StarDate

We generally think of “springing forward” as a good thing. It suggests getting ahead — in a race, in a job, or in the progress of a civilization.

Most of us in the United States will “spring forward” tonight, with the return of Daylight Saving Time. Whether that’s good or bad depends on your perspective. Some enjoy the extra hour of sunlight that’s added between the end of the work day and sunset. Others don’t enjoy having to leave for work or school when it’s still dark outside.

The idea of springing forward during the months of more daylight hours caught on during World War I, with the United States adopting it in 1918.

It lasted less than a year, but was reinstated during World War II. After the war, individual states were free to use Daylight Saving Time or not, for any part of the year they chose. It was standardized in 1966, and since then it’s been extended to take up a greater chunk of the year.

The rationale for the modern version of Daylight Saving Time is that people tend to use less energy during the dark early morning than they do after darkness falls in the evening. So the idea is that extending daylight by an hour in the evening cuts down on energy use. Study results are mixed, but most do show a small savings.

For now, just remember to set your clocks forward at 2 a.m. local time — an hour that you’ll get back when Daylight Saving Time ends and we “fall back” in November.

Tomorrow: making the night sky darker.

Script by Damond Benningfield

A bright star with a hint of color stands close above the Moon as darkness falls this evening. That subtle color reveals some important facts about the star.

Regulus is the heart of Leo the lion. It’s actually a system of four stars, but only one is bright enough to see with the eye alone — the star we know as Regulus.

If you look at it carefully, you’ll notice that Regulus shines with just a hint of blue. The color tells us that its surface is much hotter than the surface of the Sun. The hottest stars are bright blue, the coolest are orange or red, and stars in the middle, like the Sun, are yellow.

Regulus is so hot because it’s more than three times as massive as the Sun. That great weight squeezes the star tightly. That makes its core extremely hot, which revs up its nuclear reactions. As a result, Regulus’s lifespan will be billions of years shorter than the Sun’s.

The energy from the core heats the surface, making it blue — and bright. If you placed Regulus and the Sun at the same distance, Regulus would look about 130 times brighter. But because the star’s surface is so hot, it produces much of its energy at ultraviolet wavelengths. When you add that to the visible light, Regulus is about 360 times the Sun’s brightness.

So just from its color, we know that Regulus is hot and heavy, that it will live a short life, and that it produces a lot of ultraviolet energy — a blue-white beacon leading the Moon across tonight’s sky.

Script by Damond Benningfield

When a massive star reaches the end of its life, it blasts itself apart as a supernova. But this moment of death is also a moment of creation. As the star rips itself to bits, it creates new chemical elements at a furious rate. In a matter of seconds, it manufactures most of the elements that are heavier than iron — from iodine and xenon to lead and uranium. The supernova then blasts some of these elements out into space.

Other than hydrogen and helium, which were made in the Big Bang, the elements on the lightweight end of the scale were forged by nuclear reactions in the hearts of stars. But that doesn’t work for heavier elements. Even the hottest, most massive stars can’t produce enough energy in their cores to “fuse” together lighter atoms to make anything heavier than iron and nickel.

But when the star explodes, it produces enormous amounts of energy. For a few seconds, temperatures and pressures just outside the star’s core are so extreme that a huge number of atoms fuse together to make much heavier ones.

In recent years, though, research has suggested that not all of the heavy elements come from supernovae. Some of the heaviest may be forged when the dead cores of these exploded stars ram together. In fact, it’s possible that that’s how most of the gold came into existence. So that gold ring you’re wearing could be debris from the collision of two stellar corpses — the remnants of mighty stars that blasted themselves to bits.

Script by Damond Benningfield

Some giant chemical factories arc down the southwestern sky this evening: seven bright stars that outline the constellation Orion. The pattern includes the three stars of Orion’s Belt, which are roughly parallel to the horizon at nightfall, and a four-star rectangle around the belt. Orange Betelgeuse is at the top left corner, with blue-white Rigel at the opposite corner.

All of these stars are supergiants. They’re hundreds of times wider than the Sun, and tens of thousands of times brighter. Most important, they’re many times more massive than the Sun — and that’s what makes them chemical factories.

