StarDate

About 10,000 years ago, a massive star in Cygnus, the swan, blew itself to bits. For a few days or weeks, it blazed as the brightest object in the night sky other than the Moon – bright enough to see even during the day. Today, its glowing remains are still visible – a colorful bubble that’s more than a hundred light-years across and growing.

The bubble is known as the Cygnus Loop. It’s a supernova remnant – the debris from a star that was about 20 times the mass of the Sun. After a short but brilliant life, the star could no longer produce nuclear energy in its core. The core collapsed, and the star’s outer layers exploded at a few percent of the speed of light.

As the bubble expands, it rams into surrounding clouds of gas and dust. That causes parts of the bubble to glow, forming the Veil Nebula and some other structures. Images reveal ribbons of gas and dust that intertwine like the strands of a rope. They shine in shades of red, blue, green, and other colors – the result of the elements they contain. Other parts of the Loop shine in wavelengths that are invisible to the human eye.

The Cygnus Loop is in the east-northeast at nightfall, to the lower right of Deneb, the bright star at the swan’s tail. The loop spans about six times the width of the full Moon. Small telescopes equipped with the right filters reveal some of the glowing filaments – the fading remnants of a stellar spectacle.

Script by Damond Benningfield

Three tiny constellations are stacked up in the eastern evening sky this month: the arrow, the dolphin, and the little horse. There’s not a single bright star among them. But under moderately dark skies, at least one of them is pretty easy to make out.

The arrow is at the top of the stack. It’s the third-smallest of the 88 modern constellations. In ancient times, it represented a weapon used by Hercules, but there were different takes on his target. All of its stars are faint, but under especially dark skies, it does look like an arrow, aiming toward the left. It’s between two bright stars: Altair, to its lower right, and Deneb, to the upper left.

The most prominent of the three figures is the dolphin, which is below the arrow. Its five brightest stars outline the dolphin’s form. It, too, has more than one myth. One of them said the dolphin rescued a rich poet and musician. The man had jumped into the sea after he was threatened by the crew of the ship in which he was sailing.

Finally, there’s the little horse. It’s the second-smallest constellation, and it’s quite faint. And it’s not even a complete horse – it’s depicted only as a horse’s head. One of its Greek stories said it was the brother or son of the winged horse Pegasus, which rises below it.

If your skies are nice and dark, look for these tiny constellations beginning at nightfall, and rolling across the south during the night.

Script by Damond Benningfield

The Sun and the planet Jupiter are the heaviest objects in the solar system. But there’s a huge gap in their masses – the Sun is more than a thousand times heavier.

There’s a class of objects between those masses. Known as brown dwarfs, they’re much heavier than Jupiter, but no more than seven or eight percent of the Sun’s mass.

A brown dwarf probably forms in the same way as a star – from the collapse of a cloud of gas and dust. The heat of that collapse makes the brown dwarf shine. But a brown dwarf isn’t massive enough to “fuse” hydrogen atoms in its core to make helium – the power source of most true stars. It may briefly fuse a heavy form of hydrogen, but that doesn’t produce nearly as much energy. So brown dwarfs are also known as “failed stars.”

The surface of a brown dwarf can be so cool that clouds can form in its upper layers, making it look like a giant planet, such as Jupiter. And despite the name, brown dwarfs aren’t really brown. Their color can range from dull orange or red to dark purple to black – a result of the surface temperature and chemistry.

The closest brown dwarfs form a binary known as Luhman 16. The system is six and a half light-years away – closer than only two star systems. Even so, it took a special space telescope to discover the pair – faint “missing links” between true stars and giant planets.

Script by Damond Benningfield

It may sound strange to hear during the heat of the summer, but Earth is farthest from the Sun for the entire year right now. Our planet is receiving almost seven percent less energy from the Sun than it did when it was closest to the Sun, in January.

The average distance to the Sun is 93 million miles. But the distance varies by about one and a half million miles in either direction – a result of the eccentricity of Earth’s orbit. It defines how lopsided the orbit is. And it varies over cycles of hundreds of thousands of years.

