StarDate

The universe can be frustrating. Roughly two-thirds of everything in the universe appears to consist of dark energy. Despite decades of study, though, scientists haven’t been able to explain what dark energy is.

Astronomers discovered dark energy by studying a type of supernova – exploding stars. The supernovas brighten and fade in a predictable way. That allows astronomers to measure their distance and their motion away from us. Stars that are farther were moving away faster than expected. That suggested that something was causing the universe to expand faster over time: dark energy.

But a recent study said that dark energy might not exist. Instead, the researchers proposed a new model to explain what we see, called timescape.

The model notes that matter clumps together in clusters of galaxies, with huge “voids” between them. Time passes more slowly in the presence of stronger gravity – like that exerted in the denser regions. So the voids, with less gravity, could be billions of years older than the clusters – creating “bubbles” of spacetime.

If that’s correct, then it would be tough to know just when the supernovas in different parts of the universe exploded. And that makes it tough to know how fast they’re moving away from us. So the study says we don’t need dark energy to explain what we see in the universe.

But there’s still a lot of work to be done to understand dark energy – including whether it even exists.

Script by Damond Benningfield

The modern western calendar tells us that summer arrives in the northern hemisphere this year on June 20th – the summer solstice. It’s the longest day of the year, and the Sun stands farthest north for the year as well.

In ages past, many calendars had a less direct link to the solstices and equinoxes. The seasons began not on these dates, but about halfway between them. Such dates are known as “cross-quarter” days. And in the calendars of the ancient British Isles, one of those days was commemorated on May 1st. In Ireland and Scotland it was known as Beltane; in other regions, it was May Day.

The rituals of Beltane celebrated the end of the cold, dark time of year and the beginning of the longer, warmer days of summer.

The centerpiece of Beltane was a village bonfire – or perhaps two bonfires. The fires themselves chased away the darkness and ushered in the light of summer. The flames and smoke were thought to have special protective powers, so villagers doused the fires in their homes, then relit them using a torch from the bonfire. They also paraded their livestock past the fires on the way to their summer fields – providing a bit of good luck for the start of the summer growing season.

These rituals were part of a deep connection to the cycles of nature, and especially the Sun – which warms and lights the summer no matter when the season kicks off.

Tomorrow: different clocks for different flocks.

Script by Damond Benningfield

Telescope domes are designed to keep the telescopes inside safe and on-target. But just because they’re practical doesn’t mean they can’t be beautiful. That’s especially true of some built in the 1930s. They were influenced by the design style that was all the rage – known today as art deco.

The event that popularized art deco began 100 years ago this week – the International Exhibition of Decorative Arts and Modern Industries, in Paris. It was a showcase for French design in architecture, art, furniture, clothing, and other fields. Most countries participated. The only restriction: Everything had to be modern.

The exhibition inspired a design wave across the United States. Popular examples include the Empire State Building and Chrysler Building in New York, along with trains, airplanes, cars, consumer goods, and more.

Astronomy got into the act as well. The best-known example is Griffith Observatory, in Hollywood. Its domes and grounds have been featured in dozens of movies and TV shows.

The domes of Palomar Observatory feature art-deco design as well, including the one that houses the 200-inch telescope – the largest in the world for decades.

And no list is complete without our own McDonald Observatory. Its original dome was dedicated in 1939. It housed not only the observatory’s 82-inch telescope, but also labs, offices, and living space for the astronomers – all executed in beautiful art deco style.

Script by Damond Benningfield

Until about 30 years ago, Jupiter was the king of the planets – bigger and heavier than any other known planet. Today, it’s not even in the top 500. It’s still the giant of our own solar system – it’s more massive than all the other planets and moons combined. But hundreds of planets in other star systems outrank it.

The total number of confirmed exo-planets is up to about 6,000. They range from chunks of rock about as massive as the Moon to super-planets up to about 80 times Jupiter’s mass.

Such giants are much easier to find than smaller worlds. Astronomers find most exoplanets in a couple of ways. One is to watch as a star fades a bit as a planet passes in front of it. Larger planets block more starlight, producing a bigger dip.

