StarDate

The largest moon of the planet Uranus has been shrink-wrapped. Early in its history, its outer layers cooled and shrank, while its center warmed and expanded. That gave it a wrinkly crust punctuated by giant cliffs and canyons.

Titania is less than half the size of our own Moon. And it orbits Uranus at about the same distance as the Moon orbits Earth. It’s about half ice and half rock.

Its surface is pockmarked by many impact craters. But its most interesting features are canyons and cliffs. The cliffs are miles high and up to hundreds of miles long. And the canyons are even more dramatic. The longest one yet seen stretches a quarter of the way around Titania.

Planetary scientists say that’s the result of the shrink-wrapping. As Titania was being born, its surface was pelted by big chunks of rock and ice. The impacts warmed its outer layers. When the collisions stopped, the outer layers began to cool. At the same time, the decay of radioactive elements deep within Titania warmed its interior. So the outside shrank, while the inside expanded. That cracked and warped the surface — giving Titania a craggy visage.

And Uranus is putting in its best showing of the year right now. The giant planet lines up opposite the Sun, so it rises at sunset and is in view all night, in the constellation Pisces. Tonight, it’s not far to the lower left of the Moon. It’s so faint, though, that you need binoculars or a telescope to see it.

Script by Damond Benningfield

The young solar system was crowded, busy, and sometimes violent. It contained not only today’s planets, but many other planet-sized bodies. Some were thrown clear of the solar system by the gravity of Jupiter and the other giant planets, while others were hurled into the Sun.

But a few rammed into today’s planets, with impressive results. A collision between Earth and another body may have given birth to the Moon. Another collision may have caused Venus to spin backwards. And yet another may have pushed the giant planet Uranus over on its side.

Uranus is the third-largest planet in the solar system — four times the diameter of Earth. So it would have taken quite a wallop to push it over — or perhaps two wallops. Research published a few years ago suggested that the planet got hit not once, but twice. The second impact was needed to help produce the orbits of Uranus’s moons.

But a couple of years earlier, another group of researchers said you wouldn’t need a collision at all. Instead, interactions between Uranus and a giant moon could have tilted the planet over. The gravity of another planet could then have yanked the big moon away, leaving Uranus as we see it today.

And in fact, right now is a good time to see this giant planet. It lines up opposite the Sun, so it rises at sunset and is in view all night, in the constellation Pisces. It’s so dim, though, that you’ll need binoculars to pick out.

More about Uranus tomorrow.

Script by Damond Benningfield

It’ll be a long time before astronauts journey to worlds beyond our own. But that hasn’t stopped them from making journeys to exotic locations. In the last few months, for example, they’ve spent time inside a cave in Italy, and in a habitat on the floor of the Atlantic Ocean.

These projects are designed to help astronauts and ground controllers prepare for future explorations in space. The crew members gain experience in living and working in unusual environments, where they’re cut off from normal contact with the outside world. And ground controllers learn how to plan and monitor such missions.

Back in July, a team of six astronauts — two from the United States and four from other countries — entered a network of caves in Sardinia. During the week-long expedition, they explored the caves and collected scientific samples. And they conducted daily planning and debriefing sessions, just as they would during a space mission.

And not long after they returned to the light, another crew entered an underwater habitat called Aquarius. It’s 60 feet deep, three and a half miles off Key Largo. Astronauts and technicians tested tools and scientific equipment, and they conducted underwater “spacewalks.” They collected samples and helped with a coral restoration project. And they experimented with a communications time lag that was similar to what astronauts would experience during a trip to Mars — a destination that’s still decades away.

Script by Damond Benningfield

You can’t see it, but the stars of the Milky Way are in constant motion as they circle through the galaxy. Most, including the Sun, do so alone. But many others do it in groups. Some groups are tightly bound clusters. The stars in other groups are more loosely scattered around. These wide-spread collections are known as moving groups.

The best known is the Ursa Major Moving Group, which was discovered in 1869 by British astronomer Richard Proctor. It’s centered in Ursa Major, the Great Bear, and it includes five of the seven stars of the Big Dipper.