The change is caused by the gravitational pull of the other planets. The biggest impact comes from Venus and Jupiter. Venus passes closer to us than any other planet. And Jupiter is the solar system’s heaviest planet. So even though it’s a long way off, it has a big influence on Earth’s orbit.

Today, the eccentricity is less than two percent, so Earth’s orbit is almost circular. And it’s getting even more circular. When the eccentricity is lowest, the distance to the Sun will vary by only about 300,000 miles.

After that, the orbit will get much more eccentric. It’ll peak at almost six percent. That may not sound like a lot, but it’s enough to change the amount of sunlight Earth receives over the course of a year by 23 percent. That difference will have a major impact on Earth’s climate – thanks to the influence of the other worlds of the solar system.

Script by Damond Benningfield

Betelgeuse grew dramatically fainter a couple of years ago. The supergiant star blasted out a giant blob of gas, which cooled to form a dust cloud that blocked part of the star from view. And a similar star might recently have gone through the same process.

RW Cephei is at least 900 times the diameter of the Sun, making it one of the larger stars in the galaxy. It’s also hundreds of thousands of times brighter than the Sun. In late 2022, though, it dropped to a third of its usual brightness. By last summer, it was recovering.

Astronomers analyzed some especially sharp images of the star. The pictures showed that it was blobby, with bright and dark regions many times larger than the Sun.

The astronomers later found that RW Ceph had grown brighter than usual in 2019. It may have blown out a huge blob of hot gas not long after that. The gas cooled and condensed to form a cloud of dust grains. The cloud moved in front of the star, causing it to fade. As the cloud dispersed, RW Ceph returned to its usual brilliance.

The hypergiant star is near the end of its life. It’s expected to explode as a supernova sometime in the next million years or so – just like Betelgeuse.

RW Cephei is low in the northeast at nightfall. It’s about halfway between Deneb, the star at the tail of the swan, and W-shaped Cassiopeia. Even at its best, though, you need binoculars or a telescope to see it.

Script by Damond Benningfield

The four big moons of Jupiter probably are all about four and a half billion years old. But two of them look much younger. That’s because their surfaces are constantly repaved – one by fire, the other by ice.

The fire moon is Io. It’s the most volcanically active body in the solar system, with more than 400 volcanoes on its surface. Some of them release gas or lava, while others produce big explosions. That activity covers up any impact craters – the scars of collisions with big space rocks. Scientists have reported only one possible crater on Io – a good indication that the surface is young.

The ice moon is Europa. It has more craters than Io, but not a lot. That’s because it appears to have an ocean of liquid water below its icy crust. Water may ooze from the ocean, coating parts of the crust.

Some impacts by big space rocks may punch through the crust, allowing more water to reach the surface. And a recent study by scientists at the University of Texas found that an impact doesn’t have to go all the way through the ice. If it rams halfway through, it can melt enough ice for the warm water to melt the rest of the way to the ocean. That may allow some of the ocean water to reach the surface – helping Europa keep its “youthful” appearance.

Look for Jupiter near our own moon at dawn tomorrow. The planet looks like a brilliant star. Through binoculars, its big moons look like tiny stars arrayed near the planet.

Script by Damond Benningfield

Mars and Jupiter are siblings. They were born at the same time, from the same cloud of material that encircled the embryonic Sun. Yet there’s absolutely no family resemblance – they could hardly be more different.

Both planets appear near the Moon at dawn tomorrow. Mars looks like a bright orange star to the upper right of the Moon. Jupiter is even brighter, and crouches below the Moon, low above the horizon.

Mars is small – about half the diameter of Earth. It’s made of rock and metal. Jupiter, on the other hand, is the largest planet in the solar system – a giant ball of gas that’s 20 times wider than Mars, and about 3,000 times as massive. In fact, Jupiter is more massive than all the other planets and moons in the solar system combined.