The other way is to measure a tiny shift in a star’s light caused by the gravitational pull of an orbiting planet. Heavier planets exert a stronger pull, making them easier to find.

Many of the “super Jupiters” are especially close to their parent stars. So these are the easiest planets to find. Over the years, though, the list of such planets in more-distant orbits has grown as well – bumping Jupiter farther from his throne as “king” of the planets.

Jupiter is still a giant presence in our sky. It looks like a brilliant star. And it’s close to the Moon the next couple of nights – to the upper left of the Moon tonight, and a little closer below the Moon tomorrow night.

Script by Damond Benningfield

Trillions of icy bodies mark the edge of the solar system. They form a shell that extends one or two light-years from the Sun in every direction. A passing star may sometimes give some of them a nudge toward the Sun. When they get here, they become comets – visitors from the icy deep.

That distant region is known as the Oort Cloud. It’s named for Dutch astronomer Jan Oort, who was born 125 years ago today. He proposed the existence of the cloud in 1950. And today, that’s his best-known accomplishment.

Yet it’s far from his most important work. Early in his career, he confirmed that the Milky Way is a wide, flat, spinning disk. And he showed that, instead of inhabiting the center of the galaxy, the solar system is in the hinterlands – many thousands of light-years outside the heart.

Oort spent most of his career at Leiden University in the Netherlands, including decades as director of Leiden Observatory. When Germany invaded the country, though, he left his post instead of working with the Nazis.

When he returned, after World War II, he became a pioneer in the new field of radio astronomy. He mapped giant clouds of gas and dust throughout the galaxy. Their distribution provided even more proof of his picture of the Milky Way.

Oort continued his research until shortly before his death, in 1992. Scientists have named quite a few things in his honor, including an asteroid – and the icy shell known as the Oort Cloud.

Script by Damond Benningfield

Dark spots sometimes dot the surface of the Sun – magnetic storms that can last for days or weeks. But the storms on other stars can make those on the Sun look puny. They can be so monstrous that they can change the star’s brightness by quite a bit.

An example is one of the stars of Cor Caroli – the Heart of Charles. As seen by the eye alone, the star is the leading light of Canes Venatici, the hunting dogs. It’s to the right of the handle of the Big Dipper as night falls, and wheels above the dipper later on.

But a closer look shows that Cor Caroli consists of two stars in a wide orbit around one other. One of the stars is about half again as massive as the Sun, and several times brighter. The other is about three times the Sun’s mass, and more than a hundred times its brightness.

But over a period of about five and a half days, the heavier star’s brightness varies by about 15 percent. And that’s because of the starspots.

The star’s magnetic field is more than a thousand times stronger than the Sun’s. That produces giant spots – far bigger than anything ever seen on the Sun.

The spots are thousands of degrees cooler than the surrounding gas. The combination makes them darker than the rest of the surface. As the star rotates, the spots move in and out of view, causing the star to get fainter and brighter – a big “flutter” for the Heart of Charles.

Tomorrow: an astronomer with a “cloudy” name.

Script by Damond Benningfield

The stars Kochab and Pherkad serve several roles. They’re part of the body of Ursa Minor, the little bear. They form the outer edge of the bowl of the Little Dipper. And they’re “guardians of the pole” – they circle around Polaris, the star that marks the north celestial pole.

Both stars are giants – they’ve puffed up at the end of the prime phase of life. Kochab is about 50 times the Sun’s diameter, and 450 times its brightness. Pherkad looks fainter than Kochab, but only because it’s almost four times farther. In reality, it’s more than twice as bright.

The stars are so big and bright because they’ve exhausted their original supply of nuclear fuel. That’s triggered changes in the cores of the stars that have caused them to puff up.

In ages past, both stars were much closer to the pole than they are today. In fact, Kochab was the closest bright star to the pole for a millennium. It was the best pole star about 3100 years ago. But it wasn’t nearly as good a marker as Polaris – it never got closer than about seven degrees, which is almost the width of a fist held at arm’s length. Thanks to an effect called precession, it’s moved away from the pole. So Kochab and Pherkad serve as guardians of the pole.

