TEST 8A and 8B

Review

21-1 Visitors From Space (455) to 22-2 Earth's Place in the Universe (480).

Meteors are lumps of rock or metal that sometimes enter Earth’s atmosphere.

A meteorite is a meteor that strikes Earth’s surface.

Most of the evidence of meteorite impacts on Earth has been destroyed by weathering and erosion.

Comets are frozen masses of water, dust and other materials, that slowly orbit the Sun.

Asteroids: rocks and boulders that have been observed in the solar system. They are different from comets in that they have to tails.

What is shooting stars? Are not stars at all. Are rock particles or dust that had entered the atmosphere. The heat created as the particles streaked through the atmosphere caused the surrounding air to glow white hot, and the meteor burned up before it could reach Earth’s surface.

Where does the word comet comes from? From the Greek word for hair. The material in the tail of a comet gets left in space and can be responsible for meteor showers.

Comets travel around the Sun in an elliptical path. Some make the journey in less than 7 years. Others may travel in such a large orbit that it takes thousand of years to complete the orbit.

The head, or nucleus, of a comet probably consists of ice, dust, and other frozen substances. As a comet approaches the Sun, heat causes the outer layers of the nucleus to vaporize, This vaporization releases the dust and gases that form the tail. A comet’s tail may extend for 160 million kilometers across space. Solar wind pushes the comet’s tail so that it is always pointing away from the Sun.

Asteroids differ from comets in that they are made mostly of rocky materials. As a result, they do not form comet like tails. Most asteroids are found between the orbits of Mars and Jupiter, forming a band called the asteroid belt.

The comet travels at its greatest speed when it is closest to the Sun and at its lowest speed when it is farthest from the Sun.

Permanent space stations and colony on Marx will probably be reality in the next century. – Mars is more like Earth than any of the other planets.

The International Space Station (ISS) is a research facility currently being assembled in Low Earth Orbit. On-orbit construction of the station began in 1998, and is scheduled to be complete by 2011. As of 2009, the ISS is the largest artificial satellite in Earth orbit, larger than any previous space station. It orbits at an altitude of approximately 350 km above the surface of the Earth, travelling at an average speed of 27,700 kilometers per hour, completing 15.7 orbits per day.

Mars Exploration Rover (MER). Once they reach their landing sites, each rover's prime mission will last at least 90 Martian days (92 Earth days). The rovers are solar-powered, and in approximately 90 days, dust slowly accumulating on their solar arrays likely will decrease rover power, bringing to a close each robots sojourn.

- Stars vary in size, color, and temperature. – The color indicate its surface temperature, size and life span. High temperatures are blue-white, low temperatures are red or oranges. (Study table on p S147 (color and temperature) – Stars pass through stages that depend in part on their mass. – The life span of a star is billions of years.

Black hole: a small and dense object formed from a massive collapsing star (supernova) . It has a gravitational pull so strong that even light cannot escape.

Neutron star: a very small star consisting on the remnants of an exploded star. It contains the mass of several Suns, compressed to the size of a small asteroid.

Super giant: a star even larger than a giant star that is very near the end of its life.

Supernova: a high mass star that explodes producing a bright light and leaving behind a neutron star or back hole.

White dwarf: the final stage in the life of low mass stars like the Sun.

Red Giant is a very large and relatively cool star that is nearing its final stages of life. Stars become red giant as they use up their hydrogen and begin burning other fuels.

Neutron stars and black holes begin as very massive stars that explode into supernovas after their red giant stage.

The greater a star’s mass, the brighter it is, the higher tits temperature is, and the faster it uses up its nuclear fuel. Once out of fuel, the star may eventually collapse into a black hole.

The solar system occupies only a tiny part of the universe.

Distances of space are measured in astronomical units and light years. The light from stars in our galaxy was emitted thousand of years ago. The light from other galaxies was emitted millions years ago.

Light year: the distance light travels in one year (about 63,240 AU 0r 9.5 trillion kilometers.) Light travels at 300,000 km/s.