You’ll find lots of visitors in the downtown of any major city. That may also be the case with the “downtown” of our home galaxy, the Milky Way. A recent study found that one of the stars in the galaxy’s core probably was born far outside that region. The core contains a supermassive black hole that’s more than four million times the mass of the Sun. Swarms of stars encircle the black hole – some of them quite close. But the black hole’s gravity is so powerful it would stir up any star-forming gas and dust around it, preventing the birth of stars. So the stars that are close to the black hole must have been born elsewhere, then migrated in toward the black hole. One of those stars is cataloged as SO-6. The new study found that it’s no more than two-thirds of a light-year from the black hole, and perhaps a good bit closer. The star is probably about 10 billion years old – twice as old as the Sun. And it’s nearing the end of its life – it’s gotten bigger and cooler, forming a red giant. That suggests it’s about the same mass as the Sun. But its chemical composition doesn’t match that of most of the stars in the core. Instead, it’s a closer match for the stars in many of the small galaxies that surround the Milky Way. So SO-6 could have started 50,000 light-years or more from its current location, then migrated into the core – a visitor to “downtown” Milky Way. Script by Damond Benningfield

The black hole at the center of the Milky Way Galaxy is a light eater – at least it is today. But 200 years ago, it could’ve had a feast. That would have made it shine hundreds or thousands of times brighter than it is today. The black hole is called Sagittarius A-star. It’s more than four million times the mass of the Sun. That’s actually pretty small for a black hole in a galaxy as big as the Milky Way. Like all supermassive black holes, it’s encircled by a disk of gas. Some of that material funnels into the black hole. As it does, it gets hot enough to shine at many wavelengths, including X-rays. How bright it gets depends on the mass of the disk – how much stuff the black hole is eating. Today, the X-ray glow is fairly steady, but faint. But a space telescope has detected some X-ray-bright areas a couple of hundred light-years from the black hole. Those areas could have been illuminated when the black hole flared up about 200 years ago. The black hole might have wolfed down an unlucky asteroid or a small cloud of gas and dust – a feast for the black hole, accompanied by a short but bright flare-up. The black hole is in Sagittarius, which is in the southern sky on summer evenings. Its brightest stars form the outline of a teapot. The black hole is above the spout of the teapot, but it’s hidden behind clouds of dust – 27,000 light-years away. More about Sagittarius tomorrow. Script by Damond Benningfield

Sagittarius has a bit of an identity crisis. It’s easy to see – just not as what it’s supposed to be. In mythology, Sagittarius was known as the archer. But that title doesn’t tell the whole story. He was actually a centaur – a creature with the head and torso of a man, but the body and legs of a horse. He was holding a bow, however – aimed at the nearby scorpion. To modern eyes, though, the constellation looks like something a little less fearsome: a teapot. It’s low in the south-southeast at nightfall, with the handle to the left and the spout to the right. If you have even moderately dark skies, it’s not hard to find. Sagittarius lies along the glowing band of the Milky Way – millions of stars that outline the disk of the Milky Way Galaxy. And the constellation contains the brightest part of the Milky Way – the Large Sagittarius Star Cloud. It appears to rise from the spout of the teapot like a cloud of steam. It’s so bright because it’s toward the center of the galaxy, so we’re looking through a thick layer of stars. The center itself is concealed behind clouds of light-absorbing dust. So we don’t see the full glory of the Milky Way’s core. Astronomers use instruments that are sensitive to infrared and other wavelengths to see through the dust. The core also contains a supermassive black hole – a monster that’s more than four million times the mass of the Sun. We’ll have more about that tomorrow. Script by Damond Benningfield

