StarDate Billy Henry

Earth’s magnetic field is a protective blanket. It keeps charged particles from the Sun and beyond from hitting the surface and much of the atmosphere, where they could cause a lot of problems. But it’s a lumpy blanket. It doesn’t provide the same level of protection for the whole planet. Instead, the magnetic field has peaks and valleys.
Today, there’s a deep “valley” over parts of South America and the South Atlantic Ocean. Known as the South Atlantic Anomaly, it allows particles in Earth’s radiation belts to come closer to the surface than anywhere else.
That’s a big problem for orbiting spacecraft. Some have been damaged when they passed through the anomaly. The International Space Station has extra shielding to keep its crew safe.
About 3,000 years ago, there was a big “peak” in the magnetic field over the Middle East. The field was stronger than usual there, and stayed that way for centuries.
Some of the most recent evidence for it came from bricks from Mesopotamia, around present-day Iraq. The bricks contain bits of iron oxide. When the bricks were fired, the iron particles recorded the condition of the magnetic field at the time. The bricks also contained the seals of kings. Archaeologists know just when the kings ruled. That allowed scientists to piece together the magnetic history of the region — confirming a big “lump” in Earth’s ancient magnetic field.
More about the magnetic field tomorrow.
Script by Damond Benningfield

Be careful what you say — a single phrase can define a legacy.
Consider Frances Baily. He served four terms as president of the Royal Astronomical Society and compiled some of the most important star catalogs in history. But he’s best known for five little words: “like a string of beads.”
Baily was born 250 years ago today, in England. As a young man, he traveled to the wilds of North America, then joined the London Stock Exchange. He was especially good at the mathematical side of things, compiling guides about annuities and life insurance. He made a fortune, then retired in 1825 to spend all of his time on astronomy.
Baily had already helped establish the forerunner of the royal society. He used his skills from his days in business to compile star catalogs — work that required a lot of tedious calculations. One of them was the leading publication of its time.
In 1836, Baily watched a solar eclipse from Scotland. Just before the Sun vanished, he noticed little points of light around the edge of the Moon. Edmond Halley had seen the same thing more than a century earlier. Halley even explained those points: they’re sunlight shining through gaps between lunar mountains and craters.
To his fellow astronomers, Baily described them as “a row of lucid points, like a string of beads.” So today, the points are known as “Baily’s beads” — insuring a bit of immortality for an insurance expert-turned-astronomer.
Script by Damond Benningfield

Russian astronomer Friedrich Wilhelm von Struve discovered and catalogued thousands of binary stars — pairs of stars that are gravitationally bound to each other. But a system that he first saw in 1829 was so striking that he gave it a special name: Pulcherrima — “the most beautiful.” It honors the contrasting colors of the two stars. One looks pale orange, while the other looks blue-white or even green.
The system is also known by an even older name: Izar, “the girdle,” because it represents the middle of Boötes, the herdsman. Regardless of what you call it, most skywatchers agree with Struve: Seen through a telescope, the pair is quite beautiful.
The orange star is a giant. It’s burned through its original hydrogen fuel and is nearing the end of its life. As a result, it’s puffed up to many times the diameter of the Sun. That “puffiness” caused the star’s outer layers to cool, which is why it looks orange.
Its companion is much hotter, so it shines almost pure white. It looks blue or green only when it’s compared to the orange star. It’s less massive than the companion, so it has a lot longer to go before it reaches its own “giant” phase.
Boötes is in the east as night falls. Look for its brightest star, brilliant yellow-orange Arcturus. Izar is the first noticeable star to the left of Arcturus. To the eye alone, it looks like a single point of light. But a telescope reveals the true nature of this colorful duo.
Script by Damond Benningfield

The brightest star in the night sky is getting ready to leave it for a while. Sirius, the Dog Star, is low in the southwest as night falls. Over the next few weeks, it’ll sink deeper into the twilight, then disappear from view.
Sirius is almost nine light-years away. And it actually consists of two stars, not one. The one we see is a good bit bigger, brighter, and heavier than the Sun. The other is about the same mass as the Sun, but a whole lot smaller — only as big as Earth.
That star is a white dwarf. It’s the crushed core of a star that originally was more massive than its companion. Because of those extra pounds, the star aged more quickly. It puffed up to giant proportions. When it could no longer produce energy in its core, it cast off its outer layers, leaving only the dead core. The white dwarf is so small and faint that it’s visible only through a telescope.
The bright star of Sirius eventually will suffer the same fate. And so will the Sun — but not for several billion years.
Sirius will return to view — in the morning sky — in August, with the exact date depending on your location. From ancient Egypt, it disappeared for about 70 days. Sirius was important in both religious and secular life. So 70 days became the length of time set aside to prepare a dead king’s body for the afterlife. And the star’s reappearance marked the start of a new year — in a calendar regulated by the Dog Star.
Script by Damond Benningfield

Stars are huge — anywhere from about 10 times the diameter of Earth to a hundred thousand times or more. Such a scale is just hard to fathom. One way to envision it is to consider how long it would take you to make one turn around such a giant body.
An extreme example is Antares, the bright orange heart of Scorpius. It’s to the lower left of the Moon as they climb into good view tonight, after midnight, and about the same distance to the upper right of the Moon tomorrow night.
Antares is a supergiant — one of the biggest stars in the galaxy. It’s also one of the brightest and heaviest. The exact numbers are a bit uncertain. In part, that’s because its outer layers are extremely thin — they just kind of taper off into space. And Antares is blobby instead of perfectly round. But a good estimate says it’s almost 600 million miles in diameter — about 75 thousand times wider than Earth.
To get a better picture of that, imagine flying around Antares in a passenger jet at 600 miles per hour. At that speed, you could circle the Moon in about 11 hours, and Earth in about 40. And it would take six months to circumnavigate the Sun.
For Antares, though, you’d need to pack a lot of movies on your mobile device. That’s because it would take 350 years to make one full turn around it — a whole bunch of frequent-flier miles for circling around a supergiant star.
Script by Damond Benningfield

Over the millennia, stars acquire a lot of names. Some make sense, some don’t. And some of them might have gotten mixed up along the way.
An example is the fourth-brightest star of Leo, the lion, which is about 58 light-years away. It represents the lion’s hip. A few centuries ago, it was assigned the name “Delta Leonis” — an indication of its ranking within the constellation. But it also has some older names, including Zosma and Duhr.
Zosma comes from ancient Greek. It means “the girdle.” But that may be a mixed-up version of the original word, which meant “hip” or “back” — the star’s correct position in the lion’s anatomy. Duhr comes from ancient Arabic. It’s a shortened version of a phrase that means “the lion’s back.”
Regardless of the name, Zosma is a pretty impressive star. It’s more than twice the size and mass of the Sun, and about 15 times brighter. And its surface is thousands of degrees hotter.
Studies have shown that Zosma could be up to three-quarters of a billion years old. Stars of its mass burn through their nuclear fuel much faster than stars like the Sun. As a result, they live much shorter lives. Zosma should end its “prime-of-life” phase and head into old age in a few hundred million years. It’ll shine hundreds of times brighter than it does now — giving the lion a brilliant hip.
Zosma is high in the sky at nightfall. It’s well to the right of Regulus, the lion’s brightest star.
Script by Damond Benningfield