StarDate

George Ellery Hale built his first telescope when he was 14 years old. And just a decade later, as a young astronomer at the University of Chicago, he saw a chance to build one of the largest telescopes in the world. It became the centerpiece of Yerkes Observatory, on the shore of Lake Geneva in Wisconsin, which was dedicated 125 years ago today.

The observatory was named for Charles Yerkes, a shady businessman who controlled the Chicago subways.

The telescope was a 40-inch refractor, which focuses light with lenses. Astronomers used it to help establish the new field of astrophysics — analyzing what makes stars and other objects tick. They studied binary star systems, how stars evolve, the dust and gas between the stars, and much more.

In 1932, Chicago and the University of Texas joined forces to establish McDonald Observatory, with the Yerkes director overseeing both of them. The partnership lasted until the 1960s.

Viewing conditions at Yerkes weren’t always the best. And by the 21st century, the 40-inch telescope couldn’t compete with more modern facilities. So Chicago closed the observatory in 2018, then sold it — although it kept its collection of 170,000 photographic plates.

The new owners reopened the site this year for tours, outreach programs, and special events — providing access to one of the most important observatories of the 20th century.
 

Script by Damond Benningfield

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If you poke around any observatory that’s been around a while, you’re likely to find a room filled with treasure: pictures of the sky shot on glass plates. Many of the plates are old and brittle. Some have been damaged by water or other hazards. But almost all of them still have scientific value. And astronomers are trying to preserve them in both physical and digital form.

The first glass-plate images were shot in the mid-1800s. Over the next century or so, they were the main way to record the universe. Some are just a few inches per side, while many others are close to a foot across.

Today, astronomers use those plates to study how the universe has changed. They can watch the expansion of clouds of gas and dust ejected from dying stars, for example. They can extend their plots of the motions of binary stars, asteroids, and many other objects, providing better calculations of their orbits. And they can see how stars have changed brightness, helping understand what caused the changes in the first place.

Saving the plates isn’t easy. They have to be carefully calibrated, and researchers have to find out how and when the plates were shot.

Even so, astronomers are making progress. Harvard College Observatory has digitized about half a million plates. Another group has gathered more than 400,000 from several small observatories. And this year, a group in Europe finished processing almost a hundred thousand — keeping these astronomical treasures alive.
 

Script by Damond Benningfield

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The Orionid meteor shower is building toward its peak the next couple of nights. At its best, you might see a dozen or more “shooting stars” per hour — glowing sparks high in the sky.

Those sparks are debris from Comet Halley. As it approaches the Sun, some of the ice at its surface vaporizes. That releases solid particles of rock and dust. Those bits of debris spread out along Halley’s path.

Earth intersects that path a couple of times every year. When it does, it sweeps up some of the comet dust. The particles slam into the atmosphere at tens of thousands of miles per hour. They quickly vaporize, forming the glowing trails known as meteors.

The brightness and duration of each meteor depends on the size and composition of the particle. Larger particles form brighter trails. The brightest are formed by bits of debris the size of a plum or larger. But most are no bigger than pebbles.

The Orionids aren’t named for Halley’s comet. Instead, the name indicates where the meteors appear to enter the atmosphere — near a star in Orion. But you don’t have to look toward the constellation to see the meteors — they can blaze across any part of the sky.

To watch the shower, find a dark, safe viewing spot far from city lights. The best viewing time is in the hours before dawn. The Moon will be in view for part of that time, but it’s a waning crescent, so most of the meteors will shine through.
 

Script by Damond Benningfield

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Summer ended almost a month ago, but some of the stars of summer are still hanging around. And some of them will remain in view until well into winter.

On the other hand, a few others are taking their final bows. Scorpius, for example, is quite low in the sky as darkness falls. Some of the stars that outline its curving body have dropped below the horizon by then, and some others are so faint that you can’t really see them. Its bright heart, Antares, should be visible for a few days longer, in the southwest. But it’s so low that you need a clear horizon to spot it.

