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This is a bad time for a full Moon that’s especially big and bright. That’s because a meteor shower will reach its peak over the next couple of nights. But a full Moon overpowers all but the brightest meteors. And a Moon that’s especially close — making it especially bright — is an even bigger hindrance. It reduces the number of meteors you might see to just a handful — even if you’re far away from city lights. The Perseid shower is one of the more reliable meteor showers. At its peak, it usually produces a dozen or two “shooting stars” per hour, and sometimes a lot more. This year, though, the showing should be much weaker — the result of the pesky full Moon. The Moon will reach its “full” phase this evening — about 30 hours after it passed closest to Earth for the month — 223,587 miles away. That’s the Moon’s third-closest approach of the year — about 15,000 miles closer than average. At that range, the Moon shines several percent brighter than average. Some describe such a close Moon as a super-Moon, but others don’t. That’s because there’s no formal definition for a super-Moon. For some, it’s the closest full Moon of the year. For others, it’s any full Moon within a certain distance — although different groups use different distances. Super-Moon or not, this month’s full Moon will be close, big, and bright — and it’ll block out most of the Perseid meteor shower.  Script by Damond Benningfield

The Perseid meteor shower is building toward its peak. Tonight, you might see a few of its streaks of light, although the Moon will drown out all but the brightest of them. But even the ones you do see through the moonlight can’t compare to a meteor that blazed across the sky 50 years ago. It was visible during broad daylight. The fireball was first seen over Utah, during the afternoon of May 10th, 1972. Thousands watched it race across the sky. It vanished from sight over Alberta, Canada. Two people made home movies of it. And a spy satellite designed to look for nuclear test firings on Earth followed it for about two minutes. The fireball was a small asteroid — a ball of rock and metal anywhere from 10 to 45 feet in diameter — that was being vaporized by friction with the atmosphere. It dropped to an altitude of just 35 miles. But it hit the atmosphere at a shallow angle, so it skipped back into space like a rock skipping across a pond. If the asteroid had taken dead aim at Earth, it most likely would have exploded high in the sky. That might have caused some local damage — or no problems at all. The passage vaporized most of the asteroid, cutting its diameter by at least half. It also slowed the asteroid, changing its orbit around the Sun. It may come close to Earth again in the future, but it’s not expected to “skip” off the atmosphere any time soon. More about the Perseids tomorrow.  Script by Damond Benningfield

Every 12 and a half months, Earth moves past the giant planet Saturn. And that’s about the best time all year to watch it. It rises around sunset, is in view all night, and shines brightest for the whole year. That alignment is known as opposition, and it’s coming up on Saturday. But there’s not much difference in the view for days before and after opposition, so don’t wait for that moment to look for Saturn. It takes Saturn about 29 years to orbit the Sun, compared to one year for Earth. So we “lap” Saturn every 12 and a half months. If we could watch the two planets from above at high speed, the process would look like a small car on the inside lane of a race track zipping past a big car over and over. For every lap by the big guy, the little guy would make 29. Saturn is at its closest around opposition — one reason it’s so bright. But its brightness varies from one opposition to another. That’s largely because we see Saturn’s rings at different angles. When the rings are most tilted as seen from Earth, Saturn shines roughly twice as bright as when the rings are seen edge-on. This year, they’re about half way between — adding to the luster of this plodding giant. Look for Saturn low in the east-southeast at nightfall, and arcing across the south later on. It looks like a bright golden star. It’s well to the lower left of the Moon tonight, but the Moon will catch up to it over the next two nights.  Script by Damond Benningfield

