StarDate

A flickering stellar giant stands to the lower right of the Moon this evening. Bright orange Antares is one of the biggest stars in the galaxy. If it took the Sun’s place in our own solar system, it would engulf the four innermost planets, including Earth. Yet Antares won’t be around for long — it’ll explode sometime in the next million years or so.

That fate is determined by the star’s mass. Antares is at least 15 times as massive as the Sun. Such a heavy star burns through the nuclear fuel in its core in a hurry. Antares has already consumed its original hydrogen to make helium. Now, it’s probably burning the helium to make carbon.

This process makes Antares a bit unstable. Its surface appears to pulse in and out, causing its brightness to vary by about 30 percent. Unlike many other pulsating stars, though, it’s not a steady beat. So there’s no way to predict how bright the star will appear at any particular time.

That may mean that it’s not the entire surface that pulses, but individual blobs of hot gas. Some of the blobs can be as big as a small star. They percolate to the surface like bubbles in a pot of boiling water, carrying heat from deep inside Antares. These hot blobs are brighter than the surrounding gas. So they may add to Antares’s luster before they cool and sink back into the star. With many bubbles rising at different times, that could change the star’s overall brightness in unpredictable ways.

Script by Damond Benningfield

The second-brightest star in the northern half of the sky is in great view as we head toward summer. Vega is well up in the east-northeast as darkness falls, and climbs high overhead later on.

Vega is a bit like a scaled-up version of the Sun — it’s more than twice the Sun’s diameter and mass. And it’s encircled by scaled-up versions of the belts of comets and asteroids that surround the Sun. That suggests it could have a scaled-up planetary system as well.

Space telescopes have mapped the debris around Vega in detail — bits of dust, rock, and ice that glow at infrared wavelengths.

By studying the observations, astronomers determined that Vega has a ring of dust and rock that resembles the asteroid belt in our own solar system. They also found that there’s a larger ring of cold material much farther from Vega. That ring resembles the Kuiper Belt — a broad band of icy bodies beyond the orbit of Neptune, the Sun’s most distant major planet.

The Vega system is about four times wider than the solar system. But if you scaled up the solar system, those belts of debris would look almost identical.

In the solar system, there are four planets between the Sun and the asteroid belt, and four more between the asteroid belt and the Kuiper Belt. No one has yet found any planets orbiting Vega. But the presence of the debris suggests that planets could be orbiting the star — clearing out wide zones between Vega’s “dusty” belts.

Script by Damond Benningfield

The universe has been expanding since the Big Bang. Knowing how fast it’s expanding can tell us the universe’s age, its fate, and much more. But astronomers can’t agree on what the expansion rate is — different techniques give different results.

The number they’re looking for is known as the Hubble constant. It’s named for Edwin Hubble, who discovered the expansion of the universe and made the first estimate of the rate of expansion.

Today, astronomers use several techniques to measure the Hubble constant, but the best numbers come from two of them.

One technique uses space telescopes to measure the distances to certain types of stars in other galaxies. Those distances are compared to how fast the galaxies are moving away from us as a result of the expanding universe.

The other technique also used a space telescope. It measured tiny differences in the temperature of the universe soon after the Big Bang.

Both techniques have produced precise numbers. But they don’t match. They’re off by less than 10 percent. But there’s so little wiggle room in either number that there’s no way to reconcile them — even when you account for dark energy, which appears to be causing the universe to expand faster as it ages.

It’s possible that the expansion rate was different early on. But it’s also possible that there’s a lot of work to do to figure out the Hubble constant — the key number in understanding the history of the universe.

Script by Damond Benningfield

We tend to think of stars as nice round balls. In fact, though, few stars are perfectly round. Most of them bulge out a little around the middle as they spin. Some spin so fast that they’re flattened — they look more like lozenges than balls. And some are distorted by the gravitational pull of a close companion. These stars look like eggs, with the pointed ends aimed at their companions.

A pair of these “egg” stars appears close to the Moon tonight. Spica is the leading light of the constellation Virgo. It’s to the lower right of the Moon as night falls.

