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.

the correct order for energy transfer in this ecosystem? The plants are eaten before they are mature. The plants are eaten before they are mature. The plants are eaten before they are mature. 1. A polar bear hunts a seal. After the polar bear is done feeding, an Arctic fox consumes the remaining meat. Which describes the role of the Arctic fox in this situation? F scavenger G predator H producer J decomposer statement best explains why these plants have shallow root systems? J Plants in the tundra biome grow close to the ground and have shallow root systems. Which J statement best explains why these plants have shallow root systems? Plants in the tundra biome grow close to the ground and have shallow root systems. Which statement best explains why these plants have shallow root systems? J lants in the tundra biome grow close to the ground and have shallow root systems. Which The seeds must be spread quickly. The seeds must be spread quickly. The seeds must be spread quickly. 3. Hawks, grasses, songbirds, and caterpillars are some organisms found in an ecosystem. Which is the correct order for energy transfer in this ecosystem? A caterpillars → hawks → grasses → songbirds B grasses → caterpillars → songbirds → hawks C hawks → caterpillars → grasses → songbirds D songbirds → grasses → hawks → caterpillars 2. Plants in the tundra biome grow close to the ground and have shallow root systems. Which statement best explains why these plants have shallow root systems? F The plants are eaten before they are mature. G The plants can be easily transplanted. H The ground is frozen much of the year. J The seeds must be spread quickly. G G G The plants can be easily transplanted. The plants can be easily transplanted. The plants can be easily transplanted. H H H The ground is frozen much of the year. The ground is frozen much of the year. The ground is frozen much of the year.

The Life Cycle of Stars: Chapter 8, Section 2

What we are going to learn today about the life cycle of Stars The different types of stars How to read an H-R diagram How stars appear at different stages in their life cycle on the H-R diagram.

What are Stars? Stars are large balls of hot gas. They look small because they are a long way away, but in fact many are bigger and brighter than the Sun. The heat of the star is made in the centre by nuclear fusion reactions. There are lots of different colours and sizes of star.

The Beginning and End of Stars The Beginning A star enters the first stage of its life cycle as a ball of gas and dust. Gravity pulls the gas and dust together, and hydrogen changes to helium in a processes called nuclear fusion. The End Stars usually lose material slowly, but sometimes they can lose material in a big explosion. Much of a star’s material returns to space, where it sometimes forms new stars.. How many stars are estimated to be in our Milky Way Galaxy? 4 Billion and on a clear night you can only see a fraction with your naked eye.

Different Types of Stars Stars can be classified by their size, mass, brightness, color, temperature, spectrum, and age. A star’s classification can change as it ages. Main-Sequence Stars After a star forms, it enters the second and longest stage of its life cycle known as the main sequence. Energy is generated in the core as hydrogen atoms fuse into helium atoms. What kind of star is our sun??

3rd Step: Star joins the main sequence. 90% of stars spend their life here. The mass of star determines its location on the main sequence.

Main Sequence Star System: Alpha Centauri, 25 trillion miles away

Beginning of the End: Stars begin to die when they run out of hydrogen. Gravity begins to take over. Star begins to shrink; outer core of hydrogen begins to fuse. The outer part of the Star gets bigger.

Red Giants A red giant is a large, reddish (usually main sequence) star late in its life cycle, or third stage. As the center of the star shrinks, the atmosphere of the star grows very large and cools to form a red giant or a red supergiant. This is Betelgeuse, a red giant star in the Milky Way. Who has seen it through a telescope? In what Constellation is it located?

Orion Constellation

White Dwarf Stars In the final stage of its life cycle, a star that has the same mass as the sun (main sequence star) or smaller can be classified as a white dwarf. A white dwarf is a small, hot dim star that is the leftover center of an old star. It has no hydrogen left and cannot generate energy any more but it can shine for billions of years before cooling completely. In what constellation is there a white dwarf in our galaxy? White Dwarf Stars

When a star becomes a whit dwarf it uses up all its chemicals required for nuclear fusion. It just creates a large clump that will emit light until it finally darkens for good.

White Dwarf : Sirius Blue Supergiant: Rigel

Death of Stars: Low and Medium Mass Main Sequence Star Red Giant Planetary Nebula White Dwarf

H-R Diagram: A graph for studying the stars The H-R Diagram (Hertzprung-Russell diagram) is a graph that shows the relationship between a star’s surface temperature and its absolute magnitude. Reading the H-R Diagram The diagonal pattern on the H-R diagram where most stars lie, is called the main sequence. Where is our sun? The main sequence is the location on the diagram where most stars lie

H-R Diagram How hot is the surface of the sun? 5,000 – 6,000 C or 10,000 F

According to the H-R diagram, what types of stars have very low temperatures and high absolute magnitudes? A blue stars B red giants C white dwarfs D main sequence stars

When stars get old When main sequence stars get old (such as our sun) they become red giants and then white dwarfs at the end of their life cycle. Massive stars, however, generate much more energy and also don’t last as long. Massive stars may explode with such intensity that they may become supernovas, neutron stars, pulsars, or black holes. What will our sun probably become in its next stage?

Supernovas A supernova is a gigantic explosion in which a massive star collapses and throws its outer layers into space. Supernova NGC 6826 Its green gas is almost half of its mass.

Neutron Star After the supernova explosion, the center of the collapsed star contracts to form a new star. It has been smashed together so forcefully that all of its particles have become neutrons.

Neutron stars are easy to recognize for astronomers because they bend the light around them. It makes it easy to find them with infrared telescopes. Neutrons stars are rare.

Pulsars When a neutron star is rapidly spinning, it is called PULSAR. It emits rapid pulses of radio waves and optical energy. This is Pulsar B1509. It is spinning so rapidly(7 rotations/sec), 12 miles wide, it creates a hand-shaped nebula

Black Holes Sometimes the leftovers of a supernova are so massive that they collapse to form a black hole. A black hole is an object that is so massive that even light cannot escape its gravity. Black Holes are invisible: their extreme gravity can cause light to stretch ; their spinning can drag the very fabric of space around with it

Death of Stars: High Mass Main Sequence Star Red Super Giant Supernova Neutron Star Black Hole

Who took these pictures? These images were taken from the ALMA telescope, CHANDRA satellite and the Hubble Space telescope. ALMA is a radio telescope in Chile CHANDRA is a satellite launched by NASA in 1999 The Hubble is an orbiting observatory that was launched by the Space Shuttle Discovery in 1990

Let’s see how much you know about Stars now! What are some different types of stars? What does an H-R diagram tell us? What can main sequence stars (like our sun) turn into as they get old? What are some things massive stars become?