An unsettled Sun may have a big impact on some of the biggest weather-makers on Earth: El Niño and La Niña. These alternating events in the Pacific Ocean can bring floods to some parts of the world and droughts to others, and alter global temperatures for months or years. And a recent study found a strong correlation between the cycles of El Niño and La Niña and the magnetic cycle of the Sun. The solar cycle lasts about 11 years. At its peak, it produces many sunspots — dark magnetic storms on the surface of the Sun — as well as big outbursts of radiation and particles. And at the cycle’s low point, the Sun is quiet, with few if any magnetic storms. Researchers looked at records of solar activity from 1900 to 2018. They compared that to records of El Niño and La Niña over the same period. And they found a match. When solar activity was high, the temperature of the North Pacific was high as well. That correlated to longer and stronger bouts of El Niño. And when the Sun was quiet, Pacific temperatures were lower and La Niña was more likely to appear. The extra energy during the Sun’s high point may first warm a layer of Earth’s upper atmosphere. That warms the air below, changing a large circulation pattern. And that warms the North Pacific, which in turn warms the Central Pacific — the birthplace of many El Niño and La Niña events. So to get a general idea of what to expect here on Earth, we may want to look to the Sun.  Script by Damond Benningfield

The brightest star in the night sky has played a key role in the calendars of many cultures. In ancient Egypt, for example, its first appearance in the dawn sky marked the beginning of a new year, and heralded the annual flooding of the Nile. And in Greece and Rome, that dawn showing ushered in the Dog Days — the most sweltering time of year. It’s a phrase we still use today. When the phrase was coined, the star Sirius first climbed into view around the end of June — at the start of summer and a long run of hot, humid days. Sirius is the brightest star of the constellation Canis Major, the big dog. So it’s known as the Dog Star. People associated the star with the climate, so they called that time of year the Dog Days. Thanks to an effect known as precession, though, the stars gradually shift position relative to the Sun. So now, Sirius doesn’t peek into view in the dawn sky until August. From the southern states of the U.S., it’s appearing right about now. It won’t emerge from the Sun’s glare from more northerly latitudes for another week or so. For those who can see it, it’s in the east-southeast, almost directly below the line of stars that marks Orion’s Belt. That shift has changed the way we think of the Dog Days. In early times, the phrase referred to a specific time of year — generally from early July to about mid-August. Today, though, it refers simply to the hottest period of the year — the Dog Days of summer.  Script by Damond Benningfield

The star Antares is orange. That means its surface is thousands of degrees cooler than the Sun’s. Deep inside, though, it’s a different story. The temperature in the core of Antares is at least 180 million degrees, compared to 27 million for the Sun. Antares is hotter because it’s roughly a dozen times the mass of the Sun — and for a star, mass is everything. Gravity squeezes gas in the core tightly, making it hot enough to produce nuclear fusion. In the Sun, hydrogen atoms fuse together to make helium, releasing energy. As the energy radiates toward the surface, it pushes outward on the star’s surrounding layers of gas. As a star’s mass increases, so does its gravity. It squeezes the core even tighter, making it even hotter. A hotter core “burns” the hydrogen more quickly, so it uses it up in a hurry. It then moves on to fusing the helium to make even heavier elements. Radiation from the hotter core causes the outer layers to puff up to amazing proportions. Antares, for example, is hundreds of times wider than the Sun. That makes its outer layers cooler and redder. Antares should spend a total of about a million years in this phase of life before moving on to fuse other elements. When it can’t continue that process, the core will collapse and the outer layers will explode — sometime in the next million years. Look for Antares close to the lower left of the Moon at nightfall, and a little closer as they set.  Script by Damond Benningfield

Mars is tough on wheels. The metallic wheels on the Curiosity rover, for example, look like they have more holes and tears than tread. In fact, flight controllers recently had to abandon an area they wanted to explore because it was covered in sharp rocks described as “gator backs.” That’s one of the few things that’s slowed the rover, which arrived at Mars 10 years ago tonight. In its decade of travels, it’s covered more than 17 miles, and climbed up and down several hills. When it landed, Curiosity was the biggest and most sophisticated Mars rover yet. The nuclear-powered craft was as big as a minivan. It was bristling with cameras, and it carried a chemical laboratory for analyzing the rocks and dirt. It also had a laser to “zap” the rocks, allowing its instruments to study the vaporized debris. Curiosity landed in Gale Crater — an ancient impact crater with a tall mountain at its middle. Curiosity’s main mission was to find out whether the site had once had comfortable conditions for life. And it quickly found that it probably did. Water once filled the crater. Despite years of trying, though, it hasn’t found any evidence of life itself — at least not in the rocks. It has detected methane gas wafting through the crater. On Earth, methane most commonly is produced by life. But there’s no confirmation that anything is living in Gale Crater — or ever has.  Script by Damond Benningfield

