StarDate

For William Campbell and his team from Lick Observatory, it had been a long journey. It took months to sail from California to Australia, travel the full width of the country, then sail to a remote beach on the western coast. It took weeks more for the team of 30 men and five women to set up its equipment. And all of that to see five minutes of darkness — a total solar eclipse — 100 years ago today.

Campbell and his team were trying to confirm observations made during an eclipse in 1919. If they were successful, they’d provide key proof of Albert Einstein’s theory of gravity.

Einstein published his theory in 1915. Among other things, it predicted that stars and other massive objects would “warp” the space around them. The effect could be seen during a total eclipse. Astronomers would measure the positions of stars that appeared near the Sun. If Einstein was right, there’d be a tiny shift compared to the usual positions of the stars.

Observations in 1919 confirmed Einstein’s theory. But there were questions about the results. So astronomers tried again in 1922.

Campbell’s team was one of several to make the attempt. And it was the most successful by far. Its pictures showed more than a hundred stars around the Sun. Painstaking analysis confirmed that the light of the stars closest to the Sun had been deflected by the Sun’s gravity — once again proving Einstein right.
 

Script by Damond Benningfield

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A NASA spacecraft is about to commit suicide. If everything goes as planned, it’ll ram into an asteroid on Monday afternoon. Astronomers will keep an eye on the asteroid to see how the impact affects its orbit around a larger companion asteroid.

The mission is known as DART. It’s an early step in the effort to develop ways to protect Earth from asteroids or comets that might be on a collision course with our planet. An impacting spacecraft might deflect such a body just enough to miss us.

The target is Dimorphos, which is about 525 feet in diameter. It orbits Didymos, which is about half a mile across. DART will hit the little moon head on. A small companion spacecraft will snap pictures from a safe distance.

The system isn’t a threat to Earth. But it passes close enough that it’s easy to reach. And the sizes of the two bodies provide a good test of just what an impact can do. It should cause a small but measurable change in the orbit of Dimorphos. Astronomers will monitor the system for months to measure the size of that change. That will tell us how effective such an impact might be against a true danger.

Another spacecraft is scheduled to fly past the system in late 2026. It’ll take pictures to see how the collision changed the smaller asteroid. The images should reveal the layers inside it, telling us more about its history — a bonus from a mission to test a way to protect Earth from cosmic missiles.
 

Script by Damond Benningfield

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One of the twins of Gemini is getting bigger. The star is already about nine times the diameter of the Sun. But changes in its core will cause it to puff up to dozens of times the Sun’s diameter. And that’ll cause it to slow down.

Pollux is Gemini’s brighter twin. It’s quite close above the Moon at first light tomorrow. Castor, the other twin, is farther above Pollux.

Pollux has passed the end of its “normal” lifetime. It’s “fused” the original hydrogen fuel in its core to make helium. Now, it’s fusing the helium to make heavier elements. As part of that process, its core got smaller and hotter, so it radiates more energy into the surrounding layers of gas. That’s pushed on the star’s outer layers, causing Pollux to puff up like a giant balloon.

As a star gets bigger, it spins more slowly. Today, a spot on the surface of Pollux rotates at 6300 miles per hour or faster — a little faster than the Sun rotates. But Pollux will get much bigger in the future. As it does, it’ll spin more slowly.

That’s thanks to a law of physics known as the conservation of momentum. The most common example of how it works is a figure skater. When a skater pulls in its arms, it spins faster. But if the skater then extends the arms, it spins more slowly. So over millions of years, Pollux will figurately extend its own arms — causing the giant star to slow down.

Tomorrow: a spacecraft sets a collision course with an asteroid.
 

Script by Damond Benningfield

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It’s easy to see pictures in the stars. That’s how skywatchers created constellations — they connected the dots of bright stars. But it’s also easy to see pictures on a smaller scale — in star clusters.

One example is NGC 457. Stargazers have given it several names, depending on how they saw it: the Owl, the Dragonfly, and E.T., for the friendly alien in the movie. It’s in the northeast at nightfall, near another star picture: the letter W formed by the stars of Cassiopeia. The nebula’s an easy target for binoculars.

