It would be fascinating to get close to Cygnus X-3. Unfortunately, it also would be deadly. The system is bathed in X-rays and ultraviolet radiation. It features powerful “jets” that blast into space like energy cannons. And it probably has a black hole – a one-way trip to oblivion.

Cygnus X-3 is in the swan, which swoops across the eastern sky on these early summer evenings. The system itself is too faint to see. In fact, we can’t see its visible light even with the largest telescopes because it’s hidden behind thick clouds of dust.

But we can see it in other wavelengths, including X-rays, gamma rays, and radio waves. Those forms of energy have allowed astronomers to piece together the system’s likely story.

Cygnus X-3 probably consists of a black hole plus a brilliant companion. The companion probably is a dozen or more times the Sun’s mass, and a couple of hundred thousand times its brightness.

The bright star is blowing huge amounts of gas into space. The black hole grabs some of the gas, which forms a spinning disk around the black hole. Some of the gas is funneled into high-speed jets that fire into space. One of those jets is aimed almost directly at Earth.

The brilliant companion star is likely to explode in the next million years or so, with its core collapsing to form another black hole. But the blast might rip the system apart – perhaps causing Cygnus X-3 to fade away.

Script by Damond Benningfield

425 years ago, a “new” star flared to life near the neck of Cygnus, the swan. The star slowly faded, then flared twice more during the 17th century. It’s remained visible ever since. And someday soon, it’ll flare up again – for the last time: It’ll explode as a supernova.

P Cygni is more than 5,000 light-years away, so it must be extremely bright for us to see it at all. And in fact, it’s one of the brightest stars in the entire galaxy – 600 thousand times brighter than the Sun.

P Cygni is so brilliant because it’s 35 to 40 times the mass of the Sun. Such a monster burns through the nuclear fuel in its core in a hurry. So even though P Cygni is only a few million years old – compared to four and a half billion years for the Sun – it’s nearing its end.

The earlier outbursts might have erupted because the star’s interior is unstable. It gets so hot that the star blasts some of the gas at its surface into space. There’s evidence that similar outbursts took place thousands of years earlier.

P Cygni is likely to explode within a couple of million years. Its core might collapse to form a super-dense neutron star – or even a black hole.

Under dark skies, P Cygni is visible to the eye alone. At nightfall, it’s in the east-northeast, close to the right of Sadr, the bright star that connects the swan’s body to its wings.

More about the swan tomorrow.

Script by Damond Benningfield

Cygnus, the swan, soars gracefully through summer nights. Its brightest star, Deneb, is in the northeast at nightfall. It marks the swan’s tail. The swan’s body stretches to the right, parallel to the horizon. The wings extend above and below, connected to the body by the star Sadr.

Cygnus contains many star clusters. The list includes several that stretch from Sadr to the south, roughly along the swan’s neck. The clusters contain a few dozen to a few hundred stars. All of them are young – no more than about 10 million years old. And many of them are especially hot, bright, and massive.

The clusters are indirectly related. They belong to much larger collections of young stars, plus the raw materials for making more stars. A “wave” passed through that region of the galaxy, squeezing gigantic clouds of gas and dust. Clumps of material within the clouds collapsed, forming stars.

Over the next few million years, the most massive stars will explode as supernovas. Shockwaves from the blasts may compress more pockets of gas and dust, creating more stars. But the clusters themselves won’t survive much longer – at least on the galactic timescale. They’ll be pulled apart by the gravity of the surrounding stars and clouds, so their stars will go their separate ways.

The clusters are easy targets for good binoculars. One is just a whisker from Sadr. Several others trail off to the right – sparkly decorations for the swan.

Script by Damond Benningfield

The Royal Observatory at Greenwich has been one of the most important skywatching sites in history – not so much for what it told us about the stars, but for its role right here on Earth. Its location marked the starting point for measuring longitude – the position east and west on the globe. It also marked the time standard for the entire world: Greenwich Mean Time.

