StarDate

From a light-polluted city or suburb, the night sky features the Moon, the bright planets, and a few dozen to a few hundred stars. If you escape city lights, though, you’ll see that parts of the night sky glow. There’s the faint band of the Milky Way, which arcs high across the sky on September evenings. And before dawn now, there’s a glowing pyramid called zodiacal light — sunlight reflecting off countless particles of dust.

The name comes from the light’s location — along the zodiac. The particles of dust are there all the time. But they’re easiest to see before dawn around the start of autumn, and after sunset at the start of spring. The zodiac stands at a good angle then, and the Sun is just below the horizon, so it lights up the dust.

The dust grains may come from asteroids and comets. But recent research says that most of them may come from Mars.

During its cruise from Earth to Jupiter, the Juno spacecraft was hit by many grains of dust. They knocked off bits of the craft’s giant solar arrays, which provide electricity. The bits of debris from the arrays showed up as streaks of light in pictures of the space around Juno. Extensive analysis showed that most of the impacts took place from Earth to just beyond Mars — an indication that the dust came from Mars. A comparison to computer models showed a good match to the band of dust that makes up the zodiacal light — clouds that will glow in the east before dawn until the Moon overpowers them later this month.
 

Script by Damond Benningfield

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Outer space is a whole bunch of nothin’. Most of it is a near-perfect vacuum — far emptier than anything we can produce in a laboratory on Earth. Yet it’s not completely empty. It contains a few atoms and molecules. It’s filled with the afterglow of the Big Bang. And it may produce its own energy.

The quality of the vacuum depends on where you are. A couple of hundred miles above Earth, for example, the vacuum is fairly densely populated. Wisps of Earth’s outer atmosphere exert a drag on orbiting satellites. They have to fire their engines from time to time to keep from falling down.

The space between the planets is less dense — perhaps 5 to 10 atoms or molecules per cubic centimeter. Most of that consists of particles of the solar wind. Venture out between the stars, and the number drops to about one atom per cubic centimeter. And between galaxies, it’s only a fraction of that — mostly atoms of hydrogen and helium forged in the Big Bang.

Space also is filled with a type of energy known as the cosmic microwave background. It’s left over from the era shortly after the Big Bang. We see it everywhere we look.

And the vacuum of space may produce its own energy. This energy may cause the universe to expand faster over time. And as the universe expands, it creates more space, so the “vacuum energy” increases. This may explain dark energy — one of the hottest topics in modern astrophysics — an energy from the vacuum of space.
 

Script by Damond Benningfield

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Ocean waves travel across the water and sound waves travel through air. In fact, those waves don’t work without a medium — something to pass them along from place to place. So it makes sense that light waves need something to transmit them across the vacuum of space.

For centuries, scientists called that medium the ether. They couldn’t explain what it was. But they knew that you couldn’t see it, feel it, or weigh it. In fact, it wouldn’t interact with “normal” matter in any way. But it was infinite — it filled the entire universe.

By the mid-1800s, though, many scientists had some doubts about it. And an experiment in 1887 all but ruled it out.

Albert Michelson and Edward Morley figured that as Earth orbited the Sun, its speed relative to the ether was changing. And since light waves were carried by the ether, the scientists expected to be able to see a change in the speed at which light travels. So they measured the speed of light in Earth’s direction of motion, and at a right angle to that direction. But they saw no change — the speed of light was always the same.

Later, Albert Einstein’s Theory of Special Relativity explained that the speed of light in a vacuum is constant — it never changes. That ruled out the need for an ether to transmit light waves through the universe.

That doesn’t mean that the vacuum of space is a complete void, though — or that we know everything about it. More about that tomorrow.
 

Script by Damond Benningfield

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It doesn’t take long to give birth to a star. A nursery in the tail of the scorpion seems to have done it in just 150,000 years — the blink of a cosmic eye.

RCW 120 is a bubble of hot gas about 5500 light-years away. It’s about 15 light-years across. It’s mostly round, with a hole in one side that’s releasing hot gas into space.

