StarDate

Making a mirror for a giant telescope requires a long-term commitment. Back in March, for example, GMT — the Giant Magellan Telescope — began work on the sixth of its mirrors. It’ll take about three years to finish the job.

GMT will use a total of seven mirrors. They’ll work together to act as a single mirror about 80 feet in diameter — far larger than any current telescope. That will allow GMT to see stars and galaxies that are much fainter and farther, greatly expanding our view of the universe.

Each mirror is cast in a circular furnace at the University of Arizona. About 20 tons of a special glass is heated to more than 2100 degrees. The furnace rotates, sculpting the molten glass to the proper shape.

It takes about three months for the mirror to cool. Technicians then spend more than two years grinding and polishing it. The surface has to be smooth to within a millionth of an inch. Buddy Martin, who leads the process, described that level of accuracy during a March press conference.

MARTIN: If the mirror were expanded to the size of North America, 3500 miles in diameter, then the average hill would be two-thirds of an inch tall and the average valley two-thirds of an inch deep. That’s how smooth this mirror has to be for it to make the sharpest images that nature will allow.

All the mirrors are scheduled to be sent to GMT’s mountaintop site, in Chile, late in the decade.
 

Script by Damond Benningfield

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For most stars, life seems to happen in slow motion — it takes a long time for them to change. One exception appears near the Moon tonight. Over the last 25 years it’s gotten a lot brighter, and it’s created a “pancake” of gas and dust around itself.

Delta Scorpii is close to the lower right of the Moon as night falls. It’s the middle star in the “head” of the scorpion. The scorpion’s brightest star, Antares, is farther to the lower left of the Moon.

Delta Scorpii is about 450 light-years away. It consists of two stars. One of them is about 14 times the mass of the Sun. The other is about two-thirds as heavy.

The stars orbit each other once every 11 years. The orbit is stretched out, so most of the time the stars are a long way apart. At their closest, though, they’re closer than Earth is to the Sun.

By the time of a close approach in 2000, the bigger star had surrounded itself with the pancake — something that hadn’t been seen before. The star is big and puffy, and it spins in a hurry. That appears to be throwing gas from its equator, forming the disk.

As the smaller star moves inward, it may stir and heat the disk, making the system shine brighter. In fact, it got roughly twice as bright early in this century.

The stars made their last close approach 10 years ago this month, so they’ll get close again next year. Astronomers will be watching to learn more about this rapidly changing system.
 

Script by Damond Benningfield

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AUDIO: Godspeed, John Glenn. 10, ...

On the morning of February 20th, 1962, John Glenn became an American icon.

LAUNCH CONTROL: 3, 2, 1, zero. GLENN: Roger, the clock is operating. We’re under way.

Glenn became the first American to orbit Earth. He circled the planet three times aboard his tiny capsule, Friendship 7. Then came parades, a reception at the White House, and other honors.

Glenn was born 100 years ago today, in Ohio. He was an outgoing athlete in high school, and earned a pilot’s license while in college. During World War II, he became a fighter pilot. He flew combat missions during that war and in Korea.

Glenn then became a test pilot. And in 1959, he was picked as one of America’s first astronauts — the Mercury Seven. During their introduction at a press conference, Glenn emerged as the favorite.

GLENN: Well, my wife made a remark the other day, I’ve been out of this world for a long time, I might as well go on out there.

After his flight, NASA didn’t want to risk its most popular astronaut, so it grounded him. Glenn turned to politics, and was elected to the U.S. Senate.

But he never lost the desire to fly in space again. He convinced NASA to launch him on a space shuttle, in 1998.

LAUNCH CONTROL: 3, 2, 1, booster ignition and liftoff of Discovery with a crew of six astronaut heroes and one American legend.

Glenn died in 2016, at age 95 — still an American legend.

AUDIO: Godspeed, John Glenn.
 

Script by Damond Benningfield

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There’s more than one way to see the stars — or at least the patterns of stars. In western culture, for example, the stars of the Big Dipper and those around it form the great bear, Ursa Major. The dipper outlines his body and tail, while three faint pairs of stars represent his feet.