Astronomers have identified several dozen stars in the cluster. But picking out just which stars belong to a cluster takes time. When we look toward a cluster, we see both the cluster and the stars that appear in front of it and behind it. And there’s no way to tell just from looking which star is where.

Astronomers make several measurements to pick out a cluster’s members. First, they measure the motions of the stars — both across the sky and toward or away from Earth. Members of a cluster share a common motion.

But stars that aren’t in the cluster can have similar motions. So astronomers measure the distances to the stars; those in a cluster are at the same distance. The farther the cluster, the trickier that is — it can take years to get it right.

A few other measurements — the ages of the stars, for example — fill in the details — nailing down the list of members of a star cluster.
 

Script by Damond Benningfield

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Much of the Space Age has been driven by global politics. In the early days, the United States and the Soviet Union raced to send the first person to space, to send probes to the planets, and to land men on the Moon. Things began to change in the 1970s, when American and Soviet spacecraft linked up in orbit.

Yet geopolitics continues to play a role in space exploration. An example is a mission known as ExoMars, a joint project of Russia and Europe. Its launch was delayed a couple of years by Covid. Its new launch window opened this week.

But earlier this year, Europe split from Russia on ExoMars and other space projects — a result of Russia’s invasion of Ukraine. That could delay the launch until 2028 or later.

ExoMars consists of two parts — a landing platform and the Rosalind Franklin rover. Russia was providing the lander and the booster rocket, and Europe built the rover.

The planned landing site was Oxia Planum — a smooth plain that might once have held liquid water. The rover would analyze the rocks and dirt to try to figure out when the water was there, how much was there, and how it affected the formation of minerals on the surface. The goal was to figure out if the region might once have been suitable for life.

The European Space Agency has said it’ll try to find another partner to build the lander and provide the launch. But that’ll take time — a lengthy delay in space caused by a war here on Earth.
 

Script by Damond Benningfield

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The Moon anchors a beautiful lineup late tonight. It includes Mars and the two brightest stars of Taurus. The lineup climbs into view by around midnight, and is high in the sky at first light.

Mars glows bright orange — the result of iron-rich dust that coats most of the planet. The major exceptions are the polar ice caps, which are almost pure white.

There’s a lively debate about what’s at the bottom of the cap at the south pole. Some researchers say there could be liquid water mixed with the dirt. Others say that water wouldn’t work — it’s more likely to be clay, salty minerals, or even volcanic rock.

The debate is based on observations made by Mars Express. It used radar to peek below the ice cap, which is made of layers of frozen water and carbon dioxide. The radar showed bright reflections below the ice cap. The original study team interpreted the reflection as liquid water mixed with high levels of salts. A comparison to radar readings of a lake below the ice in Antarctica reached a similar conclusion.

But others say it’s too cold even for salty water, and other materials are a more likely explanation — leaving the ground below the ice cap dry.

Look for Mars close to the right of the Moon. The orange star Aldebaran — the eye of the bull — is farther from the Moon along the same line. And the bull’s next-brightest star, El Nath, is close to the left of the Moon.

More about Mars tomorrow.
 

Script by Damond Benningfield

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Like the other giant planets of the outer solar system, Neptune has a large family of moons and rings. Astronomers have logged 14 moons, and they’ve seen three skinny rings and two or three wider ones. The rings are so hard to see, though, that they weren’t confirmed until the 1980s.

The skinny rings are the most prominent. Their material is packed close together. They probably consist of tiny particles of ice. The particles may have a coating of methane that’s been turned red by radiation from the Sun and stars.

Those rings are named for three of the men involved in Neptune’s discovery. From closest to farthest, they’re known as Galle, Leverrier, and Adams.

Galle is only about 10,000 miles above Neptune’s cloud tops, with Adams about twice that far. Adams has five big clumps of material that are brighter and denser than the rest of the ring. The clumps may be held in place by the gravity of a small moon.

Several lines of evidence suggest the rings are quite young — perhaps no more than a million years old. And they appear to be changing in a hurry — sculpting their shapes as we watch.

