StarDate

Orion’s Belt is one of the best-known star patterns in the night sky — and one of the easiest to find. It’s a short line of three fairly bright stars. Right now, it’s in the south-southwest as night falls, with Orion’s other bright stars above and below it.

The star at the left end of the belt is Alnitak. The system includes two supergiants — among the biggest, brightest, and heaviest stars in the galaxy. The main star is more than 30 times the mass of the Sun, and 250,000 times brighter. The second star is less impressive, but still a monster.

Alnitak and Orion’s other bright stars were born from a huge complex of gas and dust. Deep images of the area around Alnitak reveal several clouds of this material — some of which is coalescing to make more stars.

There are a couple of ideas for how this complex of stars took shape. One says the formation of one group of stars triggered the formation of the next group.

In this scenario, there are four main groups. The first took shape to the north of Orion’s Belt. The stars of the belt are in the second group, so they’re all the same age — roughly six million to eight million years. And the youngest stars are below the belt.

The other idea says the stars were all born in the same region, but are streaming away from their birthplace. We’re looking down the streamer, with the youngest stars closest to us.

Either way, the stars of Orion’s Belt are young and vigorous — and we’ll have more about that tomorrow.

Script by Damond Benningfield

Orion’s Belt is one of the easiest star patterns to recognize. It’s a line of three moderately bright stars, with a slight dip at the left end. From most of the United States, it’s about half way up the southern sky as darkness falls at this time of year.

Not surprisingly, this lineup of stars has played a big role in the skylore and mythology of many cultures. In China, for example, the belt formed one of the 28 lunar mansions — the Chinese constellations.

Perhaps the most famous bit of mythology comes from ancient Egypt. There, the stars were associated with Osiris, the god of the underworld. They were considered his eternal resting place.

By the time the pyramids of Giza were built, the pharaoh was considered a god as well. When he died, he joined with Osiris in this same group of stars.

In fact, the first and largest pyramid at Giza, built by the pharaoh Khufu, appears to align with those stars. A shaft from the pyramid’s main chamber aims toward the location of Orion’s Belt at the time of construction — 4500 years ago. The shaft might have been a sort of pathway to heaven for the dead king — a way for him to unite with Osiris in the afterlife.

Some have even suggested that the pyramids were laid out in a way that mirrors the belt — although most experts disagree. Regardless of that alignment, though, there’s little doubt that the god Osiris was linked to the stars of Orion’s Belt.

We’ll have more about the belt tomorrow.

Script by Damond Benningfield

The North Star, Polaris, has served as a beacon for centuries. Its constant position in the night sky allows navigators to plot their latitude north of the equator.

For truly long-range travel, though, the beacon of choice is Canopus, the second-brightest star in the night sky. If you live south of about Dallas, it’s in view on winter nights, well below Sirius, the night sky’s brightest star. Right now, it’s due south in early evening, just above the horizon.

Considering its heritage, perhaps it’s not surprising that Canopus is associated with navigation. It’s the brightest star of the ancient constellation Argo Navis — the ship that carried Jason and the Argonauts. And the name “Canopus” may come from the pilot of another mythological ship, which rescued Helen of Troy.

The star was a beacon to the sailors of Polynesia, among others, who used its light to guide them from island to island.

In modern times, Canopus has guided spacecraft to the Moon and other planets. It’s bright and it’s far away from the Sun’s path across the sky, so a craft can use Canopus and the Sun to triangulate its position.

Canopus has even played a role in navigating to the stars. It was home to the planet Arrakis in the novel “Dune.” The planet contained the only supply of “spice.” Consuming a lot of it gave the user the ability to navigate between the stars. So stellar navigation was made possible by Canopus — a star that helps modern-day navigators sail to other worlds.

Script by Damond Benningfield

Some of the brightest stars in the night sky are visible on these late-spring evenings. There’s Sirius, the brightest of them all, high in the south at nightfall. Orion is off to its upper right. And stars like Regulus, near the Moon, and Aldebaran, near Orion, add to the lightshow.

You might wonder how many stars you can see in the night sky in all. The answer: it depends.

