StarDate

Two bright companions will keep pace with the Moon tonight. The brighter of the two is Jupiter, the biggest planet in the solar system. It’s well to the left of the Moon at nightfall — the brightest object in the sky at that time other than the Moon.

The second companion is the star Antares, the heart of the scorpion. It’s a little closer to the lower left of the Moon.

There are many words to describe the phases of the Moon and how the phase is changing. Tonight, it’s technically known as a waxing crescent. It’s a fat crescent, because the Sun lights up more than a third of the lunar hemisphere that faces Earth.

It’s called a “waxing” Moon because the fraction that’s illuminated is getting bigger by the night. By tomorrow night, half of the Moon will be in sunshine. That’s the moment known as first-quarter Moon — the Moon will be one-quarter of the way through its month-long cycle of phases.

The Moon will continue to “wax” for another week after that. During that time it’ll be “gibbous” — more than half of its surface will be in the full light of day.

The Moon will be full on the night of the 13th. After that, it’ll start to “wane,” so less and less of its Earth-facing side will be lit up. That’ll carry it through last quarter, then through a period of waning crescents. The Moon then will pass between Earth and the Sun — the moment of new Moon — the end of one cycle of phases and the beginning of another.

More about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

The space lanes are going to get busier in the next few years. That’s because NASA and other space agencies have recently announced plans for several new missions to the worlds of the solar system.

In May, NASA selected three commercial landers to carry scientific instruments to the Moon. One will land in the Ocean of Storms, another in the Lake of Death, and the third in the Sea of Rains. All three will launch in the next two years.

NASA also approved new missions to study the Sun. One will focus on the Sun’s hot but faint outer atmosphere, the corona. And the other will study the effects of the solar wind on parts of Earth’s magnetic field. The missions will launch together, in two years.

The European Space Agency announced a new mission of its own: Comet Interceptor — even though no one yet knows where it’s going. It’ll consist of three craft that’ll be placed in a parking orbit. When a new comet enters the inner solar system, they’ll be sent to study it.

European agencies also announced a new rover, to crawl across one of the moons of Mars. It’ll hitch a ride on an already planned Japanese mission, which will bring samples of one of the moons back to Earth. Launch is scheduled for 2024.

Finally, NASA picked three candidates for another new mission. One would study water on the Moon, another would examine space weather around Mars, and the third would visit a double asteroid. The winner — or winners — will be selected next year.

Script by Damond Benningfield

Two close neighbors are hiding in the sunlight right now. Both of them are passing behind the Sun as seen from Earth. And both will return to view next month.

Mars is going first. It’s passing behind the Sun today. And Mercury will follow it tomorrow.

A planet’s passage on the far side of the Sun is called a conjunction — an alignment of the planet, the Sun, and Earth. And in Mercury’s case, it’s called a superior conjunction.

The difference in terminology is a result of the planets’ different locations. Mars is the fourth planet from the Sun. Since Earth is the third planet, Mars always stays outside Earth’s orbit. So it has only one type of conjunction — when it passes behind the Sun.

But Mercury is the Sun’s closest planet, so its orbit is inside Earth’s. So it can have two kinds of conjunctions: when it’s behind the Sun, as it is now, and when it passes between Earth and the Sun. That alignment is known as inferior conjunction.

After its conjunction, Mars will just begin to peek into view in the dawn sky in early October. It’ll climb higher throughout the month, and will be in good view by the end of October.

Mercury, on the other hand, will climb into the evening sky around the middle of October. It won’t get all that high, though, so it’ll be tough to find. Skywatchers at southern latitudes will have the best chance to see it — during the planet’s brief interval between conjunctions.

Tomorrow: new missions of exploration.

Script by Damond Benningfield

One of the stalwarts of the evening skies of spring and summer is disappearing from view. In fact, tonight is your last best chance to see it, because it’s close to the crescent Moon.

Spica is the leading light of the constellation Virgo. The bright star stands well to the left or lower left of the Moon as evening twilight fades away.

Spica climbs into view in the east in the evening skies of April. It rises about four minutes earlier each night, so it’s a little farther across the sky from one night to the next.

That change in position is caused by Earth’s motion around the Sun.

