StarDate

Two planets line up close to the Moon tonight. Brilliant Mars is to the upper right of the Moon as they climb into view in late evening. And Uranus is closer to the upper left of the Moon. It’s much fainter than Mars, though, so you need binoculars to pick it out.

Only one spacecraft has ever visited Uranus. Voyager 2 flew about 50,000 miles above its cloud tops in 1986. Yet scientists are still learning from those observations.

Earlier this year, for example, two researchers reported that Voyager had flown through a “bubble” of the planet’s atmosphere.

Voyager recorded the strength of Uranus’s magnetic field. Scientists had looked at those observations. But the observations were averaged out over a period of minutes. For the new study, the researchers looked in greater detail — variations over as little as two seconds. And they found a “zigzag” in the data — a quick spike followed by a dip, then back to normal. It lasted only a few seconds.

The researchers concluded that Voyager had passed through a “plasmoid” — a bubble of charged particles stripped away from Uranus’s atmosphere. It was about 125,000 miles long, and twice as wide. Such bubbles had been seen at other planets, but not Uranus. They’re pulled away at the tail of the planet’s magnetic field, by interactions with the solar wind.

The observations indicate that such bubbles could have carried away much of the planet’s early atmosphere — one blob at a time.

Script by Damond Benningfield

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The Moon has an especially close encounter with the planet Mars tonight. They climb into good view by around 10:30 or 11 p.m. Mars looks like a brilliant star. At its closest, it’ll be less than one degree from the Moon — about the width of a pencil held at arm’s length.

From much of South America, the encounter will be even closer: The Moon will pass in front of Mars, blocking it from view.

Such an event is called an occultation. The Moon will “occult” Mars — from a Latin word that means “to hide.”

Occultations of Mars are possible because both Mars and the Moon stay close to the ecliptic — the Sun’s path across the sky. But occultations don’t occur every time the Moon and Mars meet up.

That’s because the paths of both worlds are tilted a bit. Mars’s orbit is tilted by about two degrees. That means it can wander two degrees away from the ecliptic. The Moon’s orbit around Earth is tilted by about five degrees. So the Moon can move a little farther from the ecliptic.

As a result, the geometry has to be just right for the Moon to occult the Red Planet — as it does tonight.

Incidentally, Mars is getting a little bit brighter by the day now. It’ll pass closest to Earth in about a month, when it’ll shine at its brightest. Right now, only the Moon and the planets Venus and Jupiter outshine it. At its peak, it’ll surpass Jupiter — shining as the third-brightest object in all the night sky.

Script by Damond Benningfield

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Summer arrived in the southern hemisphere of Mars a couple of days ago, on the summer solstice. And if a previous pattern holds, a long ribbon of clouds may be streaming away from a volcano just south of the equator.

Arsia Mons is the second-largest volcano on the Red Planet. It covers an area as big as Missouri, and it’s about 12 miles tall. But it hasn’t erupted in at least 10 million years.

Around the time of the southern summer solstice, a long cloud flows away from the summit. The cloud can extend for up to 1100 miles — roughly the distance from New York to Kansas City.

The Arsia Mons cloud has been observed several times over the years. Its most recent appearance was in 2018 — the last solstice. It appeared first thing in the morning, built across the landscape, then drifted away from the volcano and disappeared by early afternoon. It showed up in satellite images for about 90 days. Nothing else on Mars comes even close to the cloud’s length and persistence.

The cloud probably forms as warm, damp winds flow up and over the volcano. At altitudes of about 20 miles, the water vapor freezes, forming the cloud. As the planet warms in the afternoon, the ice vaporizes once again — and the cloud vanishes.

Mars trails the Moon across the sky tonight. They climb into good view by 10:30 or 11, with Mars to the lower left of the Moon. It looks like a bright orange star.

More about Mars and the Moon tomorrow.

Script by Damond Benningfield

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Astronomers are always trying to weigh the stars. That’s because precise measurements of a star’s mass can reveal what’s happening inside it. And that applies to dead stars as well as live ones.

A recent study, for example, reported the discovery of the heaviest neutron star yet seen. It could rule out some models of how such stars behave, but open up some others.

