StarDate

Jules Verne wrote science fiction, not fact. Yet his books inspired many youngsters to become scientists or engineers — turning science fiction into fact.

An example is Hermann Oberth, one of the pioneers of early rocketry. He was born 125 years ago today in Transylvania. He began reading Verne’s novels at age 11, especially those about trips to the Moon. Oberth was so entranced that he built his own rocket at age 14.

Oberth briefly abandoned rocketry to follow his father’s example and study medicine, in Munich. But he was drafted into the army during World War I, where he decided to return to his rockets.

Oberth wrote a college dissertation on rockets, but it was rejected. So he arranged to have it published as a booklet. It became popular, allowing him to pursue his research. He designed a liquid-fueled rocket engine, and launched it in 1931 — assisted by a young Wernher von Braun, future builder of the American Moon rockets.

Oberth worked with von Braun during World War II on Germany’s V-2 rocket, which was built with slave labor and aimed at civilian targets.

Years later, Oberth again joined von Braun — this time working for the U.S. Army in Alabama. He retired to Germany a few years later. But he returned to the United States in July 1969 to watch the launch of Apollo 11, the first manned mission to the Moon. It was a flight made possible in part by Oberth’s contributions to the early days of rocketry.

Script by Damond Benningfield

The Milky Way is beginning its journey into summer’s evening skies. It arcs low across the east as night falls. It’s anchored by teapot-shaped Sagittarius in the south, the graceful swan in the east, and W-shaped Cassiopeia in the north. It climbs higher during the night, and passes directly overhead in the wee hours of the morning.

That hazy band of light outlines the disk of the Milky Way galaxy. The disk contains hundreds of billions of stars, plus giant clouds of gas and dust.

Yet most of what makes up the Milky Way is dark matter. It emits no detectable energy. But it reveals its presence by tugging at the visible matter. And a team of astronomers recently used that tug to measure the mass of the Milky Way: 1.5 trillion times the mass of the Sun — one of the most impressive galaxies around.

The study used observations from two space telescopes, Gaia and Hubble. They measured the motions of globular clusters — densely packed balls of hundreds of thousands of stars. The clusters form a vast “halo” around the galaxy’s center. The halo extends far beyond the Milky Way’s disk, into a region that’s dominated by dark matter. How fast the clusters move depends on the combined mass of the dark matter and visible matter.

The telescopes provide the best measurements of the motions of the clusters to date. Because of that, the astronomers say their study also should provide the best measurement of the Milky Way’s mass.

Script by Damond Benningfield

The sharpest “eyes” to ever gaze down upon the Moon arrived at the Moon 10 years ago today. Since then, LRO — Lunar Reconnaissance Orbiter — has compiled the most detailed maps of the Moon to date. And its images will help scientists and engineers pick landing spots for future missions.

LRO carries several instruments. Perhaps the key instrument is a camera system. It’s mapped almost the entire lunar surface, showing details as small as a few feet across.

Other instruments have mapped the mineral composition of the surface. They’ve mapped the contours of the surface in detail, providing 3D views of mountains, craters, valleys, and other features.

LRO has looked into dark craters at the lunar poles. Those observations support the idea that pockets of ice lie at the bottoms of some of those craters. The ice could be a great resource for lunar bases, providing water, oxygen, and rocket fuel.

LRO has supported planning for human exploration in other ways as well. It’s measured how much radiation from the Sun and beyond rains down upon the Moon. And it’s measured how often the Moon gets hit by space rocks. Planners need to know about those hazards as they try to design safe habitats for explorers.

LRO has also photographed the landing sites of earlier explorers: the Apollo astronauts. The pictures even show the trails the astronauts left in the dirt — evidence of early explorers snapped by one that’s still going strong.

Script by Damond Benningfield

When we gaze into the night sky, it’s like looking at a projection on a giant dome — we see two-dimensional pictures, with no perception of depth. Even astronomers can have a hard time plotting that third dimension — a difficulty that can skew their understanding of how stars work.