The observatory was established on today’s date in 1675, by King Charles II. It was built on a hill near London, overlooking the Thames.

Greenwich was created to provide highly accurate maps of the stars, and to measure the motions of the Sun, Moon, and planets. The work was designed to help sailors determine their longitude. Establishing longitude at sea was extremely difficult – and dangerous; many ships crashed because their navigators didn’t know where they were.

The observations also played a key scientific role: they helped confirm that the motions of the Sun, Moon, and planets were governed by Isaac Newton’s laws of gravity.

In 1833, the observatory began a “time service.” It dropped a ball from a tall pole at precisely 1 p.m. That allowed mariners to set their clocks before they sailed. Greenwich later transmitted the time to the whole country by telegraph, then radio.

The observatory was moved in the 20th century, and closed in 1998. Today, the Greenwich site is a museum – preserving an important part of world history.

Script by Damond Benningfield

The only astronomical object most of us notice in the daytime sky is our star, the Sun. Its light makes the sky bright, which overpowers the other stars and almost everything else. But there are a couple of exceptions: the Moon and the planet Venus.

During its 29-and-a-half-day cycle of phases, the Moon spends half of its time in the daytime sky – the hours between sunrise and sunset. But it’s so pale compared to the Sun that it can be hard to notice.

That’s especially true when the Moon is in its crescent phase, as it is now. At dawn tomorrow, the Sun will light up only about one-eighth of the lunar hemisphere that faces our way. So the Sun will look millions of times brighter than the Moon.

As twilight begins, the Moon will continue to dominate the sky. But as twilight gets brighter, the Moon will appear to fade. It’s still just as bright, but against the daytime sky it’s hard to see. But you can still spot it, leading the Sun across the sky.

At dawn, Venus stands to the lower right of the Moon. It’s the brilliant “morning star.” Until sunrise, only the Moon outshines it. Venus also fades into the blue of the daytime sky. But it is visible to the unaided eye. It leads the Moon up the sky in the morning, and down the sky in the afternoon. It’s hard to find, but once you see it, you’ll wonder why you never noticed it before – a bright planet shining through the bright blue sky.

Script by Damond Benningfield

The Sun is at a standstill. Oh, it’s still orbiting the center of the galaxy at an impressive clip – about half a million miles per hour. And it’s still moving across the sky as Earth turns on its axis. But the points along the horizon at which the Sun rises and sets aren’t changing.

That’s because today is the summer solstice. It’s a point in Earth’s orbit that marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

We have seasons because Earth is tilted on its axis. At the June solstice, the north pole tilts toward the Sun, bringing more sunlight to the northern hemisphere. Six months later, the south pole tilts toward the Sun, giving the northern half of the globe shorter days and longer nights.

Between the solstices, the Sun moves north and south in the sky. So its rising and setting points move north and south as well. At some times of year, if you have a good way to mark these points, you can see the difference from day to day.

But the Sun appears to “stand still” along the horizon for a few days on either side of the solstice. In fact, the word solstice means “Sun stands still.” At the June solstice, the Sun is farthest north for the year, so it rises and sets to the north of due west. Just how far north depends on your latitude.

Incidentally, the summer solstice is also the longest day of the year, so there’s plenty of sunlight as we head into summer.

Script by Damond Benningfield

The number of confirmed planets in other star systems has reached about 6,000. But few of those planets are likely homes for life. Most are too hot, too cold, too “gassy,” or they’re zapped by too much radiation by their star.

A few planets are in the “well, maybe” category. They might be suitable for life, but the conditions aren’t perfect.

An example is a planet in the star system 82 Eridani. The system is about 20 light-years from Earth, and its star is similar to the Sun.

Astronomers have confirmed three planets in the system, with hints of more. Two of the planets are quite close to the star, so they’re too hot for life like that on Earth. But the third planet is more intriguing.

It’s about six times the mass of Earth, so it could be dense and rocky. Its average distance from the star is about a third farther than Earth’s distance from the Sun. At that range, the planet spends most of its time in the star’s habitable zone – the region where conditions are most comfortable for life.

