Grades 5 & up
produced by Evans & Sutherland
Salt Lake City, Utah
The night sky appears serene, with an occasional flash of a falling star, but this is an illusion. We live in a violent and often lethal universe that is continually changing. In the destruction, there is also creation. The sky is our window to a fantastic, ever-changing sculpture we call the universe. The universe is the outcome of a vast interplay of nuclear, magnetic, and gravitational forces that can make changes over millions of years or in millionths of a second. Some of the forces are creative, others are destructive.
An asteroid hurtling through space encounters the Earth. A star launches deadly jets of particles and energy deep into space. Stars are swallowed by black holes deep in the cores of galaxies. We live in a violent universe.
Astronomers are like detectives, searching for clues to understand the universe. Large telescopes on Earth and in space are tools the astronomers use to create a picture and provide understanding about the things that make up our universe.
In a time-lapse view, the stars of the Milky Way drift across the sky. The Milky Way is a collection of hundreds of billions of stars. We are located 26,000 light years from its center. The core of the Milky Way is a bar surrounded by a few spiral arms.
Far out in space are other galaxies. Some appear to be in catastrophic collisions. These collisions can be modeled on supercomputers. Even as galaxies containing hundreds of billions of stars collide, collisions of individual stars are unlikely. Even now, two dwarf galaxies named the Magellanic Clouds are being swallowed by the Milky Way.
Forces acting across space squeeze together clouds of dust and gas, giving birth to new stars.
Our sun orbits the Milky Way in about 220 million years. Maybe once in each orbit, the sun could pass through a thick cloud of interstellar dust. Even though the dust clouds are very thin, some of the dust could find its way into Earth's atmosphere, blocking sunlight and bringing about an extended ice age.
A drawing on the rocks of Chaco Canyon shows a brilliant star close to a crescent moon. It may be a record of a supernova that shined long ago. Today, the Crab Nebula is seen at that location in the sky. The nebula is expanding, but when the expansion is calculated backward, it began in 1054. Chinese records describe a Guest Star that appeared at that time. Briefly, it was so bright that it was visible in daylight. Supernovae occur in the Milky Way at intervals of a few hundred years. They seed the galaxy with the heavy elements needed for life. If a supernova occurred too close to Earth, it would have a devastating blow to life. The first signs would be an increase in auroras, followed by the destruction of the planet's ozone layer, allowing harmful ultraviolet radiation from the sun to wreak havoc on life.
A supernova could result in the birth of a black hole. A black hole moving through space may not be seen, but its gravitational effects would be felt if it passed near the solar system. It may gobble up a planet, but would more likely disrupt the orbits of planets or orbiting comets, which could crash into the Earth.
Meteors fall from the sky all the time. About five can be seen each hour, and storms can fill the sky with up to 5,000 per hour. While storms are rare, there are meteor showers 9 to 10 times each year. The strongest are in August and November.
On July 19, 2009, astronomers found evidence of an object crashing into Jupiter--the second time such an event has been recorded. Fifteen years earlier, Comet Shoemaker-Levy was torn apart by Jupiter's gravity, and a string of 21 comet fragments crashed into the planet, leaving dark scars on the surface. If one of these fragments had hit the earth, it could have destroyed our civilization.
Comets are unpredictable. In 1908, a small comet fell over the Tunguska region of Siberia. When it exploded above Earth's surface, 1600 square miles of forest was incinerated, and a shock wave circled the Earth twice. When scientists first visited the site twenty years later, there was no crater or debris. The object had vaporized completely. Earth has had many impacts in its history, but they are quickly eroded or erased by geologic activity.
Meteor Crater in Northern Arizona is one of the best preserved craters. Nearby is the Grand Canyon, which formed by erosion over millions of years. The crater was formed in a few seconds about 50,000 years ago. The crater allows us to explore on Earth what it would be like to visit craters on the Moon or Mars. Some lunar craters have central mountain peaks. A crater in Australia was identified by the central peak. Aerial images show the larger outer wall of the crater.
Asteroids are smaller than comets, and because their orbits are within the solar system, they are easier to track. Some have orbits near Earth. One 275 meter diameter asteroid named Apophis, after the Egyptian god of death, will pass close enough to disrupt satellites on Friday the 13th in April, 2029. At that time, Earth's gravity may alter the path, bringing the asteroid back for a collision in 2036. The first predicted asteroid collision happened in 2008, when an object a few meters across was detected 24 hours before colliding with Earth. Fragments were recovered, making it the first asteroid studied in space and on the Earth.
Another threat in the universe is a gamma ray burst. For an instant, a beam of power equal to hundreds of thousands of suns blasts its way through space. It may be the result of two neutron stars fusing into a black hole. Longer bursts, lasting up to 10 seconds, may occur as a black hole forms in a supernova. A likely candidate for this is a star called Eta Carina. Fortunately, the rotation axis is tilted away from our solar system.
A black hole with the mass of four million suns resides at the center of the Milky Way. The black hole is quiet now, but as the orbits of nearby stars decay and clouds of interstellar dust drift too close, it may become active again, creating x-rays and streaming particles and radiation from its poles. Our galaxy may someday have an active core like other galaxies that we can see far off in space.