StarDate

The night sky is disappearing. Growing cities and towns pump more artificial light into the sky all the time. That creates a glowing dome that blots out the view of the Milky Way, meteors, and other beautiful but faint sights.

Light pollution does more than make it impossible to appreciate the beauty of the night sky. It can interfere with the migrations of many animals, and it can harm human health. And it wastes energy by shining light into the sky instead of onto the ground, where it’s needed.

In recent decades, though, some places have tried to limit the light pollution. They’ve passed laws that restrict outdoor lighting, keeping the sky as dark as possible. An international organization certifies the most successful ones. And number one on the list was Flagstaff, Arizona. It was declared the first International Dark-Sky City 25 years ago this week.

Flagstaff began protecting the night in 1958. Lowell Observatory was adding a big new telescope, and it needed dark skies to get the best results. So the city placed restrictions on outdoor lighting. As the city grew over the following years, it beefed up those regulations, winning certification in 2001.

Today, there are more than 60 dark-sky communities, plus dozens of dark-sky parks, reserves, and other sites. That includes a wide swath of West Texas, which is home to McDonald Observatory. These locations help keep the night sky from disappearing.

Script by Damond Benningfield

William Lassell made a fortune selling beer to factory workers in Liverpool. He used that money to set up his own astronomical observatory, called Starfield, outside Liverpool. And he equipped it with telescopes he built himself – some of the best in the world.

Using one of those instruments, Lassell made a major discovery 175 years ago this week. Make that two discoveries: two large moons of the planet Uranus. They were named Ariel and Umbriel, after characters from the works of William Shakespeare and Alexander Pope.

The moons are almost exactly the same size – about 720 miles in diameter. And they have a similar makeup – mixtures of rock and frozen water and methane.

But they look different. Umbriel is dark, and it’s covered by many large impact craters. That suggests the moon is quiet and still – not much happens there.

Ariel is brighter, and it’s much more interesting. It’s crossed by giant canyons and cliffs, with few craters. Liquid water may bubble to the surface from an underground ocean. At the surface, it freezes. That may push the surrounding crust, causing it to crack. So Ariel may be an active world orbiting a giant planet.

Uranus is an easy target for binoculars. It’s halfway between Aldebaran – the bright eye of the bull – and the Pleiades star cluster. They climb into good view in late evening. But the view will be better before dawn, after the Moon has dropped from sight.

Script by Damond Benningfield

The modern constellations offer a convenient way to appreciate the beauty of the night sky. Using the outline of a scorpion or a lion as a landmark makes it easier to find your way around. It’s also a good way to exercise your imagination.

Our imaginations don’t all show us the same pictures, though. The western constellations were passed down from ancient Greece and Rome. And many of them are even older – they came from ancient Babylon and Sumeria. But just about every culture had its own star pictures – its own map of the night sky.

An example is Capricornus. In western mythology, it represents a sea-goat – half goat and half fish – perhaps a story about the god Pan. But records from ancient China describe something different.

Six of the stars in that region formed an ox, known as Niu – a sacrifice for mid-winter. Three others formed dams to hold water for the emperor’s fields, which were also in Capricornus. And other stars formed parts of different pictures – different stories in the night sky.

Capricornus is low in the south at nightfall. The constellation isn’t especially bright, so it’s invisible from light-polluted cities. Under darker skies, you can see the outline of a wide triangle. Tonight, the gibbous Moon is near the triangle’s eastern point. That makes it easier to find where the sea-goat is, but harder to see its faint outline.

Script by Damond Benningfield

Some high-speed bullets are firing across the night sky this week. They’re the bits of debris that produce the Orionid meteor shower – small pebbles left behind by Comet Halley. They hit the atmosphere at about 150,000 miles per hour. They vaporize almost instantly, forming the glowing streaks known as meteors.

Halley visits the inner solar system once every 76 years or so. On each approach, the Sun’s heat vaporizes some of its frozen surface. That releases bits of rock and dirt. Over time, they spread out along the comet’s orbit. Earth flies through this path twice a year, sweeping up some of the particles.

But the comet dust isn’t evenly spread out. Halley produces a new “streamer” with each pass. So the strength of the shower depends on which of these ribbons we encounter, and how deeply we pass through it.

Most years, the Orionids produce up to a couple of dozen meteors per hour. But if we pass through a denser stream, or if we pass through its middle, the rate can go up. In 2006, for example, the shower produced up to a hundred meteors per hour.

Experts aren’t forecasting that kind of performance this year. Still, the shower is worth checking out. You need a dark skywatching site, far from city lights. And the best view comes in the wee hours of the morning, after the Moon has set. The meteors can appear anywhere in the sky, so sit back, look up, and enjoy the show.

Meteorology is the study of Earth’s atmosphere and its weather and climate. Despite the name, it has nothing to do with meteors – at least not directly. But more broadly, meteors and meteorology are related – in their names. Both words come from a Greek word that meant “the heavens above” or “things high up.”

Meteorology was first used by the Greek philosopher Aristotle, around 340 B.C. A “meteor” was any particle in the sky, or that fell from the sky.

Over time, meteors were clumped into four classes. Aerial meteors referred to the wind. Aqueous meteors were rain, snow, or hail – any wet stuff that fell from above. Luminous meteors were anything that glowed, such as rainbows or the northern lights. And igneous meteors were anything that flashed through the sky in an instant – lightning and “shooting stars.”

Until a couple of centuries ago, it was thought that shooting stars had a strictly atmospheric origin – something triggered in the sky itself. It wasn’t until the early 1800s that scientists figured out their true origin: bits of space rock that are burning up in the atmosphere. So without the atmosphere, there would be no glowing meteors to light up the night sky.

