StarDate

The Moon is nowhere in sight the next couple of days. That’s because it’s new — it crosses between Earth and the Sun, so it’s hidden in the Sun’s glare. But coastal residents will definitely feel its presence. That’s because the Moon is closest to Earth for the year. The combination of the lunar phase and the Moon’s distance means that we’ll have some of the highest tides of the year.

The tides are caused by the gravitational pull of the Moon and Sun. The Moon is closer to us, so its influence is greater. The tides are most extreme when Sun, Moon, and Earth are in good alignment. The gravity of the Sun and Moon pull along the same line then, so high tides are higher, and low tides are lower.

Not surprisingly, the gravitational pull of the Moon is strongest when the Moon is closer to us. Tonight, it’ll be about 17,000 miles closer than average. That happens just two hours before the Moon is new — creating more dramatic tides around the world.

Tonight’s Earth-Moon-Sun alignment isn’t perfect — the Moon will pass just south of the Sun. But the next new Moon alignment will be perfect. The Moon will pass directly in front of the Sun, creating a total solar eclipse. It’ll be visible from the United States, Mexico, and Canada. We’ll keep you posted.

For now, look for the Moon to return to view on Monday. It’ll be a very thin crescent quite low in the west as evening twilight fades away.

Tomorrow: the stern of a mighty ship.

Script by Damond Benningfield

The Big Dipper is on the move. Not just its nightly circle around the North Star. And not even its shifting position from month to month. The stars themselves are moving through the Milky Way Galaxy. And most of them are moving together.

The stars of the Big Dipper are in Ursa Major, the great bear. The constellation has given its name to a widely spread group of stars that appear to move together — the Ursa Major Moving Group. It consists of a few dozen stars in all. Its core is in Ursa Major, but it also includes stars in several other constellations.

The stars in the group all move through space in the same direction, at about the same speed. They’re all roughly the same distance from Earth — about 80 light-years. They all appear to be about the same age — roughly half a billion years. And they have similar chemical compositions. That doesn’t mean that all the suspected members really do belong to the group. But there’s a lot of circumstantial evidence that they do.

Members of the group may have been born together — from the same giant cloud of gas and dust. The gravity of the rest of the galaxy pulled them away from each other — leaving a long ribbon of stars that move through the galaxy together.

The Big Dipper is in the northeast at nightfall, with the handle below the bowl. Only two of its stars are not members of the Ursa Major Moving Group: the stars at the end of the handle and the outer edge of the bowl.

Script by Damond Benningfield

The Sun is building toward the peak of its magnetic cycle, probably sometime this year. That’s when it produces more sunspots, flares, and giant clouds of charged particles. All of those can have an effect on our technology — knocking out satellites and power grids, disrupting radio transmissions, and more. So scientists pay close attention during these active times.

In fact, they’re planning to launch half a dozen small rockets over the next month. Three of them will look at a flare, while the others will see how a layer of Earth’s atmosphere is affected by an eclipse.

All of them are sounding rockets. They will climb above the atmosphere for a few minutes, providing glimpses that aren’t available from the ground.

The first three will launch from Alaska. They’ll head up when NASA spots a solar flare — a titanic explosion — which can erupt at any time. Two will launch close together, while the third will wait until the flare is ramping down. They’ll view what’s going on at the surface of the Sun, and in the region just above the surface. That will help scientists understand the Sun’s activity.

The eclipse missions will launch from Virginia, on April 8th. One will go up just before the eclipse, one during the eclipse, and one shortly afterward. They’ll see how the eclipse changes the ionosphere — a layer of the atmosphere that bounces radio signals around the planet — telling us more about the Sun and its impact on Earth.

Script by Damond Benningfield

A nearby star has one of the largest families of planets yet seen — an even half-dozen. Only two other known exoplanet families are bigger. But this system is different from the others. All of the planets march in time — their orbits are in perfect sync.

The star is known as HD 110067. It’s about a hundred light-years away, in the constellation Coma Berenices, which is in the east this evening.

