StarDate

Dark matter is frustrating. Scientists know it’s there, but they can’t find it. And they’ve looked for evidence just about everywhere — including inside the planet Jupiter.

Dark matter produces no detectable energy of its own. But it pulls on the visible matter around it. From that, scientists have calculated that it’s several times more common than the ordinary matter we can see.

Dark matter may consist of subatomic particles. Early ideas said those particles should be especially heavy. But a couple of decades of searches haven’t found a thing. With each study, scientists push down the possible mass of dark-matter particles.

Such particles might ram together, producing gamma rays — the most powerful form of energy. So scientists are looking for the right kind of gamma rays from different kinds of astronomical objects. A recent study, for example, looked at Jupiter.

Astronomers monitored Jupiter’s gamma rays with a space telescope for more than a decade. Overall, there’s not much there. But there was a slight excess of gamma rays at wavelengths that could be produced by dark matter. The signal wasn’t nearly strong enough to confirm the presence of dark matter. But it may help scientists narrow down the explanation for these elusive particles.

And Jupiter is putting on its best showing of the year. It looks like a brilliant star low in the east shortly after sunset, and high in the south later on.
 

Script by Damond Benningfield

Support McDonald Observatory

Clouds here on Earth often form arcs and spirals — patterns related to our planet’s rotation. The clouds on Jupiter are related to its rotation as well: Because Jupiter spins so fast, the clouds are stretched into bands that encircle the entire planet.

The bands are different colors, which means their clouds are made of different materials and hover at different altitudes. The highest clouds are white, and are made of ammonia. Clouds in the next layer contain ammonia mixed with other compounds, so they look brown or orange. The lower layers contain water vapor and water ice, so they look bluer.

The clouds form alternating light and dark bands. The clouds in the lighter bands are pushed high into the atmosphere by rising bubbles of warm gas. The darker bands consist of cooler material that’s dropping back down into the atmosphere.

Each band has its own weather, which draws much of its energy not from the Sun, as is the case on Earth, but from deep within Jupiter itself. As gravity squeezes the planet, it produces heat that wells up through the atmosphere, then escapes into space. Before it escapes, though, it helps drive giant thunderstorms, and hurricanes that can be bigger than Earth — giant weather for a giant planet.

Jupiter looks like a brilliant star. It’s low in the east at nightfall, climbs high across the south around midnight, and sets around sunrise. More about Jupiter tomorrow.
 

Script by Damond Benningfield

Support McDonald Observatory

Jupiter is the “big brother” of the solar system. It’s bigger and heavier than its sibling planets — more than twice as massive as all of them combined. And it’s also older; it might have been born tens of millions of years before Earth and some of the other planets.

Jupiter was born much farther from the Sun than Earth and the other inner planets. At that range, it was cold enough for ices to clump together with rock and metals to make Jupiter’s giant core. The core quickly grew to about seven times the mass of the present-day Earth.

The core’s gravity was strong enough to pull in enormous amounts of hydrogen and helium gas — leftovers from the formation of the Sun. That allowed Jupiter to grow in a hurry. Some models say it reached full planethood within about three million years of the Sun’s birth. That’s not long when you consider that the Sun is about four and a half billion years old. The other planets came later — first the other giant outer planets, then the rocky inner planets — including Earth.

Jupiter is putting in its best showing of the year this week. It lines up opposite the Sun, so it rises around sunset and is in view all night. It looks like a brilliant star — only the Moon and Venus outshine it. Jupiter is low in the east as darkness falls. It reaches its highest point in the sky in the wee hours of the morning, and is low in the west at dawn.

More about Jupiter tomorrow.
 

Script by Damond Benningfield

Support McDonald Observatory

Ghosts and goblins and ghouls prowl the streets tonight. And they also prowl the sky. In fact, four stars in Perseus represent the Gorgons — the mythological sisters whose heads were covered with snakes. One look at them turned the viewer to stone.

The most prominent of these stars really does do something strange. For a couple of hours every three days or so, it fades dramatically. Ancient skywatchers must have found that a bit frightening, because they gave the star a spooky name: Ras Al-gul — “the demon’s head.” Today, it’s known by a shorter version of the name: Algol.