The word “meteor,” by the way, refers only to the streak of light. When a rock is still in space, it’s a meteor-oid. And one that s hits the ground is a meteor-ite – a “thing on high” that fell to Earth.

More tomorrow.

Script by Damond Benningfield

The oldest objects on Earth didn’t come from our home planet. They were born in space more than four-and-a-half billion years ago. They fell to Earth as the most common type of meteorite.

Chondrites account for about 85 percent of all meteorites. They’re named for tiny round beads of material known as chondrules. The beads formed in the disk of gas and dust that encircled the newborn Sun. Grains of dust clumped together. The chondrules then mixed in with other particles to form asteroids. Collisions sent pieces of the asteroids racing off into space. Some of them plunged through Earth’s atmosphere, falling as meteorites.

Chondrites haven’t changed much since they formed, so they preserve a record of the early solar system. They tell us what kinds of materials came together to form Earth and the other planets.

There are three main classes of chondrites. The differences reveal where they formed. Some were born quite close to the Sun; others, near the inner edge of the asteroid belt; and still others even farther out. The different classes tell us about conditions in different regions of the early solar system.

Many chondrites contain a lot of water, so they may provide clues to the origin of water on Earth. And they contain some of the chemical building blocks of life, perhaps telling us about the origin of life itself – lessons from relics from the birth of the solar system.

More about meteorites tomorrow.

Script by Damond Benningfield

The solar system is big. Really big. It’s almost three billion miles from the Sun to Neptune, the most distant major planet. It’s more than three billion miles to Pluto. And it’s more than twice that far to the edge of the Sun’s magnetic “bubble” – the boundary with interstellar space.

It’s almost impossible to comprehend those distances – they’re just too far beyond anything we ever experience. But we can get an idea of the scale from models of the solar system – the bigger, the better. And there are some king-size models around the planet.

The largest is in Sweden – it spans most of the country. It includes all the major planets, plus many dwarf planets, asteroids, and comets. The Sun is represented by a ball-shaped arena in Stockholm that’s about 350 feet across. At that scale, Earth is bigger than a beachball, and is almost five miles away. Neptune is about 140 miles out, while the edge of the magnetic bubble is several times farther.

The biggest model in the United States is in Maine. It spans almost a hundred miles, along U.S. 1. It extends to the dwarf-planet Eris, which is more than twice as far as Pluto.

Other large models are found in New Mexico, Illinois, Michigan, and several other states. Some of them are small enough that you can walk them, while you need a car or bike for the others. But all of them can help you understand the scale of our big neighborhood.

Script by Damond Benningfield

A meteorite found in the Sahara Desert could be a fragment of a destroyed sibling of Earth. The small planet might have been blasted to rubble when the solar system was young. Some of the planet’s remains could have been incorporated into the other rocky worlds, including Earth.

NWA 12774 is a one-pound meteorite that was found in northwestern Africa in 2019. It belongs to a rare class known as angrites. They account for less than one-tenth of one percent of all known meteorites. They’re also among the oldest meteorites – they formed more than four and a half billion years ago, when Earth and the other planets were still taking shape.

Based on the composition of the meteorite alone, a team of researchers concluded that it was a fragment of a larger body that was disrupted during the early solar system. When the scientists included the structure of the meteorite, they determined that it came from near the surface of the parent body. That world would have been at least 2200 miles in diameter – as big as the Moon – and perhaps as big as Mars.

The parent world probably was destroyed in a collision with another large body. Such collisions probably were common in the early solar system. Earth probably smacked into a Mars-sized planet, for example. The impact blasted huge amounts of material into space, which eventually came together to form the Moon.

Script by Damond Benningfield

Antares, the bright star at the heart of Scorpius, huddles quite close to the Moon early this evening. They set not long after the sky gets dark, so there’s not a lot of time to look for them.

The Moon is a thin crescent now, so it’s night across most of the lunar disk. But on the bright sliver that’s in daylight, you can still make out some of the dark lunar “seas” – vast plains of volcanic rock. They formed long ago, when giant asteroids slammed into the Moon. Molten rock bubbled up from below, then cooled and hardened.

A recent study found evidence of an especially big impact three-and-a-half billion years ago. The hit would have been powerful enough to melt the surface across a wide area.

Researchers discovered the evidence in a meteorite known as Northwest Africa 12593. It was found in Mali, in 2017. It contained some tiny crystals that form only under extreme heat. The chemistry of the meteorite suggested the impact happened three-and-a-half billion years ago.

A later impact shattered the lava plain, jumbling up the rocks. And a third impact blasted some of the fragments into space, including the one that fell to Earth.

More tomorrow.

Script by Damond Benningfield

The surface of the Moon seems eternal. There’s no air or water to reshape it, and no plate tectonics to jiggle things around. But the Moon does change – sometimes in a hurry. Scientists recently discovered an impact crater that’s almost 750 feet in diameter. It had been gouged during the spring of 2024.

The crater was found in images snapped by L-R-O – Lunar Reconnaissance Orbiter. The craft’s been mapping the lunar surface for years. It’s photographed almost all of the surface many times. Scientists compare images taken at different times to see how things have changed.

The new impact crater was the biggest change seen so far. The crater is three times wider than any other crater gouged during LRO’s time in orbit. It’s about 150 feet deep, and its rim rises more than 25 feet above the surrounding landscape. The impact blasted out boulders as big as houses. And bright “rays” of smaller bits of debris were splashed far from the crater’s edge. Such a powerful impact on Earth could level a city, and kill everything within miles of the impact site.

Some good-sized pieces of debris from the crater’s formation could have traveled dozens of miles – something for designers of lunar habitats to keep in mind.

Script by Damond Benningfield