In ancient Arabia, though, those pairs represented the leaps of a gazelle, and they’re named accordingly. The first pair is known as Alula Borealis and Alula Australis — the northern and southern halves of the first leap. The second pair is Tania Borealis and Australis — the second leap. And the third pair is known by the name of its brighter star, Talitha — the third leap.

The stars in the three pairs are unrelated — they’re all at different distances from Earth. They just happen to line up in such a way that they form close pairs as we look toward them.

Perhaps the most impressive of all the “leaping” stars is Alula Borealis. It’s a red giant — a star that’s puffed up at the end of its life. It’s about 70 times wider than the Sun, and more than a thousand times brighter — bright enough that it’s visible across more than 400 light-years of space.

The gazelle leaps across the northwest as night falls. The first leap is well to the lower left of the bowl of the Big Dipper. The second leap is to the lower right of the first, with the final leap farther to its lower right — the leaps of a gazelle in the footprints of the great bear.
 

Script by Damond Benningfield

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A bright star that follows the Moon this evening shows how tough it is to know what’s happening inside a star.

Spica is the leading light of Virgo. It’s to the lower left of the Moon as night falls. It’s one of the brighter stars in the night sky, so astronomers have paid a lot of attention to it over the centuries. And they know a lot about it.

For example, they know that it’s a binary — two stars locked in a mutual orbit around each other. Astronomers can plot the orbit, which tells them how far apart the stars are. It also gives them the masses of the two stars. The bigger star — Spica A — is about 10 times the mass of the Sun. The other star isn’t quite as big, but it’s still impressive.

Studying the individual wavelengths of light from the stars reveals their composition and temperature. Combined with their masses, that tells us about each star’s phase of life.

Spica A is going through a transition. It’s completing its primary phase of life, the main sequence. That’s caused its core to shrink and get hotter, which has made the star bigger and brighter.

But astronomers aren’t sure exactly where it is in the transition. It could be just finishing it up. On the other hand, it could have finished the transition fairly recently, and is now moving full-on into the next phase of life — puffing up to become a giant. Continued studies might help resolve the question of what’s happening inside this big, bright star.
 

Script by Damond Benningfield

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Pluto shines at its best this week. It lines up opposite the Sun, so it rises near sunset and stays in view all night. It’s brightest for the year as well. Don’t bother looking for it, though; to be visible to the eye alone, it would have to shine at least a couple of thousand times brighter.

But you can spot Pluto’s location. It’s about half way between the bright planet Saturn, which is low in the east-southeast this evening, and the “teapot” outlined by the stars of Sagittarius, to Saturn’s upper right.

Pluto is hard to see because it’s tiny — only about two-thirds the size of the Moon — and because it’s a long way from the Sun — about three billion miles. Its orbit is lopsided, though. So for the next century, Pluto will move even farther from the Sun, heading for a maximum distance of 4.6 billion miles.

Pluto’s orbit was one reason the little world was dropped from the list of the Sun’s major planets. The orbit is more stretched out than any other planet’s. It’s also more tilted.

Finally, Pluto is locked in a “resonance” with Neptune, the farthest of the major planets. Pluto completes two orbits for every three made by Neptune. That suggests that Pluto is being herded along by giant Neptune — just like many other bodies in the outer solar system.

The combination spurred Pluto’s reclassification — as the Sun’s best-known dwarf planet.

Tomorrow: looking into the heart of a star.
 

Script by Damond Benningfield

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An ocean of liquid water might lurk below the icy crust of Pluto. And it might have been around since the little planet was born.

Scientists have based those conclusions in part on Pluto’s most prominent feature — a heart-shaped basin called Sputnik Planitia. It was discovered by the New Horizons spacecraft, which flew past Pluto six years ago.

The basin probably formed billions of years ago, when a giant asteroid hit the young world. The hole gouged by the collision most likely filled with water from the ocean, then was coated with ice when some of the atmosphere froze atop it.

New Horizons discovered a jumbled landscape on the other side of Pluto — a region of big ridges and cracks. The area might have been mangled by vibrations from the impact moving all the way through Pluto.

