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

Io, one of the big moons of Jupiter, might be the toughest solid body to map in the entire solar system. That’s because its surface is constantly changing – the result of major volcanic activity.

Io is about the same size as our own moon. And it’s the “rope” in a tug-of-war between Jupiter and two of its other big moons. They pull at Io, squeezing and heating its interior. That’s created about 400 major volcanic features – mountains, lava flows, and lakes of molten rock. Some of the volcanoes produce plumes that are up to 300 miles high, while the lakes are up to 300 miles long.

Scientists have wondered whether the volcanoes are fed by a global “ocean” of magma below the surface, or by individual magma chambers. Recent observations by the Juno spacecraft suggest the “individual” model.

Scientists tracked Juno’s radio waves as the craft flew less than a thousand miles from Io. The wavelength changed slightly as a result of Io’s gravity. The way it changed revealed details about Io’s interior. And the change didn’t match what scientists expected to see if there was a global ocean. Instead, Io’s volcanoes may be fed by hundreds of underground hotspots – chambers that are making it hard to keep the maps of Io up to date.

Jupiter is close to the Moon tonight. It looks like a brilliant star to the lower left of the Moon. Through binoculars, Jupiter’s four big moons look like tiny stars near the giant planet.

Script by Damond Benningfield

The Moon is taking a journey through time the next couple of nights. It’s crossing the constellation Taurus. It’ll pass close to several of the bull’s most prominent features, plus another visitor – the planet Jupiter.

Jupiter looks like a brilliant star well to the upper left of the Moon. The bull’s brightest stars, Aldebaran and Elnath, line up below and above Jupiter. And the Pleiades star cluster is close below the Moon.

These objects are at different distances from Earth, so we see them as they looked at different points in time. That’s because light travels at a limited speed. It’s a high speed – 670 million miles per hour. But cosmic distances are so vast that it takes a long time to cross them.

The Moon is our closest neighbor, so moonlight takes only about one and a third seconds to reach Earth.

Jupiter also is in our own solar system, so it’s quite close by astronomical standards. Right now, it takes about 45 minutes for its light to reach Earth.

The stars are much, much farther. Aldebaran is about 65 light-years away, so its light takes 65 years to reach us. Elnath is twice as far, so its light headed our way in the late 1800s.

And the Pleiades is farther still. Its hundreds of stars are at different distances. But the average is about 445 light-years. So the light you see from the Pleiades tonight began its journey in the 1500s.

More about the Moon and Jupiter tomorrow.

Script by Damond Benningfield

Black holes are creeping up on us. A space telescope has discovered several black holes in recent years that are much closer than any found before. The closest is just 1,560 light-years away – right in our cosmic back yard.

The black hole is a member of a binary system known as Gaia BH1. Gaia is a European space telescope that’s been looking at more than a billion stars. It’s plotting the distances to those stars with amazing accuracy. And that’s how it found BH1.

Gaia was watching a star that’s a near-twin to the Sun. But the star showed a big “wiggle” – it was being pulled by the gravity of an unseen companion. Calculations showed that the companion is almost 10 times the mass of the Sun, but it produces no energy. That means the companion must be a black hole.

The star and black hole are separated by a little more than the distance from Earth to the Sun. That’s too far for the black hole to pull gas from the star. So the black hole is dormant – it’s not feeding on anything.

Eventually, though, the star will reach the end of its prime phase of life. It will swell to dozens of times its current diameter. That should allow the black hole to roar to life – as it feasts on a dying companion.

Gaia BH1 is in Ophiuchus. The serpent bearer is high in the south at first light. Its outline looks like a giant coffee urn. BH1 is inside the urn – a black hole lurking close to Earth.

Script by Damond Benningfield

The star at the top of Leo’s head has lots of aliases. Its formal name is Algenubi – from a longer Arabic name that means “the southern star of the lion’s head.” But most astronomers call it by its “Bayer” name – Epsilon Leonis. That naming system was devised centuries ago, using letters of the Greek alphabet to indicate a star’s priority in its constellation – its brightness or position.

But Algenubi has several dozen other designations. Most of them are from catalogs compiled over the ages. Some of the catalogs highlight different forms of energy, such as radio waves or X-rays. Others classify stars based on their temperature or composition. And some are observing lists for space telescopes.

Algenubi is a class “G” star, indicating that its surface is about the same temperature as the Sun’s. But the Sun is a “dwarf” star, which means it’s in the prime of life. Algenubi, on the other hand, is a giant or sub-giant. It’s puffed up to more than 20 times the Sun’s diameter. That’s made it a few hundred times brighter than the Sun, so it’s easily visible from about 230 light-years away – one of Leo’s most remote bright stars.

Leo stretches high across the east and southeast in early evening. Look for its brightest star, Regulus. Leo’s head and mane form a backward question mark to the upper left of Regulus. Algenubi is at the outer point of the question mark – a bright star with many names.

Script by Damond Benningfield

The lion springs high across the sky on spring evenings. Leo is led by Regulus, one of the brighter stars in the night sky. It represents the lion’s heart or one of his front paws. And it really is an impressive star – bigger, brighter, and heavier than the Sun.

The star at the lion’s tail is no slouch, either. Denebola also is bigger, brighter, and heavier than the Sun. It spins much faster than the Sun – so fast that it bulges outward at the equator. And it’s billions of years younger than the Sun. Because of its greater mass, though, it will live a much shorter life than the Sun will.

