Saturn is a ball of hydrogen and helium gas wrapped around a dense, rocky core. Saturn spins so fast that it bulges outward at the equator, so the planet is much thicker at the equator than through the poles.
Saturn’s clouds are colored in subtle shades of yellow and tan. Saturn's rapid rotation and its layered structure produce a magnetic field. Observations by the Cassini spacecraft suggest that the field may be changing, which could mean that Saturn's interior is changing as well. Cassini monitored radio waves produced by the magnetic field as a way to measure Saturn's rotation rate. (Because Saturn has no solid surface, it's impossible to measure its rotation by tracking surface features like mountains or canyons.) But the craft found that the rotation rate appeared to have slowed by about six minutes since the Voyager missions two decades earlier. Scientists believe that Saturn is not actually slowing down. Instead, one possible explanation says that changes in the planet's core are creating changes in the magnetic field.
Saturn's clouds contain ammonia, methane, and other toxic compounds. They are buffeted by winds of up to 1,000 miles (1,600 km) per hour, and they contain violent storm systems that produce lightning blasts a million times more powerful than those on Earth.
Saturn's most prominent feature, though, is its extensive ring system.
Galileo Galilei discovered the rings in the early 17th century.
In his small, crude telescope, though, they looked like "bumps" on the side of the planet. Five decades later, Dutch astronomer Christaan Huygens, who had recently discovered Saturn's largest moon, Titan, detected a bit of space between Saturn and the bumps. He deduced that the bumps were really planet-circling rings.
Today, astronomers know that thousands of individual rings make up Saturn's ring system. Some rings are made of small bits of frozen water, others contain tiny grains of dust, and still others are a mixture of the two. In all, the rings are only a few hundred feet thick. Several small moons orbit inside or just outside the ring system. These "shepherd" satellites help keep the ring particles in place, but they also sculpt some rings into odd shapes, with twists and kinks.
Saturn's rings probably formed when a small moon or a comet passed close to Saturn and was pulled apart by the planet's gravity.
Although Saturn has no solid surface to stand on, humans may someday view its rings from close range. They may walk on some of its icy moons or even float above Saturn's clouds in big balloons. From such a lofty vantage point, the rings would form wide, sparkling bands across the sky. Sometimes, icy particles from the inner edge of Saturn's rings may fall into the planet's atmosphere, creating bright "shooting stars" as they streak through the sky of this delicate giant.
Showing posts with label ASTRONOMY. Show all posts
Showing posts with label ASTRONOMY. Show all posts
Friday, October 2, 2009
Sunday, September 13, 2009
Astronomy (Sept. 15th and 16th 2009)
Venus, the “morning star,” is to the lower left of the Moon at first light on the 15th, with Mars above the Moon. Venus is close to the left of the Moon on the 16th. Regulus is to their lower left.
Leo, the Lion
The zodiacal constellation Leo, the lion, is one of a handful of constellations that really does look like its namesake. Look for Leo high in south in April and May.
Leo's brightest star is blue-white Regulus, one of the brightest stars in the night sky. Regulus rises almost due east, with the body of the lion following it into the sky over the next couple of hours. Once Regulus climbs into the sky, look to its left toward the north for a group of stars forming a backward question mark. These stars outline Leo's head and mane.
About two hours later, look low in the east for Leo's tail a white star named Denebola an Arabic name that, means "tail of the lion."
Leo, the Lion
The zodiacal constellation Leo, the lion, is one of a handful of constellations that really does look like its namesake. Look for Leo high in south in April and May.
Leo's brightest star is blue-white Regulus, one of the brightest stars in the night sky. Regulus rises almost due east, with the body of the lion following it into the sky over the next couple of hours. Once Regulus climbs into the sky, look to its left toward the north for a group of stars forming a backward question mark. These stars outline Leo's head and mane.
About two hours later, look low in the east for Leo's tail a white star named Denebola an Arabic name that, means "tail of the lion."
Tuesday, September 8, 2009
Astronomy (Sept. 13th and 14th 2009)
September 13-14, 2009
Mars rises just below the Moon on the morning of the 13th (around 1-2 a.m.), and a little farther above it on the 14th. Pollux and Castor, the twin stars of Gemini, align to the left of the Moon on the 14th.
Gemini, the Twins
Gemini is easy to find as it glides high overhead in mid-winter, above and to the left of Orion. It's two brightest stars Castor and Pollux represent the mythological twins brothers of Helen of Troy.
Many cultures have seen two humans in this star pattern marked by two roughly parallel lines of stars capped by two of the brightest stars in our night sky. But the legend that endures is that of Castor and Pollux. Gemini's two brightest stars bear the names of the twins.
Pollux is the brighter of the twins. It's an orange giant star that's about 35 light-years from Earth. Castor consists of six stars, a cosmic sextet locked in a gravitational ballet. This crowded system lies about 50 light-years from Earth.
Mars rises just below the Moon on the morning of the 13th (around 1-2 a.m.), and a little farther above it on the 14th. Pollux and Castor, the twin stars of Gemini, align to the left of the Moon on the 14th.
Gemini, the Twins
Gemini is easy to find as it glides high overhead in mid-winter, above and to the left of Orion. It's two brightest stars Castor and Pollux represent the mythological twins brothers of Helen of Troy.
Many cultures have seen two humans in this star pattern marked by two roughly parallel lines of stars capped by two of the brightest stars in our night sky. But the legend that endures is that of Castor and Pollux. Gemini's two brightest stars bear the names of the twins.
