StarDate

When it was completed in 1948, the 200-inch telescope at Palomar Observatory in California was the biggest telescope in the world. It was so big, in fact, that astronomers operated it from inside a small “cage” in the top of the telescope tube. They had to manually point the telescope to keep it aimed at the right spot.

Today, the astronomers stay in a warm control room — or even at home — and let computers do the pointing. So do the astronomers who use almost any big telescope in the world. Computers also collect and store the observations, process them, and send them out to the right people. They conduct much of the analysis — sometimes with little human guidance. And they allow astronomers to “see” their observations in new ways — visualizing parts of the universe we can’t possibly see.

In other words, as with much of present-day life, astronomy would look quite different without computers.

And over the next few decades, automation will accelerate. In part, that’s driven by new projects and telescopes that are gathering enormous amounts of data — terabytes every night. That’s just too much for humans to handle.

So astronomy is using techniques from artificial intelligence to teach computers how to sort through massive amounts of data. That will detect patterns where none were seen before, or reveal a single rare object hiding among billions of stars and galaxies — leading to new discoveries about the universe.

More tomorrow.

Script by Damond Benningfield

As the Sun sets, its lingering light creates a zone between daylight and darkness: the twilight zone. It typically lasts for about an hour, as Earth’s atmosphere scatters some sunlight back into the region where the Sun has already set.

There’s a twilight zone on the Moon, too, but it’s quite different from the one here on Earth. There’s a sharper boundary between day and night, with little sunlight reflected into the nightside.

The line between day and night is known as the terminator. It’s obvious as you watch the Moon descend the western sky this evening, with the bright star Regulus off to the left of the Moon. The terminator is bringing daylight, so more and more of the lunar disk will be illuminated over the next few days.

Here on Earth, the terminator moves at more than a thousand miles an hour at the equator. But the Moon is much smaller than Earth is, and it turns much more slowly. That combination means that a jogger could outrun the terminator, as it glides along at just 10 miles an hour.

There’s no atmosphere on the Moon to speak of, so the terminator is quite sharp. As it passes, it’s almost like someone flipped a light switch — it’s dark one second, and daylight the next.

But there is a bit of twilight. Radiation from the rising Sun can make tiny grains of dust float high into the sky. These grains form a glowing layer that reflects a little sunlight back into the nightside — giving the Moon a “twilight zone” of its own.

Script by Damond Benningfield

Dark spots sometimes dot the surface of the Sun — magnetic storms that can last for days or weeks. But the storms on other stars can make those on the Sun look puny. They can be so monstrous that they can change the star’s brightness by quite a bit.

An example is one of the stars of Cor Caroli — the Heart of Charles. As seen by the eye alone, it’s the brightest star of Canes Venatici, the hunting dogs. It’s to the right of the handle of the Big Dipper as night falls, and wheels above the dipper later on.

Cor Caroli consists of two stars in a wide orbit around each other. One of the stars is about half again as massive as the Sun, and several times brighter. The other is about three times the Sun’s mass, and if you add up all forms of light, more than a hundred times brighter.

But over a period of about five and a half days, the star’s brightness at visible wavelengths varies by about 15 percent. And that’s because of the starspots.

The star’s magnetic field is hundreds of times stronger than the Sun’s. That produces giant spots — far bigger than anything ever seen on the Sun. The spots are much cooler than the surrounding gas. And they contain large concentrations of heavy elements that have been dredged up from deep inside the star. The combination makes the spots dark. As the star rotates, the spots move in and out of view, causing the star to get fainter and brighter — a big change for the Heart of Charles.

Script by Damond Benningfield

A modest meteor shower should be at its best tonight. You need dark skies to see it — the glow of city lights will erase it from view. And even at its peak, the shower produces no more than a dozen or so meteors per hour. But the Moon won’t get in the way, so if you have good weather and a good viewing spot, it’s worth a look.

The Lyrid shower occurs at this time every year as Earth passes through a trail of comet dust — debris from Comet Thatcher.

