StarDate

The full Moon has an especially close companion tonight: Spica, the brightest star of Virgo. From the eastern half of the country, they’ll appear to almost touch each other as night falls. They’ll be a bit farther apart for those in the west, but still close.

A dozen American astronauts walked on the Moon, with the final steps coming half a century ago. Their missions are among those commemorated today – the International Day of Human Spaceflight. The day was established by the United Nations, in 2011, to “celebrate the beginning of the space era for all mankind.”

That era began on this date in 1961, when the Soviet Union launched the first human into space. Yuri Gagarin made one orbit around Earth aboard Vostok 1, then parachuted to the ground after re-entering the atmosphere. Exactly 20 years later, the United States launched the first space shuttle. The U.N. General Assembly named those missions, along with the first Moon landing, as motivation for the Day of Human Spaceflight.

The first celebration of the date came in 2001. A private group created “Yuri’s Night,” which continues today. It combines science and engineering with music, art, and other activities.

Space centers, museums, planetariums, and other venues host events to celebrate the date. If you can’t make it, though, celebrate on your own by watching the Moon – the site of the first human steps beyond our own planet.

Script by Damond Benningfield

Jantar Mantar, in Jaipur, India, is a fantasy land of science and architecture. Built in the 1700s, it houses about 20 astronomical instruments: beautiful arches, domes, and spires designed to plot the motions of the Sun and other objects.

The observatory was founded by Maharaja Jai Singh II. It was one of five observatories he built across northern India, in the 1720s and ’30s. All of them were known as Jantar Mantar – a name that means “calculating machine.” The Jaipur site was the largest and most important. It’s also the best preserved.

Jantar Mantar’s instruments were all designed to observe the heavens with the eye alone. Several of those were for tracking the motions of the Sun. And some of them were the largest of their kind ever built. One sundial, for example, had a shadow-casting marker almost 75 feet tall. The instruments allowed the site’s 20 or so astronomers to determine the time with an accuracy of just two seconds. They also set the calendar.

Other instruments tracked the positions of the stars and planets. That includes a set of a dozen identical instruments, each of which aligned to one of the constellations of the zodiac. That provided important observations for court astrologers.

The site was in steady use until about 1800, and intermittent use after that. It underwent several upgrades and restorations. Today, it’s a World Heritage site – an astronomical fantasy land.

Script by Damond Benningfield

Ulugh Beg was a poor politician and warrior. Just a year after becoming leader of the central Asian kingdom of Transoxiana, he was deposed by his son – then beheaded. Yet he was one of the top scientists and educators of his time. He built a school and observatory at the capital city of Samarkand. Astronomers there made highly accurate measurements of the heavens – two centuries before the invention of the telescope.

Construction of the observatory began in 1420, and was completed a few years later. The complex consisted of a tall, round building that housed a variety of instruments.

The main one was a quadrant – a quarter of a circle. It was the largest one ever built – 130 feet from center to rim. Its base was carved into a hillside, making it highly stable. And it was aligned with the meridian – the north-south line that passes directly overhead. Astronomers used precise markings on the instrument to measure the positions of the Moon, Sun, planets, and stars.

From those observations, they determined the length of a year to within a minute of the modern value. They calculated the tilt of Earth’s axis. And they published the first major star catalog in 1600 years.

The observatory was destroyed soon after Ulugh Beg was killed. It was rediscovered in 1908 – a long-forgotten astronomical treasure.

Script by Damond Benningfield

In the modern-day universe, stars face a weight limit – about 150 times the mass of the Sun. Anything heavier would be so hot and bright that it would blow away any more gas that tried to fall on its surface, keeping it from getting bigger.

In the early universe, though, the weight limit might have been much higher – hundreds of times the mass of the Sun. Such stars would have blazed millions of times brighter than the Sun.