Pollux is the brighter of the twins. It's an orange giant star that's about 35 light-years from Earth. Castor consists of six stars, a cosmic sextet locked in a gravitational ballet. This crowded system lies about 50 light-years from Earth.
Sunday, August 30, 2009
Constellations, Sagittarius and Scorpius
Sagittarius, the Archer Sagittarius, the archer, whose brightest stars form the shape of a teapot slides low across the southern sky of summer. Sagittarius has drawn his bow, and his arrow is pointing at Antares, the bright red heart of Scorpius, the scorpion. The archer is avenging Orion, who was slain by the scorpion's sting.
The constellation Sagittarius is one of the most interesting regions of the sky. The center of our Milky Way galaxy lies inside Sagittarius, about 26,000 light years away. The constellation also contains several globular clusters tightly packed collections of hundreds of thousands of stars.
Antares
Antares is a yellow-orange supergiant star 600 light-years away in the constellation Scorpius.
The star Antares marks the "heart" of Scorpius, the scorpion. It is the brightest star in Scorpius. It's the most difficult to see in the early twilight, but as the sky gets darker, it stands out more. Antares also stands out because of its color. While most of the stars show little or no color, Antares is a vivid orange. That's the result of its surface temperature, which is thousands of degrees cooler than the Sun.
But Antares is a supergiant star, one of the biggest and most massive in our part of the galaxy, so its interior is millions of degrees hotter than the Sun's interior. Like most supergiants, Antares is likely to end its life with a bang, it'll explode as a supernova. That could happen anytime within the next few million years, or as early as tonight.
Scorpius, the Scorpion Three bright stars form the "head" of Scorpius, the celestial scorpion, while its tail curves away below it in the southern sky of summer.
The brightest star in Scorpius is Antares, which is in the middle of the scorpion's curving body. This brilliant red star is one of the behemoths of our stellar neighborhood. If you placed it at the center of our own solar system, it would swallow Mercury, Venus, Earth, and Mars, and almost reach Jupiter.
The constellation Sagittarius is one of the most interesting regions of the sky. The center of our Milky Way galaxy lies inside Sagittarius, about 26,000 light years away. The constellation also contains several globular clusters tightly packed collections of hundreds of thousands of stars.
Antares
Antares is a yellow-orange supergiant star 600 light-years away in the constellation Scorpius.
The star Antares marks the "heart" of Scorpius, the scorpion. It is the brightest star in Scorpius. It's the most difficult to see in the early twilight, but as the sky gets darker, it stands out more. Antares also stands out because of its color. While most of the stars show little or no color, Antares is a vivid orange. That's the result of its surface temperature, which is thousands of degrees cooler than the Sun.
But Antares is a supergiant star, one of the biggest and most massive in our part of the galaxy, so its interior is millions of degrees hotter than the Sun's interior. Like most supergiants, Antares is likely to end its life with a bang, it'll explode as a supernova. That could happen anytime within the next few million years, or as early as tonight.
Scorpius, the Scorpion Three bright stars form the "head" of Scorpius, the celestial scorpion, while its tail curves away below it in the southern sky of summer.
The brightest star in Scorpius is Antares, which is in the middle of the scorpion's curving body. This brilliant red star is one of the behemoths of our stellar neighborhood. If you placed it at the center of our own solar system, it would swallow Mercury, Venus, Earth, and Mars, and almost reach Jupiter.
Tuesday, August 25, 2009
Aquila, the Eagle
There are 88 constellations covering the entire northern and southern sky.
Aquila, the Eagle: Aquila glides on outstretched wings through the glowing band of the Milky Way. Look for it high in the south in late summer.
The brightest star in Aquila is a white star about 16 light-years from Earth called Altair, the Arabic word for eagle. Altair is the southern point of a pattern of three bright stars called the Summer Triangle. Deneb, in the constellation Cygnus, forms the triangle's northeastern point. Vega, in Lyra, the harp, is in the northwest. Altair is nice and bright and easy to find right up to the beginning of winter.
Cygnus, the Swan: The brightest stars of Cygnus form a cross, so the swan is also known as the Northern Cross. Find it soaring high overhead during late summer evenings.
The constellation's brightest star is Deneb, an Arabic word that means "the tail." Deneb the tail of the swan, marks the top of the cross. The swan's outstretched wings form the horizontal bar of the cross, while the head of the swan, a double star called Albireo is the bottom of the cross.
Although it lies about 1,500 light years from Earth, Deneb shines brightly in our night sky because it's a white supergiant, a star that's much larger, hotter, and brighter than the Sun. Deneb is the northeastern point of a star pattern called the Summer Triangle.
If you use binoculars to scan the area between the two bright stars that define the swan's eastern wing, you'll see the remnant of a supernova a faint, incomplete ring of light called the Cygnus Loop.
Lyra, the Harp: It's easy to find Lyra, the harp, by first finding Vega one of the brightest stars in Earth's night sky. Look for Vega high overhead in mid-summer. Lyra looks like a small, lopsided square, with Vega just beside one of the corners of the square.
Aquila, the Eagle: Aquila glides on outstretched wings through the glowing band of the Milky Way. Look for it high in the south in late summer.
The brightest star in Aquila is a white star about 16 light-years from Earth called Altair, the Arabic word for eagle. Altair is the southern point of a pattern of three bright stars called the Summer Triangle. Deneb, in the constellation Cygnus, forms the triangle's northeastern point. Vega, in Lyra, the harp, is in the northwest. Altair is nice and bright and easy to find right up to the beginning of winter.