A spectacular storm on the Sun erupted 50 years ago this week — one of the most powerful ever seen. It produced several giant outbursts, and shot a cloud of charged particles toward Earth. When the cloud got here, it created all kinds of problems. Among other things, it apparently triggered sea mines in a harbor in Vietnam. The storm began on August 2nd, 1972. The big cloud followed later, and it reached Earth in record time — less than 15 hours. That means it was traveling at more than six million miles per hour. When the cloud reached Earth, on August 4th, it created auroras that were bright enough to read by. It caused problems with power grids and communications networks in the United States. And it shorted out a Defense Department satellite. According to the Navy, it also set off magnetic mines in Hai Phong harbor in Vietnam. Naval aircraft recorded a couple of dozen explosions in just two minutes. The mines were set to explode when they “felt” sharp changes in the magnetic field. The solar storm produced several of those spikes — strong enough, the Navy concluded, to trigger the explosions. The Navy quickly changed the design of its mines to prevent a repeat. But big solar storms continue to cause big problems. And because we depend on so much more technology today, a storm like the one in 1972 could cause massive damage. But it probably wouldn’t set off any more mines.  Script by Damond Benningfield

Spica cruises along with the Moon this evening. The leading light of the constellation Virgo is close below the Moon at nightfall, and sets before midnight. Astronomers have studied Spica for millennia. In fact, Spica played a starring role in an important discovery about our own planet. Around 127 B.C., Greek astronomer Hipparchus carefully studied Spica’s location. He noted its position relative to the Sun’s position at the fall equinox. He then compared his observations to those made by other skywatchers a few centuries earlier. And he found something surprising: Spica had shifted a bit. And in fact, other stars he measured showed that same change. Hipparchus called that change the precession of the equinoxes. The entire celestial sphere — every single star — shifts by a little more than one degree per century. That isn’t caused by the stars, though. Instead, it’s the result of a “wobble” in Earth’s rotation — like the wobble of a gyroscope that’s beginning to slow down. It takes about 26,000 years to complete a single wobble. During that time, Earth’s north celestial pole draws a big circle on the sky. Different stars along that circle take turns as the pole star. The wobble also means that every star shifts position relative to the point of the equinox. So over the millennia, the entire celestial sphere rotates through the seasons — a discovery made possible in part by brilliant Spica.  Script by Damond Benningfield

Our “universe” is only part of the universe — all of matter and energy, space and time. That’s because our view of the universe is limited. We see only a tiny sliver of it — a result of the age of the universe, the expansion of the universe, and the speed of light. The fraction we see is known as the observable universe. And from what we see, it’s all the same. Everywhere we look, there’s the same mixture of galaxies and empty space, of stars and gas clouds. And everything seems to follow the same laws of physics. But we don’t know what’s happening in the rest of the universe — everything beyond the “cosmic horizon” — the limit of our viewing range. Logic suggests that everything beyond that horizon is just like everything in the observable universe. There’s no reason that the “bubble” of the universe we inhabit should be any different from the universe as a whole. But we just don’t know for sure — and we probably never will. Scientists can try to draw some inferences, though. If they observe a galaxy cluster that’s 10 billion light-years away, for example, it has its own observable universe. Some of it overlaps our own, but some extends far outside it. If the cluster is being pulled toward the region we can’t see, then scientists might conclude that it’s been dragged by the gravity of something big and heavy — perhaps a giant galaxy cluster far outside the observable universe — something we’ll never see.  Script by Damond Benningfield