The comet last visited the inner solar system in 1861, and it won’t return for almost three centuries. But each time it approaches the Sun, it sloughs off bits of rock and dirt. Over time, these particles spread out along the comet’s orbital path. When Earth flies through that path, some of the grains of material slam into our planet’s atmosphere at tens of thousands of miles per hour. They quickly vaporize, forming the glowing streaks of light known as meteors.

The shower is named for the constellation Lyra, the harp. That’s because its meteors all appear to “rain” into the sky from near Vega, Lyra’s brightest star. They can fly across any part of the sky, though, so you don’t need to be looking at Lyra to see them.

The best view comes after Lyra climbs into good view, after midnight. The Moon sets a little later, making the skies nice and dark. That will provide several good hours to watch the meteors — reminders of a comet that’s billions of miles from Earth.

Script by Damond Benningfield

The little planet Mercury just peeks into view in the dawn sky over the next couple of weeks. It’s hard to find, though, especially from more northerly latitudes.

Mercury is the smallest major planet in the solar system. It’s also the closest to the Sun. And it has the largest core in relation to its size — the core of iron and nickel makes up about two-thirds of Mercury’s diameter.

Earth and the other inner planets have much thicker layers around their cores. Since Mercury formed at the same time, from the same raw ingredients, that suggests it originally had thicker outer layers, too. If so, then something must have stripped much of those layers away.

One possibility is that the young Mercury was hit by another large object. The impact blasted much of the material in the planet’s outer layers into space. The same thing probably happened to the young Earth, with much of the expelled material forming the Moon.

But it’s also possible that Mercury never grabbed enough material to form thick outer layers — it’s always been about the same size it is now. Observations by a Mercury-orbiting spacecraft seem to support this idea, although they couldn’t confirm it.

Whatever Mercury was like in the beginning, you can see it now in the eastern sky in the early morning twilight. It looks like a fairly bright star. It’s quite low, though, so you need a clear horizon to spot it. The planet stands a little higher as seen from more southerly latitudes.

Script by Damond Benningfield

The remnants of an exploded star are changing right before our eyes. Debris from the explosion is expanding. And the star’s “corpse” produces radiation and winds that sculpt the region around it.

The Crab Nebula stands close above the Moon this evening. It’s an easy target for small telescopes. Its filaments of gas and dust resemble the outline of a crab.

A century ago, astronomers compared pictures of the Crab taken several years apart. They found that the nebula was expanding. By determining the nebula’s distance, they calculated the rate of expansion — more than two million miles per hour. From that, they calculated that the Crab started expanding almost a millennium earlier. That corresponded to a bright “new” star seen in the year 1054. For several weeks, it was bright enough to see during the day.

Today, we know that the star was a supernova — the explosion of a star that was much heavier than the Sun. When the star exhausted the nuclear fuel in its core, the core collapsed, forming an ultra-dense neutron star. The star’s outer layers then exploded. We see those layers as the filaments that form the crab.

The dead core spins about 30 times a second, producing “pulses” of energy with each turn. The star also generates a powerful magnetic field and “winds” of charged particles. They sculpt material near the dead star. The wind also helps drive the expansion of the nebula — an expansion that’s easy to see.

Script by Damond Benningfield

The Moon is a bit more than 236,000 miles from Earth this evening — a couple of thousand miles closer than average.

The Earth-Moon distance changes from day to day because the Moon’s orbit is lopsided. The average distance between Earth and Moon changes, too — by an inch and a half per year.

Scientists measure the distance by bouncing laser beams off special reflectors carried to the Moon by Apollo astronauts, and on the Soviet Union’s unmanned rovers. The experiments — most of which have been conducted at McDonald Observatory — reveal the Moon’s distance to within a fraction of an inch. Over the decades, they’ve shown that the Moon is inching away.

The change is caused by the gravitational interaction between Earth and the Moon. As the Moon orbits Earth, its gravitational pull creates tides, causing Earth to rotate a bit slower. But the overall momentum in the Earth-Moon system stays constant. So to balance the slowdown in Earth’s rotation, the Moon moves farther away.