As Earth spins on its axis, the stars rise and set every 23 hours and 56 minutes. During that period, though, Earth moves a little farther in its orbit. That changes the viewing angle to the Sun. So our planet has to turn a little farther for the Sun to reach the same point in the sky — an interval of 24 hours. If you do the math, you’ll see that on our 24-hour clock, the distant stars must rise four minutes earlier each day.

Now, that progression is beginning to carry Spica out of sight. It’s so low in the western twilight that it’s hard to pick out, even though it’s pretty bright. By two or three weeks from now, depending on your latitude, it’ll be too low in the sky to see at all.

As always, though, Spica won’t stay hidden for long. It’ll return to view in the dawn sky in early November — then return to the evening sky in the spring.

Tomorrow: disappearing planets.

Script by Damond Benningfield

A pioneering spacecraft began its final call 40 years ago today, when it plowed into the magnetic “bubble” that surrounds the planet Saturn. It flew just 13,000 miles from Saturn the following day, giving us our first up-close look at the ringed planet.

Pioneer 11 was small by today’s standards. And its pictures were crude. Yet the craft provided lots of new details about Saturn, its rings, and its moons.

Pioneer 11 and a sister ship, Pioneer 10, were launched in 1973. They staged the first encounters with Jupiter the following year. Pioneer 11 then took aim at Saturn.

Its dozen instruments discovered a new ring outside the main rings, and two small moons. They measured Saturn’s global temperature, and obtained a crude outline of its interior structure. They also measured the temperature of Saturn’s biggest moon, Titan, which has a dense atmosphere. The readings showed that Titan is too cold for life like that on Earth.

After the encounter, Pioneer 11 headed out of the solar system. NASA maintained regular contact with it until late 1995, and last heard from it a few years later. Today, it’s about nine and a half billion miles from Earth. It’s headed in the general direction of Lambda Aquila, a hot, bright star that’s about 125 light-years away. It’ll pass the star in about four million years.

And just in case anyone there grabs the derelict machine, it carries a plaque to tell them where Pioneer 11 came from — a roadmap to the solar system.

Script by Damond Benningfield

Most of the glowing clouds of gas and dust that permeate the galaxy are associated with two phases of a star’s life: its birth and its death. A star is born from a giant cloud that splits apart to form many stars. And when a star dies, it creates its own beautiful cloud.

An example of the latter is the Veil Nebula. It’s in the constellation Cygnus, which is high in the east as darkness falls. The nebula is not far from the tip of one of the swan’s wings.

Photographs reveal several bright, colorful arcs and filaments of material. Together, they form a bubble that’s perhaps a hundred light-years wide.

The Veil is the aftermath of a supernova — the explosion of a star at least 20 times as massive as the Sun. The blast took place about 8,000 years ago as seen from Earth. It would have been brighter than any other star or planet — bright enough to see during the daytime.

What we see today are filaments of gas from the explosion. They’re still expanding into space — at up to a million miles per hour.

There’s been some confusion about how far away the Veil is. A study last year put it at almost 2500 light-years — a good bit farther than other recent estimates.

The study also suggested that the visible filaments form when the expanding gas rams into surrounding clouds. In that way, the shockwave from the supernova is illuminating the clouds of gas around it — allowing us to see the contours of some otherwise dark neighbors.

Script by Damond Benningfield

A huge stellar nursery climbs high across the sky at this time of year. It’s near Deneb, the bright star that marks the tail of Cygnus, the swan. The whole complex is about 1800 light-years away. And it spans about 130 light-years.

The nursery consists of two bright clouds that are separated by a dark one. One of the bright clouds is well known — the North America Nebula. The other is the Pelican Nebula. Both are named for the figure their outline resembles.

The bright nebulae contain huge amounts of warm hydrogen gas. Ultraviolet energy from hot young stars in the nebulae give the hydrogen an electric charge, causing them to glow like neon bulbs. The dark nebulae contain dense clouds of cold gas and dust. Those clouds are also giving birth to new stars. But we can’t see the stars through the dust.

The bright nebulae reveal many “pillars of creation” — giant columns of gas and dust that contain newly forming stars. The pillars around the infant stars are being blown away by some of the stars that have already been born.