The universe might be infinitely large. And even if it’s not, it’s probably so big that it might as well be infinite. But we see only a tiny fraction of that extent — a bubble known as the observable universe. What we see is limited by the speed of light — 670 million miles per hour. That’s fast. But it’s not infinite. So light can travel only so far in a year, or a century, or a billion years. Because the universe was born 13.8 billion years ago, we can’t see any farther than light can travel in that time — 13.8 billion light-years. The farthest galaxies and quasars that we’ve seen are almost that far away. Or they were that far away. We see these objects as they looked at a distance of more than 13 billion light-years. But keep in mind that the universe is expanding. So today, there’s a lot more space between us and those early objects. In fact, today the edge of the observable universe is about 46 billion light-years away. Assuming Earth were still around, in tens of billions of years, we’d see what those objects look like today. And the limits of the observable universe might eventually reach about 60 billion light-years. But the universe is expanding so fast that we’d never see any farther — limiting us to a bubble of space and time inside a possibly infinite universe. We’ll have more about the observable universe tomorrow.  Script by Damond Benningfield

Red and green planets huddle close together the next few mornings like bulbs on a strand of Christmas lights. The red one is bright and easy to see, while the green one takes some work. Orangey red Mars is the brighter of the two. Fainter Uranus is to the upper left at first light tomorrow, and shines pale green. You need binoculars to find it. The planets will change positions over the next few days, but they’ll stay closer together. Uranus is one of two “ice giants” in the solar system — a category that scientists are still trying to figure out. Uranus and Neptune are the Sun’s farthest major planets. They’re much bigger and heavier than Earth, but smaller than Jupiter and Saturn. Until a couple of decades ago, Uranus and Neptune were classified as gas giants, like Jupiter and Saturn. But there are some big differences. Jupiter and Saturn consist mainly of hydrogen and helium, the lightest of all the elements. Uranus and Neptune, on the other hand, contain mostly heavier elements. Uranus and Neptune also are put together differently. They have a thin layer of hydrogen and helium at the top, with water, ammonia, and other compounds below. Those compounds are classified as ices, although they actually form a hot, slushy “ocean.” And scientists aren’t sure where Uranus and Neptune were born. It could have been closer to the Sun, much farther from the Sun, or about where they are today: ice giants far from the Sun.  Script by Damond Benningfield

They may not look it, but the stars at opposite ends of the stick-figure outline of Boötes, the herdsman, are a lot alike. The star at the bottom is yellow-orange Arcturus, one of the brighter stars in the night sky. The star at the top, Nekkar, looks only a few percent as bright. But that’s only because it’s more than six times farther away — about 235 light-years. Boötes is in the west as night falls. Its outline resembles a kite or an ice cream cone, with Arcturus at the bottom of the cone, half-the way up the sky. Nekkar — also known as Beta Boötis — is far to its upper right. Both stars are in a final phase of life. They’ve “burned” all the original hydrogen in their cores, causing their outer layers to puff up. That makes them giants. Arcturus is a little bigger, but Beta Boötis is a little hotter, so their true brightness is about the same. Two things that aren’t the same are their mass and age. Beta Boötis is only about 300 million years old, versus seven billion years for Arcturus. But Beta is three times heavier than Arcturus. That extra mass made the star consume its hydrogen much more quickly. As a result, it lived a much shorter “normal” lifetime than Arcturus. The stars face the same fate. Eventually, they’ll blow their outer layers into space. That will leave only their hot but dead cores — white dwarfs — the same fate that awaits the Sun in several billion years.  Script by Damond Benningfield