Models suggest that the Moon formed when another planet hit the young Earth, blasting debris into orbit. The Moon coalesced from that debris at a distance of just 25,000 miles. At the same time, Earth’s day probably lasted just six hours. So a night was barely long enough for a stroll under the brilliant Moon.

Look for the Moon in the west during twilight this evening. The star Aldebaran will stand close to the upper left of the Moon.

Script by Damond Benningfield

The clouds on Venus are beautiful to look at, but you wouldn’t want to fly through them. That’s because they’re made of sulfuric acid — a compound that can eat through just about anything.

The clouds cover the entire planet — there are no gaps anywhere. That blocks Venus’s surface from view; the only direct looks have come from Russian probes that died soon after landing.

The clouds are about 15 miles thick, and they top out at an altitude of about 40 miles. Above that, there’s a thin haze of sulfuric acid that extends miles higher. And acid rain falls from the clouds. Venus’s atmosphere is so hot and dense, though, that the raindrops evaporate high above the surface.

Like the droplets of water in the clouds here on Earth, the droplets of acid can have a strong electric charge. When enough of a charge builds up, it can trigger lightning. In fact, an orbiting spacecraft detected the “crackle” of a lot of lighting on Venus, suggesting it has frequent storms.

And the clouds are whipped around Venus by strong winds. They hit more than 200 miles per hour at the top of the clouds, although they’re much weaker at the bottom of the clouds.

Finally, the clouds reflect most of the sunlight that strikes them, which makes Venus shine brightly. And you can see just how brightly early tonight. Venus is the brilliant “evening star,” low in the west at sunset. It’s especially prominent tonight because it stands close to the crescent Moon.

Script by Damond Benningfield

The word “planet” comes from a Greek word that means “wanderer.” The title was bestowed because, over time, each of the bright planets moves against the background of “fixed” stars.

Occasionally, though, a planet stops wandering and stands still against that background — it’s stationary.

The planets Mercury and Saturn both reach such a standstill this month. For a while, each will move in sync with the surrounding stars, like members of a band marching in a parade — the result of our changing viewing angle.

Saturn, for example, spends most of the year moving from west to east across the stars. But Earth follows a smaller orbit around the Sun. So once every 13 months, our planet passes Saturn and pulls ahead of it. As it does so, the viewing angle changes, causing Saturn’s position against the stars to shift. When the angle is just right, Saturn appears to stop moving at all.

And despite what astrology tells us, there is no cosmic significance to Saturn or any other planet standing still. It’s part of the eternal cycle of the planets as they “wander” across the night sky.

Look for Saturn standing almost due south at first light. It looks like a bright golden star, with the orange planet Mars close to the lower left. They’re above the “teapot” outlined by the stars of Sagittarius. Over the coming days, Saturn will maintain its position relative to those stars, while Mars moves away from them, eastward across the starry background.

Script by Damond Benningfield

The astronomers of the 17th, 18th, and 19th centuries just loved to draw constellations — dozens of them. They drew some of them in regions with only faint stars. And they carved off pieces of existing constellations. Some of those creations are still in use today. But many more have been abandoned — the ghosts of constellations past.

A couple of examples sit on the back of Camelopardalis, the giraffe — one of the 17th-century creations that’s still around. One is the reindeer, while the other is the harvest keeper. Both of them were created to honor the science of the day.

French astronomer Pierre Charles Le Monnier created the reindeer in 1736. Le Monnier had been a member of an expedition to Lapland — northern Finland. The expedition was organized to measure Earth’s shape. And it found that our planet isn’t a sphere. Instead, it’s figured a bit like a pear. Le Monnier figured that the reindeer was a good symbol of Lapland, so he chose it to represent the expedition in the stars.

The harvest keeper was created in 1775 by Jerome Lalande, another French astronomer. The new constellation honored Charles Messier — one of the leading “harvesters” of comets. In fact, the constellation was also known simply as Le Messier, especially in France.

Both of these constellations were published in several atlases. Eventually, though, they fell out of use. Today, they’re extinct — the ghosts of constellations that didn’t survive.

Script by Damond Benningfield