Mars and Jupiter are the fourth and fifth planets out from the Sun, so you might expect them to be more alike. But Jupiter might have formed farther from the Sun than it is now. At that distance, conditions would have been quite cold. There would have been a lot of ice and gas for Jupiter to sweep up, allowing it to grow bigger and bigger.

Mars was born closer to the Sun. Solar heat and radiation cleared out most of the ice and gas in its region. That left mainly bits of rock and metal – the stuff that came together to form the planet Mars – a world quite different from its giant sibling.

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

Script by Damond Benningfield

The moons of Mars aren’t much more than big boulders that look a bit like potatoes. Phobos is about 17 miles long; Deimos, only about nine miles. But they’ve been the subject of a big scientific debate for decades — a debate about their origins.

One possibility says they’re asteroids that were captured by Mars long ago. Both bodies look like asteroids. And some of the minerals on one of them are the same as those found in some meteorites that probably came from asteroids.

The other possibility says they formed after a giant impact. A large body could have rammed into Mars early in its history. That blasted out material from both Mars and the impactor, forming a ring of debris around Mars. Phobos and Deimos formed from that debris. That idea seems to explain the moons’ orbits, but not necessarily their composition. But a recent study may have found a way to make it work.

It says that the impacting body was made mainly of frozen water. Such a body would have blasted out more debris than one made mainly of rock. And the vaporized water would have kept the debris cool enough to allow the formation of some of the minerals on the moons. Ice-rich bodies could have been fairly common in the early solar system — providing a way to create the moons of Mars.

Bright orange Mars is close to our own moon the next two mornings. It’s directly below the Moon at dawn tomorrow, and to the upper right of the Moon on Tuesday. More tomorrow.

Script by Damond Benningfield

A small, faint “shield” of stars scoots across the southern sky on early summer nights. It represents the coat of arms on the shield of John Sobieski, a 17th-century king of Poland and one of the country’s great national heroes.

The shield is the constellation Scutum. Johannes Hevelius first drew it around 1687, using a few stars from a fairly empty region of the sky. He originally named it Scutum Sobiescianum — the shield of Sobieski. But in more recent times, the last part of the name has been dropped.

Sobieski became king of Poland in 1674. He built alliances with several European neighbors, and fought the Ottoman Empire when it tried to expand westward. In 1683, he earned fame all across Europe by defending Vienna against the Ottoman army.

To honor his native country, Hevelius included the new constellation in a beautiful star atlas, which was published in 1690. He depicted several faint stars as the cross on Sobieski’s shield. The shield has kept its place in the stars ever since then.

Unfortunately, the stellar shield isn’t all that much to look at. You need fairly dark skies to see any of its stars. Right now, it’s low in the southeast as night falls. It’s to the upper left of the teapot-shaped constellation Sagittarius. Scutum wheels low across the south during the night, and is in the southwest at dawn.

Script by Damond Benningfield

Hurricanes and other big storms can cause widespread damage that can take days or weeks to clean up. So can big space weather storms. They can knock out satellites, disrupt radio transmissions, and cause power blackouts. Especially big storms have the potential to knock out power grids for weeks or months. So scientists and power operators are looking for ways to minimize the damage.

Space weather is powered by storms on the Sun. Big explosions send particles and energy racing out into the solar system. Earth’s magnetic field funnels some of the particles toward the surface. They can create powerful currents in electrical equipment and even in the ground. That can trigger blackouts. At their worst, they might fry transformers and other gear, completely wrecking power grids.

Scientists in New Zealand recently worked with the national power operator to simulate ways to minimize the impact of a major storm. Their work showed that disconnecting a limited number of key high-power transmission lines reduced the risk of a system-wide failure. It also showed that installing a sort of surge protector on some transformers could provide similar protection.

The Sun is nearing the peak of its current activity cycle. Big outbursts in March, in fact, triggered the highest warning levels in more than six years. Similar warnings could be common in the coming months — as the Sun stirs up powerful space weather.

Script by Damond Benningfield