Cygnus, the Swan: The brightest stars of Cygnus form a cross, so the swan is also known as the Northern Cross. Find it soaring high overhead during late summer evenings.
The constellation's brightest star is Deneb, an Arabic word that means "the tail." Deneb the tail of the swan, marks the top of the cross. The swan's outstretched wings form the horizontal bar of the cross, while the head of the swan, a double star called Albireo is the bottom of the cross.
Although it lies about 1,500 light years from Earth, Deneb shines brightly in our night sky because it's a white supergiant, a star that's much larger, hotter, and brighter than the Sun. Deneb is the northeastern point of a star pattern called the Summer Triangle.
If you use binoculars to scan the area between the two bright stars that define the swan's eastern wing, you'll see the remnant of a supernova a faint, incomplete ring of light called the Cygnus Loop.
Lyra, the Harp: It's easy to find Lyra, the harp, by first finding Vega one of the brightest stars in Earth's night sky. Look for Vega high overhead in mid-summer. Lyra looks like a small, lopsided square, with Vega just beside one of the corners of the square.
Sunday, August 16, 2009
Astronomy (August 15th and 16th 2009)
On August 15th and 16th Mars is to the lower left of the Moon at first light on the 15th, and closer to the upper right of the Moon on the 16th. The star Aldebaran, which looks like Mars, is to their upper right.
Aldebaran outshines all the other stars that outline the bull's face. But Aldebaran isn't a member of the Hyades cluster, it just lies in the same direction. It's about 70 light-years away, half as far as the stars of the Hyades. Aldebaran is a red-giant, an old bloated star that's used up most of its nuclear fuel. It's much larger and much brighter than our own middle aged Sun.
On August 16 the crescent Moon and the planet Venus highlight the pre-dawn sky tomorrow. Venus is the dazzling "morning star" just below the Moon. Venus, the dazzling morning or evening star, outshines all the other stars and planets in the night sky. It begins the year in the evening sky, well up in the west as darkness begins to fall. It will disappear from view in late March as it passes between Earth and the Sun. It will return to view as a “morning star” by early April, and remain in the morning sky until December.
Aldebaran outshines all the other stars that outline the bull's face. But Aldebaran isn't a member of the Hyades cluster, it just lies in the same direction. It's about 70 light-years away, half as far as the stars of the Hyades. Aldebaran is a red-giant, an old bloated star that's used up most of its nuclear fuel. It's much larger and much brighter than our own middle aged Sun.
On August 16 the crescent Moon and the planet Venus highlight the pre-dawn sky tomorrow. Venus is the dazzling "morning star" just below the Moon. Venus, the dazzling morning or evening star, outshines all the other stars and planets in the night sky. It begins the year in the evening sky, well up in the west as darkness begins to fall. It will disappear from view in late March as it passes between Earth and the Sun. It will return to view as a “morning star” by early April, and remain in the morning sky until December.
Saturday, August 8, 2009
Meteor Shower August 12, 2009
The next meteor shower is the Perseids on August 12, 2009. The shower peaks early afternoon on the 12th, so the morning of the 12th (midnight to dawn) and late evening are the best times to watch from the U.S.
Here are some tips on viewing meteor showers
An increase in the number of meteors at a particular time of year is called a meteor shower. Comets shed the debris that becomes most meteor showers. As comets orbit the Sun, they shed an icy, dusty debris stream along the comet's orbit. If Earth travels through this stream, you will see a meteor shower. Depending on where Earth and the stream meet, meteors appear to fall from a particular place in the sky, maybe within the neighborhood of a constellation.
Meteor showers are named by the constellation from which meteors appear to fall. For instance, The Perseid meteor shower is named because meteors appear to fall from a point in the constellation Perseus.
Shooting stars are name that people have used for many years to describe meteors. Streaks of light across the night sky caused by small bits of interplanetary rock and debris called meteoroids crashing and burning high in Earth's upper atmosphere. Traveling at thousands of miles an hour. Almost all are destroyed, the rare few that survive and hit the ground are known as meteorites.When a meteor appears, it seems to shoot across the sky, and its small size and intense brightness might make you think it is a star.
If you live near a city, drive away from the city lights and toward the constellation from which the meteors will appear to radiate. Find a dark spot where oncoming lights will not ruin your night vision. When you are at your observing spot, position yourself so the horizon appears at the edge of your peripheral vision, with the stars and sky filling your field of view. Meteors will get your attention as they streak by.
If you can see each star of the Little Dipper, your eyes have "dark adapted," and your chosen site is probably dark enough. Under these conditions, you should see plenty of meteors.
What should I pack for meteor watching?
If you can bring red-filtered flashlight for reading star maps and charts without ruining your night vision. Binoculars are not necessary. Its better with just your eyes.
Here are some tips on viewing meteor showers
An increase in the number of meteors at a particular time of year is called a meteor shower. Comets shed the debris that becomes most meteor showers. As comets orbit the Sun, they shed an icy, dusty debris stream along the comet's orbit. If Earth travels through this stream, you will see a meteor shower. Depending on where Earth and the stream meet, meteors appear to fall from a particular place in the sky, maybe within the neighborhood of a constellation.
Meteor showers are named by the constellation from which meteors appear to fall. For instance, The Perseid meteor shower is named because meteors appear to fall from a point in the constellation Perseus.
