StarDate

A barely-there crescent Moon teams up with the disappearing “morning star” in tomorrow’s dawn twilight. But there’s not much time to look for them.

The Moon will cross between Earth and the Sun in a couple of days. It’ll be lost in the Sun’s glare. It will return to view, in the evening sky, by Friday or Saturday.

Venus is getting ready to disappear in the dawn twilight as well. It will cross behind the Sun on January 6th. It’s a slower passage, so the planet will be hidden in the Sun’s glare for about three months. It’ll emerge as the “evening star” in February.

Most cultures figured out that the morning and evening star were actually the same object thousands of years ago. Even so, they had different names for the morning and evening appearances. In ancient Greece, morning Venus was named for the god Phosphorus. In Rome, he was Lucifer. Both names mean “bringer of light” – the god lit the dawn sky with a torch.

Venus passes behind the Sun every 584 days – a bit more than 19 months. Before and after it disappears, it’s almost full. So if you look at Venus with a telescope now, it’ll be almost fully lit up – like a negative image of the “fingernail” crescent Moon.

Look for Venus and the Moon quite low in the eastern sky beginning about 45 minutes before sunrise. Because of the timing and the viewing angle, they’ll be a little easier to spot from the southeastern corner of the country.

Script by Damond Benningfield

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

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

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

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

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

Edwin Hubble gets the credit for discovering that the universe is expanding. But that finding was made possible by work done by Vesto Slipher. He was the first to measure the motions of distant galaxies – the key to Hubble’s discovery.

Slipher was born 150 years ago today, in Mulberry, Indiana. He worked on the family farm, and developed an interest in astronomy. A college professor helped him get a job as an assistant at Lowell Observatory in Arizona, where he worked for the next five decades.

Slipher studied what were called “spiral nebulae.” It wasn’t certain whether these pinwheels were motes of matter in the Milky Way, or “island universes” of stars outside the Milky Way.

Slipher used a technique that splits an object’s light into its individual wavelengths. The object’s motion shifts those wavelengths. Objects that are moving away from us are shifted to longer, redder wavelengths.

Slipher found that most of the spirals were moving away from us in a hurry. He suggested the objects were far outside the Milky Way. But he couldn’t prove it because he had no way to measure the distances.

Hubble did measure the distances, proving that the spirals are separate galaxies. He then combined Slipher’s observations with his own to show that the farther a galaxy, the faster it was moving. Later, astronomers concluded that the universe is expanding – a finding made possible in large part by Vesto Slipher.

Script by Damond Benningfield

There’s nothing in the night sky quite like the Pleiades. The star cluster forms a tiny dipper. Depending on sky conditions and the viewer’s eyesight, anywhere from a half dozen to a dozen stars or more are visible to the naked eye.

Its unique visage has made the Pleiades one of the most important sky objects in many cultures. The people of the Andes timed the start of the harvest season to its first appearance in the dawn sky. The Aztec year began at about the same time.

In Hawaii, the Pleiades was known as Makali’i. And the year began when Makali’i first appeared in the evening twilight – the middle of November. The year, the new year, and a festival period shared a name: Makahiki.

The customs varied from island to island. But they had a lot in common. The celebration lasted for several months. Warfare and most work were banned. Instead, people danced, feasted, played sports, and reconnected with family and friends. And they made offerings to Lono, a god of agriculture, music, and peace.

The Pleiades is just climbing into the evening twilight, in the east-northeast, across Hawaii and most of the rest of the country. In some Hawaiian traditions, Makahiki doesn’t begin until the first appearance of the crescent Moon in the west after the Pleiades returns. That’s coming up on the 21st – the start of the new year and the celebration that honors it. Hau’oli makahiki hou! – Happy New Year!

Script by Damond Benningfield

The Moon shoots the gap between some bright companions tonight: the planet Jupiter and the star Pollux, the brighter “twin” of Gemini. They climb into good view by about 10:30 or 11, and stand high overhead at dawn tomorrow.

Jupiter is the largest planet in the solar system, and it has the most turbulent atmosphere. Hurricane-like storms as big as continents twirl across it.

Thunderstorms can produce lightning bolts far more powerful than any on Earth, as recorded by a passing spacecraft. And the storms might produce their own giant hailstones: “mushballs” as big as softballs.

The idea was first proposed in 2020. And a study published earlier this year supports it. The study used observations by the Juno spacecraft, which is orbiting Jupiter, along with Hubble Space Telescope and a radio telescope on Earth

The study says the mushballs may begin as droplets of frozen water far below the cloud deck. They get caught in updrafts that howl at 200 miles an hour.

They’re carried to the tops of the clouds, which can be tens of miles thick. Along the way, the ice mixes with ammonia, forming a slushy liquid. When the balls get heavy enough, they begin to drop. As they descend, they’re coated with fresh ice, giving them a hard shell around a slushy middle – mushballs.

The mushballs plunge hundreds of miles below the clouds, where they vaporize – “mushing” into the depths of the giant planet.

Script by Damond Benningfield

In the early 20th century, scientists discovered a mysterious new type of radiation. The higher they went, the stronger it became. They realized that it came from beyond Earth. And 100 years ago tomorrow, it got a name: cosmic rays.

Nobel Prize winner Robert Millikan had become fascinated by the rays from outer space in the early ’20s. He coined the name “cosmic rays” in a paper about them, which he presented to a meeting on November 9th, 1925.

Millikan thought the rays were a form of energy produced by matter that was being born in the space between the stars. Others disagreed, especially Arthur Compton – a future Nobel Prize winner himself. He argued they were subatomic particles racing through the universe at almost the speed of light.

Compton was right. Cosmic rays are electrons, protons, or the nuclei of atoms. Most of the ones that hit Earth are produced by the Sun. But others come from far beyond our own solar system – and even from beyond our galaxy. The most energetic ones come from exploding stars, or from the violent regions around black holes.

Most of these distant cosmic rays are blocked by the Sun or by Earth’s magnetic field. But a few enter the atmosphere. They strike atoms and molecules in the air, creating “showers” of other particles. If a shower occurs above the right kind of clouds, it can create lightning – a terrestrial light show with an extra-terrestrial origin.

Script by Damond Benningfield