StarDate

Pull out your binoculars and make sure you have a clear western horizon after sunset the next few nights. You’ll need them to see an amazing close encounter between the planet Mercury and the star Regulus, the heart of the lion. This evening, they’ll pass just one-tenth of a degree from each other — less than the width of a pencil held at arm’s length.

Regulus has frequent encounters with solar system bodies because it’s almost on top of the ecliptic, which is the Sun’s path across the sky.

The Moon and planets stay close to the ecliptic as well, so they periodically pass close to Regulus. Just this month, the list of close visitors has included Mars, Venus, and the Moon.

Mercury is the least frequent caller. It’s the closest planet to the Sun, so it never appears far from the Sun in our sky. That means Mercury has to wait for Regulus to come to it, shortly before sunrise or shortly after sunset.

Mercury has been creeping up on Regulus for a few nights. And it will remain close for a few more nights as it pulls away.

Look for Mercury and Regulus beginning about a half-hour after sunset, almost due west. They’re so low in the sky that any trees or buildings along your horizon will hide them from view. Mercury is the brighter of the two targets. The view is better from the southern United States because the ecliptic stands at a slightly more favorable angle — a better view of a beautiful encounter.
 

Script by Damond Benningfield

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In 1789, German chemist Martin Klaproth was checking out a dark mineral known as pitchblende, which came from a silver mine. His experiments produced a previously undiscovered element. Inspired by the discovery of the planet Uranus eight years before, Klaproth named his new element “uranium” in its honor.

It’s not the only new element whose name was inspired by the heavens. In 1803, one was named cerium in honor of Ceres, a body between Mars and Jupiter discovered just two years earlier. At the time, Ceres was considered to be a planet. As it turned out, though, it was one of millions of bodies in a region known today as the asteroid belt.

And the list doesn’t end there.

In 1940, scientists created a new element in the lab. It has an atomic number of 93, which means it has 93 protons and 93 electrons. That’s one beyond uranium, which is the heaviest of all natural elements. Since the new element was the next one in the periodic table, scientists named it “neptunium,” for the planet beyond Uranus.

Soon after that came the creation of element 94. Like uranium and neptunium, it’s radioactive. That gave it potential military uses, so its existence remained secret until after World War II. By then, scientists had named it for the ninth planet, Pluto: plutonium. And even though Pluto is now described as a dwarf planet, plutonium retains its name — a merger of exploration on the smallest and largest of scales.
 

Script by Damond Benningfield

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Gold, silver, and platinum have something in common besides their beauty. All of them are “ashes” from the destruction of stars. Every gram of these elements — not only on Earth, but throughout the universe — was forged in stellar explosions or collisions.

Hydrogen and helium — the lightest elements — were created in the Big Bang. Most other elements were forged in the hearts of stars. But almost all of the heaviest elements — everything beyond iron — were created in stellar deaths.

A lot of gold, silver, and platinum were formed in the collisions of neutron stars — the tiny, ultra-dense corpses of once-mighty stars. Such collisions blast debris into space and heat it to tens of millions of degrees. At those temperatures, neutrons stick to the nuclei of heavy elements, making even heavier ones.

Astronomers saw that process at work in 2017. They watched as colliding neutron stars created enough silver to make 50 planets as heavy as Earth, enough gold to make a hundred Earths, and enough platinum to make five hundred.

But neutron star collisions are rare, so they may not account for all of these precious metals observed in the universe. So some of them could be made in the death throes of massive stars — if they collapse to form black holes, for example.

Regardless of the details, though, one thing is certain: It takes the death of a star to forge some of the rarest and most beautiful elements on Earth.
 

Script by Damond Benningfield

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Pluto is putting in its best appearance of the year. It was at “opposition” on Sunday night, lining up opposite the Sun in our sky. So it rises around sunset and is in view all night. It’s also closest to Earth for the year — more than three billion miles away. That means it shines brightest for the year, although you still need a good-sized telescope to see it. It’s easy to find Pluto’s location, though. It’s well to the lower left of the teapot outlined by Sagittarius.