The star is a bit smaller and cooler than the Sun. But it’s probably several billion years older. And that’s one reason its planetary system is remarkable.

The planets appear to range from about two to three times the size and mass of Earth. The innermost planet orbits once every nine days, while the outermost world takes about 55 days — much shorter than the orbit of Mercury, the Sun’s closest planet. And all of the orbits are synchronized. Each of the four inner planets completes three orbits for every two orbits of the next one out. And planet number five completes four orbits for every three made by the most-distant planet.

Planetary systems may all be born in sync. But few of them stay that way. Passing stars can nudge some of the planets into different orbits. So can collisions between planets, as well as the presence of especially heavy planets.

So far, then, the HD 110067 system is unique — a family of planets that’s remained in sync for a long, long time.

Script by Damond Benningfield

Descriptions of the Coma Cluster of galaxies sound like bad car-dealership commercials. The cluster contains more than a thousand galaxies. They’re bound together by their mutual gravitational pull. The heart of the cluster is about 330 million light-years away. But the cluster may span as much as two hundred million light-years.

But wait — that’s not all! There’s a lot more to the cluster than we can see. In 1933, Fritz Zwicky found that galaxies in the cluster are moving fast — too fast for the cluster to be held together by the gravity of the visible matter. He concluded that most of the cluster must consist of dark matter — matter that produces no energy, but pulls on the visible matter around it. Today, astronomers calculate that dark matter must make up at least 90 percent of the cluster’s mass.

But wait! We’re not through yet! More galaxies are falling into the Coma Cluster. One group is led by the giant galaxy NGC 4839. Gas is being stripped from the group. It forms a hot tail that’s a million-and-a-half light-years long. The group may have plunged through the cluster once, and now is making a second pass.

But wait! Oh, well — that’s all we have time for! We’ll just give you the cluster’s address. It’s in Coma Berenices. The constellation climbs into good view, in the east, by 8 or 9 o’clock. Some of its brighter stars form sparkling ribbons — with a cluster of galaxies far beyond.

Script by Damond Benningfield

A sprinkling of faint stars stands in the east a few hours after sunset right now. It’s to the upper right of brilliant Arcturus, the brightest star in that part of the sky. Those ribbons of stars are the main features of Coma Berenices.

The constellation represents Queen Berenice II of Egypt. The legend says that when her husband was about to head into battle, she offered her beautiful golden hair to the gods in exchange for his safety. When he returned undamaged, she cut her hair and placed it in a temple. Legend says the gods then placed it in the stars.

The brightest of those stars, Beta Coma, looks a lot like the Sun. It’s about the same size, mass, and brightness. It’s also about the same color — fittingly enough, bright gold, which shows up in binoculars or a telescope.

Long-term observations reveal that Beta Coma produces a 16-and-a-half-year magnetic cycle — half again the length of the solar cycle. During that cycle, the star probably goes through periods of high and low magnetic activity. During active times, more of the dark storms known as “starspots” probably speckle its surface — the result of lines of magnetic force getting twisted and stretched. When they snap, they produce powerful outbursts known as flares — eruptions that are equal to millions or billions of nuclear bombs.

Coma’s real claim to fame isn’t its stars, though — it’s a cluster of galaxies. We’ll have more about that tomorrow.

Script by Damond Benningfield

All stars are big balls of glowing gas, powered by nuclear fusion. But stars come in many different sizes, masses, and colors. And they’re put together in different ways.

The Sun is in the middle range. It consists of three main layers — the core, the radiation zone, and the convection zone.

The core is where a star generates energy. Stars in the prime phase of life “fuse” hydrogen atoms to make helium, releasing energy in the process.

In the Sun, the core is surrounded by the radiation zone, where energy from the core travels outward. It can take hundreds of thousands of years for that energy to pass through the zone.

Finally, there’s the convection zone, which is like a pot of boiling water. Huge bubbles of hot gas rise from the bottom of the zone to the top, releasing energy into space.

Stars that are much less massive than the Sun have only the core and the convection zone. Such stars generate powerful magnetic fields, which produce dark “starspots” and enormous explosions of particles and energy. That can be bad for any planets that orbit the stars.