Regulus and Denebola both played important roles in the skylore of ancient cultures. In Persia, for example, Regulus was one of the “guardians of heaven” – four bright stars along the Sun’s path across the sky. Each guardian was thought to reign over its own quadrant of the sky.

Denebola served as a calendar marker. Ulugh Beg, a 15th-century astronomer and mathematician, called the star Al Sarfah – “the changer.” The name indicated that the weather changed as the star moved across the sky. It first appeared in the dawn sky around the middle of September, as the summer heat abated – a change in seasons pulled along by the tail of the lion.

Denebola stands a third of the way up the eastern sky as night falls, well to the lower left of the lion’s bright heart.

We’ll talk about a star in the lion’s head tomorrow.

Script by Damond Benningfield

A partial solar eclipse will dim the skies over the northeastern United States early tomorrow – weather permitting, of course. Other parts of the world will have a slightly better view, including much of Europe and Asia.

A solar eclipse happens when the new Moon passes directly between Earth and the Sun. During a partial eclipse, the alignment isn’t perfect, so the Moon covers only part of the Sun’s disk.

This eclipse begins in the wee hours of the morning in the northeastern states. At the peak of the eclipse, the Moon will cover about 90 percent of the solar disk. That’s enough to make the sky appear a little dusky, and to lower the temperature a bit.

From the United States, the eclipse will be underway as the Sun rises. The best view will be from Maine.

As we all know from recent eclipses, it’s not safe to look directly at the Sun even when it’s partially covered up – it’s still so bright that it can damage your eyes. So use eye protection to stay safe – special eclipse glasses or dark welder’s glass. You can also stand beside a tree and watch as it casts tiny images of the partially eclipsed Sun on the ground. And you can always find an eclipse broadcast online.

For the rest of the United States, the eclipse will be over by the time the Sun rises. And the contiguous 48 states won’t see another good total eclipse – when the Moon completely covers the Sun – until August of 2045.

Script by Damond Benningfield

Those are the sounds of cosmic attacks – massive storms on the Sun firing energy and particles into Earth’s magnetic field. Such outbursts can damage orbiting satellites, cause radio blackouts, foul GPS signals, and even knock out power grids on the surface. And there are indications that we haven’t seen the worst the Sun can produce.

The outbursts are generated by magnetic storms on the Sun. Lines of magnetic force get tangled up, then snap, creating a solar flare. Such an outburst also can produce a massive eruption of charged particles. When those outbursts reach Earth, they cause problems.

The most powerful outburst yet seen was the first one ever seen, in 1859. It knocked out telegraph networks and created brilliant displays of the northern and southern lights. Tree rings and ice cores provide evidence of even stronger outbursts in centuries past.

And a recent study found that Sun-like stars produce outbursts that are a hundred to a thousand times more powerful than anything we’ve seen from the Sun. The researchers looked at observations made by Kepler space telescope more than a decade ago. They studied more than 50,000 stars that are similar to the Sun. And they found almost 3,000 superflares. That’s an average of one superflare per star every century – suggesting that we haven’t seen the worst from our sometimes-cranky star.

Script by Damond Benningfield

The star cluster Messier 3 is a beautiful sight – a sparkly ball of half a million stars. But the view from the cluster would be even more spectacular. M3 is high above the plane of the Milky Way, so the galaxy would spread out below it like a brilliant pinwheel.

M3 is a globular cluster – a dense ball a few hundred light-years in diameter. Its stars are among the oldest in the entire galaxy. They formed just a couple of billion years after the Big Bang. All of the cluster’s heavy stars have long since died, so almost all that’s left are stars that are less massive than the Sun.

Such stars are fairly faint. But there are so many of them that the cluster is an easy target for binoculars, even though it’s about 34,000 light-years away.

Most of the stars and clusters in the galaxy lie in a wide, thin disk. But globular clusters range far above and below that disk. Right now, M3 is about 30,000 light-years above the disk. So most of the galaxy would spread out below it. If there are inhabited planets in the cluster, its residents would have some spectacular views – hundreds of thousands of stars close by, and a giant galaxy of stars arrayed below them.

M3 is in Canes Venatici, the hunting dogs. The cluster is low in the east-northeast in early evening, and is a beautiful sight through binoculars or a telescope.

Tomorrow: super-flares.

Script by Damond Benningfield

The universe is put together like Swiss cheese – some regions are the cheese; others are the holes. The “cheese” consists of clusters and superclusters of galaxies. The “holes” are just that – cosmic voids. The largest voids span more than a billion light-years.

Cosmic voids were discovered half a century ago. Astronomers were looking deep enough into the universe to map its structure on the largest scale. They’d expected the universe to look the same in all directions – a smooth blend of galaxies. Instead, they found a web – overlapping filaments of galaxies, with big spaces between.

The voids might be there because there were tiny differences in the density of matter in the early universe – especially dark matter. The gravity in the denser regions pulled material together to make stars and galaxies. That left the less-dense regions almost empty. They contain a few galaxies, some gas and dust, and some dark matter, but not much else.

More than 6,000 voids have been cataloged. They clump together to make supervoids. One of the closest is the Boštes Void – “the Great Nothing.” It’s centered about 700 million light-years away, and it spans more than 300 million light-years – a giant “hole” in the universe.

Boštes climbs into view in early evening. Look for the bright yellow-orange star Arcturus, which is low in the east by 9 or 10 o’clock. The Great Nothing stretches to the upper left of Arcturus.

Script by Damond Benningfield