StarDate

Learning the constellations can be hard work. Most of their connect-the-dots patterns are faint and difficult to find, especially from light-polluted cities.

Sometimes, though, Mothern Nature offers a sort of cheat sheet — one or more bright objects that point the way. And that’s the case right now for Capricornus the sea-goat.

The constellation is low in the south and southwest as night falls. Its brightest stars outline the bottom of a bikini bathing suit. Once you identify it, you shouldn’t have much trouble finding it again on later nights.

That’s especially true right now, because the solar system offers three bright lights to help you find the sea-goat: Mars, the Moon, and Venus.

Tonight, the Moon is at the constellation’s western edge, so the bathing suit is arrayed to the left of the Moon. Venus, the “evening star,” is below the Moon, just outside the constellation. It’s moving toward Capricornus, though, and will cross its borders in a few nights. It’ll spend the rest of the month transiting the constellation. So if you follow Venus through the end of the year, you’ll see all of Capricornus.

Orange Mars is also moving across the constellation. Tonight, it stands next to Iota Capricorni, a star that’s visible only from areas with dark skies. Early next week, though, Mars will pass by a couple of brighter stars, at the left end of the bikini — helping you learn this famous constellation.

More about the Moon and Mars tomorrow.

Script by Damond Benningfield

The Moon and the planet Venus form a beautiful pairing early tonight. Venus is the brilliant “evening star,” not far to the left of the Moon. They set by about eight o’clock.

Venus looks so bright in part because its atmosphere is topped by an unbroken layer of clouds. The clouds reflect most of the sunlight that strikes them back into space.

Those clouds do something that doesn’t happen on Earth or any other planet in the solar system. They race around Venus much faster than the planet spins on its axis.

Venus takes about 243 Earth days to complete one turn. But the clouds at the top of its atmosphere whip around the planet once every four days — an effect called super-rotation. That means the clouds can complete 60 trips around the planet for every Venusian day. On Earth and the other planets, the clouds rarely move any faster than the planet’s rotation rate.

The cause of the super-rotation is a mystery. Even though planetary scientists have been studying it for decades, they don’t have a good explanation. They do have some ideas, though.

One says that the atmosphere above the clouds interacts with the solar wind — a stream of charged particles from the Sun. That creates waves in the atmosphere, which carry momentum down to the cloudtops, about 40 miles above the surface. That gives the clouds a big push.

But another idea says the super-rotation is driven by pressure from the Sun’s light — revving up Venus’s high-speed clouds.

Script by Damond Benningfield

The days are continuing to get shorter here in the northern hemisphere. That provides a lot of time to get out and enjoy the night skies. But over the next few weeks, one part of that trend will reverse. The Sun will begin to set a little later each night — even though the shortest day of the year is still weeks away.

The shortest day is the winter solstice, on December 21st. So between now and then, the total amount of time between sunrise and sunset will shrink. Yet the date of earliest sunset comes before the solstice.

There are a couple of reasons for that. One is Earth’s tilt on its axis, which causes the angle and location of sunrise along the horizon to change from day to day. The other is Earth’s lopsided orbit, which causes the Sun to return to the same point in the sky a little earlier or later in the day depending on whether we’re close to the Sun or far away.

When you add these factors together, you find that the date of earliest sunset works its way from south to north. For the latitudes of Honolulu and Miami, the earliest sunsets happen about now. For higher latitudes, such as Denver, they’ll take place in another week or so. And for cities that are even farther north, like Anchorage, earliest sunset happens just a few days before the solstice.

To balance things out, the date of the latest sunrise comes after the solstice, working from north to south — a few more minutes of darkness before the dawn of another day.

Script by Damond Benningfield

When an earthquake and tsunami damaged a nuclear power station in Japan a few years ago, engineers were pretty sure that some of the reactors suffered a complete meltdown. But they couldn’t go inside to see the extent of the damage. Instead, last year they took the equivalent of a cosmic X-ray. They used cosmic rays to map the interior of the reactors.

Cosmic rays are subatomic particles that hit Earth at almost the speed of light. Most of them appear to come from exploding stars. They strike molecules high in the atmosphere, creating showers of other particles, including muons. On average, several muons pass through your body every second.

