If you ever warp over to another star, it would help to know its distance. Say, for example, you wanted to visit Spica, the brightest star of Virgo, which is quite close to the Moon at dawn tomorrow. The system is worth visiting because it consists of two giant stars. They’re so close together that their shapes are distorted, so they look like eggs.
The best measurement we have says that Spica is 250 light-years away. But there’s a margin of error of about `four percent. So you could undershoot or overshoot the system by 10 light-years.
The distances of most stars are measured with a technique called parallax. Astronomers plot a star’s position at six-month intervals, when Earth is on opposite sides of the Sun. That can produce a tiny shift in the star’s position against the background of more-distant objects. The bigger the shift, the closer the star.
But the stars are so far away that the shift is tiny – like the size of a dime seen from miles away – or hundreds of miles. And Earth’s atmosphere blurs the view, so the stars look like fuzzy blobs instead of sharp points.
So the most accurate measurements have been made from space. Spica’s distance was measured by Hipparchos, a European space telescope. An even more accurate satellite, Gaia, measured the distances to more than a billion stars – but not Spica. The star was too bright for its detectors – leaving a big margin of error for this impressive system.
Script by Damond Benningfield
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Leonid Meteors
The patchiest of all meteor showers will be at its best tomorrow night. Unfortunately, this is one of its off years. At best, it might produce a dozen or so “shooting stars” per hour.
Over the past two centuries, though, the Leonids have produced some amazing outbursts. The first of these came in 1833. Skywatchers in parts of America reported rates of a hundred thousand meteors per hour – not a shower, but a storm. The nature of meteor showers was unknown at the time, so many saw the outburst as the end of the world.
The Leonids flare to life when Earth crosses the path of Comet Tempel-Tuttle. The comet passes close to the Sun every 33 years or so. It sheds tons of material on each pass – tiny bits of rock and dirt. Each cloud of debris spreads out and forms its own stream. A shower takes place when Earth flies through one of the streams.
Newer streams are denser, so they produce more intense displays. Those streams congregate near the comet, so the outbursts occur when the comet is close to the Sun. The last outburst came in the early 2000s. And Earth probably won’t pass through another storm-producing stream until the end of the century – leaving us with meager displays of the Leonids.
To see this year’s display, find a safe viewing site away from city lights. The meteors can appear anywhere in the sky, so you don’t need to look in a particular direction to see them. The best view comes between midnight and dawn.
Script by Damond Benningfield
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Cartwheel Galaxy
Galaxies frequently collide with each other, and the results can be spectacular. The encounters can pull out giant ribbons of stars. They can trigger intense bouts of starbirth. And they can scramble a galaxy’s stars and gas clouds, creating beautiful rings that look like cosmic bulls-eyes.
One well-known galaxy that’s experienced a head-on collision is the Cartwheel. It’s about 500 million light-years away, in the constellation Sculptor, which is low in the south on November evenings.
The Cartwheel is a good bit bigger than the Milky Way. It has a bright inner ring of mainly older stars that’s offset a little from the galaxy’s middle. A brighter ring of younger, bluer stars is far outside it. Wispy spiral arms that look like the spokes of a wagon wheel connect the rings, giving the “Cartwheel” its name.
The Cartwheel probably started as a normal spiral galaxy. But a few hundred million years ago, a smaller galaxy plunged through it. The collision created a wave that rippled outward, like a rock thrown into a still pond. The wave disrupted the original spiral structure. It also squeezed clouds of gas and dust, causing them to give birth to new stars.
And the drama isn’t over. Many more stars are being born in the outer ring, in giant nurseries that look like a strand of lights on a Christmas wreath. They will continue to make the Cartwheel shine brightly as it spins through the universe.
Script by Damond Benningfield
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Sculptor
Nicolas-Louis de Lacaille had a great imagination. In the 1750s, the French astronomer mapped more than 10,000 stars from the southern tip of Africa. Lacaille used those stars to create 14 new constellations.
One of them is Sculptor. Lacaille originally called it the Sculptor’s Studio. It depicted a carved head atop a stool, plus a hammer and chisel and a block of granite.
But all of that takes a lot of imagination to see. All of the constellation’s stars are so faint that Sculptor is invisible from light-polluted cities and suburbs.
Sculptor is important to astronomers, though, because many galaxies lie within its borders. The closest of them is the Sculptor Dwarf. It’s just 300,000 light-years away, and it orbits our home galaxy, the Milky Way.
The galaxy contains only 30 million stars or so. But most of them are ancient – far older than most of the stars in the Milky Way. That means the Sculptor Dwarf may be a remnant from the early universe – like the many building blocks that came together to form the Milky Way. So studying the galaxy can tell us much more about the early universe, and the history of our own galaxy.
From most of the United States, Sculptor is low in the southeast in early evening,. But you need a dark sky to make out any of its stars – and a good imagination to “see” a pattern in them.
We’ll have more about Sculptor tomorrow.
Script by Damond Benningfield
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Moon and Regulus
The brightness of any star that’s in the prime phase of life is controlled by the star’s mass: Heavy stars are brighter than lightweight stars. But it’s not a simple one-to-one kind of relationship. A star that’s twice the mass of the Sun isn’t twice as bright – it’s more than 15 times as bright.
That’s because gravity squeezes the core of a heavier star more tightly. That increases the core’s temperature, which revs up the rate of nuclear reactions. That produces more energy, which makes its way to the surface and shines out into space.
Regulus illustrates the point. The heart of the lion consists of four stars, three of which are in the prime of life.
The star we see as Regulus – Regulus A – is a little more than four times the mass of the Sun, yet it radiates about 340 times more energy. Much of that energy is in the ultraviolet, which we can’t see. But even at visible wavelengths, it’s about 150 times the Sun’s brightness.
Regulus A has a couple of distant companions. Regulus B is about 80 percent the mass of the Sun, but only a third of the Sun’s total brightness. And Regulus C is even more dramatic: a third of the Sun’s mass, but just two percent its brightness – a cool, faint ember in the heart of the lion.
Look for Regulus standing close above the Moon as they climb into good view around 1:30 or 2 in the morning. The star will be a little farther from the Moon at dawn.
Script by Damond Benningfield
USA