StarDate

The beautiful Pleiades is high in the west as night falls at this time of year. The star cluster looks like a tiny dipper. Right now, it stands above bright orange Mars by about the width of your fist held at arm's length.

The cluster contains hundreds of stars. All of them were born at the same time, from the same cloud of gas and dust. That makes the Pleiades a great laboratory for studying how stars evolve. Since all of the stars were born from the same raw materials, any differences are the result of the evolution of the stars themselves.

Astronomers can also examine the individual stars to learn about the overall cluster.

One recent study, for example, looked at how the stars of the Pleiades rotate. The results can provide insights into conditions when the stars were born.

Researchers looked at observations of the cluster from two space telescopes and one ground-based telescope, then performed a statistical analysis.

There are a couple of models that predict how stars in a cluster should rotate. One says that the stars should inherit their rotation from the spin of the cloud that gave them birth. But the other says that conditions in a cluster are turbulent. That jumbles up the stars and makes them spin in different directions.

The study suggests that the stars of the Pleiades rotate randomly — every star spins in its own way. That supports the second idea — providing a new view into the birth of a star cluster.

Script by Damond Benningfield

When astronomers look at the universe, stuff often gets in the way — from clouds to airplanes to asteroids. And the operators of an extensive new survey of the sky have something else to avoid: the satellites that broadcast Sirius-XM radio.

The VLA Sky Survey is using the Very Large Array — a collection of 27 radio antennas in New Mexico — to make the most detailed radio maps of the sky ever. But the satellites broadcast at some of the same frequencies the VLA is studying. In fact, the satellites produce so much energy that they can swamp the observations. So operators have to be sure to aim away from the satellites.

Over the next few years, the VLA survey will scan the entire sky three times. The radio telescope will stare at half of the sky at a time — more than a month of observations per scan. That will reveal objects that are fainter and farther away than ever before — millions of targets in all.

The list will include exploding stars and the mergers of stellar corpses known as neutron stars. The survey also will examine jets of particles blasting away from the black holes at the hearts of many galaxies. The jets can zap clouds of gas that might form new stars, shutting down the process of starbirth.

The survey also will map magnetic fields in space and peer through clouds of dust in our own galaxy to help map its structure — all while avoiding satellites and other obstacles in the sky.

Script by Damond Benningfield

A giant telescope is a marvel of science and engineering — tons of glass and steel that are molded into an impressive scientific instrument.

But it's also a marvel of civil engineering — years of work just to get the site ready for construction.

Consider GMT — the Giant Magellan Telescope. When it's finished, it'll be the largest telescope in the world, with a main mirror almost as big as a basketball court. It's being built atop Cerro Las Campanas, an 8200-foot mountain in Chile.

The mountain isn't quite as tall as it once was, though. The first step of construction was to level the rounded peak. So teams blasted about 30 feet off the top of the mountain. They carted away about 50,000 cubic yards of rock.

The crop job changed the way air flows over the mountain, which could affect viewing conditions for the telescope. So the GMT project spent several years monitoring the changes and simulating airflow with computer models.

When that was done, they started excavating the base of the telescope dome. Piers have to be sunk deep into the bedrock to keep the telescope stable. Builders can't use explosives, though, because they might crack the rock. The digging takes months, and will remove thousands more cubic yards of rock and dirt.

After that, the construction team will be ready to start building the telescope and its dome — another major feat of engineering.

We'll talk about another big telescope project tomorrow.

Script by Damond Benningfield

The mirrors of most telescopes consist of a single big piece of glass — a reflective surface that gathers and focuses the light from distant objects. But there's a limit to how big you can make a single mirror. Bigger mirrors are made of smaller segments that are pieced together like the tiles on a floor.

A jumbo telescope that's under construction uses a slightly different approach. GMT — the Giant Magellan Telescope — will consist of seven mirrors. Each of them will be around the limit for individual mirrors — about 27 feet in diameter. When they're fitted together, they'll form a perfect figure for studying the stars — and span about 80 feet.