Pluto is tiny — about two-thirds the diameter of the Moon. That means its gravity is weak. Yet it’s strong enough to hold onto a thin atmosphere — wisps of nitrogen, methane, and carbon monoxide.

The New Horizons spacecraft got a good look at the atmosphere when it flew past Pluto, in 2015. The atmosphere extended almost a thousand miles above the surface — a result of Pluto’s weak gravity. But the atmosphere is so cold that it doesn’t all escape into space. And it contains about 20 layers of haze, made of hydrocarbons and other heavy elements.

Backlit by the Sun, the atmosphere looks blue — and for the same reason that Earth’s air is blue: The nitrogen molecules scatter blue light, allowing redder wavelengths to shine through. From the surface of Pluto, though, you wouldn’t see much of that air. It’s no more than a hundred-thousandth as thick as Earth’s — a cold but thin blanket around far-away Pluto.

Tomorrow: “golden” stars.
 

Script by Damond Benningfield

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Pluto doesn’t wear its heart on its sleeve -- it wears it just above its waist. It’s a region that really does look like a cartoon version of a heart. Most of it is north of the equator.

The two lobes of the heart are different. The right half is rugged, and its outline is jagged. The left half is brighter and smoother, and its outline is better defined.

That side is called Sputnik Planitia. It’s a wide, shallow bowl that might have formed when a giant asteroid slammed into Pluto. Today, it’s filled with frozen nitrogen. There are few impact craters atop the ice, so the surface is young -- less than 200,000 years old.

The surface looks like the cracked bottom of a dry riverbed. The smooth segments between the cracks average about 20 miles across, and they’re higher in the middle than at the edges.

One possible reason for that appearance is that the nitrogen ice at the bottom of the basin is warmed by Pluto’s interior -- perhaps by a deep ocean of liquid water. The warm ice bubbles to the surface. It builds “domes” and pushes older ice toward the edges, where it cools and sinks to the bottom. It warms up again, then returns to the surface -- giving Pluto a bright heart.

Pluto is at its best for the year right now. It rises at sunset and is in view all night. It’s also at its brightest. Even so, you need a big telescope to spot it, near the border between Sagittarius and Capricornus.

More about Pluto tomorrow.
 

Script by Damond Benningfield

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A giant stellar nursery in a nearby galaxy is giving birth to thousands of new stars. That includes some of the more massive stars ever seen, which will explode as supernovas. But most of the stars are much smaller and more sedate, so they’ll live long, quiet lives.

NGC 346 is 200,000 light-years away. It’s the biggest and brightest star-forming region in the Small Magellanic Cloud -- a close companion to our home galaxy, the Milky Way. The nursery probably is about three million years old, yet it may already contain tens of thousands of stars. It probably also contains thousands of stellar wannabes -- objects that have not yet lit the fires of nuclear fusion, allowing them to shine as true stars.

Until recently, astronomers had seen only the brightest and most massive of the stars that are still being born. But using James Webb Space Telescope, they found hundreds more. Most of them will form stars that are similar to the Sun or smaller. It’s the first time we’ve ever seen the birth process of such modest stars in any galaxy beyond the Milky Way.

Webb discovered dust in the disks of material around the newly forming stars -- also a first. The dust grains are made of heavy elements that could someday form planets around the stars -- especially small, rocky planets like Earth. So NGC 346 could be showing us the birth not only of thousands of future stars, but of thousands of future planets as well.
 

Script by Damond Benningfield

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A companion galaxy to the Milky Way is windy. It’s blowing enough hot gas in our direction to make 85 million stars as massive as the Sun. No one knows just what will happen to the gas. But some of it could fall into the Milky Way, where it really could form new stars.

The LMC -- the Large Magellanic Cloud -- is about 160,000 light-years away. It’s the biggest galaxy that orbits the Milky Way -- about one percent of the Milky Way’s mass. It’s home to giant clouds of gas and dust that are spawning new stars. That includes one of the most massive of all stellar nurseries.

Some of the LMC’s stars are big and heavy. They live short but spectacular lives, then blast themselves to bits as supernovas. That sends their outer layers of gas racing into space at high speeds. The gas rams into nearby clouds, pushing some of their material as well.