The bubble was formed by radiation and winds from a hot, massive young star. They push away gas and dust around the star like a snowplow clearing a highway. All of that material piles up, forming the bubble.

As the bubble expands, it sweeps up even more gas and dust. It also rams into dense knots of material. The expanding bubble squeezes those knots, causing some of them to collapse. The gravity of such a dense blob then pulls it together to form a star.

From the rate at which the bubble is expanding, astronomers calculated that it started forming only about 150,000 years ago. But several knots along the bubble’s edge have given birth to brand-new stars, or they’re in the process of giving birth — an indication that it doesn’t have to take long to make a star.

RCW 120 is in the middle of the region outlined by the curving tail of Scorpius. The scorpion is low in the south at nightfall, with the tail just above the horizon. Through a telescope, RCW 120 looks like a small ring. In fact, it’s also known as the Green Ring Nebula — a busy nursery for new stars.
 

Script by Damond Benningfield

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The hot stars at the center of a nearby nursery may have Jekyll and Hyde personalities. On the one hand, they appear to trigger the birth of new stars. On the other, they may prevent the birth of even more.

Cepheus OB4 is a giant complex of gas, dust, young stars, and newly forming stars. It’s about 3600 light-years away, along the border between Cepheus and Cassiopeia, which are in the northeast at nightfall.

The name of the complex indicates that it contains many class O and B stars. They’re especially hot, bright, and heavy. OB regions are where most stars are born, so they’re great labs for studying the birth of all stars.

O and B stars produce powerful “winds” of hot gas. The winds ram into the surrounding clouds of gas and dust. That can cause the clouds to collapse and form new stars. But it can also blow away the material for new stars, shutting down starbirth.

And a recent study says that both processes appear to be at work in Cepheus OB4.

Researchers looked at about 760 young stellar objects — either infant stars or dense blobs that are about to become stars. They found many of them in regions with dense clumps of gas and dust. But they found few of them outside those regions. So winds from the stars at the center of the complex may be triggering starbirth in some places, but clearing out regions where the raw materials are more thinly spread — blocking the birth of even more stars.

More tomorrow.
 

Script by Damond Benningfield

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If anyone in the star system 47 Ursae Majoris happens to be aiming a radio telescope at Earth in about 26 years, they’ll hear a concert of Theremin music. The concert was beamed toward the system 20 years ago today — a project known as the Teen-Age Message.

The project was conceived by Alexander Zaitsev, a top radio and electronics engineer in Russia. He wanted to send a message to other civilizations that combined science and art. So the message included the equivalent of an ID tone, 15 minutes of music, and a series of images and notes. It was aimed at six different stars. The stars and the music were selected by Russian teenagers.

The sequence was beamed into space from a radio telescope in Ukraine. The first message went out on August 29th, 2001, but it won’t reach its target star until 2070.

The message was sent to 47 Ursae Majoris and two other stars on September 3rd, and the final stars the following day.

47 Ursae Majoris was picked because it was one of the first Sun-like stars known to have a planet. Since then, astronomers have discovered two more planets in the system. None of them is considered a likely home for life. But more hospitable planets could await discovery there. And in 2047, anyone on those planets could hear music from Vivaldi and a half-dozen other composers wafting through the galaxy ... a message from Russian teenagers.
 

Script by Damond Benningfield

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Every star you see in the night sky has many names: proper names, Greek-letter names, and names that look like phone numbers. And the names keep getting more complicated.

Consider Dabih. It’s in Capricornus, which is in the southeast at nightfall. Dabih is near the right point of a wide triangle that outlines the sea-goat. Right now, the star is above the bright planet Saturn.

Dabih is a system of at least five stars. Or it used to be. Now it’s just a single star. The other stars didn’t go away. They just aren’t called Dabih any more — at least not officially.

A telescope shows Dabih as two stars. The brighter one is known as Dabih Major. But it’s also known as Beta-1 Capricorni and Beta Capricorni A. The other one is Dabih Minor, Beta-2 Capricorni, and Beta Capricorni B.

There’s more to the system than meets the eye, though. “B” consists of two stars, while “A” has three.

