StarDate Podcast

High school chemistry students the world over know the work of Russian scientist Dmitri Mendeleev — he’s one of the inventors of the periodic table of the elements. But Mendeleev’s interests went far beyond what he could see in the laboratory — and he was willing to risk his neck to pursue them. 125 years ago today he rose through the clouds in a hot air balloon to watch a total solar eclipse. Even though he was his own pilot, he didn’t know how to land a balloon. In fact, he’d never even been in one. Solar eclipses were prized scientific events. Among other things, they offered the only chance to study the Sun’s hot outer atmosphere, the corona, which is too faint to see through the daytime sky. Mendeleev took off from a village in western Russia, and climbed to an altitude of more than two miles. He recorded detailed observations of the eclipse, then turned his attention to how to get down. He figured it out and soon landed safely — his valuable eclipse notes in hand. He left his post with Saint Petersburg University a few years later. But he continued to pursue his diverse interests — helping set up Russia’s first oil refinery, for example, and establishing a national standard for vodka. Decades after his death, scientists named an element that was created in the laboratory in his honor. Mendelevium is the 101st element on the periodic table — one of the many legacies of a scientist who climbed to meet the Sun. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Since the late 19th century, the science and technology of astronomy have made great leaps forward. But one thing hasn’t changed much: the weather. Clouds can still ruin a night of stargazing. In the 19th century, though, they could do more than just blot out a few hours of observations — they could ruin months of planning and cost the equivalent of hundreds of thousands of dollars. In August of 1887, for example, Amherst astronomer David Todd led an expedition to Japan to view a total solar eclipse. Such events offered rare glimpses of the Sun’s corona — its hot but faint outer atmosphere — as well as explosions of hot gas from the Sun’s surface. Todd spent months planning the expedition. He and his crew spent a month in transit, traveling from Boston to Vancouver via railroad, then to Yokohama via steamship. Todd then spent several weeks more scouring the country for a good viewing site. The group set up several large Sun-watching telescopes, plus several smaller telescopes and cameras. A nearby volcano belched fire and smoke on the night of August 18th, but all was clear by the following morning — the day of the eclipse. An hour before the eclipse began, though, clouds arrived. Except for one short break, they remained overhead until after the eclipse was done — leaving the expedition with little to show for its months of work. An astronomer in Russia found a way to avoid the clouds — a risky one — and we’ll talk about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A star system that offers plenty of variety is in the west on August evenings. It’s above yellow-orange Arcturus, one of the brightest stars in the night sky. 44 Bootis is pretty faint, though, so you need dark skies to see it, and a good sky chart wouldn’t hurt. A good backyard telescope shows two stars, not one. The brighter of the two is quite similar to the Sun — about the same size, color, brightness, and mass. What no telescope can show you is that the other star is in fact two stars on its own. One of them is a little smaller and fainter than the Sun, while the other is smaller still. Even though 44 Bootis is only about 40 light-years away, not even big research telescopes can separate the two stars. That’s because they aren’t actually separate — they touch each other. In fact, they share the gas in their outer layers, with the gas circulating around the cores of both stars. The two cores are separated by just three-quarters of a million miles — three times the distance from Earth to the Moon — so they whirl around each other about four times a day. And recent observations suggest there’s yet another component in the 44 Bootis system — a brown dwarf. The object hasn’t been confirmed, but if it exists it’s probably a few dozen times the mass of Jupiter, the solar system’s largest planet. That would put it just below the cutoff line for true stars — adding to the variety of this odd little star system. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Family dynamics are complicated. And that’s especially true of a star system in Draco, the dragon. One or two stars in the system may be driving two more into each other’s arms. RZ Draconis is more than 1700 light-years away, so it’s far too faint to see with the eye alone. And even with a telescope, the system looks like a single pinpoint of light. But careful measurements of the system’s light reveal that it’s more than just a single star. The two largest stars of RZ Draconis are so close together that they’re almost touching. In fact, the gravitational attraction between them is so strong that each star bulges out toward the other. Observations over many years show that the stars may be moving closer together. If so, that could be the influence of one or two other stars in the system. There’s at least one other star, and some observations suggest there are two more. These stars are much smaller and cooler than the system’s two big stars. Yet their gravitational influence could rob the close-together pair of momentum, causing the stars to spiral closer together. Eventually, they