StarDate

The Sun is going through a big change. One cycle of activity is ending, while another is just beginning. Neither cycle is very active, though. In fact, the Sun probably is entering an unusually quiet year. There may be times when we won’t see anything going on at all.

The Sun follows a magnetic cycle that reaches its peak every 11 years or so. At the peak, the Sun produces lots of the dark magnetic storms known as sunspots. It also produces more outbursts of energy and particles.

Right now, the Sun is at the end of one cycle and the start of another. The ending one has been well below normal. In fact, there were many days where astronomers saw no sunspots at all. And the next cycle is expected to be even calmer.

Hints of the new cycle were seen as early as 2016. But the first strong indication came this July. A sunspot that lasted for a few days had the opposite magnetic polarity of the previous ones — a sure sign that it belongs to a new cycle.

For the next year, though, we’re expected to remain at solar minimum — a time when the Sun is especially quiet.

Solar minimum is a good thing for our technology. Solar storms can harm satellites, force airlines to reroute flights, and knock out power grids on Earth. That’s less likely to happen during solar minimum — although individual storms can still be nasty.

The new cycle should begin to ramp up by late next year, and reach its peak a few years later — one more change for our always-changing star.

Script by Damond Benningfield

One of the most popular astronomical events of the year happens tonight: the Harvest Moon. It’s the full Moon that’s closest to the autumnal equinox, which is coming up on September 23rd. The actual time of the full Moon is around midnight. That’s the moment the Moon lines up opposite the Sun, so it’ll be fully illuminated by the Sun’s rays.

The Harvest Moon occurs around the end of the growing season for much of the northern hemisphere, so it’s time to harvest the crops — hence the “Harvest Moon” name. But another reason for the name is that the light of the full Moon helps farmers bring in summer’s bounty.

At this time of year, the full Moon rises only 20 or 25 minutes later each night at mid to high northern latitudes — north of about Madison, Wisconsin, or Billings, Montana. In fact, from some latitudes, the Moon can actually rise a bit earlier for several evenings in a row. This gives farmers some extra light, extending the harvest time well into the night.

Over the course of a year, though, the Moon rises an average of about three-quarters of an hour later each day. So if it’s rising only a few minutes later now, it has to make up for that time somewhere else — in this case, around the time of the new Moon. At this time of year, the new Moon rises more than an hour later each day as seen from high northern latitudes. It’s a delay that balances the books on the Harvest Moon — the best-known full Moon of the whole year.

Script by Damond Benningfield

The surface of Mars is pretty quiet. It doesn’t constantly move and shake, as Earth’s does. Even so, it does jiggle a bit. And scientists are hoping to use those jiggles to learn more about what’s happening below the surface.

They heard their first confirmed “marsquake” back in April. It was detected by a seismometer deployed by InSight, which is probing Mars’s interior. The craft landed last November. It then used its robotic arm to place the seismometer on the surface in December.

The seismometer consists of three sensors that touch the surface. They’re housed inside a small dome that protects them from the wind and from changing temperatures. Yet the seismometer still “hears” the wind. In fact, it was recording the wind on April 6th when it heard a deeper rumble.

According to mission scientists, that was the first confirmed marsquake ever heard. One of the Viking landers of the 1970s recorded a possible quake, but it also could have been a strong gust of wind. And InSight heard a few weaker signals earlier in the year, but it’s not certain if they were caused by quakes, either.

The number and intensity of marsquakes can tell scientists how “active” the planet is — whether it has moving fault lines, for example. And as the sound waves from the quakes bounce around inside Mars, they can reveal details about how the planet is put together — all from a few “jiggles” on the Red Planet.

Tomorrow: harvesting moonlight.
 

Script by Damond Benningfield

Helium is the second-most-abundant element in the universe — only hydrogen is more common. It accounts for about a quarter of all the “normal” mass in the universe — the stuff that makes up stars, planets, and people.

Yet here on Earth, it’s quite rare. In fact, there’s a shortage of it. And that’s affecting everything from party balloons to rocket launches.

On Earth, helium is mainly mixed with natural gas. And because it’s lighter than air, if it reaches the atmosphere it’s likely to escape into space. So it takes special equipment and techniques to refine and store it.