All stars shine by fusing together elements in their cores to make heavier elements, releasing a lot of energy in the process.

The Sun and similar stars fuse hydrogen to make helium. But supergiants make many other elements as well. Because of their great mass, gravity squeezes them more tightly, making their cores much hotter. That allows them to fuse heavier and heavier elements. In the final stage of life, in fact, such a star is put together like an onion. The core is made of iron, surrounded by layers of silicon, oxygen, neon, carbon, helium, and hydrogen, all mixed with other elements.

It takes too much energy to fuse iron to make heavier elements. So the nuclear reactions come to an end. The core collapses, and the star’s outer layers explode into space — creating even heavier elements as they do. More about that tomorrow.

Script by Damond Benningfield

The Sun is a big nuclear reactor. Temperatures in its core reach tens of millions of degrees — hot enough for hydrogen atoms to “fuse” together to make helium. In fact, the Sun converts more than 650 million tons of hydrogen to helium every second. A small fraction of the hydrogen is converted to energy, which makes the Sun shine.

That same process powers most of the stars in the universe. And it’s the first step toward creating all the chemical elements on the periodic table.

For the least-massive stars, the process actually stops there. Their cores can’t get hot enough to make anything but helium. For stars that are roughly half the mass of the Sun or heavier, though, the process continues.

When a star that’s as massive as the Sun converts the hydrogen in its core to helium, the core shrinks, which makes it much hotter. When it gets hot enough, the next cycle of nuclear reactions begins. This round makes mainly carbon, nitrogen, and oxygen. Stars that are a bit heavier than the Sun make more of these elements, along with a smattering of a few others.

When the star dies, most of the heavier elements are trapped in its dead core. But a few of them are expelled into space along with the star’s outer layers, which are still made of hydrogen. These elements may then be incorporated into new stars, planets, and perhaps living organisms — creation born in the hearts of stars.

We’ll talk about what happens in the heaviest stars tomorrow.

Script by Damond Benningfield

Every time you take a breath, you’re filling your lungs with elements created in the heart of a star. If you take an iron supplement, you’re ingesting an element forged in the heart of a massive star. And if you put on a silver necklace, you’re wearing an element created in the death of a massive star.

In fact, almost all the elements were created by stars. The main exceptions are the lightest and simplest elements — hydrogen, helium, and a smidgen of lithium.

Hydrogen came first — or at least hydrogen nuclei: single protons created in the first fraction of a second after the Big Bang. After a few minutes, the universe had cooled enough that two protons and two neutrons could stick together to form the nuclei of helium.

After a few hundred thousand years more, the universe cooled enough to allow electrons to stick to the bare nuclei, turning them into complete atoms.

Over time, the hydrogen and helium started clumping together to make stars. The cores of these stars were hot enough to ignite the fires of nuclear fusion, which combine lightweight atoms to make heavier ones — eventually making almost all the elements we see in the universe today.

Yet hydrogen and helium continue to dominate the chemical brew. Hydrogen accounts for about three-quarters of all the mass in the universe, with helium accounting for about a quarter. Everything else makes up less than two percent of the total — forged in the hearts of stars.

More tomorrow.

Script by Damond Benningfield

The North Star is one of the most important beacons in the sky. It serves as a compass, pointing the way due north. And it also serves as the hub of the sky — all the other stars appear to circle around it as Earth turns on its axis.

More than 4,000 years ago, the architects of ancient Egypt used the North Star to align the pyramids of Giza. And more than four decades ago, Apollo astronauts used it to help guide them to the Moon. But the two groups were guided by different north stars. The Egyptians used a star called Thuban, in the constellation Draco. And the astronauts used Polaris, at the end of the handle of the Little Dipper.

Thuban didn’t explode or fade away — it’s still in plain sight. Instead, Earth’s axis turned away from the star — an effect called precession.

It’s caused by the gravitational tug of the Sun and Moon, which cause our planet to wobble like a spinning top. As it wobbles, the axis points toward different stars. Four millennia ago, it aimed at Thuban. Today, it aims at Polaris.