Making the mirrors is complicated. Each begins with tons of a special glass from Japan. The glass is shipped to a lab at the University of Arizona — the world's leading mirror maker.

The glass is placed in a giant oven and heated to about 2,000 degrees. The oven spins to evenly distribute the molten glass. A honeycomb structure on the back of the mirror leaves open spaces that greatly reduce its weight.

After the mirror cools, it's ground and polished. Its final surface must be shaped to within a few millionths of an inch. That shape is tested many times to make sure it's right.

Two of the mirrors are done. Three others are in various stages of preparation. And the final two will be cast in the next couple of years — finishing the eyes of the GMT.

More tomorrow.

Script by Damond Benningfield

For most of its lifetime, a star wages an internal battle — a battle between radiation and gravity. In the end, though, gravity always wins.

A star that’s nearing the final stages of that battle stands near the Moon tonight. Aldebaran, the brightest star of Taurus, is to the upper left of the Moon at nightfall.

A star is powered by the nuclear fusion reactions in its core. For stars like the Sun, hydrogen atoms are smashed together to make helium.

When the hydrogen is gone, gravity squeezes the core tighter, making it hotter. That allows the helium to fuse to make carbon and oxygen. The hotter core produces more radiation, making the star’s outer layers puff outward. And that’s what’s happening with Aldebaran — it’s puffed up to about 45 times the diameter of the Sun.

When all the helium is gone, though, fusion will stop. Without the radiation pressure, gravity will take over, squeezing Aldebaran’s core tighter and tighter.

It can squeeze only so far, though. Electrons — the negatively charged parts of atoms — exert their own pressure. As a result, there’s a limit to how tightly they can be smashed together. When they reach that limit, they’ll halt the core’s collapse. By then, Aldebaran will have shed its outer layers. So the remaining core will be about half as massive as the Sun, but only about as big as Earth. This ultra-dense corpse is known as a white dwarf — the final result of the battle in the heart of a star.

Script by Damond Benningfield

Most galaxies of any appreciable size are giving birth to new stars. But some are a lot better at it than others. In fact, early results from a survey of star-forming galaxies suggests that smaller ones are better at it than bigger ones.

Stars are born from stellar nurseries — collapsing clouds of gas and dust. The clouds break apart into smaller clumps that then form stars. Individual nurseries can give birth to anywhere from a few stars to hundreds of thousands of them.

Astronomers are using an array of radio telescopes to study more than a hundred thousand nurseries in 74 large galaxies. The array, known as ALMA, is in Chile, so it's looking at galaxies that are visible from the southern hemisphere. The galaxies are all fairly close, and we see them pretty much face-on. That provides a detailed look at their gas clouds.

Early results indicate that nurseries in smaller galaxies are more efficient at making stars — they convert more of the gas into stars in a shorter time.

Astronomers aren't sure why that\'s the case. One idea is that as big galaxies get older, they get more stirred up. That spreads out their gas, so it's harder for it to come together to make stars.

The survey isn't done yet, though. As astronomers look at the remaining galaxies — and analyze the rest of their data — they may come to a more complete understanding of why some galaxies are better at making stars.

Script by Damond Benningfield

There’s a lot of talk these days about sending people to the Moon and Mars — not just for a few days, but for weeks or longer.

Such expeditions won’t be able to get all the supplies they need from Earth. Instead, they’ll need to live off the land. They might use ice to provide drinking water, oxygen, and rocket fuel, for example.

And they might be able to use the dirt, too. In fact, research teams around the world are making simulated Moon and Mars dirt for testing.

The dirt could be used to make bricks and other building materials. They would protect explorers against radiation from the Sun and beyond.

The European Space Agency, for example, has been making bricks from a lunar simulant — a material that has similar characteristics to the real thing. Real lunar dirt may be especially hard to deal with because much of it is electrically charged. Combined with some of the physical properties of the dirt, that makes it obnoxious — it sticks to everything, and could jam up equipment.

