Stars and Galaxies  UNIT 11  STANDARDS: NCES 1.1.1, 1.1.2, 1.1.3, 1.1.4, 1.1.5,  LESSON 2

Lesson Objectives  In this lesson, you will learn about:  Comets and Meteors  Why the moon has more craters than the Earth  Relative size of our galaxy  Other galaxy shapes  Classifying stars

Small Space Bodies  There are smaller objects in space besides stars, planets, and moons. Asteroids, for instance, are rocks in space. They come in all sizes, from 60 miles across to as small as several feet or yards.  Asteroids are made of hard, rocky material that is left over from when our solar system formed 5 billion years ago.  The asteroids in our solar system orbit the sun. Most of them are between the orbits of Mars and Jupiter.

Meteors  A meteor is like an asteroid in that it is a hunk of rock. A meteor travels through space at a very high speed, and it can run into the sun, a moon, or a planet if one is in its path. Meteors come from a number of different sources.  They can be broken off from asteroids, for instance, or they can be left behind when comets travel through the space and lose solid material.  Meteors have “pulled away” from the gravity of the sun and have been captured by a planet’s or a moon’s gravity.  They are pulled toward the surface of the capturing body.

Meteorites  Meteorites are meteors that have actually struck the surface of a planet or moon.  You might wonder why there are more craters on the moon’s surface than on the Earth.  There are two reasons. First meteors enter the Earth’s atmosphere and heat up as they travel through the air.  Meteorites actually get hot enough to burn up as they pass through the air. This is because of friction.  When meteors pass through the earth’s atmosphere, they slow down and get hotter  Meteors actually get hot enough to burn up as they pass through the air.  Then there is nothing left but ashes that fall to the ground.  If you have ever seen a falling star at night, the bright streak of light in the sky is really a meteor burning up.  If the meteor actually hits the ground, then you have a meteorite.

Moon vs Earth craters  One reason there are fewer craters is because the earth has air but the moon does not.  Meteors seldom hit the earth because most of them are small enough to burn up in the atmosphere.  However, there is not any atmosphere on the moon, so there is no friction to slow meteors down and burn them up.  More meteors hit the moon and make craters.  The other reason is that the surface of the earth is always changing.  If a meteorite falls into the sea, it cannot make a crater underwater.  If the meteorite hits land, erosion will remove the crater.  One of the biggest craters that still exist is in the state of Arizona.It is more than a mile wide.

Our Universe  If the universe could be made smaller, the sun was the size of a beach ball, the Earth would be about the size of a BB.  The next nearest star would be several miles away from our BB-sized earth. Because of the great distances between stars, we cannot think in terms of miles when we measure the distance between them.  Things are so far apart that we much measure distance in light years. A light year is the distance that light travels in one year, about 6 trillion miles.

Our Galaxy  Our galaxy is called the Milky Way.  It is in the shape of a spiral. Think about a swirl of a pinwheel.  If you look up at the sky at night, you can find a bright band of stars across the sky. People thousands of years ago thought the sky looked like something white had spilled in it--something the color of milk. So they called the bright band of stars we see in our sky, the Milky Way.  The Milky Way has about one hundred billion stars and is 100 thousand light years wide.

Other Galaxies  This means it takes light 100,000 years for light to travel from one side of our galaxy to the other. Since we do not have spaceships that can travel that far in any reasonable time, we can’t explore our galaxy, yet…  The Milky Way is not the only galaxy in our universe. There are more than we can count. Each of them is made up of millions and millions of stars. The three most common shapes of galaxies are: Elliptical, Spiral, and Barred-Spiral. Remember the Milky Way is a spiral galaxy.

Stars  The 4 different kinds of Stars based on size are:  Super-Giant  Giant  Sub-Giant  Dwarf  Stars have different colors according to how big and how hot they are. The coolest stars are red.  Medium stars are orange to yellow.  The hottest stars look blue-white to us through a telescope.  Our sun is a sub-giant and burns yellow.

Section Review  Compare and contrast analog and digital forecasting.  Why are long-term forecasts not as accurate as short-term forecasts?  What is “The Almanac” and how does it make weather predictions?