Shooting stars are name that people have used for many years to describe meteors. Streaks of light across the night sky caused by small bits of interplanetary rock and debris called meteoroids crashing and burning high in Earth's upper atmosphere. Traveling at thousands of miles an hour. Almost all are destroyed, the rare few that survive and hit the ground are known as meteorites.When a meteor appears, it seems to shoot across the sky, and its small size and intense brightness might make you think it is a star.
If you live near a city, drive away from the city lights and toward the constellation from which the meteors will appear to radiate. Find a dark spot where oncoming lights will not ruin your night vision. When you are at your observing spot, position yourself so the horizon appears at the edge of your peripheral vision, with the stars and sky filling your field of view. Meteors will get your attention as they streak by.
If you can see each star of the Little Dipper, your eyes have "dark adapted," and your chosen site is probably dark enough. Under these conditions, you should see plenty of meteors.
What should I pack for meteor watching?
If you can bring red-filtered flashlight for reading star maps and charts without ruining your night vision. Binoculars are not necessary. Its better with just your eyes.
Tuesday, July 28, 2009
Stargazing (Equipment Tips)
Though the best instrument for stargazing is your own two eyes, there's nothing like bringing lunar craters, star clusters, or nebulae into focus with a quality pair of binoculars or a small starter telescope.
Around $250 will buy a refractor scope with a 60 to 90 millimeter lense (about two and half to three inches), a tripod mount and a couple of eyepieces. Look for one with a filter , not for solar viewing, which should never be done directly, but for observing the Moon. Seen unfiltered, the glare of the full Moon can be as painful as a car's headlights. Also, steer clear of the generic models sold at discount department store chains.
A pair of 7x50 binoculars offers a comparable field of view and magnification of an entry-level telescope for a bit less money. Planetary conjunctions, lunar occultations, even the next great comet, will look just as sharp through good binoculars. The view suffers only with the lack of a tripod mount. You may want to brace yourself against a tree for steady observing. On the otherhand, binoculars are much more portable than a telescope, a handy feature if you have to drive beyond the glare of city lights to do your stargazing.
Around $250 will buy a refractor scope with a 60 to 90 millimeter lense (about two and half to three inches), a tripod mount and a couple of eyepieces. Look for one with a filter , not for solar viewing, which should never be done directly, but for observing the Moon. Seen unfiltered, the glare of the full Moon can be as painful as a car's headlights. Also, steer clear of the generic models sold at discount department store chains.
A pair of 7x50 binoculars offers a comparable field of view and magnification of an entry-level telescope for a bit less money. Planetary conjunctions, lunar occultations, even the next great comet, will look just as sharp through good binoculars. The view suffers only with the lack of a tripod mount. You may want to brace yourself against a tree for steady observing. On the otherhand, binoculars are much more portable than a telescope, a handy feature if you have to drive beyond the glare of city lights to do your stargazing.
Tuesday, May 13, 2008
Wednesday, April 16, 2008
The Milky Way and the Galaxies
Star chart above showing the Milky Way in the region of Scorpius and Sagittarius. Visible nebulae are indicated by the position of the yellow NGC numbers. Star spectral colors of stars, such as red for Antares, are also indicated.
On the Frontiers of the Cosmos: The Milky Way and the Galaxies
One of the most imposing celestial sights is the Milky Way, a band of light produced by billions of stars. The single stars, if they each stood isolated in the sky, would be too faint to be seen, but all of them together combine into a band of light. Interspersed among these billions of stars are clouds of dark dust that in places block the light from reaching Earth and give the Milky Way an uneven, ragged look. The universe includes more than the Milky Way, there are other, similar formations in space that are made up of stars and dust and gasses, each formation is a "galaxy" like our Milky Way. ("Galaxy" and "Milky Way" have the same meaning since gala is Greek for "milk. ")
One of the most imposing celestial sights is the Milky Way, a band of light produced by billions of stars. The single stars, if they each stood isolated in the sky, would be too faint to be seen, but all of them together combine into a band of light. Interspersed among these billions of stars are clouds of dark dust that in places block the light from reaching Earth and give the Milky Way an uneven, ragged look. The universe includes more than the Milky Way, there are other, similar formations in space that are made up of stars and dust and gasses, each formation is a "galaxy" like our Milky Way. ("Galaxy" and "Milky Way" have the same meaning since gala is Greek for "milk. ")
One of these galaxies is the Large Magellanic Cloud in the southern sky, visible to the naked eye even at full moon as a large, misty area. When viewed through a telescope it turns out to be a huge aggregation of stars. The Magellanic Clouds (there is a small as well as a large one) are named after the navigator Magellan. The Large Magellanic Cloud is at a distance of about 179,000 or about 180,000 light years. Astronomers estimate that it contains approximately 15 to 30 billion stars. It also includes many nebulae, star clusters, and other obiects that show up in varied colors in photographs of the clouds.
All the galaxies together, many of them millions or billions of light years away make up the universe, which today's astronomers can explore with a vast array of instruments: radio telescopes like the 300-foot (100-m) antenna in Effelsberg/Eifel, sophisticated mirror telescopes like the one at the European Observatory in Chile that can cancel out air disturbances automatically, and the Hubble space telescope, which is able to photograph distant celestial bodies with previously unattainable accuracy.