The stars stand to the right of Polaris at nightfall, and wheel high above the Pole Star later on. Kochab is the second-brightest star of the little bear, shining just a touch fainter than Polaris.

Script by Damond Benningfield

A Chinese spacecraft that’s scheduled for launch as early as next month has a double destination: a “quasi-moon” of Earth and an asteroid that acts like a comet.

The first destination for Tianwen-2 is an asteroid, Kamo’oalewa. It’s a chunk of rock no more than the length of two or three football fields. What makes it intriguing is that it weaves around the Sun in a pattern that makes it look like a satellite of Earth.

The asteroid spends half of its time farther from the Sun than Earth is, the other half closer to the Sun. Seen from Earth, it appears to loop around our planet – like a moon. Some research suggests it was a chunk of the Moon that was blasted into space by a big impact.

Tianwen-2 is scheduled to arrive at Kamo’oalewa next year. It’ll spend a year traveling along with the asteroid. It’ll drop off a small lander and rover, and collect a few ounces of rocks and dirt.

The craft will swing by Earth to drop off the samples, then journey to 311P Panstarrs. The object is a third of a mile wide, and orbits the Sun at about twice Earth’s distance.

Observations reveal that Panstarrs is rocky, like an asteroid. But soon after it was discovered it sprouted several long tails, so it was classified as a comet. It may be a loosely bound pile of rocks and dust. If so, it may sometimes lose some of the dust, and sunlight then pushes it away – giving this asteroid the tails of a comet.

Script by Damond Benningfield

A beautiful triangle decorates the dawn sky tomorrow. Two of its points are easy to see: the crescent Moon and the planet Venus, the “morning star.” The final point is a bit tougher: the planet Saturn, to the upper right of the Moon. It’s just half of one percent as bright as Venus, but its proximity to the brighter bodies will help it stand out.

Saturn is about as faint as it ever looks right now. One reason is that it’s just emerging from behind the Sun, so it’s about as far as it ever gets from Earth – more than 950 million miles.

The other reason is our view of Saturn’s rings. The rings span almost the distance from Earth to the Moon, and they’re made mainly of small bits of ice, which reflect a lot of sunlight. But the angle at which we see the rings changes – a result of Saturn’s changing seasons.

Saturn is tilted at about the same angle as Earth. At the solstices, one of Saturn’s poles dips toward the Sun, so we see the rings at their best angle. That makes the planet especially bright.

At the equinoxes, though, the rings are “closed” – we see them edge-on. The rings are no more than a few hundred feet thick, so they all but disappear. That makes the planet look much fainter than average.

Saturn will reach an equinox in early May, so the rings have basically vanished. They’ll slowly tilt back into view over the coming months, and reach their greatest angle at Saturn’s winter solstice – in 2032.

Script by Damond Benningfield

Two bright crescents team up in the early morning the next couple of days: the Moon and the planet Venus – the brilliant “morning star.” They’re quite low as twilight begins to paint the dawn sky.

The Moon is an obvious crescent. The Sun illuminates only about one-sixth of the lunar hemisphere that faces our way – the crescent. It’s nighttime across the rest of the lunar disk.

It’s not especially dark, though. That’s because that part of the Moon is awash in earthshine – sunlight reflected off of Earth. Earth is much bigger than the Moon, and it’s more reflective. And it’s close to full as seen from the Moon, so the landscape on the nighttime part of the Moon would be much brighter than a moonlit night here on Earth.

Venus is a crescent as well. The Sun is lighting almost a quarter of the planet’s Earth-facing hemisphere. But you can’t see Venus’s phase with the eye alone – you need good binoculars or a telescope to see the shape.

Venus is fairly close to Earth now, so it’s just about as bright as it ever gets. It appears larger than average, and it’s completely covered by clouds that reflect most of the sunlight that strikes them. Over the next few months, Venus will move farther away from us. But the Sun will light up more of the hemisphere that faces Earth. So Venus will remain a bright presence in the morning sky well into fall.

We’ll have more about Venus and the Moon tomorrow.

Script by Damond Benningfield