There’s just one place to catch a wave outside Earth: Titan, the largest moon of Saturn. It’s the only other world in the solar system with bodies of liquid on its surface. And the waves there could reach heights of 10 feet. But future surfers will need to dress carefully; the surface temperature is almost 300 degrees below zero.

Titan is half-again the size of Earth’s moon, and it has a dense atmosphere. Rain fills its lakes and seas with liquid methane, ethane, and nitrogen. The largest sea covers about 200,000 square miles – twice the area of all the Great Lakes combined. It could be several hundred feet deep.

The Cassini spacecraft used radar to measure Titan’s ponds. It saw waves of no more than an inch or so high. But a recent study says the waves could get a lot bigger.

Based on 20 years of observations of waves on Lake Superior, scientists built a computer model of how waves might work on other worlds. The model accounted for gravity, the pressure of the atmosphere, and the properties of the liquid. When the model was applied to Titan, it showed that even gentle breezes could whip up some big waves. But the waves would move more slowly than those on Earth – a slow-motion trip across the sea.

Saturn looks like a bright star close to our moon the next couple of mornings. It’ll stand to the left of the Moon at dawn tomorrow, and the lower right of the Moon on Tuesday.

Script by Damond Benningfield

The dawn twilight has a bright visitor the next few mornings – the planet Mercury. It’s farthest from the Sun for its current morning appearance. It looks like a bright star, but it’s so low in the sky that it’s tough to find.

Mercury holds an important spot in the history of astronomy and physics. It provided some of the first confirmation of General Relativity – Albert Einstein’s theory of gravity.

Mercury’s orbit around the Sun is lopsided, so the planet’s distance from the Sun varies. For a long time, astronomers had seen that the orbit’s closest point shifted a tiny bit over time. Isaac Newton’s laws of gravity explained most of the difference. But there was still a tiny amount that couldn’t be accounted for.

Einstein’s theory of gravity held that massive bodies warp the space around them. Since Mercury is the Sun’s closest planet, its orbit is influenced by that “warpage” more strongly than any other planet’s. In fact, general relativity accounted precisely for the shift in the orbit. So Mercury’s orbit provided some of the first evidence to support general relativity – a new way of thinking about gravity.

Look for Mercury quite low in the eastern sky during the waxing twilight. It’ll shine a little brighter each day over the next few mornings. But it’ll also drop a little closer to the Sun, so you’ll need a clear horizon to spot it.

Tomorrow: catching waves.

Script by Damond Benningfield

The Sun is getting bigger, hotter, and brighter. The change isn’t enough to notice during a human lifetime – or even a thousand lifetimes. It plays out over hundreds of millions of years. And it’s all the result of changes deep inside our star.

Like all stars in the prime phase of life, the Sun is “fusing” atoms of hydrogen in its core to make helium. That generates the energy that makes the Sun shine. As the amount of helium builds up, the core gets denser, so gravity squeezes it more tightly. That speeds up the fusion reactions, making the core even hotter.

Radiation from the hotter core pushes on the Sun’s outer layers, making the Sun bigger. It also makes its surface hotter. The combination of bigger and hotter makes the Sun brighter. So over its four-and-a-half-billion-year lifetime, our star has grown about 15 percent wider, and perhaps 40 percent brighter.

That should mean that the young Earth would have been an iceball. But studies suggest the atmosphere was much thicker when Earth was young. The atmosphere also contained much more carbon dioxide and other greenhouse gases. They trapped more heat, keeping Earth from freezing over.

The Sun’s bigger-hotter-brighter trend will continue. In perhaps a billion to two billion years, it’ll be so hot and bright that Earth’s air and oceans will boil away. That will reduce our planet to a bare cinder.

Script by Damond Benningfield

Eta Aquilae is big, bright, and unsteady. Over a bit more than seven days, the star pulses in and out like a beating heart. That causes its brightness to change. How it changes makes the star a good “standard candle” – a type of object that astronomers use to measure the scale of the universe.