The Hubble space telescope and other instruments have recently made possible the discovery of planets outside our solar system. By the middle of 2006, about 170 such planets were found. More sophisticated instruments are scanning the skies and more, smaller "extra-solar" planets are being discovered. This increases the likelihood of discovering intelligent life on another world. Such a discovery would be the most profound in the history of our planet.
The Constellations
According to Greek mythology, Queen Cassiopeia and her husband Cepheus once ruled over Ethiopia. One day Cassiopeia bragged that their daughter Andromeda was more beautiful than the Nereids, the daughters of the sea god, Nereus. When the Nereids complained to their father about Cassiopeia's arrogance, Nereus sent a sea monster to ravage the shore of Ethiopia. In desperation King Cepheus consulted the oracle of Delphi. There he was told that the only way to save his country was to sacrifice Andromeda to the monster. Andromeda was chained to a rock by the sea. However, salvation came at the last minute in the form of Perseus, who managed to subdue and kill the sea monster in a ferocious battle. As his reward Perseus received Andromeda in marriage and Ethiopia as her dowry. The gods later immortalized all the participants as constellations in the heavens, including the sea monster, which appears there as Cetus, the Whale.
This is just one of many stories told by ancient bards, stories whose protagonists the Greeks thought they recognized in the skies. These ancient people looked for bright stars and combined them in patterns that they then named after legendary figures. In the southern half of the celestial sphere, we find startlingly different names, such as Antlia, the Air Pump. Many of the southern constellations were not named until the eighteenth century, when astronomers no longer had much use for ancient mythology and preferred to elevate the most recent scientific inventions to the heavens one of which was the air pump.
From a number of different traditions modern astronomers have selected a total of 88 constellations and drawn up internationally recognized boundaries between them. Each constellation has its own characteristic shape. Today the constellations no longer have meaning beyond orienting the observer of the starry sky, they constitute a kind of "coordinate grid" of the sky.
From a number of different traditions modern astronomers have selected a total of 88 constellations and drawn up internationally recognized boundaries between them. Each constellation has its own characteristic shape. Today the constellations no longer have meaning beyond orienting the observer of the starry sky, they constitute a kind of "coordinate grid" of the sky.
Stars: Points of Light in the Cosmos
Cosmic Bolts of light
Often during a clear night what we call meteors or shooting stars streak briefly across the sky. These bright trails of light that move across the sky at lightning speed are caused by tiny metallic and rock particles that enter Earth's atmosphere from outer space. The particles become extremely hot, excite the air to incandescence with their great speed, and are incinerated completely in the process. A grain of dust weighing less than one gram can give rise to a meteor that momentarily appears brighter than the brightest stars.
The Stars: Points of light in the Cosmos
If one looks up at the sky during a clear night and far from the air pollution of cities, one has the impression of seeing innumerable stars. In fact, "only" about 2,500 stars are visible to the naked eye. When one looks through binoculars or a telescope, the number of visible stars increases to hundreds of thousands or several million. All the stars rise and set in the sky just like
the sun, moon, and planets, because Earth rotates once a day. Apart from this nightly rising and setting, the stars exhibit practically no motion, their position in relation to each other remains essentially constant. Because of this apparent immobility the astronomers of antiquity called them the "fixed stars."
The reason why the stars seem to be glued to their places in the sky is that they are separated from Earth by incredibly vast distances. The stars are so very far removed from Earth that astronomers had to invent a new unit for measuring distance, the light-year.
One light-year is the distance that light travels (at a speed per second of 186,282 miles or 300,000 km, a distance equal to 7 1/2 times around Earth's equator) in exactly one year. It is equivalent to 5.88 trillion miles (9.46 trillion km). (A trillion is a "1" followed by 12 zeroes.)
How is it possible for us to see stars at all at such incredible, "astronomical" distances? Because they emit huge amounts of heat and light, just like our sun. All fixed stars are suns, some bigger, some smaller than ours.
Fixed stars and planets are two entirely different things. Stars are spheres of incandescent gas that produce their own light, the planets are solid, cold bodies that orbit around the sun and are illuminated by it. The stars are light years away from us, trillions of miles - while the planets move much closer to Earth, being separated from us by "mere" millions or billions of miles. The other big difference between stars and planets is that the latter do not stay in one place in the sky. They revolve around the sun and keep changing their positions as seen from Earth, appearing now in one constellation, now in another.
Often during a clear night what we call meteors or shooting stars streak briefly across the sky. These bright trails of light that move across the sky at lightning speed are caused by tiny metallic and rock particles that enter Earth's atmosphere from outer space. The particles become extremely hot, excite the air to incandescence with their great speed, and are incinerated completely in the process. A grain of dust weighing less than one gram can give rise to a meteor that momentarily appears brighter than the brightest stars.
The Stars: Points of light in the Cosmos
If one looks up at the sky during a clear night and far from the air pollution of cities, one has the impression of seeing innumerable stars. In fact, "only" about 2,500 stars are visible to the naked eye. When one looks through binoculars or a telescope, the number of visible stars increases to hundreds of thousands or several million. All the stars rise and set in the sky just like
the sun, moon, and planets, because Earth rotates once a day. Apart from this nightly rising and setting, the stars exhibit practically no motion, their position in relation to each other remains essentially constant. Because of this apparent immobility the astronomers of antiquity called them the "fixed stars."
The reason why the stars seem to be glued to their places in the sky is that they are separated from Earth by incredibly vast distances. The stars are so very far removed from Earth that astronomers had to invent a new unit for measuring distance, the light-year.