A neutron star is the corpse of a once-mighty star. When the star’s core can no longer produce nuclear reactions, it collapses, forming a neutron star. The star is heavier than the Sun, but no more than 15 or 20 miles in diameter. That makes it extremely dense — the densest form of matter in the universe.

Yet scientists aren’t sure just what form that matter takes. It could be a form that’s a bit “squishy,” or other forms that are stiffer. The new discovery could narrow down those ideas.

Scientists used radio telescopes to measure a binary system that contains a neutron star and another type of stellar corpse. The neutron star is also a pulsar. It spins about 350 times per second, emitting a “pulse” of energy with each turn. The gravity of its companion, though, produces tiny changes in the timing of those pulses.

Astronomers timed the pulses for more than a dozen years. And they found that the neutron star is about 2.14 times the mass of the Sun. That gives scientists something to think about as they ponder the interiors of these odd stellar corpses.

Script by Damond Benningfield

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During World War II, British physicist James Stanley Hey discovered that the Sun produces radio waves. He was studying radar technology for the military at the time, though, so he couldn’t reveal the discovery until after the war.

The war ended 75 years ago today, when Japan signed a formal declaration of surrender. Hey’s discovery was declassified soon after. And within a couple of years, scientists around the world were using war-surplus radar equipment to study the universe in great detail.

Many areas of science and technology benefitted from the advances made during the war, from nuclear physics to computers. But perhaps none benefitted as much as radio astronomy. Before the war, there was only one full-time radio astronomer in the world. By a decade after the war, there were dozens, along with big radio observatories.

Radar was developed to locate and track enemy aircraft well before they could reach their target. It sent out beams of radio waves, then tracked the “echo” when those waves reflected off the aircraft.

Scientists who had worked on radar systems during the war snatched up leftover receivers and converted them into telescopes. Experience with this early equipment led to better telescopes. Eventually, that allowed astronomers to study the hearts of galaxies, map the shape of the Milky Way, and discover quasars and pulsars. We’ll talk about a modern pulsar discovery made with radio telescopes tomorrow.

Script by Damond Benningfield

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DOUGLAS McARTHUR: We are gathered here, representatives of the major warring powers, to conclude a solemn agreement whereby peace may be restored.

75 years ago, aboard the U.S.S. Missouri, in Tokyo Bay, General Douglas McArthur was overseeing the formal surrender of Japan, ending World War II. American soldiers and civilian workers would soon be returning home, to the lives they’d established before the war.

That included many scientists, whose work had helped win the war. They’d made amazing advancements in electronics, rocketry, nuclear physics, radar, and other fields. Edwin Hubble, for example, for whom Hubble Space Telescope is named, had worked on rockets. And Lyman Spitzer, who was the driving force behind space telescopes, helped create sonar.

After the war, scientists built on those accomplishments.

Gerard Kuiper, for example, adapted military technology to make infrared detectors for telescopes. Using those detectors at McDonald Observatory, he discovered carbon dioxide in the atmosphere of Mars.

Scientists had more than just new equipment to keep them going, though. The successes of war-time science led to more government funding for post-war science — 10 times more than before the war. And astronomy was among the fields that benefited. Government funding paid for new instruments, telescopes, and even observatories — peaceful science that built on war-time accomplishments.

More about post-war astronomy tomorrow.

Script by Damond Benningfield

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Oxygen is one of the most essential elements on Earth. It makes up about one-fifth of the mass of the atmosphere, nine-tenths of the mass of water, and two-thirds of the mass of the human body. It’s a by-product of plant life, and a necessity for animal life. And we use it for everything from medical treatments to rocket propellant.

All of the oxygen atoms on Earth — and throughout the universe, for that matter — were made by stars.

When a star is born, it’s made mainly of hydrogen, the simplest chemical element, which was forged in the Big Bang. For most of its life, the star fuses the hydrogen in its core to make helium. At the end of its life, a star as massive as the Sun or heavier fuses the helium to make heavier elements. A star like the Sun makes carbon and oxygen. Heavier stars make even more elements — all the way up to iron.

Over the 14-billion-year history of the universe, stars have made more oxygen than any other element. Today, it accounts for about one percent of all the atoms in the universe.

