StarDate

The Moon’s gravity pulls on the water in Earth’s oceans. That creates “bulges” in the oceans that move as Earth rotates on its axis, creating the daily cycle of high and low tides.

Tides aren’t limited to planets and moons, though — they’re also found on stars. In fact, a good example is a star system that keeps company with the gibbous Moon late tonight: Spica, the leading light of Virgo. It’s to the lower left of the Moon at nightfall, and closer to its left as they set in the wee hours of the morning.

Spica actually consists of two stars, each of which is much bigger, brighter, and heavier than the Sun. They’re so close together that they orbit each other once every four days.

At that range, each star exerts a powerful gravitational pull on the other. That pull is strongest on the sides of the stars that face each other, just as the Moon’s pull is strongest on the side of Earth that faces it. The difference in the pull on the two sides of each star causes the stars to bulge toward each other. As a result, the stars are slightly egg-shaped, with the tapered ends pointing at each other.

We can’t see this effect directly because the stars blur together to form a single point of light. But we can see it indirectly. As the two stars orbit each other, we see them from different angles. When we look at the system from the side, where the bulges are most obvious, Spica grows a tiny bit brighter — the result of giant tides on giant stars.

Script by Damond Benningfield

Our brilliant Sun may have a dark side: It may be a thief.

In particular, there’s evidence that it stole Sedna, a world more than twice as far from the Sun as Pluto is.

Sedna is much smaller than Pluto. But at the time of its discovery, in 2003, it was unique. That’s because, unlike Pluto and the other objects in the distant Kuiper Belt, it never approaches the paths of the giant planets, such as Neptune. That means that no giant planet’s gravity could have hurled Sedna from the inner solar system, where Pluto and similar objects are thought to have been born, into its remote orbit. Instead, the gravitational tugs of stars that were born with the Sun could have yanked Sedna outward.

In 2012, astronomers found another Kuiper Belt object that, like Sedna, never approaches the orbits of the giant planets. This discovery motivated them to investigate another idea: that the Sun stole Sedna from another solar system.

Computer simulations showed that the idea is plausible. They also revealed that the other star was more massive than the Sun, and that it passed quite close to the Sun.

If the Sun is a thief, both Sedna and the other object should come closest to the Sun on the same side of the Sun — and they do. But that could be just a coincidence. So astronomers hope to find more objects like Sedna. If they all come closest to the Sun on the same side of the Sun, then our home star probably is guilty of interstellar theft.

Script by Ken Croswell, Copyright 2015

Anyone who’s concerned about their weight might not want to visit Jupiter. The giant planet’s surface gravity is more than twice as strong as Earth’s. So a person who weighs 150 pounds on Earth would weigh about 380 pounds on the surface of Jupiter.

Of course, Jupiter doesn’t actually have a surface for you to stand on. The planet is a big ball of gas, with nothing solid until you penetrate tens of thousands of miles below its cloudtops.

For comparison purposes, though, scientists have come up with a definition for the “surface” of Jupiter and the solar system’s other gas-giant planets. It’s the depth in the atmosphere where the pressure is equal to the surface pressure on Earth.

That’s many miles below the tops of Jupiter’s highest clouds, which are made mainly of ammonia. But there are zones in the atmosphere where the clouds aren’t nearly as high, so the “surface” isn’t necessarily below the clouds.

All of this means that no one will ever walk on Jupiter. It might still be possible to visit the planet, though. Visitors could float through the atmosphere in balloons or blimps, or cruise in specially designed aircraft. But the seats would need to be very well padded — to handle the passengers’ extra weight on the solar system’s largest planet.

And that giant world is in good view tonight. It looks like a brilliant star to the upper right of the Moon at nightfall, and to the lower right of the Moon as they set in the early morning.

Script by Damond Benningfield

[SFX: Voyager radio waves]

In March of 1979, Voyager 1 was cruising toward Jupiter, the solar system’s largest planet, when it ran into what sounds like a hurricane. That “roar” is caused by the interaction between Jupiter’s magnetic field and the solar wind — a “breeze” of charged particles from the Sun’s outer atmosphere.

