Saturn is cold and dark. But it’s not quite as cold as you might expect. Saturn actually puts out more than twice as much energy as it receives – heat radiating from deep inside the planet.

Saturn is made mostly of hydrogen and helium – the lightest and simplest chemical elements. But its core contains a lot of rock, metal, and other heavy materials – more than 15 times the total mass of Earth. Gravity squeezes the core tightly, causing it to shrink. That produces heat, which rises to the surface and shines out into space.

But that doesn’t explain all of Saturn’s heat. The rest may come from an odd type of rainfall. Droplets of liquid helium may fall toward the core. As they fall, they produce friction, which produces heat.

Saturn’s internal heat drives much of the weather in its atmosphere, including storms that can be as big as continents – swirling clouds on a cold, dark planet.

Despite the lack of sunlight, Saturn looks bright in our sky because it’s huge – about nine times the diameter of Earth. It’s easy to see how bright the next couple of early mornings because it’s close to the Moon. Tomorrow, it’s to the lower left of the Moon at dawn. It’ll be a little farther to the right of the Moon on Wednesday.

Script by Damond Benningfield

That far point is known as aphelion or ap-helion. The term comes from a mash-up of Latin and Greek. “Ap” is from a Latin word that means “far away,” while “helion” is a Greek word for the Sun.

The changing distance is a result of the shape of Earth’s orbit. Instead of a nice, round circle, it’s an ellipse – like a lopsided circle.

Over tens of thousands of years, the shape changes – the result of the gravitational influence of the Sun, Moon, and planets. The orbit seesaws between being a little more circular and a little more lopsided. Right now, we’re toward the more-circular end of the seesaw.

Today, aphelion always comes about two weeks after the summer solstice. But that won’t always be the case. Thanks to a slow wobble in Earth’s rotation, aphelion shifts an average of one day later every 58 years. So it occurred on the solstice about 900 years ago. And about 4600 years from now, it’ll occur on the fall equinox, in September.

Incidentally, the lopsided orbit has a big impact on the length of the seasons. Our planet moves slowest when it’s farthest from the Sun. That makes summer in the northern hemisphere almost five days longer than winter.

Script by Damond Benningfield

One light-year is the distance light travels in a year – almost six trillion miles. So each of the anniversary stars is about 1.5 quadrillion miles away – the number 15 followed by 14 zeroes.

The distances were measured with a technique known as parallax. Astronomers look at a star when Earth is on opposite sides of the Sun. That causes a tiny shift in the star’s position against the background of more-distant objects. The size of that shift reveals the star’s distance. But there’s a slight margin of error, so the distances might not be exact.

The best measurements say that Bellatrix is a little more than 250 light-years away. Omega Herc is a little less. Spica is in the middle – almost exactly 250 light-years from Earth. So we see it as it looked around the year 1776.

Spica is the brightest member of that trio. It’s low in the southwest as night falls. Earth won’t see the light it emits tonight until the American quincentennial – 250 years from now.

Script by Damond Benningfield

Regardless of where it takes place, a meteor shower happens when a planet flies through the orbital path of a comet or asteroid. Bits of rock and dust shed by the small body ram into the planet’s atmosphere at high speed. They heat up and vaporize, forming the glowing streaks known as meteors.

In this case, the source of the particles could be two asteroids. They have a similar composition, and they follow similar paths around the Sun.

A team of European astronomers recently plotted the orbits of the two bodies a hundred-thousand years into the past. The study found that, about 20,000 years ago, both asteroids passed especially close to the Sun many times. And the asteroids were so close to each other that they could have been one larger asteroid.

Warmed by the Sun, the surface of the asteroid could have cracked and splintered. The way the asteroid heated up could have caused it to spin faster. The weakened asteroid then split apart, spewing debris into space. Venus periodically slips through this trail of debris – perhaps triggering a meteor shower.

From Earth, only the brightest of those meteors might be visible through a telescope – streaking through Venusian skies.

Script by Damond Benningfield

Uranus is a giant – about four times the diameter of Earth. But it’s so far away that it’s faint. Under especially dark skies, people with good eyesight can just make it out. Moonlight or light pollution mask it from view, so you need binoculars to find it.

And even then, it looks like a meager star, perhaps with a hint of blue-green. Methane in its upper atmosphere absorbs red light, so only the blue and green can reach us.

Mars is much smaller – only a bit more than half of Earth’s diameter. But it’s also much closer, which makes it easier to see.

Even with the eye alone, it’s no problem to make out the planet’s orange color. That’s produced by iron oxide in the rocks and the tiny dust grains that coat much of the surface. That color will become easier to make out over the coming months, as Earth and Mars get closer and closer.

For now, look for Mars low in the east-northeast beginning a little before dawn. It’s quite easy to make out. Tomorrow, Uranus will stand a little to the lower left of Mars, so both of them will fit in a binocular field of view. And Uranus will be even closer above Mars on Saturday – a faint giant appearing to almost touch the Red Planet.

We’ll talk about a much brighter planet tomorrow.