When a star dies, it expels much of its gas into space. Stars like the Sun do so in a fairly gentle process, creating beautiful clouds that eventually dissipate. More massive stars do it more explosively, blasting out debris at a few percent of the speed of light. This mixture of elements can then be incorporated into new stars and planets — and, at least in the case of our own Earth, into living organisms as well.

Script by Damond Benningfield

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The swan soars high overhead on late-summer nights. It’s high in the east at nightfall, with its body roughly parallel to the horizon, and its graceful wings extending above and below. Its brightest star, Deneb, marks the swan’s tail.

If your eyes were sensitive to X-rays, you’d see a giant horseshoe looping around Cygnus. That’s the Cygnus Superbubble, a cloud of hot gas that spans perhaps 1500 light-years. It may have formed from the explosion of a monster star.

The superbubble lies along one of the galaxy’s spiral arms. So when astronomers look at it, they’re looking into a region that’s full of bubbles, clouds, and other structures. That’s made it hard for them to figure out the bubble’s nature.

Over the years, they’ve come up with several possible explanations. One is powerful winds from hundreds of massive young stars. Another is the explosions of dozens of such stars.

In recent years, though, they’ve started to zero in on another explanation: a hypernova — a blast far more powerful than a supernova. The shockwave would clear out gas and dust far away from the star — forming a superbubble.

The shockwave also would create X-rays — like those seen from the Cygnus Superbubble. And it would create cosmic rays — particles accelerated to almost the speed of light — which also come from the superbubble.

So a giant bubble around the swan may have formed in one of the most powerful explosions in the universe.

Script by Damond Benningfield

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When lightning strikes on the planet Saturn, it can be a real blast. A single bolt can be 10,000 times more powerful than one on Earth.

The Cassini spacecraft orbited Saturn for 13 years. During that time, its instruments recorded radio waves from many lightning strikes. But they weren’t spread out, as lightning is here on Earth. Instead, they came from three main regions — but not at the same time.

The first group crackled through lightning alley — a narrow band in the southern hemisphere. Storms there occasionally produced lightning from 2004 until late 2010 — a few flashes per minute.

By then, a giant storm had roared to life in the northern hemisphere. Known as the Great White Storm, it was thousands of miles wide and tens of thousands of miles long. And it produced the most intense lightning that Cassini ever recorded — tens of blasts per second.

As that storm faded away, a smaller one took over — a white circle a couple of thousand miles in diameter. It produced periodic outbursts from late 2011 through 2013. After that, Cassini didn’t hear any lightning at all for the final four years of its mission.

Scientists are trying to understand why the lightning was concentrated in small areas — and why it disappeared.

Look for Saturn to the upper right of the Moon as night falls. It looks like a bright star. The brighter planet Jupiter is to the right of Saturn.

Script by Damond Benningfield

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Volcanoes don’t have to be hot. In fact, volcanoes on several worlds of the solar system may belch liquid water, forming mountains of ice.

These worlds have oceans of water trapped below their icy crusts. Some of the water may escape through cracks or thin spots in the crust. It spews out onto the surface, forming a mound of ice.

There’s evidence of such ice volcanoes on Pluto; on Titan, the largest moon of Saturn; and on Ceres, the largest member of the asteroid belt. And there’s some evidence of ice volcanoes on Europa, one of the big moons of Jupiter.

Europa is one of the most intriguing objects in the solar system. Its ocean appears to be deep, but fairly close to the surface. Telescopes on the ground and in space have detected water vapor around Europa, suggesting that water from the ocean is squirting out into space.

Europa Clipper, a mission scheduled for later this decade, will look for evidence of ice volcanoes. It’ll search for more plumes of water vapor around the big moon. And scientists will compare its pictures to those taken by earlier missions. That will show whether any ice mounds have appeared in recent decades — evidence of cold volcanoes on a cold moon.

Jupiter appears near our own Moon tonight. It looks like a brilliant star. Europa and three other moons are visible through binoculars, arrayed like tiny stars near the giant planet.

We’ll talk about the Moon and another giant planet tomorrow.

Script by Damond Benningfield

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