Motions deep within Jupiter’s core produce a “dynamo” effect, which generates a powerful magnetic field. The field encases Jupiter in a sort of magnetic bubble, which is sculpted in part by a doughnut-shaped ring of gas around Jupiter.

The bubble extends a few million miles in toward the Sun, and hundreds of millions of miles away from the Sun. It’s so big that if it were visible to the human eye, it would be about five times bigger than the Moon.

Particles in the solar wind form waves in front of the bubble, like the waves that pile up in front of a ship as it moves across the ocean. The region where the waves form is known as the bow shock. It causes the solar wind to slow down and get hotter as it flows around Jupiter’s magnetic field — a protective bubble around a giant planet.

And Jupiter is in great view tonight. The giant planet looks like a brilliant star close to the upper left of the Moon at nightfall. It’ll stand even closer above the Moon as they set in the wee hours of tomorrow morning.

We’ll have more about Jupiter and the Moon tomorrow.

Script by Damond Benningfield

[MUSIC: Over there, over there, send the word, send the word over there,
that the Yanks are coming, the Yanks are coming,
the drums rum-tumming everywhere.]

A hundred years ago, World War I was raging across Europe. And less than a year later, the Yanks headed into the fray, as the United States joined the war.

American astronomers contributed to the war effort. Some provided their technical expertise, while others served as soldiers or sailors. And others tried to get into the fighting, but couldn’t.

That list included Edwin Hubble, of Hubble Space Telescope fame. He’d just been offered a job at Mount Wilson Observatory in California, home of a brand-new 100-inch telescope — the world’s largest. But Hubble decided to join the army instead. He quickly finished his Ph.D., then enlisted in mid-1917. He was made a major and given command of a battalion. But he didn’t make it to France until shortly before the war’s end, so he didn’t see combat.

Back at home, there wouldn’t have been much for him to do, anyway. The optical shop for Mount Wilson was converted to military work, and made lenses and prisms.

Other astronomers designed new optics for aerial cameras. Others devised ways to test thousands of clocks and watches for military use, while some who were skilled at tracking meteors helped plot trajectories of artillery shells.

Their work helped assure victory for the allies — over there — in World War I.

Script by Damond Benningfield

Otto Struve was destined to be an astronomer. His great-grandfather had established Pulkovo Observatory in Russia, and his grandfather and father were astronomers as well. And Struve enrolled in a Russian university to study astronomy and mathematics. But thanks to World War I, he became an astronomer not in his native Russia, but in the United States.

Struve enlisted in the Russian army in 1916. He was an artillery officer, and served on the Turkish front. Russia signed a peace treaty with Germany in early 1918, and Struve returned to his studies. But the war had ravaged Russia’s economy. That led to a civil war. Struve enlisted again — on the losing side.

Struve was forced to flee Russia. He spent time in Turkey, living in refugee camps and finding occasional work as a lumberjack. He had no money, no home — and no prospects.

But thanks to a series of letters, Struve was offered a job with the University of Chicago’s Yerkes Observatory. He began work there in 1921, and quickly became an expert in spectroscopy — a technique that reveals an object’s motion, composition, and much more.

Struve was tireless, and in 1932 he became director of Yerkes. That year, he also helped work out an agreement with the University of Texas to operate its new observatory. So Struve became the founding director of McDonald Observatory — a facility that owes the details of its birth, at least in part, to World War I.

More about astronomy and the war tomorrow.

Script by Damond Benningfield

When Albert Einstein completed his theory of general relativity, only a few people in the world understood it. In fact, the first person to solve Einstein’s equations wasn’t Einstein himself. Instead, it was a fellow German scientist, who at the time was serving in the German army.

Karl Schwarzschild was the director of the Astrophysical Observatory in Potsdam — the top job in German astronomy. And he was interested in the emerging field of general relativity — a theory of gravity.

When war broke out in 1914, the 41-year-old Schwarzschild quickly volunteered for military service. He became an artillery officer, and served on both fronts.

But during breaks he continued his research. And when Einstein completed his theory in November of 1915, Schwarzschild dove into the equations — and came up with the first solution.

