StarDate

A stellar vanishing act led to a revelation about an iceball far from the Sun: It has a thin atmosphere. It’s the smallest object with a known atmosphere in the entire solar system.

The object is 2002 XV93. It’s in the Kuiper Belt – a wide “doughnut” beyond the orbit of Neptune, the Sun’s outermost major planet. The belt contains millions of icy bodies, including Pluto.

XV93 is about 300 miles in diameter – just one-fifth as big as Pluto.

Astronomers in Japan watched the little iceball in January of 2024. They’d calculated that XV93 would pass in front of a star, hiding the star from view. As they watched the star disappear, it didn’t blink out instantly. Instead, it dimmed a bit before it passed behind XV93. And it took a moment to reach full brightness when it returned to view. That meant that something was partially obscuring the star: an atmosphere. It’s only about one percent as thick as Pluto’s atmosphere, which is a bare wisp.

XV93’s gravity is extremely weak, so it can’t hang on to any atmosphere for long. So the gases might vent into space from its interior, which would keep the atmosphere going. Or they might have surrounded the object after it was hit by a small comet. In that case, the atmosphere would start to vanish quickly – eventually leaving XV93 airless.

Script by Damond Benningfield

After teaming up with the Sun to produce a solar eclipse today, the Moon will make another skywatching spectacle possible tonight – the Perseid meteor shower. It’s expected to be at its peak tonight. And since the Moon is new, it won’t be around to interfere with the sparklers.

The Perseids occur every August, as Earth flies through the orbital path of Comet Swift-Tuttle. The comet is a ball of frozen gases mixed with bits of rock and metal. As it approaches the Sun, some of its gas vaporizes. That releases some of the heavier material, known as comet dust.

As Earth zips through this material, some of the dust grains slam into our atmosphere at more than a hundred thousand miles per hour. They vaporize instantly, creating meteors – streaks of light across the sky.

Swift-Tuttle returned to the inner solar system a third of a century ago. That was its first appearance since the Civil War, so the Perseids were especially good for a while. With the comet retreating into the outer solar system, though, there’s less comet dust to feed the shower.

The meteors enter the atmosphere from the direction of Perseus – hence the name. But they can streak across any part of the sky, so you don’t have to look to a specific region to see them.

To view the Perseids, find a safe, dark observing site away from the pesky glare of city lights. Then watch the sky for cosmic sparklers.

Script by Damond Benningfield

The top of the world will see a total solar eclipse tomorrow. A partial eclipse will encompass a wider slice of the globe, including Alaska and parts of the northeastern United States.

A solar eclipse occurs when the Moon passes directly between Earth and the Sun, blocking the Sun from view. The Sun’s hot but faint outer atmosphere, the corona, looks like silvery tendrils radiating away from the Moon.

This eclipse begins when the lunar shadow first touches Earth, over northeastern Russia. The eclipse path then passes near the north pole, slides across parts of Greenland and Iceland, and finally over northern Spain before vanishing over the Mediterranean Sea. At its peak, off the coast of Iceland, totality will last for 2 minutes, 18 seconds.

A partial eclipse, where the Moon covers only a portion of the solar disk, will flank that path. In addition to parts of North America, it’ll encompass much of western Europe and western Africa.

From far-northern Alaska, the Moon will cover more than half of the Sun’s disk, at about 8:30 a.m. From Anchorage, about a quarter of the Sun will be covered. And from the northeast, the greatest eclipse takes place in northern Maine, shortly before 2 p.m.

If you’re in one of those areas, remember to protect your eyes. Watch the eclipse only through special glasses or dark welder’s glass, and never look at the unfiltered Sun.

Script by Damond Benningfield

A total solar eclipse is coming up on Wednesday. The Moon will cover the Sun, turning day to night across a narrow slice of the globe. Parts of Alaska and the northeastern United States will see a partial eclipse.

The timing of the eclipse is known down to the second, and has been for decades; astronomers can predict eclipses far into the future. But making such predictions isn’t easy. It requires a detailed knowledge of the Moon’s orbit around Earth, Earth’s orbit around the Sun, and even the shapes of Earth and the Moon.

Just when the first prediction was made is unclear.

There’s no doubt that people have been predicting lunar eclipses for thousands of years. But they’re easier to forecast. Earth’s shadow is roughly 35 times wider than the Moon’s, so you don’t need to be quite as precise to get it right.

There are stories that the Chinese were predicting solar eclipses more than 4,000 years ago, but no confirmation. An eclipse in 585 BC that stopped a war supposedly was predicted by a Greek scientist. But many present-day scientists doubt that.

The first confirmed prediction was made by Edmond Halley, using the laws of gravity recently devised by Isaac Newton. Halley forecast that an eclipse would cross England on May 3rd, 1715. And he was right. So the event is known as Halley’s Eclipse – honoring the prediction of an astronomical spectacle.

Script by Damond Benningfield

The Moon forms a nice triangle with the twins of Gemini at dawn tomorrow – the stars Castor and Pollux. Castor is to the left of the Moon, with brighter Pollux about the same distance to the lower left.

Castor consists of six known stars. We haven’t found planets orbiting any of them. Pollux is a single star. And it has one likely planet – a giant that’s much heavier than any of the planets in our own solar system.

The planet was discovered 20 years ago, by astronomers at McDonald Observatory. They’d seen evidence of the star earlier, but they couldn’t confirm it.

The planet is known as Pollux b. It also has a formal name – Thestias – a variation of the name of Pollux’s mother in Greek mythology. The planet is almost three times the mass of Jupiter, the Sun’s largest planet. It’s farther from Pollux than Earth is from the Sun. But that’s much too close for the planet to be habitable.

That’s because Pollux has passed beyond the prime phase of life. It’s puffed up to about nine times the Sun’s diameter, so it’s much brighter than the Sun. That extra energy makes Thestias much too hot to have liquid water at its surface – a key ingredient for life.

The temperature could have been more comfortable in the past. The planet itself probably is a big ball of gas – not a good place to live. But if it has any moons, it’s possible that they could have offered better environments for life.

Script by Damond Benningfield