The group that names astronomical objects has been assigning official proper names to stars. Most of the names have been around for centuries — like Dabih. For systems that contain multiple stars, though, the group decided to assign the classical name to only one star. So “Dabih” was given to one of the stars of system A.

On many star charts, though, the name still applies to the entire system. So many skywatchers are likely to keep thinking of the point of light that’s visible to the eye as Dabih — one of many names for a crowded star system.
 

Script by Damond Benningfield

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We often tell you about optical illusions in the night sky — things that aren’t what they seem. And a great example is in view right now: the planet Venus and the star Spica. They’re low in the southwest as evening twilight fades away. And the situation definitely isn’t what it seems.

Venus is the brilliant “evening star” — the brightest object in the night sky other than the Moon. Spica is close to the left of Venus tonight. The two objects will move closer over the next few evenings, though. By Sunday evening, Venus will stand a little above the star.

Venus looks so bright because it’s wrapped in reflective clouds, it’s close to the Sun, and it’s close to Earth — about a hundred million miles at present. But Spica is about 15 million times farther than Venus is. If you lined them up at the same distance, Spica would look about 200 million million times brighter than Venus. So you’d have to spread them out to be able to see Venus at all through Spica’s glare.

Another part of the illusion is the number of objects we see. Venus is a single planet. But Spica is a binary star — two stars locked in a mutual orbit. Because of their great distance from Earth, though, their light blurs together to form a single pinpoint. The larger of Spica’s stars is more than 800 times wider than Venus — completing a beautiful illusion in the early evening sky.

Tomorrow: many names for a crowded star system.
 

Script by Damond Benningfield

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It’s always iffy to bestow a superlative on a star. That certainly seems to apply to the Pistol Star. It’s definitely one of the most impressive stars in the Milky Way Galaxy. But it’s probably not quite as impressive as first reported.

The star was discovered three decades ago. It wasn’t seen earlier because it’s hidden behind clouds of dust that make it appear much, much fainter.

The star is named for the outline of a surrounding bubble of gas — the Pistol Nebula. It was created by the star itself. The star is so big and hot that it’s blowing away its outer layers at a furious rate.

When astronomers first saw the Pistol, they estimated its mass at about 250 times that of the Sun. That made it the heaviest star yet seen. Since then, the star’s been studied in more detail. That’s shown that it’s only a few dozen to perhaps a hundred times the Sun’s mass. That’s heavier than all but a tiny percentage of other stars, but not quite at the top of the list.

And the Pistol may not be quite as bright as first thought, either. Estimates range from about 1.6 million to 3.3 million times the brightness of the Sun. Either way, it’s an impressive star — just not the most impressive.

The Pistol Star is in Sagittarius. The constellation is low in the south at nightfall. Some of its stars form the outline of a teapot. The Pistol Star is in the “steam” above the spout of the teapot — a brilliant star hiding at the heart of the galaxy.

Script by Damond Benningfield

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We all know that an atom looks like a tiny solar system. It has a dense mass in the middle, with smaller objects orbiting around it. That picture was first drawn by Ernest Rutherford, who was born 150 years ago today.

Rutherford studied math and science in his native country, New Zealand. He did graduate work in England, then began his professional career in Canada. He moved back to England a few years later, and stayed there the rest of his life.

Rutherford spent much of his career studying radioactivity and the structure of the atom. He discovered several radioactive elements. And he realized that the contemporary idea of the atom was wrong. Instead of a solid mass, it was mostly empty space. It consisted of a small, heavy nucleus with smaller particles orbiting around it. The nucleus contained all of the atom’s positive electric charge, while the orbiting particles contained the negative charge.

Rutherford also discovered a way to characterize individual atoms — a finding that allowed scientists to study matter at the smallest scales for the first time.

Rutherford won many accolades for his work. He was knighted in 1914, and made a baron in 1931. He won the Nobel Prize in Chemistry in 1908. And in 1997, a newly discovered element — number 104 — was named rutherfordium in his honor.

Rutherford died in 1937. Today, he’s considered one of the fathers of nuclear physics — the scientist who gave us the atom.

Script by Damond Benningfield

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