It depends on how dark your sky is, for example. If you have a clear, moonless night, and you can get away from city lights, the number goes way up. Good eyesight helps, too.

Under perfect conditions, most experts say the human eye might be able to see almost 10,000 individual stars. That covers the entire sky. Practically, of course, we see only half of the sky at any moment. So the top number visible at any given time is fewer than 5,000.

As the viewing conditions change, though, the numbers drop dramatically. A full Moon, like we have tonight, casts a bright glare that overpowers most of the stars. Artificial lights add their own glare. And dust and other junk in the air dim the view even more.

So from the suburbs, your view might be limited to a few hundred stars at a time. And from the center of a city, it might be no more than a few dozen.

But there are a few tips for improving the view. Get away from streetlamps and other lights, and give your eyes a few minutes to get used to the darkness. Then enjoy the stars — no matter how many you can see.

Script by Damond Benningfield

The brightest of the Sun’s naked-eye planets points the way to the faintest this evening. The fainter world is so dim, though, that you’ll need binoculars or a telescope to spot it.

The brighter world is Venus, the brilliant “evening star.” It far outshines all the other planets and stars in the night sky, so it’s impossible to miss. It’s well up in the west as night falls.

The other world is Uranus, the seventh planet from the Sun. It’s to the left of Venus by two or three degrees — about the width of your finger held at arm’s length. It’ll quickly drop away from Venus over the following nights.

Under especially clear, dark skies, Uranus is just visible to the eye alone — especially for those with sharp eyesight. The circumstances are so rare, though, that hardly anyone has seen it. And even those who have seen it probably didn’t realize what they were looking at.

The glare of the Moon brightens the sky tonight, making Uranus impossible to spot without help — even from the darkest skywatching sites. Through binoculars, it looks like a small, faint star. A telescope shows a tiny disk with a hint of its blue-green color.

Uranus is the third-largest planet in the solar system — four times the diameter of Earth. It looks so faint only because it’s far away — an average of about 1.8 billion miles.

Even without binoculars or a telescope, at least you can know where Uranus is — a couple of billion miles beyond the evening star.

Script by Damond Benningfield

Neutrinos are the ghosts of the particle world. They almost never interact with other forms of matter, so they can pass through walls, planets, stars — and people: Trillions of them stream through your body every second.

Neutrinos are the most common particles in the universe other that particles of light. They have no electric charge, and almost no mass. They’re produced by the nuclear reactions in the cores of stars, as well as in giant stellar explosions. Since they zip through the outer layers of stars without stopping, they’re the only direct probes of what’s going on inside the stars. That makes them valuable for studying the stars.

But catching a ghost isn’t easy. Since neutrinos pass through normal matter without stopping, you can’t study them with normal detectors. Yet scientists have devised some clever ways to nab them.

Most of their detectors consist of giant tanks of liquid — from super-pure water to drycleaning fluid. The tanks are buried deep underground to screen out cosmic rays and other radiation. On the rare occasion that a neutrino does interact with an atom in the tank, it emits a flash of light. Instruments track where the flash came from.

Other detectors are buried in the ice at the south pole, or anchored to the bottom of the Mediterranean Sea. They look for a neutrino to zap atoms in the ice or seawater. And an even bigger one is being built in the Mediterranean — a new “trap” for catching ghosts.

Script by Damond Benningfield

If you eat a bowl of chocolate ice cream, you can be pretty sure it won’t change to vanilla before you finish it. That’s not the case with the particles known as neutrinos. They come in three “flavors.” And they can change flavor as they zip through the universe — a trait that gave astronomers headaches.

Neutrinos are the second-most-common particles in the universe, after the ones that make up light. Many were created in the Big Bang. Others are forged in the hearts of stars, in the decay of radioactive elements, or inside nuclear reactors. Yet neutrinos almost never interact with other forms of matter. That makes them almost impossible to study.

Almost impossible, but not quite. Neutrino detectors do catch a few of the ghostly particles. And some of the early detections created a mystery.

The reactions in the Sun’s core produce enormous numbers of neutrinos. Yet early detectors found only a third as many as theory had predicted. That created some worry that perhaps the ideas about how stars work were off.

