StarDate Billy Henry

Archaeologists know of only a few major artifacts of the pharaoh Khufu, who ruled Egypt more than 4500 years ago. The list includes some small statuettes — some of which might have been created long after his reign. But one artifact is at the opposite end of the size scale: the Great Pyramid of Giza, one of the seven wonders of the ancient world.
The pyramid was built with the help of a guiding light — the star Thuban. At the time, it was the Pole Star. It marked due north in the sky, making it a good tool for laying out the pyramid. And as the Pole Star, it was the hub of the sky, with all the other stars rotating around it — a position that held great power for many cultures.
Thuban stands due north as the sky gets dark right now. It’s in Draco, the dragon, high above today’s Pole Star, Polaris. Thuban isn’t very bright, so it’s hard to see from light-polluted cities.
Thuban lost its position as the north celestial pole because of an effect known as precession. Earth wobbles on its axis like a gyroscope that’s running down. It takes 26,000 years to complete a single wobble. During that time, Earth’s axis draws a big circle on the northern sky, so different stars take turns marking the pole.
Thuban held that position for a couple of thousand years, including the time when Khufu’s pyramid was built. It’ll return to that celebrated spot in the sky again — in about 20,000 years.
Script by Damond Benningfield

Our universe appears to be “flat” — like a sheet of paper stretching to infinity. If so, that would mean it’s finely balanced — a sort of “just right.”
Albert Einstein’s theory of gravity, known as General Relativity, allows the universe to assume one of three basic shapes. One shape is “closed” — like a sphere. In such a universe, two lights beamed out parallel to each other eventually would circle all the way around to their starting point.
Another possible shape is “open” — curved like a saddle or a really big Pringles chip. The light beams in such a universe would move away from each other for all time.
Finally, there’s a “flat” universe. Two light beams would remain parallel to each other forever — never spreading apart or coming together.
The actual geometry is dictated by the density of the universe — how much matter is packed into its space. In a closed universe, there’s enough matter for its gravity to cause the universe to collapse. An open universe would expand forever. And a flat universe would be balanced — neither collapsing nor expanding without end.
So far, the evidence supports a flat universe, although the matter isn’t completely settled.
Not surprisingly, it’s all pretty complicated. The flat universe is flat in three dimensions — after all, we see galaxies in every direction. To a cosmologist, it all makes sense — a “flat” universe that’s the same every way we look at it.
Script by Damond Benningfield

When it comes to understanding a star, it’s all a matter of perspective. The angle at which you view the star makes a big difference in what you know about it.
Consider Vega, the leading light of the constellation Lyra and one of the brighter stars in the northern sky. It’s in the northeast at nightfall, and climbs high overhead later on.
For a long time, astronomers thought Vega was about three times as massive as the Sun, and no more than a hundred million years old. So when they discovered a cloud of dust grains around Vega, they thought it might be raw material for planets.
But it turns out they were seeing Vega from a different angle than thought. We’re looking almost directly down on one of the star’s poles. That perspective makes it more difficult to measure Vega’s details.
Once they knew the correct angle, astronomers determined that the star spins so fast that it’s almost ripping itself apart. They also found that Vega’s a bit smaller than thought, and hundreds of millions of years older.
Today, perhaps the best estimate puts Vega’s age at about 455 million years. That’s too old for the dust around Vega to be making new planets. In fact, Vega appears to already have at least one planet — a giant that’s much bigger than Earth, and much closer to its star. So the dust probably is debris from collisions between asteroids or other bodies — maybe even fully grown planets.
Script by Damond Benningfield

Like a mixed litter of puppies, sibling stars don’t necessarily look alike. That can make it hard to figure out which stars are related to each other.
One example is Regulus, the heart of the lion. It’s close to the left or lower left of the Moon as darkness falls.
To the eye alone, Regulus looks like a single bright star. Instead, it’s a system of four stars — two pairs of stars that are separated by a third of a light-year.
What we see as Regulus is the brightest of the four stars. Known as Regulus A, it’s much bigger, heavier, and brighter than the Sun. It’s paired with a star that’s so faint, and so close to Regulus A, that we can’t actually see it, even with the largest telescopes. It reveals its presence only to special instruments. It’s probably a stellar corpse — a white dwarf.
The other pair is known as Regulus BC. Both of its stars are smaller, less massive, and fainter than the Sun. One of them, in fact, is less than one percent of the Sun’s brightness.
Despite the differences in the four stars, there’s evidence that they’re all siblings. They’re all about the same distance away, for example — about 79 light-years. The pairs are close enough to each other for their gravity to hold them together. And the stars move through the galaxy in the same direction, and at the same speed — indications that they’re members of a stellar family.
Script by Damond Benningfield

Our home galaxy is a cosmic melting pot. While many of its stars were born in the Milky Way, many others came from outside. They were born in smaller galaxies that were captured by the Milky Way. Over time, the smaller galaxies were ripped apart, and their stars were scattered throughout the Milky Way. And one of the Sun’s close neighbors may be an example.
Kapteyn’s Star is about 13 light-years away. Only about 20 other star systems are closer. The star is about a third the size and mass of the Sun. Don’t try looking for it, though — it’s only one percent of the Sun’s brightness, so you need a telescope to see it.
The star’s composition and motion don’t match that of the stars that are native to the Milky Way — or at least to the Milky Way’s bright disk. Kapteyn’s Star has a lower proportion of heavier elements — an indication that it’s extremely old. And it orbits the center of the galaxy in the opposite direction from most of the stars around it.
The combination suggests that Kapteyn’s Star came from the Milky Way’s halo, a vast region that surrounds the disk. In fact, there’s evidence that Kapteyn’s and a few other stars came from a giant cluster known as Omega Centauri.
It’s likely that the cluster is the core of a small galaxy captured by the Milky Way long ago. The stars in the galaxy’s outer precincts were pulled away — making them new residents of our home galaxy.
Script by Damond Benningfield

The biggest globular star cluster in the Milky Way Galaxy may not be a child of the Milky Way. Instead, it may be a sort of orphan — the surviving core of a smaller galaxy that was captured by the Milky Way.
Omega Centauri contains perhaps 10 million stars, all packed into a dense ball about 150 light-years across. In the cluster’s middle, the stars are packed so tightly that they’re only about a tenth of a light-year apart. Compare that to our part of the galaxy, where the nearest neighbor star is more than four light-years away.
The cluster appears to be about 12 billion years old — one of the older clusters in the entire galaxy. But the composition of its stars, and the way it orbits the center of the Milky Way, suggest that Omega Centauri wasn’t born here. Instead, it appears to be one of many dwarf galaxies captured by the Milky Way. Over time, the stars in the smaller galaxy’s outer regions were pulled away. So over the eons, that left only Omega Centauri’s core — a possible “orphan” adopted by the Milky Way.
Omega Centauri is about 16,000 light-years away, in the constellation Centaurus, which is quite low in the south at nightfall. If you live south of about Dallas, and you have dark skies, you might just make out the cluster as a hazy patch of light about as wide as the Moon.
We’ll talk about one of the possible escapees from Omega Centauri tomorrow.
Script by Damond Benningfield