These stars, plus several others in Ursa Major, are all about the same distance from Earth, and they’re all moving at the same speed and in the same direction. Their chemistry is similar as well, and they’re all the same age. That suggests that the stars were born together, then spread out over time.

The group isn’t limited to the stars of Ursa Major, though. It appears to include dozens of stars in many constellations, including Orion, Aquarius, Taurus, and Draco. Yet even though they’re widely dispersed, they share the same characteristics as the stars in Ursa Major.

There are other moving groups as well. One is centered in the southern constellation Doradus, for example, and another on the star Beta Pictoris. And several others have been discovered in just the last few years. They show that many of the stars that twinkle in the night still move through the galaxy with their siblings.

Script by Damond Benningfield

The science of astronomy is influenced by the same vagaries of life as any other endeavor. A financial panic 150 years ago, for example, forced one would-be astronomer to pick up the pace of his work. That led to a successful career in research and in presenting astronomy to the public.

In 1866, Richard A. Proctor was just 29 years old. He’d written a magazine article about double stars, and a book about the planet Saturn. But he’d inherited a great deal of money, so he worked at a leisurely pace — he wrote only a few lines each day.

That spring, though, a financial panic hit London, and it quickly spread. It wiped out a bank in New Zealand in which Proctor was a major investor. That left him almost bankrupt.

Fortunately for Proctor, a magazine had just asked him to write some articles about telescopes. He agreed. And over the next few years he worked tirelessly, writing books and articles, and conducting research. He measured the length of the Martian day to an accuracy of less than a tenth of a second, and published an early map of Mars. And he made important discoveries about the distribution of stars in the Milky Way, and about star clusters. In fact, he discovered a whole new type of cluster; more about that tomorrow.

Later, Proctor became a lecturer in the United States — and in New Zealand. Those appearances helped bring financial stability for an astronomer who’d been forced to work harder by a financial panic.

Script by Damond Benningfield

As darkness falls this evening, some bright stars with famous names are in good view. Arcturus is low in the west, with Antares, the heart of the scorpion, even lower in the southwest. And the stars of the Summer Triangle crown the sky — Vega, Deneb, and Altair.

These names have been around for thousands of years. But astronomers didn’t make them official until this summer.

The names were approved by the Working Group on Star Names. It’s a committee of the International Astronomical Union, which approves names for all astronomical objects.

The committee was set up to provide standardized names for bright stars and those that have scientific or historic significance. The first step is to make well-known names official. So names like Arcturus and Vega were some of the first to be adopted. The committee is scouring astronomy history to come up with even more names.

It’s also come up with some early guidelines for adopting new names. All stars have catalog designations, but most of them have no proper names. The guidelines say that names should reflect astronomical and cultural heritage, they should be pronounceable, and they shouldn’t be too long. Commercial, political, and military names are out. And just so you don’t waste your time suggesting it, they won’t pick the names of your pets, either.

The committee will publish groups of star names as they’re approved — making official many of the names that people have been using for centuries.

Script by Damond Benningfield

As anyone who’s looked at the clouds passing overhead on a pleasant autumn afternoon can tell you, it’s easy to see shapes in them. And the same thing is true with the clouds of gas and dust sprinkled through the galaxy. One well-known example is the California Nebula. It really does look like the outline of the Golden State — except that it’s red rather than gold.

The red color actually comes from a blue star, known as Xi Persei. The star is so hot that it emits lots of ultraviolet radiation. Some of this energy strikes atoms of hydrogen gas that make up most of the nebula. That rips the hydrogen’s proton and electron away from each other. The two may later rejoin. As the electron settles into position, it emits red light — the glow that colors the nebula.

The nebula is about 1500 light-years away, in the constellation Perseus, which is low in the northeast at nightfall, and high in the east by the time the Moon sets around midnight.

Even though the nebula spans dozens of light-years, it’s just a small part of a much larger cloud of gas and dust. Normally, such clouds spawn new stars. For some reason, though, this cloud is producing very few. In fact, it didn't even make the blue star that causes the nebula to glow. Instead, that star was born elsewhere, and it’s simply passing near the nebula.