Muons can pass through just about anything — even solid rock. So scientists have been using them to look into big objects on or below the surface. Looking at how muons pass through an object, or scatter off of it, reveals some of the object’s interior structure.

50 years ago, a physicist used muons to look for hidden chambers in the Great Pyramid of Khufu in Egypt. Since then, others have developed ways to examine cargo ships for nuclear weapons, to inspect concrete slabs and buried pipes, and to study the interiors of nuclear reactors, such as the ones in Japan.

Geologists have used muons to look deep into volcanoes, and they’re evaluating the technique as a way to find good underground chambers for storing carbon — exploring our own planet with the byproducts of exploding stars.

Script by Damond Benningfield

The Sun’s interactions with Earth are part sword, part shield. Outbursts from the Sun pelt our planet with radiation and charged particles. That can knock out satellites, damage power grids, and cause other problems.

On the other hand, the Sun shields Earth from cosmic rays — charged particles from exploding stars and other sources. These particles hit molecules in the upper atmosphere, creating showers of other particles that then hit the surface.

These particles may help trigger lightning, and may even play a role in cloud formation. Over the course of a year, they also contribute a bit more than one-tenth of the radiation dosage that most people receive from the natural environment. The levels are higher for airline pilots, who may receive half of their radiation from cosmic rays.

The level of cosmic rays varies, thanks largely to the Sun. Our star generates a strong magnetic field, which deflects many of the particles that make up cosmic rays. So without the Sun’s magnetic field, we’d all get zapped by more of them.

The Sun’s field is especially strong when the Sun belches out more of its own particles toward Earth. During those active periods, the number of incoming cosmic rays drops dramatically.

A few studies have even shown that the number of deaths caused by heart attacks goes down when solar activity goes up — suggesting that we need the solar shield to protect us from cosmic rays.

We’ll have more about cosmic rays tomorrow.

Script by Damond Benningfield

Our planet is constantly pelted by energy and particles — from sunlight to tiny grains of comet dust. But some of the particles that hit us may come from a great deal farther — from black holes and exploding stars in other galaxies.

These particles are known as cosmic rays. Most of them are bare protons — the nuclei of hydrogen atoms. A few are the nuclei of helium atoms, while about one percent come from even heavier elements.

Cosmic rays were discovered more than a century ago, but the details of their origin remain a bit mysterious. In part, that’s because they don’t travel to us in a straight line. They have an electric charge, so they’re pushed around by magnetic fields. Since they zigzag through space before reaching Earth, we can’t trace where they come from.

But studying the types of particles that make up cosmic rays provides some clues. The proportion of heavy elements is much higher than in the universe overall, for example. That suggests that many cosmic rays come from heavy-element factories — the exploding stars known as supernovae. Such a star produces some of the elements before it explodes, and others during the blast itself. It also produces a shockwave that could accelerate the particles to almost the speed of light.

Some cosmic rays may be created by giant black holes in the hearts of distant galaxies — particles dispatched across the vast cosmos many millions of years ago.

More about cosmic rays tomorrow.

Script by Damond Benningfield

If you’re an Earthling, you probably think that all stars are nice round balls. After all, our star, the Sun, certainly is. But if you lived around another star, you might have a different opinion, because some stars spin so fast that they bulge out at the middle like a squashed beachball.

A prime example is the luminary of the constellation Eridanus, which flows low across the south tonight. Achernar spins so fast that its equator bulges outward. It’s about 10 million miles in diameter through the equator, but only about seven million through its poles. For comparison, the Sun\'s diameter is a little less than a million miles no matter how you measure it.

Achernar is 140 light-years from Earth, and it’s one of the 10 brightest stars in the sky. It’s hotter than the Sun, which makes its surface look blue — if you’re lucky enough to be able to see it. The trouble is, Achernar is so far south that, for most Americans, it stays below the horizon. Only those in Hawaii and southern Texas and Florida can see it.

