StarDate

It might be winter here in the northern hemisphere, but the Sun is biggest and closest to us for the entire year today. Earth is at a point in its orbit called perihelion. The Sun is about 91.4 million miles away – about one and a half million miles closer than average.

Earth’s orbit isn’t a perfect circle. Instead, it’s an ellipse – a shape that looks like a slightly flattened circle. So over the course of a year, the Earth-Sun distance varies by about three percent. The oceans and atmosphere distribute heat around the planet, so the changing distance doesn’t cause a change in global temperatures.

The date of perihelion isn’t fixed. Instead, it shifts forward by an average of about one day every 58 years. That’s because Earth “wobbles” on its axis like a gyroscope that’s running down. About 800 years ago, Earth was closest to the Sun on the winter solstice, in December. And about 4300 years from now, it’ll be closest on the spring equinox, in March.

The changing distance to the Sun doesn’t create the seasons. Instead, the seasons are caused by Earth’s tilt on its axis. But the distance to the Sun does have an impact on the seasons. Earth moves fastest in its orbit when it’s closest to the Sun, and slowest when it’s farthest away. That means the seasons are different lengths. In the northern hemisphere, winter is the shortest season – about five days shorter than summer, when Earth is farthest from the Sun.
 

Script by Damond Benningfield

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When Geoffrey Duffield returned to Australia in late 1924, after a decade in England, he had a big job ahead of him. Duffield had lobbied for Australia to build a Sun-watching observatory since he was an undergraduate. The government finally agreed, in 1923, and hired Duffield as its first director. And the Commonwealth Solar Observatory was officially established 100 years ago today. It would be built on Mount Stromlo, near the city of Canberra. And it’s still there today, renamed the Mount Stromlo Observatory.

When Duffield first arrived at the site, though, he was stunned to find that the mountain was bare. There were no buildings, no staff, and no telescopes. Duffield and his family lived in a Canberra hotel for two years. When he hired staff members, they set up labs and workshops at the same hotel. It was years before anyone could live or work at the observatory – and years more before it was finished.

Duffield didn’t see that completion. He was living on the mountain when a massive winter storm hit, in July 1929. He came down with the flu, but there was no way to get medical help. He died before the road cleared up.

Much of the observatory was destroyed in a forest fire in 2003. But one of its original telescopes survived. It’s used mainly for public programs. And despite the losses, Mount Stromlo remains a major center for astronomy research – a century after its creation.

Tomorrow: Close to the Sun.
 

Script by Damond Benningfield

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As the night grows late, and 2024 approaches – or perhaps after you’ve enjoyed the midnight countdown, and the new year is aready here – take a moment to look at the sky. Even if the fireworks are all over, you’ll still see some beautiful and colorful lights.

At midnight, the Moon is in the east. Sunlight illuminates three-quarters of the lunar hemisphere that faces our way, so it’s nice and bright. Its glare washes out the view of many fainter stars – especially those close to the Moon. But plenty of bright lights will shine through.

High in the south, for example, look for Sirius, the brightest star in the night sky. It should be twinkling more than any other star, shifting from red to blue to pure white. And if you’re in the southern parts of the country – south of about Dallas – you might also spot Canopus, the second-brighest star. It’s directly below Sirius, just above the horizon.

Orion stands to the upper right of Sirius. It may be the most beautiful of all constellations – and the easiest to find. Look for a short diagonal line of three stars – Orion’s Belt. It’s inside a rectangle of brighter stars.

And if you want a light that’s brighter still, look in the west for Jupiter, the largest planet in the solar system. It far outshines everything else in the sky at that hour except the Moon – teaming with the Moon to bookend the sky on the final hours of 2023.
 

Script by Damond Benningfield

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The Moon slides between two of the brighter stars of Leo tonight. They all climb into good view in mid-evening. Regulus, the lion’s brightest star, will stand to the lower right of the Moon. And Algieba, the third-brightest, will be about the same distance to the lower left. The Moon will pass between them during the night.

It’ll actually pass much closer to a third member of the constellation, Eta Leonis. The star is a good bit fainter than the other two, so it’s harder to see through the Moon’s glare. But the Moon will pass within about a degree of it — half the width of your finger held at arm’s length.

Eta Leonis looks fainter than Regulus and Algieba mainly because it’s almost 1300 light-years away — hundreds of light-years farther than the other two.

The star is big, bright, heavy, and hot — about 10 times as massive as the Sun, and perhaps 20,000 times brighter. It’s so heavy that it’s likely to end its life as a supernova — a titanic explosion that’ll rip the star to bits. Only its dead core will remain — probably a neutron star — a superdense ball more massive than the Sun but only a few miles across.

There are hints that Eta Leonis might have one or more companion stars. So far, though, astronomers haven’t been able to confirm any of them.

Watch as the Moon slides just past Eta Leonis during the night. Binoculars will help you pick out this impressive but tough-to-see star.
 

Script by Damond Benningfield

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If you have some spare time on your hands, you might want to spend it helping out astronomers. You can sift through pictures and other data to help scientists find what they’re looking for. Projects include classifying stars and galaxies, searching for planets in other star systems, and many others.

At least one project is preserving part of astronomical history. Project Phaedra is going through 2500 notebooks recorded in the late 19th and early 20th centuries. The notebooks were kept by women working at Harvard College Observatory.

Known as “computers,” the women pored over images taken by male astronomers, and made the tedious calculations needed to analyze the observations.