The fat gibbous Moon creeps up on the planet Saturn tonight. Saturn is to the lower left of the Moon as they climb into good view, before midnight, and looks like a bright star. If you remove its beautiful rings, Saturn itself looks a bit bland – like a slightly flattened beachball colored in bands of yellow, tan, and white. The bands are formed by clouds. Saturn is a big ball of gas that spins rapidly, so the clouds are stretched into bands that completely encircle the planet. If you look at those bands closely, though, Saturn takes on a more artistic appearance, like the works of a great Impressionist. Waves form at the boundaries between bands, spinning off whorls and eddies that are as big as continents. Giant storms sometimes bubble up from deep within the planet. These blobs are quickly sheared apart by Saturn’s rotation. As they spread, they form waves and gyres that resemble cream swirling into a cup of hot coffee. Saturn’s poles are among the most amazing views of all. The cloud bands around them form hexagons – the result of standing waves that constantly slosh around the planet. And there are vortexes at the poles themselves, with splashes of white clouds floating atop them – brilliant accents that crown Saturn’s beauty. Again, look for the bright planet Saturn close to the Moon tonight, beginning before midnight. Tomorrow: an arrow-wielding centaur transforms into a teapot. Script by Damond Benningfield

[Launch Control: 25 seconds…] When space shuttle Columbia headed for orbit 25 years ago tomorrow, it made history. It was the first mission commanded by a woman – Air Force pilot Eileen Collins. And it was carrying the heaviest payload ever lofted by a shuttle: Chandra X-Ray Observatory – the largest X-ray telescope ever flown. [Launch Control: 5, 4, 3, we have a go for engine start, zero. We have booster ignition and liftoff of Columbia! Reaching new heights for women and X-ray astronomy.] And Chandra is maintaining those heights – it’s still working. The telescope studies some of the hottest and most energetic objects and events in the universe – exploding stars, outbursts from normal stars, gas around black holes, and much more. Such objects produce much of their energy in the form of X-rays. But Earth’s atmosphere blocks most X-rays, so the only way to study them is from space. Chandra’s orbit carries it more than a third of the way to the Moon. That puts it outside most of Earth’s radiation belts, which can “fog” X-ray images. X-rays go right through a normal telescope mirror. So Chandra uses a set of mirrors along the sides of the telescope tube. X-rays graze off those mirrors and come to a focus at the telescope’s instruments. Chandra is still making history today – by keeping a sharp “eye” on the X-ray sky. Script by Damond Benningfield

Pluto is at its best now. It’s lining up opposite the Sun. It rises around sunset and is in the sky all night. It’s brightest for the year as well. Don’t bother looking for it, though, unless you have a good-sized telescope. Clyde Tombaugh was using a good-sized telescope when he discovered Pluto, in 1930. He’d been searching for a possible planet beyond Neptune for about a year, from Lowell Observatory in Arizona. When he found it, the little world was moving through Gemini. Almost a century later, Pluto has advanced only a third of the way around the sky. That’s because Pluto is so remote that it takes 248 years to orbit the Sun – and to complete a single loop through the constellations. Today, it’s in the southwestern corner of Capricornus. Pluto doesn’t move evenly across the sky. Its distance from the Sun varies from about 30 to almost 50 times Earth’s distance – a difference of 1.8 billion miles. It moves a lot faster when it’s closest to the Sun, so it crosses more of the starry background. Pluto won’t complete its first orbit since its discovery until the year 2178 – when it will once again appear in Gemini. For now, although you can’t see it, you can at least see its location. It’s between the handle of the “teapot” formed by the constellation Sagittarius, and the wide triangle that marks Capricornus. Tonight, that puts it not far to the upper right of the Moon. Script by Damond Benningfield

Black holes are everywhere. There could be a hundred million black holes that are the remnants of dead stars in the Milky Way Galaxy alone. But because they’re completely dark, they’re hard to find. That applies even to the biggest member of the class yet discovered. It’s 33 times the mass of the Sun – more than half again the mass of the galaxy’s previous record holder. The black hole is in a system known as BH3. It was discovered by the Gaia space telescope, which is mapping more than a billion stars in the galaxy. The system is almost 2,000 light-years from Earth. The black hole revealed its presence only because it has a “normal” companion star. The companion is nearing the end of its life, so it’s becoming a giant – bigger and brighter than the Sun. Gaia measured a wobble in the star’s motion. Astronomers analyzed the wobble, and decided that it was caused by the gravitational pull of a black hole. The black hole probably formed when a supergiant star collapsed at the end of its life. That happened billions of years ago, when the galaxy was young – a conclusion supported by the age of the companion. The composition of the supergiant allowed it to form an especially heavy black hole – the biggest remnant black hole in the galaxy. BH3 is to the left of the bright star Altair, the breast of the eagle, which is in the east at nightfall. But the system is much too faint to see without a big telescope. Script by Damond Benningfield