Although Achernar is brilliant, its constellation is not. The star is at the southern end of Eridanus, which represents a river. In fact, the star’s name derives from Arabic words that mean “end of the river.” If you have a dark sky, you can see most of the rest of Eridanus. But you’ll have to travel south to see its brightest star, Achernar — a star that spins so fast that it has a bulging waistline.

Tomorrow: cosmic bombardment.

Script by Ken Croswell, Copyright 2016

Harry Potter fans may boo when they hear its name, but Bellatrix, one of the stars of Orion, is nothing to sneer at. It’s one of the hottest, brightest stars in the neighborhood. It forms one of the shoulders of Orion, the hunter. It climbs into good view by 8 or 9 o’clock, to the upper right of the hunter’s other shoulder, bright orange Betelgeuse.

J.K. Rowling filled the Harry Potter universe with characters named for stars and constellations. The best known are Sirius Black, Harry Potter’s godfather, and Black’s cousin, Bellatrix Lestrange, a nasty follower of Lord Voldemort.

The star Bellatrix isn’t nasty at all. In fact, it’s quite impressive. It’s much hotter than the Sun, and thousands of times brighter, so it’s easy to see even though it’s about 250 light-years away.

The key to the star’s power is its mass — about nine times the mass of the Sun. Heavier stars burn through the nuclear fuel in their cores in a hurry, so they produce far more energy than stars like the Sun.

But they also live much shorter lives. In fact, even though it’s only about a half a percent the age of the Sun, Bellatrix is nearing the end of its life. It’s not massive enough to explode as a supernova, so its fate most likely is similar to that of the Sun. In a few million years, it’ll cast its outer layers into space, leaving only its hot, dead core. This tiny ember will be far too faint to see from Earth, so one of Harry Potter’s greatest foes will fade from view.

Script by Damond Benningfield

Lewis Rutherfurd was a picture of early American aristocracy. Various ancestors had served as the first governor of New Jersey, signed the Declaration of Independence, and served in the U.S. Senate. Rutherfurd went to law school with a future Secretary of State, and set up practice with the son of the first Chief Justice.

Yet Rutherfurd turned away from law and politics to pursue an even higher ambition: astronomy. He was an early pioneer in the field of astrophotography, and in studying the composition of the stars.

Rutherfurd was born 200 years ago today in what is now the Bronx. He studied science at college before earning his law degree, and soon turned to astronomy. In 1856, he built a private observatory at his house in New York, where he soon snapped his first pictures of the Moon.

Rutherfurd was an inventive thinker, and he designed his own telescope — one that served as a camera lens. That allowed him to take some impressive photos of the Moon, star clusters, and other objects.

Before long, Rutherfurd applied his talents to spectroscopy, which reveals important details about astronomical objects. He created instruments that allowed him to make highly detailed observations, and used them to devise a way to classify stars.

Rutherfurd’s work made him part of the American scientific aristocracy. He was a founding member of the National Academy of Sciences, for example — an honor earned through his valuable contributions to astronomy.

Script by Damond Benningfield

As the Moon orbits Earth, its gravitational pull creates tides in our oceans. And Earth returns the favor — its gravity creates tides in the lunar crust.

The big moons of the planet Jupiter also experience the effects of tides. Each one feels a tug of war between Jupiter and the other moons. That creates tides that can have dramatic effects. Io, for example, is covered by hundreds of volcanoes — fed by rock that’s melted by powerful tides inside the moon.

The moon Europa experiences tidal effects as well. Its interior is pulled and squeezed, generating heat that melts some of the ice below its crust — producing a global ocean. It probably contains more water than all of Earth’s oceans combined.

There’s evidence that some of the water in that ocean squirts high above Europa — perhaps through cracks in the crust created by the tides.

Hubble Space Telescope has detected possible plumes of water shooting out from near the south pole. They rise up to 125 miles above the surface. Most of the water probably falls back onto Europa, creating fresh ice.

The discovery means that a future spacecraft may be able to sample Europa’s ocean without drilling through its ice — simply by flying through plumes of water created by the tides.

Look for Jupiter to the upper right of our own moon at first light tomorrow. It looks like a brilliant star. The true star Spica, which is fainter than Jupiter, is to the lower right of the Moon.

Script by Damond Benningfield