One light-year is the distance that light travels (at a speed per second of 186,282 miles or 300,000 km, a distance equal to 7 1/2 times around Earth's equator) in exactly one year. It is equivalent to 5.88 trillion miles (9.46 trillion km). (A trillion is a "1" followed by 12 zeroes.)
How is it possible for us to see stars at all at such incredible, "astronomical" distances? Because they emit huge amounts of heat and light, just like our sun. All fixed stars are suns, some bigger, some smaller than ours.
Fixed stars and planets are two entirely different things. Stars are spheres of incandescent gas that produce their own light, the planets are solid, cold bodies that orbit around the sun and are illuminated by it. The stars are light years away from us, trillions of miles - while the planets move much closer to Earth, being separated from us by "mere" millions or billions of miles. The other big difference between stars and planets is that the latter do not stay in one place in the sky. They revolve around the sun and keep changing their positions as seen from Earth, appearing now in one constellation, now in another.
Tuesday, April 15, 2008
Astronomy (Sun,Moon,and Earth)
Sun, Moon, and Earth
For us, Earth is the most important celestial body. Earth is a spherical object 7,926 miles (12,756 km) in diameter and enveloped by a layer of air (the atmosphere) that, by protecting us from dangerous cosmic radiation, makes life possible for us. Once a day, every 24 hours, Earth rotates around its own axis, which is an imaginary straight line that runs from the north to the south pole. Because of Earth's rotation we see the stars rise in the east and set in the west. In the course of the night the starry sky changes its appearance completely. New stars appear, and others vanish from sight.
For us, Earth is the most important celestial body. Earth is a spherical object 7,926 miles (12,756 km) in diameter and enveloped by a layer of air (the atmosphere) that, by protecting us from dangerous cosmic radiation, makes life possible for us. Once a day, every 24 hours, Earth rotates around its own axis, which is an imaginary straight line that runs from the north to the south pole. Because of Earth's rotation we see the stars rise in the east and set in the west. In the course of the night the starry sky changes its appearance completely. New stars appear, and others vanish from sight.
The sun is crucial for Earth and its inhabitants. It is a huge, blazing ball of gas, in whose core atomic nuclei are fused in a process that releases energy. Thanks to the incredibly vast amounts of energy produced, the sun radiates great quantities of light and heat toward Earth and provides the energy that is necessary for life to emerge. The rising and setting of the sun create our days and nights.
When the sun is in the sky during the day, it shines so brightly that all other celestial bodies which are overhead not just at night but during the day as well, fade from sight. It is only in the evening, when the sun sinks below the horizon and darkness falls, that we can see the other, much less luminous celestial bodies.
The sun's disk frequently displays dark spots. The number of these so-called sunspots fluctuates in an eleven-year cycle. The "solar activity" associated with sunspots will increase during most of the period from 2007-2010. Astronomers expect the next sunspot flare-up in about 2011.
Only one other celestial body is sometimes visible during the day, the moon, which measures 2,159 miles (3,476 km) in diameter and is considerably smaller than Earth. The moon revolves around Earth approximately once a month. It is Earth's companion or satellite, a cold celestial body that is inhospitable to life. Humans first set foot on the moon on July 20, 1969.
Only one other celestial body is sometimes visible during the day, the moon, which measures 2,159 miles (3,476 km) in diameter and is considerably smaller than Earth. The moon revolves around Earth approximately once a month. It is Earth's companion or satellite, a cold celestial body that is inhospitable to life. Humans first set foot on the moon on July 20, 1969.
Like Earth, the moon derives its light from the sun, and it reflects this light back to Earth. The moon appears to us in continually changing form as it circles around Earth, and we speak of its "waxing" and "waning" as, in the course of 29 1/2 days, it passes through the different phases of the lunar cycle. Depending on the moon's position in relation to the sun, we see sometimes the entire lit-up side of the moon (full moon), sometimes only half of the lit-up side (half-moon) and when the moon is closest to the sun, we don't see anything at all because the side of the moon facing us is unlit (new moon).
As it revolves around Earth, the moon occasionally produces the most dramatic celestial events we can observe, lunar and solar eclipses. Earth and the moon throw shadows, like any other body that is lit up. When Earth's shadow falls on the moon, we see a lunar eclipse, when the moon's shadow hits Earth, it causes a solar eclipse. Solar eclipses are always visible from only a small part of Earth's surface lunar eclipses on the other hand can be seen on about half of Earth's night side.
Although the moon goes completely into the Earth's shadow during a totol lunar eclipse, it does not completely disappear. Earth's atmosphere deflects the sun's rays into the shadows and colors them red. This gives the moon an impressive copper tone during an eclipse. Both lunar and solar eclipses can be total or partial depending on whether the solar or lunar disk is entirely covered up or only partially. In a total solar eclipse we can see the sun's corona for a few minutes. This ring of radiating light consists of highly diffused gases heated to a temperature of several million degrees Celsius, but its luminosily is too small to be seen except during total eclipses.
Solar and lunar eclipses are quite rare, and they are not visible from all parts of Earth.
Solar and lunar eclipses are quite rare, and they are not visible from all parts of Earth.
