StarDate

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