Some of the women became astronomers in their own right, and made some of the most important contributions of the era. Annie Jump Cannon developed a new way to classify stars, and it’s still in use today. Henrietta Swan Leavitt devised a way to measure the distances to other galaxies. And Cecilia Payne was the first to propose that stars are made mainly of hydrogen and helium.    

Project Phaedra volunteers transcribe their notebooks. The logs include the women’s calculations, notes about the glass plates they were examining, tables of data, and more. The project has been going on for several years, so many of the notebooks have been finished. But others remain — preserving an important era in the history of astronomy.
 

Script by Damond Benningfield

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A low “hum” ripples through the universe — the possible rumble of pairs of supermassive black holes. The waves that make up the hum are light-years long, so they’re hard to pick up. In fact, you need a receiver as big as a galaxy. And astronomers recently discovered the hum using such giant receivers.

Gravitational waves are ripples in space-time created by the motions of massive objects. Scientists have detected the waves produced by the mergers of smaller black holes. But the waves produced by supermassive black holes are much too long for detectors here on Earth.

Instead, astronomers have created galaxy-spanning detectors using pulsars — the ultra-dense corpses of exploded stars. They spin at up to hundreds of times per second, sending out “pulses” of energy. The spin rate is extremely stable, so a pulsar “ticks” like a very steady clock.

But when a gravitational wave passes between Earth and a pulsar, the pulsar spins a bit faster or slower. Since the waves are so long, it can take years to see a difference in the timing. Combining observations of many pulsars over many years makes the changes easier to see.

Several teams of astronomers have measured those changes. They say the most likely explanation is waves from pairs of supermassive black holes that are about to merge. Their work shows that millions of such mergers could be in progress — producing a deep “hum” across the universe.
 

Script by Damond Benningfield

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Gemini is in prime viewing time during these early weeks of winter. The constellation is low in the east-northeast at nightfall, and remains in view all night. It’ll remain visible for most of the night throughout winter. And tonight, the Moon is passing through the constellation’s middle.

Gemini is best known for the bright “heads” of the twins, the stars Pollux and Castor. Pollux is the brighter of the two, with slightly fainter Castor above it during the evening hours.

Both stars are impressive, but for different reasons.

Pollux is nearing the end of its life, so it’s puffed up to giant proportions. It’s many times wider than the Sun, and dozens of times brighter. Eventually, the nuclear reactions in its core will shut down, and its outer layers will puff out into space. Only the star’s dead core will remain.

Castor is impressive not for its size, but for sheer numbers. What we see as Castor is actually at least a half-dozen individual stars — one of the largest families of stars yet seen. The stars span a wide range — from much smaller and fainter than the Sun, to much bigger and brighter.

Because of that range, the stars will live to reach different ages. The heavier ones will burn out within a few million years. But the little ones will continue to shine for billions of years longer. They’ll remain faint, though. So the heads of both celestial twins are destined to fade from sight.
 

Script by Damond Benningfield

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In the early 20th century, radium was all the rage. It was used in paints that made the faces of clocks and watches glow in the dark. It was the key element in early medical radiation treatments. It was infused into water and chocolates, and was a big selling point for spas whose waters had a lot of the element. Alas, all of those were bad ideas. Radium is highly radioactive, and most likely was responsible for the deaths of thousands.

Radium came to the world’s attention 125 years ago today. Marie and Pierre Curie announced its discovery to the French Academy of Sciences. The discovery earned the Curies half of the 1903 Nobel Prize in Physics.

Marie Curie discovered the first hint of the element. She was studying pitchblende — a dark ore that contains a lot of uranium. Her experiments showed that the ore was producing far more radioactivity than could be accounted for by uranium alone. She thought it must contain another radioactive element. It took a while, but she and Pierre eventually isolated it. After Pierre died, Marie and another colleague isolated the metal — work that helped her earn a second Nobel, for chemistry.

Radium is produced by the radioactive decay of uranium. Radium itself decays quickly, so there’s none left from Earth’s formation.

Today, radium’s use is limited — mainly to scientific research and instruments — non-lethal applications for a prize-winning element.
 

Script by Damond Benningfield

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The Moon and two bright planets highlight the early evening sky. Some bright stars climb into view later, with the brightest pinpoint of light in all the night sky taking over at dawn.

As the color of twilight fades into the darkness of night, look about a third of the way up the southwestern sky for Saturn. It looks like a bright star, but it’s really the second-largest planet in the solar system.

From there, shift your gaze to high in the southeast for the largest planet, Jupiter. It outshines every other planet and star in view this evening — a brilliant beacon that shines through most of the night.

The only light that outshines it is the gibbous Moon, low in the east-northeast. El Nath, at the tip of one of the horns of Taurus, the bull, is quite close to the Moon. And Aldebaran, the bull’s bright eye, lurks to the upper right of the Moon.

Two or three hours later, some other prominent stars add their luster to the canvas. The constellation Orion stretches across the east and southeast. It’s marked by its three-star belt, which extends straight up from the horizon. And if you follow the belt down toward the horizon, you’ll come to Sirius, the brightest star in the night sky.

Finally, as the pale glow of dawn starts to color the sky, the planet Venus shines low in the southeast. It’s the brilliant “morning star,” so you can’t miss it — a final bright decoration for the Christmas-night sky.
 

Script by Damond Benningfield

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