1. An engineer is designing a machine to reduce the force required to move objects. The engineer

1. 1. An engineer is designing a machine to reduce the force required to move objects. The engineer tests a prototype of the machine. Which tool should the engineer use to test the amount of force needed to move objects? F anemometer G spring scale H thermometer J electronic balance 2. A bridge that crosses a small river was damaged by a flood. After engineers repair the bridge, which engineering procedure should be performed next? A test the strength of the bridge B build a small-scale model of the bridge C identify how fast the water in the river travels D measure the width of the river 3. New fluorescent bulbs use less electrical energy and last longer than traditional incandescent bulbs. What is a benefit of this technological advance? F The bulbs will never need to be replaced. G There will be more solar energy available. H Fewer bulbs will be disposed of in landfills. J Homes will need fewer light sources.

2. Galaxies

3. What we will talk about today • What are different shapes that a galaxy can have? • What are galaxies made of? • How do galaxies form?

4. What is a Galaxy? • A galaxy is a large group of gas, dust, and millions of stars bound together by gravity.The biggest galaxies contain more than a trillion stars. Scientists can’t actually count the stars, of course. They estimate how many stars are in a galaxy by measuring the size and brightness of the galaxy. The bigger and brighter the galaxy, the more stars it has. Three most common shapes are spiral, elliptical and irregular. What is the name of our galaxy???

5. Spiral Galaxies A spiral galaxy has two parts: a central bulge and arms that form a spiral around the center.The bulge is a dense group of old stars. The arms are made of gas, dust, and much younger stars. It can form after the collapse of a protogalactic cloud. Where are the older stars in this galaxy? The Milky Way is a spiral galaxy. Our sun is one of the 200 billion stars in the Milky Way. From Earth, the edge of the Milky Way looks like a bright belt of stars that stretches across the night sky. Andromeda Galaxy – probably similar To our Milky Way

6. Spiral Galaxy Spiral galaxies are complex objects and have several components: a disk, a bulge, and a halo. The disk contains gas, dust, and young stars in its spiral arms. The dense bulge in the center of the disk contains mostly old stars and no gas or dust. The four distinguishing characteristics of the spirals are: (a) they have more orderly, rotational motion than random motion (the rotation refers to the disk as a whole and means that the star orbits are closely confined to a narrow range of angles and are fairly circular); (b) they have some or a lot of gas and dust between the stars; (c) this means they can have new star formation occurring in the disk, particularly in the spiral arms; and (d) they have a spiral structure.

7. We live in a spiral galaxy…The Milky Way. How do we know the Milky Way is a spiral galaxy? How do the astronomers tell the shape of our galaxy (the Milky Way), even though it is not possible to take a photograph of it because to do that we would have to go away from it? The clues we have to the shape of the Milky Way are: 1) When you look toward the galactic center with your eye, you see a long, thin strip. This suggests a disk seen edge-on, rather than a ellipsoid or another shape. We can also detect the bulge at the center. Since we see spiral galaxies which are disks with central bulges, this is a bit of a tipoff. 2) When we measure velocities of stars and gas in our galaxy, we see an overall rotational motion greater than random motions. This is another characteristic of a spiral. 3) The gas fraction, color, and dust content of our galaxy are spiral-like.

9. Elliptical Galaxies • An elliptical galaxy is made of many stars and looks like a snowball. Elliptical galaxies are among the largest galaxies in the universe. Mostly full of old stars. Some may contain as many as 5 trillion stars! There is very little free gas in an elliptical galaxy. Therefore, few new stars form there. Elliptical galaxies are thought to be formed as a result of a merger of two disk or spiral galaxies.

10. Because elliptical galaxies contain older stars and less gas, scientists think that they are nearing the end of the evolution line for galaxies. The universe is a violent place, and collisions between galaxies are frequent — indeed, the Milky Way is due to crash into the Andromeda Galaxy in a few billion years. When two spirals collide, they lose their familiar shape, morphing into the less-structured elliptical galaxies. A supermassive black hole is thought to lie at the center of these ancient galaxies. These gluttonous giants consume gas and dust, and may play a role in the slower growth of elliptical galaxies. Born from collision, elliptical galaxies are more commonly found around clusters and groups of galaxies. They are less frequently spotted in the early universe, which supports the idea that they evolved from the collisions that came later in the life of a galaxy.

11. Because elliptical galaxies contain older stars and less gas, scientists think that they are nearing the end of the evolution line for galaxies. The universe is a violent place, and collisions between galaxies are frequent — indeed, the Milky Way is due to crash into the Andromeda Galaxy in a few billion years. When two spirals collide, they lose their familiar shape, morphing into the less-structured elliptical galaxies. A supermassive black hole is thought to lie at the center of these ancient galaxies. These gluttonous giants consume gas and dust, and may play a role in the slower growth of elliptical galaxies. Born from collision, elliptical galaxies are more commonly found around clusters and groups of galaxies. They are less frequently spotted in the early universe, which supports the idea that they evolved from the collisions that came later in the life of a galaxy.