Helium has many scientific uses. It fills the giant balloons that carry telescopes to high altitudes, and pressurizes the fuel tanks on rockets. In its liquid form, at a temperature just above absolute zero, it chills the superconducting magnets used in particle colliders. It also cools detectors on telescopes. And it’s a critical resource for many experiments in chemistry and physics.

The United States has been the world’s leading helium producer for decades. But supplies have been dwindling. And the federal government is selling off a major helium reserve it’s held in the Texas panhandle. So prices have soared.

Some new supplies are expected in the next couple of years, in Qatar and Russia. And a couple of possible helium fields have been identified elsewhere. But demand continues to climb. So scientists and others will keep scrambling to find supplies of this common but rare element.

Script by Damond Benningfield

Like a lot of boys of his era, young Robert Leighton learned how to take apart clocks and other mechanical devices. Unlike many boys, though, he also learned how to put them back together. That led to a career of inventing and building instruments for studying the universe — including the first cameras to photograph Mars from close range.

Leighton was born a century ago today, in Detroit. His parents soon split up, and he and his mother moved to Los Angeles. As he grew up, he bought a telescope and taught himself calculus.

He enrolled at Caltech in the 1930s, and during World War II he worked on rockets and missiles. After the war he earned his PhD in physics, then joined the Caltech faculty.

Leighton invented instruments for studying cosmic rays and the surface of the Sun. A discovery he made about the Sun led to a new branch of science: helioseismology — using sound waves to probe the Sun’s interior.

In the 1950s and ’60s, Leighton developed new cameras for photographing the planets. So when engineers at the Jet Propulsion Laboratory began planning the first missions to Mars, they picked Leighton to build the cameras. Using Leighton's design, Mariner 4 snapped the first close-range pictures of the Red Planet, in 1965.

Leighton then turned to a type of radio astronomy. He built large dish antennas for studying newly forming stars and other objects. Some of those dishes are still in use today — instruments that continue to probe the universe.

Script by Damond Benningfield

For a star that doesn’t have any close companions, its future is determined at its birth: Heavy stars live much shorter lives than lightweight stars. In fact, if you give astronomers a star’s mass, they can tell you just how long the star will spend in the prime of life — a phase known as the main sequence.

The leading light of the constellation Cassiopeia has already completed that phase. Now, it’s in the next phase of life — as a red giant.

Schedar is between 100 million and 200 million years old. By comparison, the Sun is four and a half billion years old. And it’ll spend billions of years more on the main sequence before it becomes a giant.

The difference is mass. Schedar was born about five times as massive as the Sun. At that great heft, gravity squeezed the star’s core much more strongly than the Sun’s core. That made the core extremely hot, which revved up its nuclear reactions. As a result, Schedar “burned” through its original hydrogen fuel in a hurry.

When the hydrogen was gone, the star’s outer layers puffed up, making Schedar much bigger. That also caused the surface to cool off. So while the star spent its time on the main sequence shining blue-white, now it’s reddish orange — a big change for a big star.

Cassiopeia is about a third of the way up the northeastern sky as night falls. Its stars form a prominent letter “W.” Schedar is at the bottom right point of the W — a young star that’s already nearing its end.

Script by Damond Benningfield

Drones are everywhere these days. Everywhere on Earth, that is. But they’re about to buzz other worlds as well. A small one will head for Mars next year. And a much bigger and more sophisticated one will be sent toward the biggest moon of Saturn in 2026, with arrival eight years later.

That one is known as Dragonfly. It’ll be about the size of a lawnmower. Its nuclear generator will power it for years, allowing it to fly more than a hundred miles through the atmosphere of Titan.

Titan is one of the most intriguing worlds in the solar system. It’s as big as Mercury, the smallest planet. It has an atmosphere that’s denser than Earth’s. It has clouds, rains, and rivers and lakes. Because the temperature hovers near 300 below zero, though, the liquids are methane, not water. But a giant ocean of water may lie far below the surface. That combination of ingredients means Titan is a place to look for signs of life.