But early detectors were sensitive to only one type of neutrino — the kind produced by the Sun. The discovery that there are three types — three “flavors” — seemed to solve the problem: Most of the Sun’s neutrinos were transforming themselves on the way to Earth. Later instruments, which were sensitive to all three flavors, counted the right number of neutrinos — showing that the Sun is working just as it should.

More tomorrow.

Script by Damond Benningfield

Dark matter makes up about 85 percent of all the matter in the universe. So far, though, no one can tell us what it is. And a few studies suggest we can’t even be certain when it was created.

Dark matter doesn’t produce any detectable energy — hence the name. But we know it exists because it exerts a gravitational pull on the visible matter around it. It holds clusters of galaxies together. And it causes stars on the outer edges of galaxies to move faster than they would without the dark matter.

The leading idea says dark matter consists of subatomic particles. And it says the particles would have been forged in the Big Bang — the moment of creation for matter and energy, almost 14 billion years ago.

At the very beginning of that process, there was a period known as cosmic inflation. In a tiny fraction of a fraction of a fraction of a second, the universe puffed up faster than the speed of light. The “bang” came at the end of that period, as the first matter and energy took shape.

A few studies have said that dark matter could have been born during the period of inflation — before the birth of normal matter. And a study last year suggested the idea could be confirmed by studying how galaxies are spread across the sky. So looking at galaxies could tell us when dark matter was born. And it could even help scientists narrow down their searches for these elusive particles.

We’ll talk about the hunt for other particles tomorrow.

Script by Damond Benningfield

Like the search for cities of gold in the American west, the search for dark matter keeps coming up empty. But scientists keep devising new tools and techniques for continuing the search.

One big difference between the two searches is that scientists are certain that dark matter exists. It exerts a gravitational pull on the visible matter around it.

Dark matter appears to account for about 85 percent of all the matter in the universe. But no one knows what dark matter is. The leading idea says it consists of subatomic particles. They’d be hard to find, though, because they wouldn’t interact with normal matter.

Most of the direct searches look for a particle of dark matter to hit or pass near a particle of normal matter. That would give the normal particle a slight nudge, causing it to “jiggle” — or to produce a flash of light.

Detectors are placed deep underground, where interference from other particles is screened out. One research group, in Italy, has reported several detections of dark matter. But no other experiments have been able to replicate the result.

An upgraded detector is being prepared in an abandoned gold mine in South Dakota. Known as Lux-Zeplin, it’ll contain more than 10 tons of liquid xenon. Scientists hope dark matter will stage occasional interactions with the molecules of xenon — confirming the existence of the stuff that makes up most of the matter in the universe.

More about dark matter tomorrow.

Script by Damond Benningfield

LAUNCH CONTROL: 3, 2, 1, we have booster ignition and liftoff of Endeavour on a voyage to view the universe! JOHN GRUNSFELD: We spent about 16 days doing astronomical observations from a very high mountaintop that was moving very fast.

John Grunsfeld was a scientist and astronaut who was making his first trip to space. He and six crewmates headed for orbit aboard space shuttle Endeavour 25 years ago today.

Endeavour carried telescopes for observing everything from the Moon to distant galaxies — a mission known as Astro-2. It was a follow-up to a shorter flight five years earlier.

The crew operated three telescopes. The telescopes observed the universe in ultraviolet light, which is impossible to see from the ground. They took pictures and other observations of hundreds of targets.

Doing astronomy from the shuttle had both good points and bad points, as Grunsfeld recalled in this 2010 interview:

GRUNSFELD: From a technical perspective of trying to do high-precision astronomy, the shuttle’s not the best place. People moving around inside the system, attitude maneuvers, all conspire against you. Other than that, the space side, we offered an on-site problem solving that allowed extremely high observing efficiency for an observatory that was built around the space shuttle.

Today, most space astronomy is conducted by free-flying satellites, such as Hubble Space Telescope. But some is being done from the International Space Station, with some instruments tended by astronauts — just like Astro-2.

Script by Damond Benningfield