Over the next century, the pole will actually take slightly better aim at Polaris. Right now, the star is about two-thirds of a degree from where the axis is pointing. Around the year 2100, it’ll be less than half a degree from the pole.

After that, though, the pole will move away from Polaris. By around the year 4100, it’ll take aim at a star that’s one constellation over, in Cepheus — a North Star to guide future generations.

Script by Damond Benningfield

The Moon and the bright star Aldebaran continue a game of “peek-a-boo” this evening that they’ve been playing for more than two years. The Moon will pass directly in front of the star, blocking it from view. The entire event will be visible across most of the United States.

This is just one of a series of such disappearing acts, known as occultations, that began in January of 2015. The Moon has passed in front of the star every month since then, although not all of the events have been visible from the U.S.

Over the decades, occultations have helped astronomers learn a lot about quite a few stars, including Aldebaran. The amount of time it takes the star to disappear behind the Moon, for example, helps reveal how big the star is. In the case of Aldebaran, occultations and other techniques show that it’s more than 40 times the diameter of the Sun — a true giant among stars.

Occultations can also reveal companion stars. In those cases, a system’s brightness exhibits a two-step drop as the star disappears behind the Moon, and a two-step rise as it returns to view — one “step” for each star. Aldebaran shows no such profile, indicating that it travels alone.

Look for Aldebaran close above the Moon as darkness falls. It passes behind the nighttime portion of the Moon, then emerges below the illuminated portion of the Moon a bit later. The exact timing depends on your location, as the Moon and Aldebaran once again play peek-a-boo.

Script by Damond Benningfield

 

The Sun has been pretty quiet the last few years. It’s on the downward slope of its 11-year magnetic cycle, so only a few dark sunspots have marked its surface. The numbers should stay low awhile longer, until the cycle heads toward its peak in the next decade.

Astronomers have measured magnetic cycles in quite a few other stars. And they’ve found one star with a cycle that appears to be a little longer than the Sun’s — more than 11 years. And thanks to an orbiting planet, they’ve even been able to map its starspots, which show a pattern similar to the Sun’s.

HAT-P-11 is a bit smaller, cooler, and redder than the Sun, and it takes about the same amount of time to spin on its axis.

It’s orbited by a planet that’s about the size of Neptune, one of the giants of our own solar system. The planet crosses in front of the star every few days, blocking some of the star’s light. Observations by telescopes on the ground and in space found that the amount of starlight that’s blocked varies by a tiny amount. That’s because the planet sometimes passes in front of the dark starspots, which don’t add much to the star’s overall brightness.

By tracking the planet through 200 crossings, astronomers mapped hundreds of starspots. They found that the star has more spots than the Sun, and many of them are bigger than typical sunspots. But they appear at the same latitudes as the spots on the Sun, giving HAT-P-11 some dark bands on either side of its equator.

Script by Damond Benningfield

Our closest planetary neighbor remains in good view early this month. Venus is the “evening star,” shining from about 32 million miles away. Despite its beauty, though, it’s not a friendly place to visit. Its surface is extremely hot, and it has a dense, toxic atmosphere.

The closest planet beyond our solar system could be similar to Venus. Then again, it could be similar to our own Earth.

Proxima Centauri b orbits our closest neighboring star, Proxima Centauri, which is four and a quarter light-years away. The planet is probably dense and rocky, like Earth and Venus. And it lies inside the star’s habitable zone — the distance from the star where temperatures are just right for liquid water.

That doesn’t mean the planet is actually habitable, though. A lot depends on what happened when it was young.

Proxima Centauri is small, cool, and faint. When the star was born, though, it was much hotter and brighter than it is now. That means a lot could have happened to the young planet.

Researchers looked at many possible early conditions for it — with a thick atmosphere and lots of water on its surface, for example. They found that the young star could have vaporized both of them, leaving the planet dry and airless, or with a Venus-like atmosphere. But many scenarios led to conditions that were more like Earth.

We won’t know what Proxima Centauri b is really like until future telescopes allow us to get a direct look at this neighboring world.

Script by Damond Benningfield