Among other things, his work demonstrated that any mass that was small enough and heavy enough would collapse to a single point. Its gravity would be so strong that nothing could escape its grip. In today’s language, the object would become a black hole.

Schwarzschild published a couple of other papers in 1915 as well. By then, however, he was suffering from a skin disease that he’d contracted on the Russian front. He was released from service in March of 1916 — but it was too late. Schwarzschild died on May 11th — 100 years ago today.

We’ll talk about another astronomer who served on the Russian front tomorrow.

Script by Damond Benningfield

[AUDIO: It’s a long way to Tipperary, It’s a long way to go,
It’s a long way to Tipperary, To the sweetest girl I know!]

As British soldiers sang themselves off to the battlegrounds of Europe a century ago, most of them put their former lives on hold. But a few scientists in their ranks found a way to continue their work — or at least they tried to. And so did soldier-scientists from other countries.

The head meteor watcher for the British Astronomical Society, for example, tried to count meteors from the front lines. In a report to his colleagues, though, he noted a problem: it was impossible to tell the shooting stars from the star shells — a type of artillery shell that sprayed sparks across the sky.

A few who fought on the German side, on the other hand, were more successful with their scientific endeavors.

Friedrich Kottler, an Austrian physicist who commanded an artillery unit, published his own interpretation of general relativity — Albert Einstein’s new theory of gravity, which Einstein completed in late 1915. And Hans Reissner, an engineer who won the Iron Cross for his aircraft designs, also found time to work on relativity. His calculations helped lead to the concept of black holes, which came from Einstein’s theory.

The first person to find black holes in Einstein’s equations was also the first person to solve those equations — a German officer who didn’t even believe his own discovery. More about that tomorrow.

Script by Damond Benningfield

Timing, as they say, is everything. That was especially true for a German expedition to watch a solar eclipse in August of 1914. After many months of planning, the scientists headed to Crimea. During the eclipse, they hoped to test some predictions by a young Albert Einstein. His equations were suggesting that the Sun’s gravity would deflect starlight that passed close to its surface.

When the expedition left Germany, there was talk about a recent political assassination in Austria. By the time it got to Russia, though, talk had turned to war. Russia arrested the scientists, although it traded them for some German prisoners. For these and many other astronomers, though, Albert Einstein would have to wait — the first World War was under way.

In fact, most astronomical matters would have to wait. Hundreds of astronomers and physicists fought in the war. Others helped develop and apply technology for military purposes. They devised better lenses for navigational instruments, for example, or calculated the paths of artillery shells.

Only a few leading astronomers managed to continue their scientific work during the war. Britain’s Arthur Eddington, for example, was excused from service to plan for an eclipse expedition in 1919. During that expedition, shortly after the war’s end, Eddington confirmed Einstein’s now-completed theory of gravity — by measuring the deflection of starlight around the Sun.

More about astronomy and the war tomorrow.

Script by Damond Benningfield

The bodies of the solar system are like the hands on a complicated clock, returning to the same point at regular intervals. The Sun returns to the same position against the stars, for example, in exactly one year. The Moon crosses between Sun and Earth about once a month. And Mercury crosses in front of the Sun in May every 13 or 33 years.

In fact, early tomorrow the Sun’s closest and smallest planet will stage just such a crossing, known as a transit. It begins when Mercury’s outline first makes contact with the solar disk at 6:12 a.m. Central Daylight Time, and ends five-and-a-half hours later.

Because of the orbits of Mercury and Earth, Mercury transits can happen only in May and November. The May transits take place when Mercury is near its farthest point from the Sun, and its closest point to Earth. As a result, Mercury covers a slightly larger fraction of the solar disk during May transits.

Because of that geometry, though, Mercury is more likely to miss the Sun, so May transits are only half as common as November ones. They happen at intervals of 13 years, followed by 33 years.

All of tomorrow’s transit will be visible from east of a line from Louisiana to North Dakota. From west of that line, the transit will be underway as the Sun rises. Don’t look at the Sun directly because it’s dangerously bright. Instead, find the transit online or at a local museum or planetarium — and enjoy the clockwork precision of the solar system.

Script by Damond Benningfield