12. What is an Irregular Galaxy? • An irregular galaxy has no clear shape. It may have as few as 10 million or as many as several billion stars. Some irregular galaxies form when two other galaxies collide. The Large Magellenic cloud is an irregular galaxy close to our own.

13. Irregular galaxies have no particular shape. They are among the smallest galaxies and are full of gas and dust. Having a lot of gas and dust means that these galaxies have a lot of star formation going on within them. This can make them very bright.

15. According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe. They've counted the galaxies in a particular region, and multiplied this up to estimate the number for the whole universe.

17. Contents of Galaxies Nebulas Globular clusters Open Clusters

18. What Objects May Be Found in Galaxies? • What are galaxies made of???? Remember that galaxies are made of gas, dust, and billions of stars. Some of these stars form different features, such as nebulas, open clusters, and globular clusters.

19. Nebulas • A nebula (plural, nebulae or nebulas) is a large cloud of gas and dust. Stars may be born here or end their lives here. -Some nebulas glow or reflect starlight, but others absorb light and are too dark to see. -Therefore, although nebulas can be found throughout a galaxy, they can be hard to see. This is the Hourglass Nebula

20. . Nebulae are the basic building blocks of the universe. They contain the elements from which stars and solar systems are built. They are also among the most beautiful objects in the universe, glowing with rich colors and swirls of light. Stars inside these clouds of gas cause them to glow with beautiful reds, blues, and greens. These colors are the result of different elements within the nebula. Most nebulae are composed of about 90% hydrogen, 10% helium, and 0.1% heavy elements such as carbon, nitrogen, magnesium, potassium, calcium, iron. These clouds of matter are also quite large. In fact, they are among the largest objects in the galaxy. Many of them are dozens or even hundreds of light-years across.

22. Clusters • A globular cluster is a group of up to 1 million stars that are packed closely together.A globular cluster looks like a ball. Some globular clusters orbit spiral galaxies, such as the Milky Way. Others can be found near giant elliptical galaxies.

23. Open Clusters • An open cluster is a group of 100 to 1,000 stars. The stars in an open cluster are closer together than stars in other parts of space. Open clusters are usually found in the arms of a spiral galaxy. All of the stars in an open cluster are the same age. They formed at the same time from the same nebula. Newly formed open clusters have many bright blue stars.

24. Quasars Remember that light from stars can take millions of years to reach Earth. Therefore, looking at distant stars is like looking back in time. Scientists study the early universe by studying objects that are very far away. Looking at distant galaxies shows what early galaxies looked like. By studying distant galaxies, scientists can learn how galaxies form and change. Among the most distant objects are quasars. Quasars are star like sources of light that are very far away. They are among the strongest energy sources in the universe. Some scientists think that quasars may be caused by black holes, but they are not sure how this happens. This quasar is 10 billion light years from Earth

25. Quasars…what we know very little about. Quasars are extremely distant objects in our known universe. They are the furthest objects away from our galaxy that can be seen. Quasars are extremely bright masses of energy and light. The name quasar is actually short for quasi-stellar radio source or quasi-stellar object. Quasars are the brightest objects in our universe, although to see one through a telescope they do not look that bright at all. This is because quasars are so far away. They emit radio waves, x-rays and light waves. Quasars appear as faint red stars to us here on Earth.

26. A quasar is believed to be a supermassive black hole surrounded by an accretion disk. An accretion disk is a flat, disk-like structure of gas that rapidly spirals around a larger object, like a black hole, a new star, a white dwarf, etc. A quasar gradually attracts this gas and sometimes other stars or or even small galaxies with their superstrong gravity. These objects get sucked into the black hole. When a galaxy, star or gas is absorbed into a quasar in such a way, the result is a massive collision of matter that causes a gigantic explosive output of radiation energy and light. This great burst of energy results in a flare, which is a distinct characteristic of quasars. The light, radiation and radio waves from these galaxies and stars being absorbed into a black hole travel billions of light years through space. When we look at quasars which are 10-15 billion light years away, we are looking 10-15 billion years into the past. Pretty amazing, right?

28. How do scientists think the universe formed? Like all scientific theories, theories about the beginning and end of the universe must be tested by observations or experiments. The study of how the universe started, what it is made of, and how it changes is called cosmology. To understand how the universe formed, scientists study the movements of galaxies. Careful measurements have shown that most galaxies are moving away from each other. This indicates that the universe is expanding. Based on this observation, scientists have made inferences about how the universe may have formed.

30. End Of Section • Write your summary and question. I’ll pull names to share.