South Korea is getting ready to launch its first mission to the Moon. Among other things, it’ll scope out lunar resources — things like water ice, aluminum, and silicon — that could support future colonies. But it’ll also look for a resource that no one will be able to use for many decades, if ever. Helium-3 is a form of the second-most common element in the universe. While “normal” helium has two protons and two neutrons, helium-3 has only one neutron. Helium-3 could someday be used as a fuel for nuclear fusion. It would produce less radioactive waste than normal helium, and it should “burn” more efficiently. Here on Earth, it’s quite rare — only about three atoms for every 10,000 atoms of regular helium. But it’s a lot more common on the Moon. That’s because there’s a fair amount of it in the solar wind. The Moon has no magnetic field or atmosphere to stop the solar wind, so its particles embed in the surface. So some folks have dreamed of pulling the helium-3 from the lunar dirt and bringing it to Earth. And that requires good maps of the highest concentrations of the element. There are all kinds of caveats, though. You’d have to sift through millions of tons of dirt to get enough helium-3 to be worth it. Shipping it to Earth would be expensive. And working fusion reactors are decades in the future at best. So efforts to find helium-3 are a long-term investment in the future.  Script by Damond Benningfield

South Korea plans to join the club: countries that have sent missions to the Moon. KPLO — Korea Pathfinder Lunar Orbiter — is scheduled to launch as early as next month. If it succeeds, it’ll make South Korea only the seventh nation or group of nations to reach the Moon. The all-time leader in successful Moon missions is the United States, with the Soviet Union not far behind. In fact, they had a monopoly on the Moon until late in the last century. But in the last 25 years they’ve been joined by China, Japan, India, and Europe. And the club soon could get even bigger. The United Arab Emirates plans to launch a mission this fall. And Mexico, Australia, Turkey, the UK, and others plan to send craft to the Moon, too. KPLO is designed mainly as a test flight. It’ll build the technology — in space and on the ground — for more-ambitious missions in the future. The craft will do some science. It’ll orbit the Moon from pole to pole, at an altitude of about 60 miles. From there, it’ll map the surface to help find good spots for future landers and rovers. And its instruments will look for lunar resources. The list includes frozen water, uranium, silicon, and helium-3, which we’ll talk about tomorrow. Those resources might someday be put to use by South Korea — potentially the next member of the “we’ve-been-to-the-Moon” club.  Script by Damond Benningfield

A mission to an asteroid will have to wait a while. It was scheduled to head for space as early as next week. But a series of technical problems has kept it on the ground for at least another year. The spacecraft is named for its asteroid target: Psyche. The asteroid is in the asteroid belt, between the orbits of Mars and Jupiter. It’s shaped like a potato, with an average diameter of about 140 miles. It could be a fragment of the core of a small planet that was blasted apart in a long-ago collision. That idea is based on Psyche’s composition — it contains a lot of iron and nickel. In fact, it’s the largest of all the known metal-rich asteroids. Scientists are especially interested in it because it could have formed in the same way as Earth did, and it could provide a peek into a planetary core that we can’t get here at home. The Psyche spacecraft is about the size of a Smart Car, with solar panels big enough to cover a tennis court. It’ll use ion power to maneuver — electric thrusters that deliver low thrust, but that can fire for weeks or months without stopping. Psyche will get a gravitational boost from Mars to help it reach the asteroid. It’ll spend almost two years orbiting the heavy space rock, eventually dropping as close as about 50 miles. It’ll take pictures and measure Psyche’s magnetic field and its composition — giving us a detailed look at a body that could tell us a lot about our own planet. Script by Damond Benningfield

In the “Star Trek” universe, most of the good real estate is on “Class M” planets — worlds like Earth, which can support human life. Present-day scientists don’t use that classification — not yet, anyway. But they do classify some asteroids as type M. And NASA is about to send a spacecraft to study the largest of them. Psyche — named for the Greek goddess of the soul — is in the asteroid belt, between the orbits of Mars and Jupiter. It’s shaped a bit like a potato, with an average diameter of about 140 miles. An asteroid is a member of type M if it has a high concentration of metals — especially iron and nickel. And that’s true of Psyche. Originally, scientists said it might be almost completely metal. They even estimated the value of that metal at around 10 billion billion dollars. More-recent observations say the proportion of metals could be around half, with much of the asteroid consisting of empty space. Psyche might once have been part of a small planet. Its gravity was strong enough to melt the interior, so heavy elements — like iron and nickel — settled in the core. Lighter elements floated upward, forming the mantle and crust. Psyche would have been part of the core. A collision could have shattered the original body, blasting Psyche into space. Studying Psyche could tell us more about how planets with metallic cores formed, especially the most famous class-M planet of all: Earth. More tomorrow.  Script by Damond Benningfield