Spica consists of two big, bright, heavy stars. The bigger of the two is more than 11 times the mass of the Sun, and about seven and a half times the Sun’s diameter. The smaller star is about seven times the Sun’s mass and less than four times its diameter.

The stars are quite close together. On average, their surfaces are only about seven million miles apart. Because the stars are so heavy, each one exerts a powerful gravitational pull on the other. At such close range, that distorts the shapes of the stars — each one bulges toward the other. So seen in profile, the stars of Spica would look like eggs, with the pointed ends aimed at each other.

This configuration won’t last for long. The bigger star is at the end of its “normal” lifetime. Within a few million years, it will explode as a supernova — blasting away some of the outer layers of its egg-shaped companion.

Script by Damond Benningfield

Jupiter travels with a big entourage, including almost 80 known moons, several dark rings, and two clumps of asteroids.

The asteroids are known as Trojans. One clump orbits 60 degrees ahead of Jupiter, while the other is 60 degrees behind it. Each group contains thousands of asteroids. But the leading group has about half again as many as the trailing one. That difference could be telling us something about the formation of Jupiter itself.

Most models suggest there shouldn’t be any difference in the two clumps at all. So a team of European astronomers ran its own simulations. The team found that the only way to match what we see is if Jupiter was born far from its current location.

The simulations showed that Jupiter began as an Earth-sized ball of ice and rock. It was about four times farther from the Sun than it is today. Interactions with a disk of leftover gas and dust around the Sun caused the young planet to spiral inward. It migrated for about 700,000 years, adding to its heft by pulling in chunks of ice and rock, plus lots of the gas and dust. It also locked chunks of ice and rock in its own orbit — forming the Trojans.

Other studies have also found that Jupiter moved around when it was younger. This one, though, would place its origin much farther from the Sun.

Jupiter is low in the southeast at nightfall, and looks like a dazzling star. It moves low across the south during the night, and sets at sunrise.

Script by Damond Benningfield

Every planet in the solar system appears to have a solid core — a dense, heavy ball of rock and metal. But scientists aren’t quite as sure as they used to be about the core of Jupiter, the biggest planet. Observations from an orbiting spacecraft hint that Jupiter’s core could be partially liquid — or the planet might not even have a core at all.

Jupiter probably is made of layers. The outer layer consists mainly of hydrogen and helium — the same elements that make up the Sun. At greater depths, the hydrogen and helium are squeezed more tightly by Jupiter’s gravity, so they eventually form a liquid.

Below that, the pressure is even greater. Electrons are stripped away from the hydrogen atoms, forming a layer of metallic hydrogen. Motions within this layer generate electric currents, which in turn produce Jupiter’s magnetic field.

And at the center of the planet is the core — or at least the spot where the core should be. The Juno spacecraft is measuring Jupiter’s magnetic and gravitational fields. Those readings should tell scientists what’s really there. So far, they’re hinting that perhaps the core has dissolved — leaving Jupiter as the only planet without a solid heart.

Look for Jupiter in the southeast as night falls. It looks like a brilliant star — shining at its brightest for the entire year. It scoots across the south during the night, and sets in the southwest around sunrise.

More about Jupiter tomorrow.

Script by Damond Benningfield

There’s a graphical code for just about everything. The barcode on a can of beans, for example, contains information about the product and its price. And QR codes on ads send you to web pages with a longer sales pitch.

The stars come with their own graphic codes. And over the last century and a half, astronomers have developed ever-better “scanners” for reading them.

The scanners are spectroscopes. They break the light from a star into its individual wavelengths or colors. The intensity of light at each wavelength reveals important details about the star.

Consider Regulus, the bright heart of Leo, the lion. The star is quite close to the lower right of the Moon this evening.

Spectroscopy tells us that the surface of the bright star we see as Regulus is thousands of degrees hotter than the Sun. It tells us that the star is made mainly of hydrogen and helium, with smatterings of other elements. And it helps reveal that the star spins must faster than the Sun does.

Perhaps most important, it reveals a companion star that’s too close and faint to see through the glare of the bright star. It probably is a white dwarf — the corpse of a star that once was much brighter and bigger.