may touch each other, and even trade the gas in their outer layers. In essence, that would create two stellar cores surrounded by a single envelope of hot gas. In time, they could even merge to form a single star — an event that would really stir up the family dynamics. More about stars that reach out and touch each other tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Many stars have close companions — other stars that are so close that the two whirl around each other once every few days. But a few take closeness to the extreme — they enfold each other in a warm embrace. The first “contact binary” ever discovered is known as W Ursae Majoris. It’s in Ursa Major, the great bear, which is the home of the Big Dipper. The Dipper is in the northwest at nightfall, with faint W Ursae Majoris well to its right. More than a century ago, two German astronomers noticed that the system’s brightness varied by a factor of two every four hours. They considered several possibilities for the rapid change. Their best guess was that the two stars were so close together that they eclipsed each other every four hours. Later observations found that one star is a bit bigger and heavier than the Sun, while the other is smaller. But the two stars are the same brightness and color — something that shouldn’t happen for two stars of different mass. That means the stars are not just touching each other, but they’re also sharing the gas in their outer layers. The gas from the bigger star pumps up the temperature and brightness of the other. The stars may have formed a bit farther apart and slowly spiraled together, or they could be the product of a single star that split apart soon after its birth. Either way, the two are among the closest of stellar siblings — locked in a perpetual embrace. More about contact binaries tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If you like sunrises and sunsets, the planet Mercury would be an interesting world to visit. The planet has no atmosphere, so there’s none of the vivid color that comes with sunrise and sunset here on Earth. But Mercury has something that Earth doesn’t. It can have two sunrises and sunsets, or two sunsets and sunrises, all within a few hours of each other — and all at the same point along the horizon. Mercury is visible for a few days through the glow of our own sunrise. It’s quite low in the east about 30 or 40 minutes before sunrise. It looks like a fairly bright star, but you need a clear horizon to see it. It’s easier to find tomorrow morning, because it’s close to the lower left of the Moon. The odd mixture of sunrises and sunsets is a result of Mercury’s long day and its orbit around the Sun. Mercury spins slowly, so on average, it’s about six Earth months between one sunrise and the next. But Mercury’s orbit is stretched out, so its orbital speed varies. As a result, the Sun moves across the sky at an uneven pace. It can stop and even reverse direction — creating the odd sequences of sunrises and sunsets. Although there’s no air to create twilight, the sky would brighten a bit before the Sun climbed into view — the result of the Sun’s hot outer atmosphere, called the corona. The silvery corona would form a hazy dome of light above the horizon — one more reason to enjoy a sunrise on the little planet Mercury. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Only three large bodies are closer to the Sun than Earth is right now — the Moon and the planets Venus and Mercury. And all three of them are on display in the dawn sky for the next couple of mornings. Shortly after first light tomorrow, look for brilliant Venus, the “morning star,” above the Moon, with much fainter Mercury farther to the lower left of the Moon. Earth’s average distance to the Sun — a measurement known as the astronomical unit — is about 93 million miles. Since the Moon orbits our planet, its average distance to the Sun is the same. But right now, the Moon is on the sunward side of its orbit, getting ready to cross the line between Earth and the Sun. Because of that, it’s a couple of hundred thousand miles closer to the Sun than Earth is. Venus is the next planet inward — a bit less than three-quarters of Earth’s distance from the Sun. Venus follows the most nearly circular orbit of any planet in the solar system, so its distance from the Sun changes by only a tiny amount. Mercury is the closest of the Sun’s planets — only about a third of Earth’s distance. But Mercury’s orbit is highly eccentric, which means its distance to the Sun varies dramatically — by about 15 million miles. Because of that, the Sun would appear obviously larger and smaller in the sky over the course of Mercury’s year. The Sun can do some other odd things in Mercury’s sky as well, and we’ll have more about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The work week kicks off with a beautiful encounter in the dawn sky — a conjunction between the crescent Moon and Venus, the “morning star.” After the Moon, Venus is the brightest object in the night sky. It’s so bright that at first glance, you might think it’s a lot closer than it really is — perhaps an approaching airplane with its landing lights turned on. Even the professionals can get confused. Early last year, for example, a pilot who was waking up from a nap on an overnight trans-Atlantic flight briefly mistook the planet for a nearby cargo plane. That’s not the first time a pilot has mistaken Venus for something else. Over the years, some pilots have even given chase. People on the ground have chased the planet, too, while