Someday, though, this mostly dark cloud may begin making large numbers of stars — lighting up Perseus, but obliterating the outline of the California Nebula.

Script by Ken Croswell, Copyright 2016

This may sound a bit odd, but planetary scientists say it’s true. Since the last ice age ended on Mars, more than 20,000 cubic miles of ice have been added to the planet’s polar ice caps. And more is being added even today.

Here on Earth, the ice caps get bigger during an ice age. On Mars, though, the ice caps get smaller, while ice forms closer to the equator.

That’s because Martian ice ages are caused by a big change in the planet’s tilt on its axis. Right now, the tilt is almost the same as Earth’s. A couple of million years ago, however, Mars was tilted more severely — perhaps almost over on its side. That meant that the Sun was shining down on the planet’s poles. The solar heat vaporized much of the ice caps.

The water vapor froze back onto the surface at latitudes close to the equator, where there was much less sunlight to warm the surface. So instead of white “caps” at its poles, Mars probably had a “belt” of white around its middle.

That ice age ended about 400,000 years ago, when the planet’s tilt changed to roughly its current angle. So the polar ice caps have been getting thicker ever since. Radar aboard a Mars orbiter recently confirmed that scenario by peering deep into the northern ice cap — seeing layers of ice added over millions of years of Martian history.

Look for Mars to the lower left of the Moon this evening, shining like a bright orange star — a cold world that’s emerging from an even colder past.

Script by Damond Benningfield

Like dogs and Heinz condiments, there’s a wide variety of planets. That’s true even here in our own solar system, where three planets are in view this evening.

Venus is the brilliant “evening star” quite low in the western sky shortly after sunset. Saturn is close to the lower right of the Moon, with orange Mars farther to the left of the Moon.

Venus is our closest planetary neighbor. And it’s also the planet that’s closest to our own Earth in size and mass. Its surface, though, is quite different from Earth’s. The temperature is hot enough to melt lead, and the pressure is the equivalent of being about two-thirds of a mile deep in Earth’s oceans. And the atmosphere is topped with an unbroken blanket of clouds that are made of sulfuric acid.

Mars is only about half of Earth’s diameter. Its air is thin, cold, and dry, although a few clouds scud across the sky. Its surface more closely resembles Earth’s than that of any other known planet, with riverbeds, ice caps, sand dunes, and other familiar features.

Saturn is a planetary giant. It’s about nine times Earth’s diameter, and it’s encircled by beautiful rings and an entourage of dozens of moons. The planet has no solid surface, though — it’s a big ball of gas. And its upper atmosphere is cold and turbulent, with storm systems as big as Earth swirling through its clouds — part of the great variety in the solar system’s planets.

We’ll have more about the Moon and Mars tomorrow.

Script by Damond Benningfield

You don’t need gold or gemstones to make beautiful rings. Sometimes all you need are chunks of plain ice and rock — like the rings encircling the planet Saturn. Those rings are among the most beautiful features in the entire solar system.

The rings probably represent the remains of small moons. One or more moons may have spiraled too close to Saturn, where the giant planet’s gravity pulled them apart. Or two moons may have collided, blasting them to bits. Or perhaps both processes have been at work.

Today, the rings are renewed by some of Saturn’s moons. Big chunks of ice and rock slam into their surfaces, blasting out debris. And the moon Enceladus squirts geysers of water and ice out into space, resupplying one of Saturn’s more distant rings.

Moons also keep the rings in place. Several small moons orbit inside the ring system. Their gravity herds the bits of ring material like a sheepdog guiding its flock.

Over time, some of the material may coalesce to form new moons. But collisions or Saturn’s gravity may rip them apart again — creating new rings for this giant planet.

And Saturn is in good view tonight. The planet stands close to the left of the Moon as night falls. It looks like a bright golden star, with the rings adding greatly to its luster. Any telescope will reveal the rings — beautiful bands made from the most ordinary materials.

We’ll talk about the Moon and another bright planetary companion tomorrow.

Script by Damond Benningfield