Monday, April 7, 2008
Tuesday, January 15, 2008
MERCURY
For most people in the United States you have a chance at seeing Mercury by the middle of the month around dusk. Look in the southwestern sky, right near the horizon just after the sun sets. Mercury is at about magnitude -0.9 and will get brighter by the Jan. 22 when it will reach its greatest eastern elongation (angle between the sun and Mercury when it is visible after sunset), and a magnitude of -0.5. Sometimes you can see Mercury before the sun rises, this is when it is at its greatest western elongation. Mercury will reach its greatest eastern elongation on May 14th. For all of you astronomy people there are some new toys out. They are called mySKY by Meade and the SkyScout Personal Planetarium by Celestron. Both are about the same thing they show you what you are looking at in the sky and teach you about them. They are basically GPS instruments that you can use to locate sky objects. All you do is point the instrument at the area of the sky you are interested in, and you not only know what star you are looking at but also the constellation.
Tuesday, December 11, 2007
EQUINOX
Equinox can have two meanings:
The moment when the Sun is positioned directly over the Earth's equator and, by extension, the apparent position of the Sun at that moment - see below.
A moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system - see Equinox (celestial coordinates)
An equinox in astronomy is that moment in time (not a whole day) when the center of the Sun can be observed to be directly above the Earth's equator, occurring around March 20 and September 23 each year.
At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points the vernal point and the autumnal point.
There is either an equinox (autumn and spring) or a solstice (summer and winter) on approximately the 21st day of the last month of every quarter of the calendar year. On a day which has an equinox, the center of the Sun will spend a nearly equal amount of time above and below the horizon at every location on Earth and night and day will be of nearly the same length. In reality, the day is longer than the night at an equinox. Commonly the day is defined as the period that sunlight reaches the ground in the absence of local obstacles.
From Earth, the Sun appears as a disc and not a single point of light; so, when the center of the Sun is below the horizon, the upper edge is visible. Furthermore, the atmosphere refracts light, so, even when the upper limb of the Sun is below the horizon, its rays reach over the horizon to the ground. In sunrise/sunset tables, the assumed semi-diameter (apparent radius) of the sun is 16 minutes of arc and the assumed refraction is 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon its center is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects together make the day about 14 minutes longer than the night at the equator, and longer still at sites toward the poles. The real equality of day and night only happens at places far enough from the equator to have at least a seasonal difference in day length of 7 minutes and occurs a few days towards the winter side of each equinox.
The moment when the Sun is positioned directly over the Earth's equator and, by extension, the apparent position of the Sun at that moment - see below.
A moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system - see Equinox (celestial coordinates)
An equinox in astronomy is that moment in time (not a whole day) when the center of the Sun can be observed to be directly above the Earth's equator, occurring around March 20 and September 23 each year.
At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points the vernal point and the autumnal point.
There is either an equinox (autumn and spring) or a solstice (summer and winter) on approximately the 21st day of the last month of every quarter of the calendar year. On a day which has an equinox, the center of the Sun will spend a nearly equal amount of time above and below the horizon at every location on Earth and night and day will be of nearly the same length. In reality, the day is longer than the night at an equinox. Commonly the day is defined as the period that sunlight reaches the ground in the absence of local obstacles.
From Earth, the Sun appears as a disc and not a single point of light; so, when the center of the Sun is below the horizon, the upper edge is visible. Furthermore, the atmosphere refracts light, so, even when the upper limb of the Sun is below the horizon, its rays reach over the horizon to the ground. In sunrise/sunset tables, the assumed semi-diameter (apparent radius) of the sun is 16 minutes of arc and the assumed refraction is 34 minutes of arc. Their combination means that when the upper limb of Sun is on the visible horizon its center is 50 minutes of arc below the geometric horizon, which is the intersection with the celestial sphere of a horizontal plane through the eye of the observer. These effects together make the day about 14 minutes longer than the night at the equator, and longer still at sites toward the poles. The real equality of day and night only happens at places far enough from the equator to have at least a seasonal difference in day length of 7 minutes and occurs a few days towards the winter side of each equinox.
SKY DARKNESS
The fact that the sky isn't absolutely dark at night can easily be observed. Were the sky (in the absence of moon and citylights) absolutely dark, one would not be able to see the silhouette of an object against the sky.
The intensity of the sky varies greatly over the day and the primary cause differs as well. During daytime when the sun is above the horizon direct scattering of sunlight (rayleigh scattering) is the overwhelmingly dominant source of light. In twilight, the period of time between sunset and sunrise, the situation is more complicated and a further differentiation is required. Twilight is divided in three segments according to how far the sun is below the horizon in segments of 6°.
After sunset the civil twilight sets in, and ends when the sun drops more than 6° below the horizon. This is followed by the nautical twilight, when the sun reaches heights of -6° and -12°, after which comes the astronomical twilight defined as the period from -12° to -18°. When the sun drops more than 18° below the horizon the sky generally attains its minimum brightness.
Several sources can be identified as the source of the intrinsic brightness of the sky, namely airglow, indirect scattering of sunlight, scattering of starlight, and artificial light pollution.
The intensity of the sky varies greatly over the day and the primary cause differs as well. During daytime when the sun is above the horizon direct scattering of sunlight (rayleigh scattering) is the overwhelmingly dominant source of light. In twilight, the period of time between sunset and sunrise, the situation is more complicated and a further differentiation is required. Twilight is divided in three segments according to how far the sun is below the horizon in segments of 6°.
After sunset the civil twilight sets in, and ends when the sun drops more than 6° below the horizon. This is followed by the nautical twilight, when the sun reaches heights of -6° and -12°, after which comes the astronomical twilight defined as the period from -12° to -18°. When the sun drops more than 18° below the horizon the sky generally attains its minimum brightness.
