StarDate Billy Henry

Just like magic, big “islands” appear to come and go on the lakes and seas of Titan, the largest moon of Saturn. They first showed up in radar images snapped 10 years ago by the Cassini spacecraft. And planetary scientists have been trying to explain them ever since.
Titan is bigger than the planet Mercury. It has a cold, thick atmosphere. Hydrocarbons at the top of the atmosphere create an orange haze — like the smog that blankets many cities. Methane and ethane form clouds. They also fill the lakes and seas.
In most of Cassini’s images, these bodies of liquid looked dark and calm — any waves would be no more than a fraction of an inch high. But occasionally, a bright patch would appear — like an island suddenly rising from the depths.
There are several possible explanations: big waves, patches of nitrogen bubbles, and others. And a study this year suggested sheets of ice. In this scenario, particles would drop from the haze layer, forming ice grains along the way. The grains could collect in sheets along the shore. The ice would be porous, like a sponge or a honeycomb. A sheet might break away and float into a lake or sea. Eventually, though, the spaces would fill up, the ice would sink, and the island would vanish — just like magic.
Look for Saturn near our own moon the next few mornings. It’ll stand well to the left of the Moon at dawn tomorrow, but much closer to the Moon on Thursday.
Script by Damond Benningfield

Almost all of the planetary action is in the morning sky now. Mercury is trying to climb into view in the evening sky, but it’s low and tough to see. It’ll be in slightly better view in a few days.
Three planets are in the morning sky. Two of them climb into view a good while before dawn, so there’s plenty of time to look for them. The third is just coming into view after passing behind the Sun. It’s quite bright, though, so it’s pretty easy to pick out.
As twilight begins to paint the morning, look half-way up the southeastern sky for Saturn, which looks like a bright golden star. Tomorrow, it’s far to the upper left of the Moon. But the Moon will soon catch up to it, and we’ll have more about that tomorrow.
Saturn is the second-largest planet in the solar system. But it’s best known for its beautiful rings. They’re made mainly of bits of ice, so they reflect a lot of sunlight. That enhances the planet’s brightness.
Next look for Mars, which is due east. It’s only about half as high as Saturn is, but it shines just as brightly. The dust that coats much of its surface gives Mars an orange tint, so it’s hard to miss.
Finally, as twilight brightens, look well to the lower left of Mars for Jupiter, the Sun’s largest planet. Although it’s low, it’s quite bright — only the Moon outshines it in the current night sky. So it’s easy to see deep into the waxing twilight — the dawn of a new day.
Script by Damond Benningfield

Altair is the brightest star in the constellation known as the eagle, and one of the 12 brightest stars in the night sky. But a fainter star that appears just above it as night falls is actually a whole lot brighter. It only looks fainter because it’s a whole lot farther away.
Tarazed looks only about one-sixth as bright as Altair. But it’s 35 times farther than Altair. When you take that into account, Tarazed shines a couple of hundred times brighter.
Over the past few years, astronomers have refined the distance to the star using observations from Gaia, a European space telescope. It’s measuring the distances to more than a billion stars, and compiling detailed profiles of many of them.
Gaia determines a star’s distance by measuring its parallax. It observes a star at six-month intervals, when Gaia is on opposite sides of the Sun. The star appears to move back and forth a tiny bit against the background of more-distant objects. The angle of that shift reveals the star’s distance.
Gaia found that Tarazed is a couple of hundred light-years farther than astronomers had thought. That means it’s also bigger and brighter than thought — and much more impressive than nearby Altair.
Watch Tarazed as it leads Altair across the sky on summer nights. The stars are low in the east as darkness falls, due south in the wee hours of the morning, and high in the southwest at dawn.
Tomorrow: planets in the dawn sky.
Script by Damond Benningfield

A young eagle soars across the sky on summer nights. Right now, it’s low in the east at nightfall, due south in the wee hours of the morning, and high in the southwest at dawn. And it’s easy to spot — it’s the 12th-brightest star in the night sky.
Altair represents the breast of the constellation known as the eagle. The name “Altair,” in fact, means “the flying eagle.”
According to current understanding, it’s a young eagle — barely more than an eaglet. It’s about a hundred million years old, compared to four and a half billion years for the Sun. And it’s just entering stellar adulthood — what’s known as the “main sequence.” That means it’s fully formed, and it generates energy through nuclear fusion in its core — it “fuses” together hydrogen atoms to make helium.
One of the hallmarks of young stars is that they spin in a hurry — a result of the collapse of the cloud of gas and dust that gave them birth. And Altair is no exception. It turns on its axis once every eight hours, compared to almost a month for the Sun. That’s about 75 percent of the speed needed to make Altair fly apart.
The whirligig action also flattens the star, so it’s almost 25 percent fatter through the equator than through the poles — an effect clearly seen in images of Altair — a young, bright eagle flying through summer nights.
Altair has a close attendant, and we’ll talk about that star tomorrow.
Script by Damond Benningfield

There’s an astronomical coincidence today: It’s the first full day of summer in the northern hemisphere, and there’s a full Moon. The exact moments of the full Moon and the summer solstice are a bit more than one day apart — a coincidence that happens, on average, once every couple of decades.
At full Moon, it’s daylight across the entire lunar hemisphere that faces our way. But not every location sees the Sun. Some craters near the lunar poles are so deep that sunlight never reaches their bottoms.
That doesn’t mean the crater floors are completely dark. The lighting may be comparable to a family den or even an office building.
Scientists have measured the light levels with a NASA instrument called ShadowCam. It’s on a Korean spacecraft that’s been orbiting the Moon for the past year and a half. The instrument can see into regions that are too dark for other spacecraft.
There’s no atmosphere on the Moon to scatter sunlight. But sunlight that hits the rims of the craters or nearby mountains is reflected into a crater’s depths. Scientists recreated those lighting conditions in an office. And they found that there was plenty of light for working.
Craters near the south pole are prime landing sites for future missions because they may contain a lot of frozen water. Astronauts probably won’t need headlights to find their way around those craters — reflected sunlight should provide all the light they need.
Script by Damond Benningfield

For many countries in Europe, today is Midsummer Day. It’s marked with bonfires and other celebrations. It marks the middle of summer, which began back in May.
Astronomically, though, today marks the start of summer in the northern hemisphere. It’s the summer solstice — the longest day of the year. It marks a turning point for the Sun, which will begin to move southward after today.
Regardless of whether it was considered the start of summer or its middle, the solstice had great significance for cultures around the world. They held festivals and religious ceremonies to celebrate the light.
Many cultures used natural alignments to track the Sun’s motions along the horizon, allowing them to pinpoint the date. They also made their own alignments.
One of the most famous examples is Stonehenge in England. But there are plenty of examples in the Americas as well.
In the United States, many are still found in the southwest, in the remnants of ancient pueblo sites. Many of the solstice markers are spirals carved or painted on rock surfaces. The rising Sun passes through cracks or notches in the nearby rocks, creating daggers of light across the spirals.
Other markers were built into houses or ceremonial structures. Narrow windows, for example, might allow the sunlight to shine onto symbols on the opposite wall — symbols dedicated to the rising Sun on the summer solstice.
We’ll have more about the solstice tomorrow.
Script by Damond Benningfield