Sagittarius, the archer, stands to the upper left of Scorpius. Some of its bright stars form the outline of a teapot. It’s tilted to the right, as though pouring its brew onto the scorpion’s tail. It will linger until around Thanksgiving.

Arcturus, the brightest star of Boötes the herdsman, is dropping lower in the west, but it, too, should remain visible through the end of the month.

After that, the only holdout is a star pattern named for the season: the Summer Triangle. Right now, it stands directly overhead as night falls, marked by the bright stars Vega, Deneb, and Altair. Because of their high northern latitudes, the stars are in view in the evening sky most nights of the year. And all three will remain in view well into January — bringing a bit of summer to the night skies of winter.
 

Script by Damond Benningfield

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Stellar nurseries are scattered throughout the galaxy — giant clouds of gas and dust that are collapsing to make new stars. Many of them are big, and most are far away. But a fairly small one is just 350 light-years from home. And it’s one of the youngest nurseries as well — only about five-and-a-half million years old.

The nursery is known as the Epsilon Chamaeleontis Association. It’s in the constellation known as the Chamaeleon, which is too far south to see from the United States.

Astronomers have logged only a few dozen stars in the cluster. Most are smaller and fainter than the Sun. The list also may include something rare: a quintuple system.

Despite its small size, the cluster is a great place to watch the process of starbirth. The stars were all born at the same time, in the same place, and from the same material, so it’s easy to compare them.

It’s also a good place to look for the birth of planets. A planet is born from gas and dust left over from the formation of a star. But it’s uncertain just how the process plays out. Having so many young stars to observe may help astronomers figure it out. So far, they haven’t found any planets in the cluster. But they’ve seen several stars that are encircled by disks of gas and dust. And there’s evidence that one of the disks contains a giant planet.

So astronomers will keep an eye on Epsilon Cam as it gives birth to more stars — and maybe planets.
 

Script by Damond Benningfield

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When you fly across several time zones, it takes your body a while to adjust — to reset its internal clock to its usual rhythm. It gets help from the Sun — the 24-hour cycle of day and night.

Sometime in the future, people may experience the biggest jet lag of all — a trip to Mars. But adjusting to Mars time might not be all that difficult. For one thing, the length of a day on Mars is only about 40 minutes longer than an Earth day. And for another, research has shown that the human body actually prefers a day that’s more than 24 hours long. Those cues of light and dark pull it back down.

In fact, some experiments have shown that the body can adopt a much longer cycle. People have been isolated in caves or other remote locations with no clocks, watches, or access to the Sun. In those cases, people’s internal clocks have reset to a day length of up to 48 hours.

Living on Mars will provide a lot of challenges — extreme cold, lack of a breathable atmosphere, and a lot of nasty dust. But it looks like the length of a Martian day probably won’t be one of them.

Mars continues to nose its way into the sky earlier by the evening. Right now, it climbs into good view in the east-northeast by about 10:30 or 11, and looks like a bright orange star. It will grow brighter through early December.

Tomorrow: the closest field of newborn stars.
 

Script by Damond Benningfield

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Mars is bitterly cold. Temperatures seldom climb above freezing, and can slide far below minus-100 Fahrenheit. Yet the planet can get even colder. There’s evidence that Mars goes through periodic ice ages that can last for hundreds of thousands of years.

Ice ages can have several causes. On Mars, the most likely is a change in the planet’s tilt on its axis. Right now, the tilt is almost identical to Earth’s. That means the seasons are similar to Earth’s as well.

Over many millions of years, though, that angle can change dramatically. Mars can stand almost upright, or it can lie almost on its side. That affects how much sunlight reaches different parts of the planet, and how the Sun’s heat is distributed around it.

When Mars is on its side, the poles warm up and their ice caps vaporize. That makes the atmosphere warmer and wetter. Some of the extra water in the atmosphere may freeze around the equator, but overall, the planet is warmer than average.

Eventually, though, Mars flips upright again. The poles get colder, and the ice caps re-form. That makes Mars colder overall — perhaps triggering ice ages, with ice covering much of the planet. One recent study says this has played out many times in the past few hundred million years, giving Mars many ice ages.