Dragonfly will land in a dune field near Titan’s equator. Each Titan day — about 16 Earth days — it’ll fly to a new location. It will analyze rocks on the surface, listen for quakes below the surface, and measure Titan’s weather. In particular, it’ll look for the chemical building blocks of life. And it’ll look for evidence of current life on this intriguing world.

Look for Saturn to the right of our own moon tonight. It looks like a bright star. Good binoculars or a telescope will reveal Titan, shining like a tiny star near the giant planet.

Script by Damond Benningfield

Several billion years ago, a giant space rock slammed into Proteus, the second-largest moon of the planet Neptune. The impact blasted rock and ice into orbit around Neptune. Eventually, some of that material came together to form another moon.

That’s the scenario outlined by the astronomers who discovered the moon, which they announced early this year. They named it Hippocamp, after a mythological creature that was half horse, half fish.

Hippocamp is Neptune’s 14th known moon, and the smallest of them all — only about 20 miles in diameter. It was discovered by a team led by Mark Showalter. The astronomers combined images from Hubble Space Telescope that were taken starting in 2004. That revealed the moon and allowed the scientists to plot its orbit. It’s about 50,000 miles above Neptune’s clouds.

Hippocamp’s orbit brings it to within about 7500 miles of the orbit of Proteus — one of the clues to the little moon’s birth. A giant crater mars the surface of Proteus. The impact that created it would have blasted out more than enough material to make Hippocamp — Neptune’s most recently discovered moon.

And Neptune is at its best right now. The planet will line up opposite the Sun on Monday. It rises around sunset and stays in the sky all night. And it’s brightest for the year, too. Even so, you’ll need a telescope to pick out the giant planet. It’s in the eastern sky at nightfall, near the edge of the constellation Aquarius.

Script by Damond Benningfield

Hurricane season is roaring toward its peak about now. But even the biggest hurricanes are tiny compared to storms on some other planets. Late last year, for example, astronomers discovered a storm on Neptune that’s almost wide enough to swallow Earth.

It’s known as a “great dark spot.” Not the spot, but a spot. That’s because it’s not the first one astronomers have seen.

The first was discovered by Voyager 2. It flew past Neptune in 1989 — and it’s still the only craft ever to visit the planet. It found what was dubbed the Great Dark Spot. It was as wide as our entire planet. When Hubble Space Telescope took its first look at Neptune five years later, though, the spot was gone.

The new dark spot isn’t quite as big. But Hubble may have seen its birth over the last few years. Beginning in 2015, it photographed a blob of bright clouds at the same latitudes where the dark spot showed up last year. Those clouds may build at high altitudes while the dark spot is taking shape lower in the atmosphere.

That could mean that it takes a few years to make a dark spot. The spot then vanishes after a few years more, leaving Neptune spotless — until the next one comes along a few years later.

And Neptune is putting on its best showing of the year. It will line up opposite the Sun next week, so it rises at sunset and is in view all night. It’s brightest for the year, too. But you still need some help to spot it, near the western edge of Aquarius.

Script by Damond Benningfield

The four outer planets of the solar system have a lot in common. They’re all giants — at least four times Earth’s diameter. They’re all made mainly of hydrogen and helium, the lightest elements. They all have lots of moons. And they’re all encircled by rings.

The rings of Saturn are wide and bright, and easily visible through any telescope. The rings of the other giants, on the other hand, are thin and faint. In fact, they’re so faint that they weren’t discovered until late in the last century.

The rings of Jupiter are a case in point. They were discovered in 1979, by a spacecraft that was approaching the planet. In all, scientists have identified four rings, although each of them is made of smaller “ringlets.”

Jupiter’s rings are wider than the distance from Earth to the Moon — wider even than the rings of Saturn. But they contain much less material than Saturn’s rings — widely spread grains of dust.

Most of the dust comes from a few of Jupiter’s moons. Space rocks from outside the Jovian system strike the moons, knocking debris into space. The dust grains eventually spiral inward all the way to Jupiter itself. But more collisions add fresh material — keeping Jupiter’s hard-to-see rings from vanishing entirely.

And Jupiter is easy to spot tonight. It looks like a brilliant star — brighter than any other star or planet that’s visible right now. And it’s quite close to the first-quarter Moon — a beautiful duo in the evening sky.

Script by Damond Benningfield