Eta Aquilae is a Cepheid variable – the first one ever discovered. Such stars brighten and fade in a predictable way. By timing the cycle, astronomers can determine the star’s true brightness. Comparing that to how bright the star looks allows them to calculate the star’s distance. Cepheids are bright enough to see hundreds of millions of light-years away – in galaxies beyond the Milky Way.

To go even farther, astronomers rely on another type of standard candle: the exploding stars known as Type Ia supernovas. Like the Cepheids, the way they brighten and fade reveals their true brightness. Some of them appear in galaxies with Cepheids, where we already know their distance. That provides a way to calibrate all of the supernovas, which can be seen from billions of light-years away.

Of course, it’s all a little more complicated than that. There are different classes of Cepheids, for example. So astronomers have to understand all the details – making sure that a standard candle really is a good distance marker.

Eta Aquilae is high above the Moon in early evening, near Altair, its constellation’s brightest star.

Script by Damond Benningfield

Saturn feels like it has a big region of the early morning sky practically to itself right now. The giant planet climbs into good view after midnight, and stands high in the south at first light. It looks like a bright golden star. You have to scan a long way in every direction to find another planet or star that rivals it.

Saturn is traveling through Pisces, skimming along the border with Cetus. That region of the sky is well below the Milky Way – the hazy band of light that outlines the disk of the Milky Way Galaxy. When we look at the Milky Way, we’re looking into the most heavily populated part of the galaxy. So not only are there a lot more stars in and around that band, there are a lot more bright stars.

At the same time, Saturn’s location is a quarter of the way around the sky from the center of the galaxy, which is in Sagittarius. Again, that means we’re looking into more thinly settled parts of the galaxy. It’s like looking toward the suburbs of a major city instead of its busy downtown – there’s just a lot less to see.

Saturn is so far from the Sun that it takes the planet about 30 years to make one full circle against the starry background. So the planet will stay in this dimly settled region of the sky for a couple of years – making it especially easy to find as you look into the darkness.

Tomorrow: bright “mile markers” for measuring the scale of the universe.

Script by Damond Benningfield

Gliese 710 isn’t much to look at. It’s smaller and lighter than the Sun, and just one-tenth as bright. So from its current distance of 62 light-years, it’s much too faint to see with the eye alone. But come back in about 1.3 million years and it’ll be a different story. The star will shine about three times brighter than Sirius, the night’s current brightest star.

All the stars are on the move. Like the Sun, they’re orbiting the center of the Milky Way Galaxy. Each star follows its own path, so its direction and speed are a little different from all the other stars. Some stars are moving toward us, while others are moving away.

Gliese 710 is moving toward the Sun at more than a quarter of a billion miles per year. Studies have shown that it’ll pass just one-sixth of a light-year away – just four percent the distance to the current closest neighbor. That’s closer than any other star will approach the Sun over the next several million years.

Gliese 710 will pass through the Oort Cloud – a huge shell of rocky, icy bodies that surrounds the Sun. That will push many of those objects toward the Sun. Some of them could slam into Earth – some un-neighborly gifts from a close neighbor.

Gliese 710 is in Serpens, the serpent. The star is about half way up the south-southeastern sky at nightfall. You need a telescope to see it – for now.

Script by Damond Benningfield

In April, engineers had to shut down one of the scientific instruments aboard the Voyager 1 spacecraft. The device had been studying charged particles in the interstellar medium – the space between the stars. But Voyager is slowly losing power, so the instrument was shut down to help extend the craft’s life.

Voyager 1 is the most-distant object ever sent into space – 16 billion miles from Earth. At that range, it takes almost 24 hours for its radio transmissions to reach Earth.

The craft and its twin, Voyager 2, were launched in the summer of 1977. Their mission was to study the giant planets Jupiter and Saturn. Voyager 2 continued on to Uranus and Neptune.

Since then, both craft have just kept on going. In 2012, Voyager 1 became the first craft to leave the solar system. It passed outside the magnetic “bubble” generated by the Sun. Voyager 2 followed in 2018.