Mars climbs into good view in the east-northeast by 10:30 or 11, and looks like a bright orange star. Tonight, it’s well to the upper right of the Moon.

More about Mars tomorrow.
 

Script by Damond Benningfield

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There’s been a change of plans for bringing bits of Mars back to Earth. Instead of another rover, scientists will send a couple of helicopters. But it’s still going to take years to get the job done.

The Perseverance rover arrived at Mars early last year. Among other things, it’s examining the planet’s rocks and dirt. It’s looking for evidence that its landing site could have been a comfortable home for life in the distant past. It’s also looking for evidence of life itself.

But the rover’s lab isn’t nearly as sophisticated as those on Earth. So Perseverance is also drilling a few inches into the surface and storing those samples in tubes for return to Earth.

The plan has been for another rover to land nearby, pick up the tubes, and ferry them to a small rocket on yet another lander to start the trip to Earth. But NASA recently changed things up.

The new plan calls for only one landing, of the sample-return rocket. Perseverance will tote the samples to the rocket. But the rocket will carry a couple of helicopters. They’re based on the design for Ingenuity, a small copter that went to Mars with Perseverance. If Perseverance can’t get the samples to the rocket, the copters will. If the plan holds, the samples would arrive at Earth in 2033.

Mars is growing brighter by the day. Tonight, it’s quite close to the Moon as they climb into good view, around 10:30 or 11. It looks like a bright orange star.
 

Script by Damond Benningfield

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The Sun is pretty big as stars go — bigger than more than 90 percent of all the other stars in the universe. It’s more than a hundred times the diameter of Earth — big enough to fit about 1.3 million Earths inside it.

At the end of its life, however, the Sun will grow far larger than it is today. In fact, it’ll closely resemble Aldebaran, the bright eye of the bull. The star rises to the lower right of the Moon late this evening.

Aldebaran is classified as a giant. It’s about 44 times the Sun’s diameter, and about 85,000 times its volume.

For most of its lifetime, Aldebaran probably wasn’t too much bigger than the Sun is today. Eventually, though, it burned through all the hydrogen gas in its core. Today, it’s probably consuming a shell of hydrogen around the core. That’s caused its outer layers to puff up like a giant balloon. It’s also caused those layers to get thinner and cooler. The lower temperature makes Aldebaran shine bright orange.

Before long, Aldebaran will begin burning the helium that now makes up most of its core. When that happens, it’ll briefly get even bigger and brighter. At the end, it will shed its outer layers, leaving behind only its hot but dead core — a tiny ball of cosmic ash known as a white dwarf. It’ll spend billions of years cooling and fading from sight.

The Sun will go through that whole process as well — beginning in about five billion years.

Script by Damond Benningfield

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Four centuries ago, James Ussher calculated our planet’s birthdate. Ussher was an archbishop and a professor at Trinity College in Dublin. Using clues from the Bible, he decided that Earth was born on today’s date in 4004 BC. That would make Earth 6,026 years old. Other scholars of the day, including Isaac Newton, came up with similar dates.

Ussher was using the best evidence available at the time. Since then, though, scientists have come up with new evidence. Studies over the past century have put Earth’s age at 4.54 billion years, with a margin of error of just one percent.

To find that age, scientists have used both Earth rocks and space rocks — meteorites that have fallen to Earth.

Radioactive elements in the rocks decay at a predictable rate, changing to other elements. Comparing the ratios of those elements reveals a rock’s age.

The oldest Earth rock found so far clocks in at 4.4 billion years. That means our planet can’t be younger than that. But most of Earth’s original rocks are gone — destroyed by the motions of the crust and other effects. So Earth must be older than its oldest rocks.

To find out how much older, scientists have studied meteorites. They’ve found that the oldest of these space rocks were born from the same cloud of gas and dust that gave birth to the Sun and planets. So Earth and the other planets should be the same age as the meteorites: more than four and half billion years.
 

Script by Damond Benningfield

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