Script by Damond Benningfield

This is the second asteroid encounter for Hayabusa2, which launched in 2014. Its main mission was a detailed study of the asteroid Ryugu. It orbited the asteroid for a year and a half. It gathered a few grams of dust and pebbles and dropped them off at Earth in late 2020. Studies have shown that the samples contain all the key ingredients of DNA – the building blocks of life.

Hayabusa then continued its trek. And this weekend, it’ll pass by the asteroid Torifune – a chunk of rock about a quarter of a mile in diameter.

Torifune’s average distance from the Sun is just a fraction farther than Earth’s distance. But its path is lopsided, so it regularly crosses Earth’s orbit. It’s not currently a threat to hit our planet. But it could be sometime in the distant future.

Right now, the asteroid is at its closest point to the Sun, and about 60 million miles from Earth. Hayabusa will scan it with several instruments as it swings by. But the high speed makes that tough. The entire spacecraft has to turn to keep the asteroid in view. And it can’t turn fast enough to keep an eye on it through the entire encounter. So it’ll have to settle for a quick glimpse as it blazes by this potentially hazardous asteroid.

Script by Damond Benningfield

We know for sure that Deneb is one of the more imposing stars around. But the details are a little hazy because the star’s distance is hazy. In part, that’s because of Deneb’s impressiveness.

The most accurate stellar distances come from Gaia, a space telescope. But Deneb is so bright that Gaia can’t look at it directly. Instead, it has to study the star indirectly – sort of like checking something out through the corner of its eye. It takes a lot of work to translate those glimpses into solid numbers.

In addition, the star’s outer layers are puffy and unstable, so it’s hard to know just where its surface is. And you need a good idea of the surface to measure the star’s location.

The best estimates say that Deneb is about 1500 light-years away – one of the most remote stars that’s visible to the eye alone. But other estimates say it’s almost twice that far. So based on that range, Deneb is about 15 to 20 times the mass of the Sun, 100 to 200 times the Sun’s diameter, and 50 thousand to 200 thousand times its brightness – impressive numbers for a very impressive star.

Deneb is a third of the way up the northeastern sky at nightfall, and soars high overhead during the night.

Script by Damond Benningfield

Prominences can span many thousands of miles; the largest are about half the size of the Sun itself. They’re actually thousands of degrees cooler than the surface of the Sun. They look bright only when they’re seen against the dark background of space. When they’re seen against the Sun, they form dark streaks.

Prominences are powered by the Sun’s magnetic field. Strands of the field can levitate above the surface. The strands can be filled with plasma – hot gas that has an electric charge.

Some prominences are common around magnetically active regions. They can erupt in minutes, loop into the corona, then collapse within hours. Others form in regions that are fairly quiet. They can take days to bloom into the corona, then remain visible for weeks or months.

Some prominences don’t stop at the corona. They can send huge clouds of plasma into the solar system. If they hit Earth, these outbursts can trigger brilliant auroras and disrupt technology – prominent impacts from the Sun.

Script by Damond Benningfield

Consider Tarazed, the second-brightest star of the eagle. It’s only about six percent the age of the Sun. But because it’s about three and a half times the Sun’s mass, it’s already completed the “prime” phase of life. Now, it’s well into the next phase – as a red giant.

Mass is critical because, as the star’s mass increases, so does its gravity. Stronger gravity squeezes the star’s core more tightly, increasing its temperature. That revs up the rate of nuclear reactions in the core.

When a star is born, its core is mostly hydrogen. In the prime phase of life, the star “fuses” the hydrogen atoms to make helium. When the hydrogen is gone, the core shrinks, so it gets even hotter. That causes the star’s outer layers to puff up, which is what’s happened to Tarazed – it’s more than 90 times the Sun’s diameter.

Higher core temperatures trigger the next round of reactions. So today, Tarazed is fusing the helium to make heavier elements. Eventually, that will end as well. Tarazed will shed its outer layers, leaving only its tiny, dead core – ending the star’s fairly short but bright life.

Tarazed is low in the east at nightfall. It’s close above even brighter Altair, at the southern point of the Summer Triangle.

Script by Damond Benningfield

Because Altair is so close and bright, we know quite a bit about it. And we’re learning more all the time. A study a couple of years ago, for example, refined the likely age of the star – 88 million years, give or take 10 million. That’s just two percent the age of the Sun.

Altair is about twice the size and mass of the Sun. And because it’s so young, it spins in a hurry – one turn every eight hours or so, versus 25 days for the Sun. That whirling rotation makes the star look squished – it’s about 25 percent wider through the equator than the poles.

In 2022, astronomers “listened” to the star with a space telescope. It measured vibrations on the surface of the star. Combined with observations from the ground, that revealed a total of 34 vibration modes – like 34 different musical notes.

The vibrations travel deep into the star. Each “note” reveals details about Altair’s interior. Piecing together the whole symphony, the astronomers found that the core of Altair contains more than 97 percent of the hydrogen it was born with. As a star ages, it converts its hydrogen to helium. So the amount of hydrogen reveals that Altair is just starting out.

Script by Damond Benningfield