The discovery of the white dwarf told astronomers that the system is older than they’d thought. And it helped them deduce that the bright star has changed over time as it interacted with the companion — a companion with its own stellar code.

Script by Damond Benningfield

When John Couch Adams was growing up in Cornwall, he received little formal instruction in math. Instead, he learned the subject on his own. And when he saw Comet Halley in 1835, he decided to apply his math skills to calculating the motions of heavenly bodies. And a decade later, he calculated the motions of something that no one had ever seen: Neptune, the Sun’s farthest major planet.

Adams was born 200 years ago this week. He was the son of a poor farmer. But he was able to attend Cambridge University, where he earned a degree in mathematics.

By then, he’d heard about a problem with the orbit of Uranus, the seventh planet from the Sun. It didn’t match predictions based on Isaac Newton’s laws of gravity. The leading idea said the giant planet was being tugged at by another world farther from the Sun.

Adams set to work on the problem, and calculated where the planet should be found. British astronomers delayed in searching for the new world, though. In the meantime, French astronomer Urbain le Verrier had made the same calculations. The director of Berlin Observatory agreed to look for the planet, and quickly found it.

Despite some controversy, astronomers decided to credit both le Verrier and Adams for discovering the new planet — by calculation, not observation.

Adams later became director of Cambridge Observatory, where he spent the final three decades of his life — studying the intricate motions of the heavens.

Script by Damond Benningfield

AUDIO: We interrupt our program to bring you a special broadcast. The German news agency Transocean said today in a broadcast that the Allied invasion had begun. EISENHOWER: A landing was made this morning on the coast of France by troops of the Allied Expeditionary Force. This landing is part of a concerted United Nations plan for the liberation of Europe. [:20]

         Dwight Eisenhower confirmed what Americans had been hearing for hours: It was D-Day for the war in Europe. Thousands of ships and aircraft, and about 160,000 troops, were invading the beaches of Normandy 75 years ago today.

         The Moon played a crucial role in the success of that invasion -- through its light, and through its influence on the tides.

         The invasion would begin around midnight, when paratroopers and gliders dropped behind the beaches. They’d need light to see what they were doing, so planners wanted a full or almost-full Moon.

         More important, they wanted the tides to be just right. German defenders had placed obstacles on the beaches to wreck landing craft coming in at high tide. So planners wanted a fairly low tide, allowing craft to land below the obstacles. But they didn’t want the tide to be too low, because then Allied troops would have to cross a wider section of beach against enemy fire.

         Using mechanical computers, an Allied team calculated that the best days for the invasion were June 5th, 6th, and 7th, 1944, when the Moon would be full and the tides would be just right at dawn. The weather looked bad for the 5th, so Eisenhower gave the go-ahead for June 6th: D-Day.

Script by Damond Benningfield

Thousands of weather stations dot our planet’s landscape. They tell us what conditions are like at locations from the south pole to the Nile.

Earth isn’t the only planet with weather stations, though. Two of them are operating on Mars. One is on the Curiosity rover, which has been exploring the Red Planet for almost seven years. The other is on InSight, which landed on Mars late last year. Their observations help scientists understand the Martian climate.

Curiosity and InSight are only a couple of hundred miles apart, so conditions at the two sites are similar. InSight is just north of the equator, with Curiosity just south of it.

The readings mainly tell us that it’s cold on Mars. Daytime temperatures don’t climb above the single digits during winter, although they can rise above freezing during summer. And at night, they drop to a hundred below or colder, regardless of the season.

Winds tend to be moderate, but gusts can top 30 miles per hour. And if a dust devil sweeps by, the gusts can be even stronger.

A few clouds drift through the sky. There’s no rain or snow from them, though -- any precipitation would vaporize long before reaching the surface.

So the weather report from Mars is always about the same: cold, gusty, and dry.

Look for Mars to the lower right of the Moon shortly after sunset tonight. It looks like a moderately bright star. The much brighter planet Mercury is farther along the same line, just above the horizon.

Script by Damond Benningfield