others thought it was chasing them — a bright light in the sky that they couldn’t seem to shake. And lots of people have reported the planet as a UFO. That’s all just an illusion, though. If you watch for a minute or so, you’ll see that Venus isn’t moving — it’s remaining in the same spot compared to the stars around it. So if you happen to be driving down a dark country lane before dawn over the next few months, and a brilliant point of light in the sky seems to be following you, just relax. That’s not a flying saucer, it’s the brightest pinpoint of light in the night sky — the planet Venus. Well, it’s probably Venus, anyway. More about Venus, the Moon, and another bright object tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon couldn’t be in a more perfect spot tonight. For one thing, it forms a beautiful display in tomorrow’s pre-dawn sky as it lines up between Jupiter and Venus, the brightest objects in the night sky after the Moon itself. Venus is well below the Moon at first light, with Jupiter above it. And for another, the Moon is a thin crescent, so it adds almost no glare to the night sky. And that’s important because the Perseid meteor shower it at its best tonight. The lack of brilliant moonlight will make it easier to see the fireworks — but only if you can get away from city lights. The Perseids are one of the year’s best showers. At its peak, you can generally see several dozen “shooting stars” over a period of a few hours. Those streaks of light have nothing to do with the stars, though. They’re bits of rocky debris left behind by Comet Swift-Tuttle as it orbits the Sun. As Earth flies through the comet’s path, some of the bits of cometdust slam into the atmosphere at tens of thousands of miles per hour. They quickly vaporize, creating bright but brief streaks of light in the night sky. As seen from the United States, the Perseids should be at their best before dawn tomorrow. So if you’re out in the wee hours of the morning, you could be in for a double astronomical treat — the lineup of Jupiter, the Moon, and Venus, and a brief display of celestial fireworks. We’ll have more about the Moon and its companions tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A planet that may have helped give the Moon a pummeling huddles close to the Moon tomorrow morning. Jupiter looks like a brilliant star to the lower left of the Moon. They climb into view by about 2 or 2:30, and are high in the sky at first light. And to spice things up a bit, the bright orange star Aldebaran is about the same distance to the lower right of Jupiter. Earth, the Moon, and the other planets of the inner solar system took a beating from giant asteroids during the solar system’s first half-billion years or so. But a recent study by researchers at the NASA Lunar Science Institute found that it was especially intense at the end of that period — about four billion years ago. The researchers studied the contours of craters around an ancient volcanic plain. The observations suggest the craters were formed by asteroids that were moving much faster than those that hit the Moon before or after. The bombardment may have been triggered by changes in the orbits of Jupiter and Saturn. As their distance from the Sun changed, the gravity of the two planets — particularly Jupiter — kicked a group of large asteroids toward the inner solar system. Some of the asteroids then slammed into the Moon and Earth. Wind, rain, and the motions of the crust have erased any traces of this bombardment on Earth, but it’s preserved in the craters of the Moon — the scars of an ancient pummeling. More about the Moon and its companions tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A bright triangle adorns the western sky the next few evenings. It’s fairly low in the west-southwest as night begins to fall, and slides to the lower right over the following couple of hours. The top point of the triangle is the planet Saturn, with the star Spica to its lower left and the planet Mars to its lower right. Saturn is the brightest of the three, although not by a whole lot. The configuration will change from night to night as Saturn and particularly Mars move against the background of true stars. That’s because the planets are much closer to Earth than the stars are. As these worlds orbit the Sun, they loop all the way through the starry background. Mars is less than one-fifth as far as Saturn is right now, so it moves a greater distance across the sky from night to night — the result of the combined orbital motions of Earth and Mars itself. The three objects will remain close together for a while, but their configuration will change. Mars will pass between Saturn and Spica early next week, so for a couple of nights the triangle will become a more-or-less straight line. And after that, Mars will move to the left of the other two, forming an ever-widening triangle. Spica and Saturn are dropping closer to the Sun as seen from Earth, so they’ll disappear in the twilight by late next month. But Mars won’t be done for quite a while. It will remain in view until early next year. Tomorrow: One big happy family. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon climbs into good view by midnight tonight. It’s just a couple of days before last quarter, so sunlight illuminates a bit more than half of the lunar hemisphere that faces our way. The rising Moon has played a big role in the skylore, mythology, and even the artwork of many cultures. The Luba and Tabwa cultures of modern-day Congo, for example, have associated it with divination. The rising Moon represents a heightened state of awareness, and shamans often paint their faces with a white pigment that represents moonlight. Special bowls created for those ceremonies are among the artworks on display at a new exhibit at the Smithsonian’s National Museum of African Art in Washington, D.C. Called “African Cosmos: Stellar Arts,” it’ll continue until December. The exhibit shows how the Moon, Sun, stars, and other sky phenomena have inspired African artists from ancient times to the present. It includes more than a hundred sculptures, masks, paintings, and other objects. An Egyptian mummy board, for example, shows the sky goddess Nut. And sculptures by the Dogon people of Mali depict origin myths that connect Earth and the sky — a disk for each realm linked by giant trees. And if you can’t make it to the museum, you can always get your own inspiration from the rising Moon and the rest of the night sky — a great canvas with a new picture every single night. And we’ll talk about one of those pictures — a star and two planets — tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The second-brightest star in the sky is starting to emerge from the glare of the brightest. According to centuries-long tradition, that brings to an end to Dog Days of summer. Sirius is the brightest star in the night sky. It’s just climbing into view in the morning glow of the brightest star in the daytime sky — the Sun. Sirius is quite low in the east-southeast a little before sunrise. It’s best seen from the southern tier of states, although it’ll pull into better view from the northern states during August. Sirius is the leading light of the constellation Canis Major, the big dog, so it’s also known as the Dog Star. And that’s where we get the name for this part of summer — the Dog Days. Sirius makes its closest approach to the Sun during the summer, disappearing for a few weeks in the Sun’s glare. In ancient times, it returned to view in the morning sky by early July — just as the weather was reaching its hottest. It seemed logical that Sirius was the cause — its light and heat added to the Sun's to bring things to a simmer. So the people of ancient Greece and Rome named the period of the year after Sirius returned to view in the morning sky in the star’s honor. Thanks to an effect known as precession, over the centuries the stars shift position with respect to the Sun. So Sirius now returns to view a few weeks later, with the heat in full force at mid-northern latitudes — the Dog Days of summer. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The plan for landing the Curiosity rover on Mars sounds like something created by the “Mythbusters”: Use a heat shield, a parachute, retrorockets, and a “sky crane” — a hovering platform that’ll winch the rover the final few feet to the surface. Oh, and you’ve got just seven minutes for the entire sequence — and unlike one of the Mythbusters’ favorite sayings, failure is not an option. Curiosity is scheduled to land tonight in Gale Crater, a wide basin with a tall mountain at its center. The crater may once have been filled with water. During its two-year main mission, the nuclear-powered rover will look for evidence of that ancient water in layers of rock at the base of the mountain, plus the rocks and dirt around the mountain. Its measurements will help scientists determine whether the region was habitable in the distant past. That mission depends on a successful landing, which is the most complicated yet attempted. A precisely controlled entry into the Martian atmosphere should place Curiosity inside a target landing zone that’s just 12 miles long. Earlier rovers used airbags to cushion their final drop. But Curiosity is too big for that — it weighs a ton, and it’s the size of a minivan. Instead, a rocket-powered descent stage will hover just 65 feet above the surface and use the sky crane to winch the rover to a gentle landing — and the start of the most extensive exploration of the Martian surface to date. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

What do the Mars Opportunity rover and a bear have in common? They both hibernate during the winter. In the rover’s case, it’s because it needs all the power its solar cells gather during the short days to keep it warm during the bitter nights. The next Mars rover won’t have that problem. Curiosity, which is scheduled to land tomorrow night, will be powered by a small nuclear generator. The radioactive decay of plutonium will generate heat. The generator will convert some of the heat to electricity, while the rest goes directly toward keeping the rover warm. That’ll allow it to keep moving — and working — all year ’round. Nuclear generators have been flying in space for decades. They powered the instruments that Apollo astronauts left on the Moon, and the twin Viking missions to Mars in the 1970s. They’ve also powered every spacecraft that’s visited Jupiter and the other outer planets. Two of those craft are still working after 35 years in space. Curiosity is the largest and most ambitious Mars rover yet. It needs far more power than the earlier rovers to keep its wheels turning and its cameras clicking. The nuclear generator offers one other advantage. Martian dust settles on top of solar cells, blocking some of the sunlight and cutting the amount of power the cells can produce. The nuke won’t have that problem. It should keep Curiosity working through dust storms, darkness — and the long Martian winter. More about Curiosity tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.