Several sources can be identified as the source of the intrinsic brightness of the sky, namely airglow, indirect scattering of sunlight, scattering of starlight, and artificial light pollution.
POLARIS
POLARIS - more commonly known as The Pole Star, The North Star is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole 42′ away, making it the current northern pole star.
Polaris stands almost motionless on the sky, and all the stars of the Northern sky appear to rotate around it. It makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry. At present, Polaris is 0.7° away from the pole of rotation (1.4 times the Moon disc) and revolves around the pole in a small circle 1½° in diameter. Only twice during every sidereal day does Polaris accurately define the true north azimuth; the rest of the time it is only an approximation and must be corrected using tables or a rough rule of thumb.
Due to the precession of the equinoxes, Polaris will not always be the pole star. Over tens of thousands of years, perturbations to the Earth's axis of rotation will cause it to point to other regions of the sky, tracing out a circle. Other stars along this circle were the pole star in the past and will be again in the future, including Vega. Polaris has been close to the actual position of the north pole for over 1000 years and during the course of the 21st century it will continue to approach the exact theoretical position, reaching its closest approach on 24 March 2100 (almost 0.45° away). Subsequently it will begin to pull away.
In the Northern Hemisphere, it is easy to find Polaris by following the line traced from Merak to Dubhe and α Ursae Majoris, also known as the Pointers), the two stars at the end of the bowl of the Big Dipper (or Plough). One can also follow the central point of the "W" shape of Cassiopeia. Polaris is not visible from the Southern Hemisphere except from an elevated position near the equator.
Polaris's fame as the North Star has given rise to a persistent misconception that it is the brightest star in the sky. Although Polaris is a relatively bright star and is conspicuous since no other stars of similar brightness are close to it, it is nowhere near the brightest; it is actually the 48th brightest star in the night sky. The brightest star in the night sky is Sirius.
There is no real southern pole star. The only star visible to the naked eye that is close to the south celestial pole is the dim Sigma Octantis, sometimes called Polaris Australis. The bright Southern Cross (Crux) points fairly accurately towards the south celestial pole.
Polaris stands almost motionless on the sky, and all the stars of the Northern sky appear to rotate around it. It makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry. At present, Polaris is 0.7° away from the pole of rotation (1.4 times the Moon disc) and revolves around the pole in a small circle 1½° in diameter. Only twice during every sidereal day does Polaris accurately define the true north azimuth; the rest of the time it is only an approximation and must be corrected using tables or a rough rule of thumb.
Due to the precession of the equinoxes, Polaris will not always be the pole star. Over tens of thousands of years, perturbations to the Earth's axis of rotation will cause it to point to other regions of the sky, tracing out a circle. Other stars along this circle were the pole star in the past and will be again in the future, including Vega. Polaris has been close to the actual position of the north pole for over 1000 years and during the course of the 21st century it will continue to approach the exact theoretical position, reaching its closest approach on 24 March 2100 (almost 0.45° away). Subsequently it will begin to pull away.
In the Northern Hemisphere, it is easy to find Polaris by following the line traced from Merak to Dubhe and α Ursae Majoris, also known as the Pointers), the two stars at the end of the bowl of the Big Dipper (or Plough). One can also follow the central point of the "W" shape of Cassiopeia. Polaris is not visible from the Southern Hemisphere except from an elevated position near the equator.
Polaris's fame as the North Star has given rise to a persistent misconception that it is the brightest star in the sky. Although Polaris is a relatively bright star and is conspicuous since no other stars of similar brightness are close to it, it is nowhere near the brightest; it is actually the 48th brightest star in the night sky. The brightest star in the night sky is Sirius.
There is no real southern pole star. The only star visible to the naked eye that is close to the south celestial pole is the dim Sigma Octantis, sometimes called Polaris Australis. The bright Southern Cross (Crux) points fairly accurately towards the south celestial pole.
STAR
A star is a massive, luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun. A star shines because nuclear fusion in its core releases energy that traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created inside the cores of stars.
Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including the diameter, rotation, movement and temperature.
Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star are determined by its evolutionary history, including the diameter, rotation, movement and temperature.
FORMING A STAR
A star is a massive, luminous ball of plasma. Stars group together to form galaxies, and they dominate the visible universe. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth, including daylight. Other stars are visible in the night sky, when they are not outshone by the Sun. A star shines because nuclear fusion in its core releases energy which traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created inside the cores of stars.
Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star that are determined by its evolutionary history include the diameter, rotation, movement and temperature. A star begins as a collapsing cloud of material that is composed primarily of hydrogen along with some helium and heavier trace elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. Once the hydrogen fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to become a red giant, fusing heavier elements at the core, or in shells around the core. The star then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment, where it will form a new generation of stars with a higher proportion of heavy elements.
Astronomers can determine the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its evolution and eventual fate. Other characteristics of a star that are determined by its evolutionary history include the diameter, rotation, movement and temperature. A star begins as a collapsing cloud of material that is composed primarily of hydrogen along with some helium and heavier trace elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. Once the hydrogen fuel at the core is exhausted, those stars having at least 0.4 times the mass of the Sun expand to become a red giant, fusing heavier elements at the core, or in shells around the core. The star then evolves into a degenerate form, recycling a portion of the matter into the interstellar environment, where it will form a new generation of stars with a higher proportion of heavy elements.
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