But a study suggests that to form such a large area of mangled terrain, Pluto must have had a deep but hidden ocean at the time of the impact. And the only way to keep the ocean from freezing was for Pluto to have formed quickly — in less than 30,000 years. The fast build-up would have made Pluto’s interior hot. As the heat worked its way outward, it would have kept the ocean warm and wet.

The ocean has undergone many changes over the eons. It’s not as deep now, and it’s probably slushy. But it appears to still be there — helping make Pluto a dynamic little world.

Pluto is at its best for the year this week, and we’ll talk about that tomorrow.
 

Script by Damond Benningfield

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Making a planet is complicated — even a dwarf planet. It involves pushing things together, blasting them apart, and moving them around. And it takes millions of years to finish.

Consider Pluto. It’s beyond Neptune, the outermost major planet. It’s about two-thirds the diameter of the Moon. And it has one big moon of its own, plus four little ones.

A spacecraft flew past Pluto in 2015, and a smaller object even farther out in 2019. Scientists pieced together the observations of both bodies to create a possible formation story for Pluto.

Pluto began forming more than four and a half billion years ago, in a wide, thin disk around the Sun. Tiny pebbles of ice and rock began sticking together in the outer regions of the disk. They built up into balls a few dozen miles in diameter. Some of those balls gently smushed together to make an even bigger body. As it grew, it swept up more pebbles, plus wisps of gas.

A stronger collision blasted debris from the newly forming Pluto into space, making its big moon, Charon. After that, Neptune moved farther from the Sun, into Pluto’s region. Its gravity kicked many of the big planetary building blocks farther from the Sun, so Pluto stopped growing.

Neptune’s gravity also pushed the little world farther from the Sun. And it locked Pluto and Neptune in step. The process was done in about a hundred million years — giving Pluto the basic configuration we see today.

More tomorrow.
 

Script by Damond Benningfield

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The Moon will be busy over the next year or so. The United States plans to launch its first lunar landers since the Apollo missions of the 1970s. Russia and Japan plan to send their own landers. And several tiny satellites will enter orbit or fly past the Moon.

The American landers are being built by private companies. They’ll carry instruments from NASA, plus other payloads.

The first, Peregrine 1, will study how the craft itself affects the lunar surface, and look for evidence of water ice.

Both Peregrine and the second lander, Nova-C, will carry special mirrors to reflect laser beams from Earth. The experiments probe the Moon’s interior and test theories of gravity.

The Russian craft, Luna 25, will land near the south pole. It’ll study the Moon’s thin “atmosphere” — mainly a few atoms captured from the solar wind. Japan’s lander will test the technology for more complex missions in the future. And India and South Korea are preparing lunar missions as well.

The U.S. also plans to make the first test flight of a big new rocket. It’ll propel about a dozen “cubesats” to the Moon. They’ll conduct experiments and check out new technologies.

The missions are supposed to launch late this year or early next year — opening a busy new era for the Moon.

The Moon is in the west as night falls. The star Regulus stands to its lower left. Venus, the “evening star,” is to the lower right of the Moon, with tiny Mars beside Venus.
 

Script by Damond Benningfield

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The three big astronomical objects that pass closest to Earth appear close to each other in the western sky early this evening: the Moon and the planets Venus and Mars. Venus is the “evening star,” to the left of the crescent Moon. Mars is only about one-half of one percent as bright as Venus. But it’s just a skosh to the left of its brilliant sibling, making it fairly easy to pick out. The trio is quite low in the sky as darkness falls, so the viewing window is short.

The Moon is always the closest major object to Earth. It averages less than a quarter of a million miles away. The only bodies that get closer to us are small asteroids. But no asteroid gets closer on a regular basis.

Venus is next on the list. At its closest, it cozies about 25 million miles from Earth. It’s not that close now, though. It’s on the opposite side of the Sun, so it’s about 133 million miles away. But it’s getting closer. It’s looping toward us, and will be closest in about six months, when it passes between Earth and the Sun.

Mars can get as close as about 36 million miles. It’s about six times that distance now, and moving farther. It’ll be farthest in early October, when it will line up behind the Sun. After that, it’ll start moving closer again. The Red Planet will be closest in December of next year, so it’ll put on a good show in late fall and into the winter.
 

Script by Damond Benningfield

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