The human eye is tuned to a narrow band of wavelengths: visible light. But the electromagnetic spectrum extends far beyond our ability to see – from radio waves to gamma rays. Each slice of the spectrum tells us different things about the universe. Consider X-rays. We’re most familiar with them in medical settings. But many astronomical objects produce their own X-rays, allowing astronomers to diagnose their details. The list includes many types of stars. Many stars have hot, X-ray-producing outer atmospheres. Stars also generate big eruptions, known as flares. Studying these events tells us more about how stars age, and how they interact with the universe around them. X-rays are especially common in some of the most violent objects and events in the universe. Exploding stars heat their environment to millions of degrees – producing X-rays galore. And disks of hot gas around black holes are also X-ray sources. The X-rays can reveal the amount of gas, the size of the disk, and how fast the gas is moving. There’s one problem, though: Earth’s atmosphere absorbs X-rays. So astronomers loft their telescopes as high as possible. They’ve used rockets, balloons, and a rocket-balloon combination called a rockoon. But most of what we know about the X-ray sky came from space telescopes. The largest and most powerful X-ray telescope to date was launched 25 years ago next week, and we’ll talk about that on Monday. Script by Damond Benningfield

If you ever visit the planet Mercury, take along your old eclipse glasses. They’re not for looking at the Sun – you might need something even darker for that. Instead, you might want them just to see your way across the planet itself. Mercury is so close to the Sun that sunlight is more than 10 times more intense than on Earth. Mercury is the closest planet to the Sun – an average of about 40 percent of Earth’s distance. But Mercury’s orbit is the most lopsided of any of the Sun’s major planets. So when Mercury is closest to the Sun, sunlight is almost two-and-a-half times as intense as when the planet is farthest. All of that solar energy makes Mercury the second-hottest planet – only Venus is hotter. At the equator, temperatures hit about 800 degrees Fahrenheit. But that doesn’t mean you couldn’t beat the heat. Mercury doesn’t have an atmosphere to circulate heat around the planet. So nighttime temperatures drop to almost 300 below zero. And the bottoms of some craters at the poles never see the Sun at all. They stay cold enough to preserve big deposits of ice – perfect places to beat the heat on a scorching planet. Mercury is just peeking into view in the evening twilight. It looks like a fairly bright star, quite low in the west as night falls. The view is better from southern locations. So while you might not see it at all from Minneapolis, you shouldn’t have any trouble from San Antonio or Miami. Script by Damond Benningfield

You don’t have to be an astronaut to see the far side of the Moon – at least some of it. A little bit of that hemisphere wobbles into view every month – an effect known as “libration.” So we can actually see 59 percent of the lunar surface. The Moon is “locked” in such a way that the same hemisphere always faces Earth. That means we see the same features all the time – the same dark volcanic plains, and the same lighter-colored jumbles of mountains, valleys, and craters. Almost. As the Moon orbits Earth, we get some peeks at the other hemisphere – the far side. The Moon is tilted a bit on its axis, for example. So as it orbits Earth, it appears to “nod” up and down a bit – just as Earth appears to nod as seen from the Sun. That allows us to see just beyond the north and south poles. Also, the Moon’s distance from Earth isn’t constant – it varies by almost 30,000 miles. As a result, the Moon’s orbital speed goes up and down. But the rate at which the Moon spins on its axis remains constant. That allows us to see a little bit around the eastern and western edges – glimpses of a little bit of the lunar farside. As darkness falls this evening, we’ll see a little bit beyond the north pole. We’ll also see a little bit beyond the western limb – or would if that part of the lunar disk weren’t in darkness. As a bonus, the Moon has a close companion: Antares, the bright heart of the scorpion. Script by Damond Benningfield