And speaking of watching, Neptune is putting in its best appearance of the year this week. It rises at sunset and is in view all night. It’s also brightest for the year. Yet it’s so far away that you need a small telescope to see it. As night falls, it’s to the upper right of the brilliant planet Jupiter.
 

Script by Damond Benningfield

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The giant planet Neptune is at its best this week as it lines up opposite the Sun. It’s in view all night, and it’s closest to Earth, so it’s at its brightest. It’s so far away, though, that you need a telescope to spot it.

That’s too bad, because Neptune is a beautiful sight — it shines with a rich blue color.

Like Earth, Neptune is tilted on its axis — and by about the same amount. So as Neptune orbits the Sun, it experiences four seasons. Right now, it’s the middle of winter in the northern hemisphere. But winter won’t end for two more decades. That’s because a year on Neptune lasts for about 165 Earth years. So each season is more than 40 years long.

If it’s winter in the north, then it must be summer in the south. Astronomers have been watching the southern hemisphere since the season began. They expected to see that part of the planet warm up. But it hasn’t — it’s gotten colder. So far, no one can explain why.

Although a year on Neptune is much longer than on Earth, a day is much shorter — about 16 hours. So if you could spend a full year on Neptune, you’d see almost 90,000 sunrises and sunsets.

If you don’t have a telescope, you can still find Neptune’s location. In early evening, find Jupiter, which looks like a brilliant star, low in the east. Neptune is to the upper right of Jupiter by about the width of your fist held at arm’s length.

More about Neptune tomorrow.
 

Script by Damond Benningfield

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Cosmologists have a puzzle to work on. Their measurements and models of how the universe is expanding don’t match up. That suggests either that something is wrong with the models or observations, or that something is happening in the universe that we don’t know about.

In a recent study, scientists used Hubble Space Telescope to observe exploding stars in many galaxies. The stars brighten and fade in a way that reveals their true brightness. From that, astronomers can calculate how far they are. They also measure how fast the stars and their host galaxies are moving relative to Earth. They then use those numbers to calculate how fast the universe is expanding.

The new study came in at the upper end of the range of results using other techniques. Those techniques have studied exploding stars; old, bloated stars; and stars that pulse in and out. Astronomers also use measurements of the “afterglow” of the Big Bang. The results vary by about 10 percent.

And that makes a big difference. The numbers are critical to our knowledge of when the universe was born, how it’s evolved, and its fate. So a 10 percent range really gums things up.

The difference could mean some of the observations or the models are off. It also could mean that we don’t fully understand the effects of dark energy or dark matter. It could even mean that there are forces or forms of matter awaiting discovery — parts of the complex puzzle of our expanding universe.
 

Script by Damond Benningfield

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It’s time to get serious about Mars. The Sun’s fourth planet is moving into a spectacular phase, getting brighter and rising earlier by the night. It’ll shine at its absolute best in early December.

But you don’t have to wait that long to appreciate it. Right now, Mars climbs into view by midnight, low in the east, and stands high in the sky at first light. It looks like a bright orange star. The fainter true star Aldebaran, which is also orange, is close by.

Only five nighttime objects visible in northern skies outshine Mars: the Moon, two planets, and two stars. But Earth is catching up to Mars in our smaller, faster orbit around the Sun. We’ll overtake the Red Planet in early December. As Mars draws closer, it’ll also get much brighter. By the time of closest approach, near a point called opposition, it’ll shine more than four times brighter than it does now. For a while, only the Moon, Venus, and Jupiter will outdo it.

Mars reaches opposition every couple of years. But no two oppositions are just alike. Mars’s orbit is more lopsided than Earth’s is, so the planet’s distance at opposition varies by tens of millions of miles. This will be a close one, so Mars will put on a great show.

And as Mars brightens, you’ll have more time to enjoy it — it rises a little earlier each night. At opposition, it’ll rise at sunset and be in view all night. So enjoy Mars as it shines brilliantly through autumn and well into winter.
 

Script by Damond Benningfield

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