The Moon and the planet Venus — the “morning star” — stage a beautiful encounter tomorrow. They’re low in the sky as twilight waxes. But they’re quite bright, so as long as you have a clear horizon, they’re easy to see. Venus is completely dry. Even so, it has giant “continents” that tower high above the surrounding plains of volcanic rock. One is called Ishtar Terra. It’s about as big as Australia. And it contains the highest spot on the entire planet: a massive mountain range called the Maxwell Mountains. The Maxwells tower more than seven miles above “sea level” on Venus — the elevation that geologists use for measuring the height or depth of the planet’s features. What’s even more impressive is that one side of the Maxwell range is quite steep. The mountains climb four miles over a horizontal distance of just six miles — a slope unlike any seen anywhere else in the solar system. Because of their elevation, the Maxwells are one of the coolest spots on the planet. The average temperature is more than 700 degrees, but that’s about 150 degrees below average. And the atmospheric pressure is about half of that at lower elevations. Geologists aren’t sure why the Maxwells are so high. They could be squeezed upward as different sections of Venus’s crust mash together. Or they could be pushed upward as molten rock bubbles toward the surface. Either way, the Maxwell Mountains would be quite a challenge to climb.  Script by Damond Benningfield

It’s hard to look at Hoag’s Object and not think of food. The galaxy’s core looks like an egg yolk, while a ring of stars around it resembles a glazed doughnut. The problem for astronomers is that they’re not sure of the recipe that cooked it up. Hoag’s Object is about 600 million light-years away. It stands high in the southwest at nightfall, just below the semicircle of stars known as Corona Borealis, the northern crown. The galaxy’s ring appears to be giving birth to many new stars. But unlike other ring galaxies, there’s not much material connecting the ring to the core. Hoag’s Object might have started as a spiral galaxy, but was shot through by a smaller galactic “bullet.” The impact would have created ripples that reshaped the spiral. But there’s no evidence of a second galaxy anywhere close. Another possibility is that a second galaxy sideswiped the bigger spiral. The second galaxy would have been pulled apart and its stars and gas incorporated into Hoag’s Object. But there are problems with this idea, too. A third possibility is that the galaxy originally had a long bar of stars across its middle. The motions of the bar would have whipped up the galaxy like egg whites in a blender — yet another reminder of food. So far, astronomers haven’t seen any other galaxies that are just like Hoag’s Object. That leaves them with little help as they try to decipher the recipe for this tasty-looking galaxy.  Script by Damond Benningfield

The swan climbs high across the southern sky on summer nights. It’s marked by its bright tail, the star Deneb. It’s the lower left point of the wide-spread Summer Triangle. The swan’s body angles to the upper right of Deneb, as though the swan were taking flight from a pond. Its long, graceful wings flank its body. The brightest star of the top wing is Delta Cygni. It’s a system of at least three stars. Two of them are a good bit bigger, brighter, and heavier than the Sun, while the third is less massive than the Sun. The heavier stars orbit each other at an average distance of almost 15 billion miles — roughly 150 times the distance from Earth to the Sun. But the little guy is much farther out. It’s possible that when the system was born, the third star was closer in. But as the stars danced their complex orbital ballet, they swapped some of their energy. The lightweight star was pushed outward, while the heavier stars spiraled closer together. Those stars were pushed into a stretched-out orbit that looks a bit like an oval racetrack. It takes the two stars almost 800 years to make one lap around the track. But the lonely third member of the trio needs more time. It takes many thousands of years to orbit its brighter companions. Look for Delta Cygni above Deneb as darkness falls. It’s about a third of the way up from Deneb to brilliant Vega, the brightest member of the Summer Triangle.  Script by Damond Benningfield