Mars dirt might be similarly tough to deal with. But engineers can test their building techniques using a simulant developed by the University of Central Florida. It sells for about 10 dollars a pound — a down payment on trips to Mars.

And Mars is easy to spot the next couple of evenings. It’s in the west at nightfall, and looks like a fairly bright orange star. It’ll stand well above the Moon tonight, and closer to the Moon tomorrow night.

Script by Damond Benningfield

Orion is a big constellation with a big story. The story is so big, in fact, that it incorporates several other constellations. Some of them surround the hunter, while another is on the opposite side of the sky — a separation designed to keep two mortal enemies apart.

Orion is high in the south as night falls. The bright orange star Betelgeuse marks his shoulder, and blue-white Rigel is his foot. His three-star belt stands between them.

In mythology, Orion was one of the major celebrities of his day. He was strong, handsome, and a great hunter. Two of his hunting dogs follow him across the sky — Canis Major and Canis Minor. They’re pursuing Lepus, the rabbit, which bounds below Orion’s feet.

But Orion’s celebrity eventually went to his head, and it cost him his life.

There are different versions of his demise, but they end the same way. One says that Orion boasted that he could kill any animal on Earth. That didn’t sit well with the Earth goddess, who sent a giant scorpion after him — a scorpion that stung him to death. Another version of the story says he was pursuing the goddess Diana too vigorously. So her brother, Apollo, dispatched the scorpion to protect her. Either way, Orion met his fate through the scorpion’s sting.

The gods placed both of them in the stars — but halfway around the sky from each other. So Orion dominates the winter sky, while his mortal enemy, the scorpion, rules the nights of summer.

Script by Damond Benningfield

Astronomers recently reported the sixth planet orbiting a star in the constellation Aquarius. Known as K2-138g, it’s been classified as a “sub-Neptune” — a planet that’s bigger than Earth, but smaller than Neptune, the Sun’s outermost planet.

That brings the number of systems with at least six known exoplanets to nine. And most of those worlds were discovered with the most successful planet hunter to date: the Kepler space telescope, which was launched 10 years ago and wrapped up its mission late last year.

Kepler looked for a planet to transit — to pass in front of its parent star, briefly dimming the star’s light by a bit. Analysis of the event, combined with follow-up work by other telescopes, provides details on the planet.

K2-138 consists of a cool orange star that’s almost as big as the Sun. Volunteers in a crowdsourcing project sorted through Kepler’s observations of the system and discovered five planets. All of them are closer to the star than Mercury is to the Sun.

The project also found evidence of a sixth planet. But Kepler shut down before it could confirm the planet. So astronomers aimed another space telescope at the system, and saw another transit — confirming the sixth planet.

Planet “g” orbits the star every 42 days, well outside the orbits of the other five. It’s about two-thirds the diameter of Neptune. It’ll take more study, though, to uncover more details about one of Kepler’s most recent discoveries.

Script by Damond Benningfield

The most-prolific planet hunter to date took flight 10 years ago today.

By the time it was retired, late last year, Kepler had discovered about 5500 confirmed or possible planets. And astronomers will sift through its decade of observations for decades more.

The space telescope discovered planets by looking for a star to grow a tiny bit fainter as a planet passed in front of it, blocking some of its light. How much the star faded, and for how long, revealed the planet’s size. And repeated sightings revealed the planet’s orbit. Follow-up observations with other telescopes added more details.

Kepler’s work told us that planets come in an amazing variety — different sizes, compositions, and more. And astronomers may find even more variety as they analyze the rest of Kepler’s information.

During its original mission, Kepler kept a steady eye on about 150,000 stars. A few years into the mission, though, its pointing system failed. So NASA gave it a new mission: It looked at patches of sky for about three months at a time. It kept hunting for planets, but it also watched for exploding stars, objects in our own solar system, and more.

Kepler consumed the last of its fuel last year, so it could no longer keep a steady aim. It was shut down at the end of the year — retiring as the all-time champion planet hunter.

More about Kepler tomorrow.

Script by Damond Benningfield