Consider the Coathanger, a pattern of 10 stars that looks like an upside-down coat hanger. It’s in the faint constellation Vulpecula, the fox.

For decades, astronomers thought those stars formed a cluster. A cluster’s stars are all the same age and same distance, and they formed from the same ingredients. But some of its stars are small and light, while others are big and heavy. Seeing how the different weight classes have evolved helps astronomers understand how all stars age.

But a study in 1970 found that only a few of the Coathanger’s stars were related. And a later one, which used a satellite to plot the distances to stars with great precision, found that none of them were related — they just happened to line up in the same direction. So plotting the third dimension robbed the Coathanger of some of its scientific value — but none of its beauty.

The Coathanger is a great target for binoculars. Sweep them from the bright star Altair, which is low in the east at nightfall, toward even brighter Vega, far to its upper left. The Coathanger is about a third of the way along that line — a beautiful grouping that’s not really a group at all.

Script by Damond Benningfield

Meteorologists will tell you that summer started on June 1st. Students in Spokane, Washington, will tell you that it started last week, when the school year came to an end. And astronomers will tell you it starts today, when the Sun is farthest north for the entire year.

All three dates are perfectly valid. The meteorological calendar, for example, groups the months by weather conditions. For the northern hemisphere, it’s hottest in June, July, and August, so it makes sense for summer to start on June 1st.

For many families, the calendar that really matters is the school calendar. It’s not as consistent as the other types of calendars, though. Depending on the district, classes can end anywhere from late May to mid June, so summer gets rolling on different dates. That means that summer ends on different dates, too — between mid-August and early September.

The astronomical seasons are based on the motions of the Sun across the sky. As Earth orbits the Sun, our star moves north and south across the sky. The Sun actually stays put. It appears to move because Earth is tilted on its axis. The north and south poles “nod” toward the Sun at different times of year.

The seasons are defined by four points in the Sun’s motion: when it appears farthest north and south, and when it crosses the equator. It’s farthest north today, at 10:54 a.m. Central Daylight Time — the summer solstice — the start of astronomical summer.

Script by Damond Benningfield

Summer arrives in the northern hemisphere tomorrow morning. At that moment — the summer solstice — the Sun will stand farthest north for the entire year. It will stand directly overhead for skywatchers at 23-and-a-half degrees north latitude. That line is called the Tropic of Cancer, because several thousand years ago, the Sun appeared in the constellation Cancer at the solstice.

Today, though, the Sun is a long way from Cancer. Just hours after the solstice it enters Gemini, which is 30 degrees away from the crab — one-twelfth of the way across the sky.

The stars of Cancer haven’t moved much since the constellations were first drawn. The stars are all so far away that they appear to remain fixed in space — even over hundreds or thousands of years.

The Sun is moving into Gemini because of an effect called “precession of the equinoxes.” The gravitational tug of the Sun and Moon cause Earth to wobble on its axis like a spinning gyroscope. It completes one wobble every 26,000 years. As the planet wobbles, the north pole draws a circle on the sky, so it points to different stars — giving us a different Pole Star every few thousand years.

The wobble also causes the Sun’s path across the sky to change. The Sun doesn’t move any differently, but our view of the Sun against the starry background changes. Because of this, today the Sun is almost ready to move into Gemini — not Cancer.

Script by Damond Benningfield

The stars in a binary system can be quite intimate. One star can take material off the surface of its companion, for example. And in extreme cases, the stars can even merge, forming a single star. That can make the stars look a lot younger than they really are.

Many examples of such stars are found in Messier 10. It’s a globular cluster — hundreds of thousands of stars all packed into a ball a few dozen light-years across.

The cluster includes an unusually larger number of blue stragglers — stars that look a lot younger and bluer than the cluster should contain.

The cluster itself is billions of years older than the Sun. It probably was born with many hot, blue stars. But such stars burn out quickly. So there’s no way that any of M10’s original blue stars could still be around.

Instead, the blue stragglers probably were rejuvenated. Some appear to have stolen gas from a companion. The extra material “revs up” the nuclear reactions in the recipient, making it look much younger than it really is.