But the planet’s orbit is so lopsided that the distance varies by more than a hundred million miles. So as the planet moves around 82 Eridani, surface temperatures range from hot enough to boil water to cold enough to freeze the entire surface. That makes it unlikely that anything lives on the planet. It is possible that life could exist below the surface – avoiding the extremes on this “yo-yoing” planet.

Script by Damond Benningfield

Astronomers have been searching for planets around one of our closest neighbor stars for decades. And they’ve reported the discovery of several. But the reports have come to naught – until now. Earlier this year, a team confirmed the presence of four planets – all of them smaller than Earth.

Barnard’s Star is six light-years away. Only the three stars of the Alpha Centauri system are closer. The star is much smaller and less massive than the Sun, and less than one percent as bright. In fact, it’s so faint that it wasn’t discovered until a little more than a century ago.

Barnard’s Star is ancient – probably twice the age of the Sun or older. So if it has planets, there’s been plenty of time for life to take hold. That’s made finding planets a high priority.

Last year, a team of astronomers confirmed one planet, and said there might be three more. All of those were confirmed in March. None of the planets is more than a third the mass of Earth. And they’re so close in that they orbit the star in a week or less. So even though Barnard’s Star is faint, the planets are all too hot to provide comfortable conditions for life.

Barnard’s Star is in Ophiuchus, the serpent-bearer. The constellation stretches across the east and southeast in early evening, and stands high in the south later on. But Barnard’s Star is too faint to see without a telescope.

We’ll have more about exoplanets tomorrow.

Script by Damond Benningfield

If you stare at one of the giant planets of the outer solar system long enough, with a big enough telescope, you’re likely to find some moons.

That was certainly the case a couple of years ago for Saturn. A research team scanned the space near Saturn with a large telescope in Hawaii. And earlier this year, the team reported its results: a haul of 128 previously unseen moons. That brought the planet’s total to 274. That’s three times the number of moons for second-place Jupiter – at least for now.

The newly found moons are small and faint – no more than a few miles in diameter. They follow odd orbits, including some that orbit backwards – in the opposite direction from Saturn’s rotation.

Some of the moons may be chunks of space rock that were captured by the giant planet’s gravity. Others may be the remains of larger moons that were blasted apart by collisions.

About a third of the moons may be the remnants of a single impact. They form a group named Mundilfari for a Norse god related to Saturn. It’s possible the impact took place within the past hundred million years – adding lots of little moons to Saturn’s family.

Look for Saturn near our own moon the next couple of mornings. The planet looks like a bright star. It’ll stand to the lower left of the Moon at dawn tomorrow, and closer to the right of the Moon on Thursday.

Tomorrow: a passel of planets for a nearby star.

Script by Damond Benningfield

If you sit on a big beachball, it gets mashed down. That makes it a little wider through the middle, and a little narrower from top to bottom. And that makes it look a lot like Alderamin, the brightest star of the constellation Cepheus the king. The star is about a third wider through the equator than through the poles. That’s not because some cosmic giant is sitting on it. Instead, it’s because the star spins like crazy.

Alderamin is about 50 light-years away, so it’s a fairly close neighbor. It’s nearing the end of the prime phase of life, even though it’s billions of years younger than the Sun. That’s because it’s twice as massive as the Sun. Heavier stars “burn” through their nuclear fuel much faster than lighter stars.

What really stands out about Alderamin, though, is its shape. The star’s equator rotates once every 12 hours, versus almost four weeks for the Sun. That forces gas outward around its middle, making the star look a bit more like a fat lozenge than a ball. As Alderamin continues to age, though, it will puff up to many times its current diameter. That will slow down its high-speed rotation, giving Alderamin a “rounder” appearance.

Cepheus is in the north and northeast at nightfall. Under fairly dark skies it’s easy to make out. It looks like a child’s drawing of a house. The peak of the roof is on the left during the evening, with Alderamin marking the top right corner of the sideways house.

Script by Damond Benningfield