On the other hand, stars that are a few times more massive than the Sun are just the opposite. They have a deep radiation zone, but no convection zone. Those stars generate only a weak magnetic field, if any. So there are no big storms to pelt any orbiting planets.

When a star moves out of the main phase of life, its structure changes dramatically. But that’s a tale for another day.

Script by Damond Benningfield

The night sky plays tricks. Objects that appear close together in the sky can actually be far apart. As an example, look at the Moon and the star Antares before dawn tomorrow. There’s almost no separation between them. In fact, for some parts of the eastern U.S., there won’t be any separation at all — the Moon will cover the star for a while, hiding it from view.

That makes it look like the Moon and Antares are close together in space. But that’s not the case. The Moon is our closest astronomical neighbor — about a quarter of a million miles away. Antares is much farther. Much, much farther. There’s a little uncertainty in the exact distance, but it’s about 550 light-years. That’s 13 billion times farther than the Moon.

Astronomers determine a star’s distance by measuring its parallax. They pinpoint its location when Earth is on opposite sides of the Sun. The star appears to shift back and forth by a tiny bit against the background of more-distant objects. The size of that shift reveals the star’s parallax. From that, astronomers calculate the distance.

Stars that are farther are harder to measure because the back-and-forth shift is tinier. It’s a special problem for stars like Antares, which puffs in and out. That means the star’s position on the sky is hard to pinpoint. So it takes a lot of work to tell us how misleading the night sky can be — revealing the huge gap between the Moon and the stars.

Script by Damond Benningfield

Many bright stars highlight the sky this evening: Sirius, the brightest of them all; Regulus, the heart of the lion; several sparklers in Orion, and more. Astronomers know a lot about these stars. But most of what they know is a bit uncertain. So when they pin numbers to a star, they give themselves some wiggle room to compensate.

Consider Sirius, which is in the south at nightfall. It’s one of the Sun’s closest neighbors, at a distance of about 8.6 light-years. But that could be off by up to a few percent of a light-year either way. That’s a total variation of perhaps half a trillion miles.

There’s a similar uncertainty in the distance to Regulus, the brightest star of Leo, which is in the east at nightfall. It’s measured at 79 light-years away — give or take that same half a trillion miles.

And the uncertainty is much greater for stars like Betelgeuse — an orange supergiant at the shoulder of Orion. It puffs in and out, and its outer layers are so thin that it’s hard to tell just where its surface is. That makes it harder to get a fix on its position, so it’s harder to measure the distance. Betelgeuse is thought to be roughly 550 light-years away. But it could be perhaps a hundred light-years farther, or 50 light-years closer.

Without an exact distance, it’s hard to determine a star’s size, its true brightness, and more. So the stars are pretty well known — but with sometimes big uncertainties.

Script by Damond Benningfield

The remaining dates of 2024 will take a big leap. They’ll jump over a day of the week. That’s because this is leap year, and today is leap day — extending the year from 365 days to 366.

Leap years are needed to keep the calendar in sync with the seasons. Without it, the equinoxes and solstices would slide across the calendar. So after many centuries, the spring equinox would happen in February, with the winter solstice backing into November. And over the ages, the shift would grow even larger.

The modern calendar is based on one instituted by Julius Caesar. It had a 365-day year, with a leap day added to every fourth year, for an average of 365 and a quarter days per year. But the true year is about 11 minutes shorter than that average, so the calendar drifted out of alignment with the seasons.

To fix that problem, in 1582 Pope Gregory XIII instituted an update. Under this calendar, three leap days are dropped off for every 400 years. With this change, the difference between the calendar year and the astronomical year adds up to one day every 3300 years.

The name “leap” year comes from the fact that the extra day causes succeeding dates to leap over a day of the week. For example, Christmas fell on a Monday last year. Without the leap day, this year it would fall on a Tuesday. But with the extra day, it will “leap” over Tuesday and fall on Wednesday.

Script by Damond Benningfield