The star doesn’t really do anything ghoulish, though. Instead, its “fainting” spells are the result of eclipses.

Algol consists of three stars. Two of them are close together, so they orbit each other in a bit less than three days. We see them eclipse each other during each orbit.

One of the stars is a couple of hundred times brighter than the Sun, while the other is much fainter. But the fainter star is also the bigger of the two. So when it passes in front of the brighter star, the system drops to about a third of its normal brightness. Skywatchers in ancient times knew nothing about the cause of the fading act, though — only that it was a ghoulish thing for a star to do.

The “demon” star is low in the northeast at nightfall, not far to the lower right of Mirphak, the constellation’s brightest star. It’s a perfect companion for a Halloween night.
 

Script by Damond Benningfield

Support McDonald Observatory

The gibbous Moon perches near the neck of Taurus, the bull, this evening. It’s roughly the same distance from the bull’s face and its shoulder. Both features are represented by star clusters: the Pleiades, to the upper right of the Moon, and the Hyades, to the lower right. The clusters are especially close and bright, so both are easy to see.

The Pleiades represents the shoulder. Its brightest stars form a small but easy-to-see dipper. The cluster is more than 400 light-years away.

The name comes from ancient Greek — from a word that means “to sail.” Sailing season in the Mediterranean began about the time the cluster first appeared in the dawn sky. In Greek mythology, the stars were the Seven Sisters — the daughters of Pleione, an ocean goddess.

The Hyades outlines the face. It looks like a letter V. It’s the closest star cluster of all, at a distance of about 150 light-years. The brightest star in the pattern is Aldebaran, at the top left point — the bull’s orange eye. It’s not a member of the cluster, though — it’s only about half as far.

The name Aldebaran comes from ancient Arabic. It means “the follower” — the star follows the Pleiades across the sky. A version of the name was sometimes applied to the Hyades as a group. In that case, Aldebaran was Nayyir al-Dabaran — “bright one of the follower.”

Watch Aldebaran and the Hyades as they follow the Pleiades across the sky — with the bright Moon close by.
 

Script by Damond Benningfield

Support McDonald Observatory

AUDIO: Godspeed, John Glenn. 3, 2, 1, zero, ignition, liftoff! The MA-6 vehicle has lifted off...

John Glenn was an instant legend. On February 20th of 1962, he became the first American to orbit Earth. The feat earned him a trip to the White House and the biggest ticker-tape parade in 35 years.

Glenn found there was a problem with his new status, though. NASA didn’t want to risk its most famous astronaut, so he wasn’t allowed to fly in space again. He left the space program and went into politics, and eventually was elected to the United States Senate.

Glenn still wanted to fly in space again, though. His flight aboard his Mercury capsule, Friendship 7, had lasted just five hours, and that just wasn’t enough.

Eventually, Glenn lobbied NASA to allow him to fly on a space shuttle. He’d serve as a guinea pig — researchers could study the effects of spaceflight on the aging process. The agency gave in. And 25 years ago today, at age 77, John Glenn returned to space — the oldest person ever to reach orbit.

LAUNCH CONTROL: 3, 2, 1, booster ignition, and liftoff of Discovery, with a crew of six astronaut heroes and one American legend.

The flight lasted almost 10 days. Back on Earth, Glenn and his crewmates received a ticker-tape parade — one more honor for a legendary astronaut.
 

Script by Damond Benningfield

Support McDonald Observatory

In most ways, Jupiter is the most impressive planet in the solar system. It’s heavier than all the other planets combined. It has by far the strongest magnetic field, and the deadliest radiation belts. And it keeps jockeying with Saturn for the leadership in the number of moons.

One category where Jupiter is clearly outranked is rings. It has four main rings, but they’re puny compared to the rings of Saturn. Although their span is greater than the distance between Earth and the Moon, the rings are so faint that they weren’t discovered until 1979, when the Voyager 1 spacecraft flew past them.

The innermost ring is actually more like a doughnut — it’s thousands of miles thick. It begins not far above Jupiter’s clouds. Next out is the main ring, which contains most of the material in the ring system. And outside that is a pair of gossamer rings — rings that are so thinly spread that they’re especially hard to see.