The difference is caused by slight changes in the recipe for making stars. The early universe contained only hydrogen, helium, and a tiny smattering of a couple of other elements – all forged in the Big Bang. As the universe expanded and cooled, these elements clumped together to make stars.

The cores of these newborn stars were hot enough to ignite nuclear fusion, which forces lighter elements together to make heavier ones. More-massive stars plowed through their hydrogen and helium quickly, forging carbon, oxygen, and many other elements. And when they could no longer sustain the fusion reactions, they exploded. The energy of these blasts created many more elements.

The explosions filled the universe with many of these heavier elements, which could be incorporated into later generations of stars.

Models of star formation say these extra ingredients inhibit the growth of stars that are born today. The stars can still grow to monstrous proportions – just not as monstrous as when the universe was young.

Script by Damond Benningfield

Almost every star is a ball of hydrogen and helium, the simplest of all chemical elements. All of the hydrogen and most of the helium were forged in the Big Bang.

Stars also contain smatterings of heavier elements. In astronomical jargon, these elements are known as metals. They were forged by the stars themselves. As the stars die, they expel some of these elements into space, where they can be incorporated into new stars. So each generation of stars contains a higher fraction of metals – everything from carbon and oxygen to iron and lead.

Based on the amount of metals, astronomers divide stars into two broad categories – population I and II.

The Sun belongs to population I. These stars contain fairly high levels of metals – about two percent in the case of the Sun. Such stars formed fairly recently – after earlier generations had pumped the heavy elements into space.

The earliest generations yet seen form population II. These stars have a much smaller percentage of metals, which means they formed when there were fewer metals around – perhaps less than a billion years after the Big Bang. In our home galaxy, the Milky Way, many population II stars are found in globular clusters – balls of hundreds of thousands of stars on the galactic outskirts.

The levels of metals indicate that some of these stars are up to 13 billion years old.

The very first stars shouldn’t contain any metals at all. More about that tomorrow.

Script by Damond Benningfield

The star that marks the heart of the lion has received a giant gift from a companion star. That gift has completely changed both stars.

Regulus is below the Moon as night falls this evening, and even closer to the Moon as they set, in the wee hours of the morning.

The star we see as Regulus is called Regulus A. It’s much bigger, brighter, and heavier than the Sun. But it’s even more impressive now than when it was born. That’s because it has a close companion that was heavier than Regulus. More-massive stars die more quickly. As they die, they puff up. So as the companion expired, it began dumping gas onto Regulus A. That made Regulus A much bigger and heavier.

Those weren’t the only effects, though. The surface of Regulus A got much hotter and brighter. That made the star look at least a billion years younger than it really is.

As gas flowed in from the companion, it also made Regulus A spin much faster. Today, it rotates once every 16 hours. By comparison, it takes almost a month for the Sun to rotate. So Regulus A bulges out at the equator.

Finally, the surface of Regulus A has a higher concentration of “metals” than the Sun does – elements other than hydrogen and helium. Many of the heavier elements were forged in the heart of the companion, then dumped onto the surface of Regulus A – one of many changes triggered by a now-dead stellar companion.

We’ll have more about the metals in stars tomorrow.

Script by Damond Benningfield

Most stars consist almost entirely of hydrogen and helium, the lightest and simplest chemical elements. But there’s a smattering of other ingredients as well – everything from oxygen to platinum. These elements can be tough to measure, though. For one thing, there’s not much of them – they add up to only a fraction of one percent of all of a star’s atoms. And for another, they’re usually concentrated deep inside the star, where they’re hidden from astronomical instruments.

But one class of stars likes to show off some of those elements. All of the stars in this class are much hotter than the Sun. They’re known as mercury-manganese stars, because they can show concentrations of these and similar elements that are thousands of times greater than in other stars.

Such a star doesn’t really have more of these elements, though. Instead, more of the elements have been dredged up from deep inside. Radiation from the star’s core may push these elements to the surface, where we can see them. On the other hand, gravity pulls other types of elements toward the core, so the stars show unusually low levels of those elements.