Both Voyagers are powered by the radioactive decay of plutonium. Today, that generates less than half as much energy as it did at launch. So as the power levels have dropped, engineers have shut off most of the scientific instruments. Two instruments are still going on Voyager 1 – studying the space between the stars.

In 300,000 years, the craft is expected to fly about one light-year from a small, faint star that’s 47 light-years away – a dead emissary from the people of Earth.

Script by Damond Benningfield

The religion of ancient Egypt said that when a king died, his soul ascended to the heavens to join with the god Osiris, in the modern-day constellation Orion.

His tomb was filled with items he might need to help him on his way. And in the case of at least one pharaoh, some of those items probably came from the heavens.

The tomb of King Tutankhamen contained thousands of artifacts. Many of them were made of gold, including a dagger buried inside his coffin. But the boy king also had a second dagger, made of iron.

When Tut was buried, more than 3300 years ago, Egypt hadn’t started to work with iron ore, so the dagger probably was made from an iron meteorite – a space rock that fell to Earth. The composition of the dagger’s metal is much like that of a metallic meteorite – a mixture of iron and nickel, with a pinch of cobalt.

Another Tut artifact was an elaborate piece of jewelry known as a pectoral. Its centerpiece is a scarab beetle carved from yellow glass.

The glass formed about 26 million years ago, when an asteroid or comet plunged toward Earth. It either hit the surface or exploded in the atmosphere. Heat from the explosion melted some of the desert sand, creating chunks of glass. One of those chunks eventually made its way to an Egyptian artist, and then to Tut’s tomb – a piece of glass from the heavens for a king traveling to the heavens.

Tomorrow: into the void.

Script by Damond Benningfield

Planetary scientists have had a hard time classifying a world that orbits a faint star in Ophiuchus. Since the planet’s discovery in 2009, they’ve described it as a super-Earth, a mini-Neptune, and a super-Venus. In other words, it’s not like anything in our own solar system.

The planet orbits the star GJ 1214. It’s in the serpent bearer, which is high above the Moon this evening. The star is less than 50 light-years away. But it’s less than one percent as bright as the Sun, so you need a good-sized telescope to see it.

A few years ago, the International Astronomical Union assigned formal names to both the planet and the star. The names come from Kenya, from the Maa language. The star is Orkaria, from the name of a red pigment used by warriors in tribal ceremonies – the color of the star. The planet is Enaiposha – a word for lake or sea, or for their stormy nature.

The planet is bigger and heavier than Earth. That led to its early classification as a super-Earth. But it’s not very dense, which makes it more like a miniature version of Neptune – the smallest of the Sun’s giant planets.

Enaiposha has a thick atmosphere, which is hot because the planet is quite close to the star. Observations by Webb Space Telescope suggest the atmosphere contains a lot of carbon dioxide. That hot C-O-2 atmosphere makes the planet like Venus – one of several identities for this hard-to-classify world.

Script by Damond Benningfield

Cygnus X-1 contains the first black hole ever confirmed. And it recently recorded another first. Astronomers measured the details of twin “jets” of particles that shoot into space from its poles. The jets are firing at almost half the speed of light. And they have the power of 10,000 Suns.

The system consists of the black hole and a supergiant star. The black hole, which was discovered in 1964, is 20 times the mass of the Sun. The star is twice that mass.

The star is extremely hot and bright. It blows a thick wind of hot gas into space. The black hole captures some of the gas, which forms a swirling, super-hot disk around it. Magnetic fields grab some of the gas before it falls into the black hole, and fire it back into space through the jets.

Astronomers have seen jets from many black holes. But this is the first time they’ve precisely measured a jet’s power and speed. Those details are important because the jets can have a big influence on the surroundings. They can blow away gas and dust, preventing the birth of more stars. Or they can squeeze clouds of gas and dust, triggering the birth of stars. So the details help us understand the role of black holes in the evolution of entire galaxies.

Cygnus is in the eastern sky at nightfall. Although Cygnus X-1 is too faint to see, it’s about half way between the swan’s bill and the intersection of its body and wings.

Script by Damond Benningfield