The rings consist of dust grains and larger bits of rock and ice. That material quickly spirals into Jupiter. But the rings are kept supplied by collisions between space rocks and some of Jupiter’s moons. The impacts blast fresh material into orbit around Jupiter — keeping its rings from vanishing entirely.

Jupiter is in great view tonight. It looks like a brilliant star close to the Moon. They stay close as they arc high across the sky during the night. But Jupiter’s rings are too faint to see.
 

Script by Damond Benningfield

Support McDonald Observatory

Some eclipses are spectacular, such as the annular solar eclipse of a couple of weeks ago. Others — well, not so much.

An example of the latter comes up tomorrow — a partial lunar eclipse. The full Moon — the Hunter’s Moon — will pass through the outer portion of Earth’s shadow, the penumbra. That part of the shadow isn’t very dark, so most people won’t really notice a difference in the Moon’s appearance.

Midway through the eclipse, the Moon will barely dip into the dark inner shadow, the umbra. At most, that part of the shadow will cover just six percent of the Moon — like someone carved a notch at the bottom of the lunar disk.

There’s a relationship between this month’s eclipses: They’re members of the same eclipse season.

Eclipses occur when the Moon crosses Earth’s orbit at just the right time, bringing Moon, Earth, and Sun into alignment. The alignment happens twice, about two weeks apart — an eclipse season. One alignment creates a solar eclipse, while the other creates a lunar eclipse. They can happen in either order. And if one eclipse is especially good — like this month’s annular eclipse — the other is usually poor — like tomorrow’s.

At least part of the eclipse will be visible across most of the globe. From the United States, though, only the northeastern states and northern Alaska will see any of it, and only for a few minutes — the final play of an eclipse season.

Script by Damond Benningfield

Support McDonald Observatory

During most lunar eclipses, the Moon turns orange or red as it passes through Earth’s long shadow. Occasionally, though, it can turn black. Volcanic ash high in the sky can block the sunlight that normally shines through the atmosphere. At times, that can make it look like the Moon has vanished.

Scientists recently looked at records of ancient eclipses to identify some of those vanishing acts. The records helped the scientists pinpoint major eruptions in the 12th and 13th centuries. They may also help scientists better understand the start of the Little Ice Age — a 60-year period that was unusually cold.

The scientists looked at records from Europe, the Middle East, and East Asia. They found a half-dozen eclipses that were especially dark. They compared the dates of the eclipses to layers of ash found in arctic ice cores, and to similar records in tree rings. That helped them lock down the year and even the month of several major eruptions — including one of the most powerful of the past thousand years.

The ash from these eruptions cooled Earth’s surface. That could have contributed to the start of the Little Ice Age, in 1280. Scientists will continue to study the eruptions to learn more about the connection — with the help of lunar eclipses.

An eclipse is coming up on Saturday. It won’t be dark, though. In fact, the Moon will barely look any different from normal. We’ll have more about that tomorrow.
 

Script by Damond Benningfield

Support McDonald Observatory

A pair of supermassive black holes may have trimmed down a bit. The black holes themselves didn’t change — only our understanding of them.

Together, the pair is known as OJ 287. It was the first supermassive black hole binary ever confirmed.

Through decades of observation, astronomers pieced together a model of the system. The dominant member of the pair was more than 18 billion times the mass of the Sun — one of the largest black holes yet seen. Its companion was only about one percent as massive, but still a beast.

OJ 287 has produced a pair of bright eruptions every 12 years or so. That was interpreted as the smaller black hole plunging through a disk of hot gas around the larger one, creating some brilliant fireworks. But an eruption that was expected late last year was months late.

A team kept an eye on the system for six years. The astronomers used several telescopes on the ground and in space, covering everything from radio waves to X-rays. That allowed them to measure the mass of the disk of hot gas. It turned out to be a lot lower than expected. That means the main black hole has to be less massive than expected as well — about a hundred million times the Sun’s mass. That’s still a monster, but one that’s a lot trimmer than expected.

OJ 287 is about five billion light-years away, in Cancer, the crab. The constellation is high in the southeast at first light.
 

Script by Damond Benningfield

Support McDonald Observatory