Loki Patera — the largest active volcano in the solar system.

We can’t see Io right now, but we can see Jupiter — barely. The giant planet is close to the left of the crescent Moon shortly after sunset. Although it’s quite low in the sky, if you have a clear horizon it should be fairly easy to spot through the fading twilight.

Script by Damond Benningfield

With summer just about ready to give way to fall, one of the signature star patterns of the new season is climbing into prominence in the evening sky. The Great Square of Pegasus is in the east as night falls. It’s tilted a bit as it rises, so it looks a bit more like a diamond than a square.

The jewel at the top of the diamond is known as Beta Pegasi. It’s a red giant — an old, bloated star that shines reddish orange. That color isn’t visibile to the unaided eye because the star is relatively faint — mainly because it’s about 200 light-years away. But the tint should be easy to see through binoculars.

A star’s color is the result of its surface temperature. Hot stars are blue-white, while cool stars are orange or red. Beta Pegasi is thousands of degrees cooler than the Sun. That’s because the star is nearing the end of its life. Changes in its core have caused its outer layers to puff outward, so the star is almost a hundred times the Sun’s diameter. That caused the gas in those layers to get cooler — and redder.

The change in temperature also produces a change in the type of energy the star radiates into space. Stars like the Sun produce most of their energy at visible wavelengths. But most of the light from Beta Pegasi is in the infrared — wavelengths that are too long for human eyes to see. When you add all the wavelengths together, Beta Pegasi shines about 1500 times brighter than the Sun — a red jewel sparkling across the galaxy.

Script by Damond Benningfield

 

Cepheus the king passes high overhead tonight. The constellation’s five main stars form a pentagon. None of them is especially bright, though, so you’ll probably need a star chart to find his majesty.

Even so, the brightest star in Cepheus has quite a future: It’s destined to become the North Star.

Right now the North Star is Polaris, the star at the end of the handle of the Little Dipper. The star marks true north because Earth’s axis happens to point nearly straight at it. So as Earth spins, Polaris remains in the same position, never rising or setting.

However, as the gravitational forces of the Sun and Moon tug at our planet, it wobbles. That makes its rotation axis gradually point elsewhere. In the year 7500 A.D., it’ll point at the brightest star in Cepheus, Alderamin.

Alderamin won’t be as good a North Star as Polaris is now. For one thing, it isn’t quite as bright. For another, while Polaris is less than a degree from the celestial pole, Alderamin won’t get closer than a couple of degrees.

Alderamin is a white star. In astronomical jargon, it’s of spectral type A, which means it’s hotter than the Sun. It’s also about 20 times brighter than the Sun. And as stars go, it’s fairly close by — just 49 light-years away. That’s much closer than Polaris, which is hundreds of light-years away.

Alderamin is easily visible from dark country locations, and even from many suburbs, passing high overhead tonight: our future North Star.

Script by Ken Croswell, Copyright 2017

The brightest planet and star in all the night sky are in good view at dawn right now. The planet Venus is low in the east. It’s the “morning star,” so it’s a brilliant target. And the star Sirius twinkles far to the upper right of Venus. No other star in the night sky outshines it.

Astronomers have long viewed the splendor of Sirius — first with the unaided eye, then with telescopes large and small. But through all these years of looking, they’ve missed something: a cluster of stars that lies in nearly the same direction as Sirius but far beyond it, in the outer part of the Milky Way galaxy.

The cluster was discovered in data from the Gaia space telescope, which is measuring the distances and velocities of a billion stars. Astronomers spotted a collection of stars just a sixth of a degree east of Sirius — about the width of a toothpick held at arm’s length. The stars were all the same distance from Earth: about 15,000 light-years, indicating they belong to a cluster, now named Gaia 1.

The cluster is 38,000 light-years from the Milky Way’s center. That’s 11,000 light-years farther out than the Sun and Earth are. The cluster is about 60 light-years across, and it emits 10,000 times more light than the Sun.

Such a bright cluster should have been seen long ago. It eluded detection by hiding behind the glare of Sirius. As a result, it took a sensitive new spacecraft to unveil this star-filled denizen of the Milky Way’s outer reaches.

Script by Ken Croswell, Copyright 2017