One good example of a mercury-manganese star is Gienah, the brightest star of Corvus, the crow. The constellation is low in the southeast as night falls, and due south around midnight. Its brightest stars form the outline of a small sail. Gienah is at the top right corner of the sail.

Script by Damond Benningfield

The Mars InSight lander has been silent for two and a half years. Yet the craft is still teaching us about the Red Planet. In particular, it’s revealing more about what killed it: dust and the fickle Martian winds.

InSight landed in late 2018 and operated for four years. It listened for marsquakes, and monitored the weather. It even recorded the soft sigh of the winds.

The wind lofts the dust that coats much of Mars high into the sky. The dust then settles back to the surface.

That “settling” was a problem for InSight. The lander was powered by the Sun. But as dust fell on its solar panels, they generated less and less energy. Scientists hoped the wind would clear the dust away, but it didn’t. So by late 2022, with its solar panels coated with dust, InSight fell silent.

Scientists still keep an eye on the craft through images from a Mars orbiter. The pictures show that dust has completely covered the solar panels, giving them the same reddish orange appearance as the surrounding landscape. And the area cleared away by the lander’s rocket blast has filled in with dust as well. That tells scientists more about the planet’s winds and dust – the “killers” of Mars InSight.

Mars stands close to the lower right of the Moon at nightfall. Its dust gives the planet an orange tint. Pollux and Castor – the twins of Gemini – line up farther to the right of the Moon.

Script by Damond Benningfield

The first-quarter Moon is gliding across the constellation Gemini tonight. Gemini’s twin stars and the planet Mars form a bright arc above and to the upper left of the Moon at nightfall.

Mars is the brightest member of the arc. It’s roughly twice as bright as the star Pollux, which is twice as bright as Castor.

Pollux is just 34 light-years away. And it hosts a giant planet – one of our closest planetary neighbors. The planet isn’t likely to be inhabited, though – the star, the planet, and the system’s age all conspire against life.

The star is past the prime stage of life, so it’s puffed up to giant proportions. That bathes the planet in light, making it hot. The planet – known as Thestias – is about three times the mass of Jupiter, the giant of our own solar system. That means it’s a ball of gas, with no solid surface – probably not a good home for life. And the system is only a bit more than a billion years old, so there hasn’t been a lot of time for life to take hold.

On the other hand, if the planet has big moons, conditions there might be a bit more favorable for life. But those conditions won’t last long. Pollux will grow bigger and brighter in the future, making the moons even hotter. After that, the star will cast off its outer layers, blasting the planet and moons. Only the star’s hot, dead core will remain – zapping the surroundings with deadly radiation.

More about the Moon and Mars tomorrow.

Script by Damond Benningfield

The United States has launched a couple of dozen nuclear-powered space missions. But only one used nuclear fission – the process that powers commercial power plants on Earth. Called Snapshot, it was launched 60 years ago today.

The Atomic Energy Commission had been experimenting with nuclear power systems for space for years. It came up with a couple of alternatives. One used the decay of radioactive elements to generate heat, which is converted to electricity. That system has powered many missions throughout the solar system.

The other design used nuclear fission – it split atoms apart, releasing energy. The commission developed a reactor called SNAP-10A. It was launched on April 3rd, 1965. And it quickly went to work, as explained in a commission film about the project:

During the second orbit, less than four hours after launch, a radio command signal to activate the startup circuits was transmitted. Approximately six hours after initiating the startup command, the reactor was operating. At the beginning of the ninth orbit, a little more than eight hours after reactor startup, the SNAP-10A system was at full power, producing more than 500 watts of electricity. Mission accomplished.

Snapshot operated for 43 days. The United States hasn’t launched another fission reactor since then. But it’s considering reactors for future missions to the Moon and Mars – descendants of a “snapshot” in space.

Script by Damond Benningfield