And that’s what’s driving the winds. Astronomers have measured the winds on the side of the LMC that faces our way. They’ve found top speeds of about 360,000 miles per hour. Some of the gas may be flowing into a long ribbon of gas, dust, and stars that connects the LMC and the Milky Way. That could fuel the birth of more stars. And more of the gas could wind up in the Milky Way itself -- adding to our home galaxy’s already impressive population of stars.
 

Script by Damond Benningfield

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Some things just make sense. Venus and Mercury are the closest planets to the Sun. They’re also the hottest planets in the solar system. That makes sense. But Venus, the second planet from the Sun, is much hotter than Mercury, the closest planet. And that doesn’t seem to make sense -- at least at first.

Mercury is the smallest of the Sun’s major planets, and its gravity is weak. So if Mercury ever had an atmosphere, it was blown away by the Sun. Without an atmosphere to spread some of the Sun’s heat, there’s a huge range in temperature. On the dayside, it can peak at 800 degrees Fahrenheit. And on the nightside, it can plummet to hundreds of degrees below zero.

Venus is bigger and heavier, so its gravity is stronger. That allowed it to retain its atmosphere, which trapped more and more heat. That evaporated the oceans and boiled gases out of the rocks. The atmosphere got thicker, so it held on to even more heat. Today, temperatures on Venus average about 860 degrees, day and night, around the entire planet. So it just makes sense that Venus is hotter than its closer sibling.

Look for Venus and Mercury close together in the western sky the next few evenings. Venus is the “evening star.” Tonight, fainter Mercury is to its right, by about the width of your fist held at arm’s length. Over the coming days, Venus will drop toward the Sun while Mercury pulls away from it -- hot planets headed in opposite directions.
 

Script by Damond Benningfield

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During four years of operations, the InSight lander recorded more than 1300 “marsquakes” -- events that sent sound waves rumbling through the planet. Like this one, many were triggered by space rocks slamming into Mars. Others were caused by Mars itself. They’ve all helped scientists refine their models of how Mars is put together.

InSight shut down at the end of 2022. Its main instrument was a seismometer it placed on the surface to record the marsquakes. The way the sound waves rippled through the planet revealed details about its interior.

They showed that the crust is thinner than expected, for example, and there’s less difference between the crust in the northern and southern hemispheres.

InSight also showed that pools of molten rock lie below large volcanic regions -- perhaps indicating that the volcanoes aren’t quite dead.

The lander also revealed that the planet’s core is more than 2200 miles in diameter -- bigger than thought. That means it must contain a lot of lightweight elements, and it must still be molten.

Scientists haven’t finished analyzing InSight’s readings -- and they won’t for years. But they’ve already gotten a better picture of the interior of the Red Planet.

Look for Mars close to the left of the Moon early this evening. It looks like a modestly bright star. Venus, the “evening star,” is below the Moon, with fainter Mercury off to the lower right of Venus.
 

Script by Damond Benningfield

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The Moon and the “evening star” stage a beautiful encounter early tonight. They’re close together as the Sun sets. They’re an especially beautiful sight because they’re immersed in the colors of twilight.

Despite its appearance, the evening star isn’t a star at all -- it’s the planet Venus.

Long before the invention of the telescope, skywatchers knew there was something different about this brilliant light. While the true stars all maintain their position relative to each other, Venus and the other “planets” change position from week to week or even night to night. That’s why they’re called planets -- an ancient Greek word that means “wanderers.”

Those wandering lights were a nuisance to those who tried to explain the workings of the heavens. Most thought that Earth was the center of the universe. And that seemed to be a reasonable explanation for the Sun, Moon, and stars.

But it was harder to explain the motions of the planets. They periodically stop and reverse course. And Venus swings between evening and morning skies, always staying close to the Sun. In fact, it’ll move into the morning sky in less than a month. The explanations for these motions got pretty complicated, which made them hard to believe.

These complicated motions convinced astronomers that Earth circles the Sun, along with the other planets -- moving our world out of the center of the universe.

More about the Moon and another planet tomorrow.
 

Script by Damond Benningfield

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