Astronomers have also seen “jets” of gas shooting away from several newly forming stars. The jets can stretch across billions of miles — heralding the birth of new stars in a busy nursery.

Look for Deneb high in the eastern sky this evening, at one point of the bright Summer Triangle. The nebulae stand just below Deneb, and are easy targets for a small telescope.

We’ll talk about another nebula in Cygnus tomorrow.

Script by Damond Benningfield

A black hole in the constellation Cygnus keeps popping off. Over the last eight decades or so, it’s produced several big eruptions. And during the most recent one, astronomers saw that the black hole is “dragging” the space around it.

The system is known as V404 Cygni. It has two members. One is a black hole about nine times as massive as the Sun. The other is a “normal” star a little less massive than the Sun.

They’re so close together that the black hole “steals” gas from the companion. The gas forms a wide, swirling disk around the black hole. Every few decades, so much gas piles up in the disk that it causes an eruption. That makes the system flare thousands of times brighter than normal.

In 2015, V404 Cygni staged an outburst that was especially bright in X-rays. The outburst wasn't steady, though. Instead, it consisted of a series of flashes that lasted up to about an hour.

This year, researchers reported an interesting conclusion about those outbursts. They found that the disk isn’t quite aligned with the black hole. So material in the inner portion of the disk is warped. As the black hole spins, its powerful gravity drags the space around it. That causes the inner disk to wobble.

Magnetic fields squirt some of the hot gas in that part of the disk back into space as narrow “jets.” As the disk wobbles, the jets move like the streams of a spinning water sprinkler — shooting out material at more than half the speed of light.

More about Cygnus tomorrow.

Script by Damond Benningfield

Cancer, the crab, is famed for its position in the zodiac. Yet other than its location, there’s not much to recommend it. The outline of the crab itself isn’t all that crab-like, and even its brightest stars are mere pinpricks of light.

Cancer’s main highlight is a star cluster known as Messier 44. Astronomer Charles Messier added it to his catalog of astronomical objects 250 years ago.

M44 buzzes with so many tightly packed stars that it’s also known as the Beehive. That appearance isn’t deceiving, because M44 is one of the busiest clusters around, with a thousand stars or more.

The cluster is about 600 light-years away, and probably about 600 million years old. Astronomers deduced its age by determining the types of stars it contains — and the types it does not. Missing are the hottest, brightest, and most massive stars. Such stars burn through their nuclear fuel in a hurry, so they disappear quickly, placing a limit on the cluster’s age.

Most of the cluster’s members are the faint embers known as red dwarfs, while about a third are somewhat like the Sun. And only a handful of stars are much brighter and more massive than the Sun.

M44 is low in the eastern sky at first light tomorrow. It might be a bit tough to see, though, because the Moon is passing directly in front of it, blotting out some of its stars. Even so, binoculars reveal several stars, adding a bit of sparkle to the otherwise drab crab.

Script by Damond Benningfield

Most of the stars that dot the night sky are quite different from our own star, the Sun. An example is Antares, the heart of the scorpion. It’s low in the south at nightfall, close to the lower right of the brilliant planet Jupiter.

Bright orange Antares is a supergiant — it’s much bigger and heavier than the Sun, and thousands of times brighter.

Under dark skies, though, you can just make out another star in Scorpius that’s a near twin to the Sun: 18 Scorpii, high above Antares. It’s just a few degrees hotter than the Sun, and a little bit brighter and more massive.

18 Scorpii is one of more than a dozen “solar twins” identified so far. Studying these stars can help us understand more about the Sun itself — particularly since these stars are different ages from the Sun. Seeing them at different points in their evolution can help explain how the Sun changes over time.

One thing astronomers are particularly interested in is the magnetic fields of these stars.

The Sun’s magnetic field goes through an 11-year cycle. At the cycle’s peak, the Sun produces more magnetic storms, which can interfere with modern technology. At the same time, the Sun’s total energy output goes up by about a tenth of a percent.

18 Scorpii’s magnetic field varies by about the same amount. But its cycle lasts just seven years. That may be because the star is only about half as old as the Sun. So 18 Scorpii may be showing us what our own star was like in the distant past.

Script by Damond Benningfield