Other blue stragglers may be the results of binary mergers — the two stars spiral together. That would increase the rate of nuclear reactions as well — turning two old stars into what looks like a brand new one.

Messier 10 is in Ophiuchus, the serpent bearer. The cluster is in the southeast as night falls, well to the upper left of the brilliant planet Jupiter. Through binoculars, it looks like a hazy smudge of light.

Script by Damond Benningfield

Saturn’s moons and rings have a complicated relationship. Some of the moons act as shepherds, keeping the ring particles in line. Other moons supply some of the material that makes up the rings. At the same time, bits of ice and dust from the rings coat some of the moons.

Earlier this year, in fact, scientists reported evidence that ring material is coating five small moons. All of the moons are near the outer edge of the main bands of rings.

The two of the moons that are closest to Saturn appear to have a fluffy coating with a slightly reddish color. The coating probably consists of particles of dust from the nearby rings, which are also slightly red. The coatings have built up around the moons’ equators, so the moons are elongated instead of round.

The three other moons are a little farther from Saturn — just beyond the outer edge of the rings. They look blue and icy. That suggests they are coated with ice from another moon, Enceladus. Geysers of water and ice shoot out from its south pole. The ice forms a thin outer ring around Saturn. But some of it drops toward the planet. The ice can add to the main rings, fall into Saturn’s atmosphere — or add a frosty coating to Saturn’s other moons.

Saturn appears near our own moon tonight. It’s just a whisker above the Moon as they climb into view in late evening. The giant planet looks like a bright star. It’ll be a little farther to the right of the Moon at first light tomorrow.

Script by Damond Benningfield

The Sun can turn nasty. But we don’t know just how nasty it can get. Astronomers have been keeping a close eye on it with telescopes for only a couple of centuries. In the lifetime of the Sun, that’s barely the blink of an eye. So scientists are looking farther into the Sun’s past — through tree rings and layers of ice that are hundreds or thousands of years old.

The Sun turns “nasty” when it produces big explosions of energy and charged particles. They can damage orbiting satellites, interfere with aircraft schedules, and knock out power grids on the ground. The largest of these explosions yet seen came in 1859. But no one knows how much bigger such outbursts might get. And that means no one knows how to prepare for the worst the Sun can give us.

Scientists had already found evidence of two big outbursts in tree rings and ice cores — layers of ice pulled up from far beneath the surface. The biggest happened more than 1200 years ago.

A recent study found evidence of a third — about 2700 years ago. Researchers studied ice cores from Greenland. They found high concentrations of a radioactive form of beryllium. They also found high levels of other radioactive elements, both in the ice and in tree rings from that era.

Those elements formed when particles from a solar storm slammed into Earth’s atmosphere. The radioactive elements then fell to the surface — carrying evidence of a powerful blast from the Sun.

Script by Damond Benningfield

The solar system serves up a couple of beautiful pairings just after sunset this evening. One of them disappears with the twilight. But the other will be on magnificent display all night long.

The planets Mercury and Mars are quite low in the west-northwest a half hour after the Sun drops from view. Mercury is bright, so it’s a fairly easy target, although you need a clear horizon to spot it. Mars is only a few percent as bright as Mercury. But it’s only a degree or so to the upper left of Mercury, which can help you pick it out.

Mercury and Mars will vanish by about the time the sky gets fully dark, as they follow the Sun below the horizon.

As that happens, though, the other pair will be climbing skyward in the southeast: the full Moon and the planet Jupiter, which looks like a brilliant star to the upper right of the Moon.

Both worlds align opposite the Sun right now, so they’re in view all night. Their path stays quite low in the south, though, so they won’t climb very high into the sky.

That path is known as the ecliptic. Technically, it’s the Sun’s path. But the Moon and planets stay quite close to the ecliptic, so they outline the Sun’s annual migration across the sky. Mercury and Mars, for example, are near the western edge of the constellation Gemini — just where the Sun will stand in a few weeks. And the Moon and Jupiter are in southern Ophiuchus — the Sun’s home in the first half of December.

Script by Damond Benningfield