Suppose you shine the beam of a flashlight against the wall of a darkened room. You then measure the size of the circle made by the beam on the room. What do you think would happen to the size of the circle if you moved closer to the wall? Farther from the wall? Explain your answer. What is the structure and composition of the universe?

End of Chapter Preview

Section 1:Telescopes • What are the regions of the electromagnetic spectrum? • What are telescopes and how do they work? • Where are most large telescopes located?

Electromagnetic radiation Visible light (Optical) Energy that travels through space in the form of waves All colors that can be seen Roy G. Biv – colors in the rainbow, through a prism Red, orange, yellow, green, blue, indigo, violet. Electromagnetic Radiation

Types of radiation Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays Electromagnetic spectrum

Electromagnetic Radiation • The electromagnetic spectrum includes the entire range of radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

Types of Telescopes • A refracting telescope uses convex lenses to focus light. A reflecting telescope has a curved mirror in place of an objective lens.

Four Views of the Crab Nebula • Different type of telescopes collect electromagnetic radiation at different wavelengths. Astronomers are able to learn a great deal about the Crab Nebula by examining these different images. The images are shown at different scales.

Types of Telescopes

Links on Telescopes • Click the SciLinks button for links on telescopes.

Telescopes • Click the Video button to watch a movie about telescopes.

The Hubble Space Telescope • Click the Video button to watch a movie aboutthe Hubble Space Telescope.

End of Section:Telescopes

Section 2:Characteristicsof Stars • How are stars classified? • How do astronomers measure distances to the stars? • What is an H-R diagram and how do astronomers use it?

Constellation Stars Imaginary pattern of stars Made up mostly of H (hydrogen) Produce energy through nuclear fusion Color shows temperature red – cool stars (3200°C) yellow – hotter stars (5500°C) blue – hottest stars (20,000°C) Classifying Stars

Giant or supergiant Medium size Small size Very large stars Our sun’s size White dwarf – size of Earth Neutron stars – 20 km diameter. Size of Stars

Star Size • Stars vary greatly in size. Giant stars are typically 10 to 100 times larger than the sun and more than 1,000 times the size of a white dwarf.

Spectrograph 73% hydrogen (H) 25% helium (He) 2% other elements Breaks light into different colors Can determine gases in stars. Chemical Composition

Star Spectrums • Astronomers can use line spectrums to identify the chemical elements in a star. Each element produces a characteristic pattern of spectral lines.

Amount of light given off Depends on size and temperature Betelgeuse – cool and large, shines brightly Rigel – hot, brighter than Betelgeuse though smaller Brightness as seen from Earth Comparative. Brightness of Stars Apparent Brightness

Absolute Brightness No matter where you measure the brightness, it has the same measurement Can compare brightness of all stars to each other. Brightness of Stars

Astronomical Unit Light year 1 A.U. is the distance between Earth and the sun 1.44 X 108 kilometers (km). Measure distances between stars Distance light travels in one year 9.5 X 1012 kilometers (km). Measuring Distances to Stars

The Hertzsprung-Russell Diagram • Astronomers use H-R diagrams to classify stars and to understand how stars change over time. Compare 2 stars – color, brightness, temp.

H-R Diagram • On the H-R diagram: • Bottom X axis shows temperature, hottest on left, coolest on right • Top X axis shows color of stars, blue on left, red on right • Y axis shows brightness increasing

Summary of Section • Use the following as a guide to write a summary of this section: • Stars are classified by ___________, _________, _______, ________, __________. Some stars appear brighter than others because ___________. Light years are used to measure distances between stars because ___________. The H-R diagram is used to _________.

More on Types of Stars • Click the PHSchool.com button for an activityabout types of stars.

End of Section:Characteristicsof Stars

Section 3:Lives of Stars • How does a star form? • What determines how long a star will exist? • What happens to a star when it runs out of fuel?

A Star Is Born • Nebula – large cloud of gas & dust, large volume • Gravity pulls gas & dust together • Forms protostar (no nuclear fusion) • When gas & dust are very dense & hot, nuclear fusion starts, a star is born • Stars with more mass use up fuel faster than smaller stars • Small stars – 200 billion years • Medium stars – 10 billion years (our sun) • Large stars – 10 million years

The Lives of Stars • A star’s life history depends on its mass. After a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole.

Deaths of Stars • Hydrogen fuses to become helium and releases a lot of energy • When star uses up hydrogen helium can start fusing and creating new elements • Helium fuses in core to become carbon, oxygen • Massive stars produce heavier elements like iron • Stars without fuel become white dwarf, neutron star or black hole • Low mass star red giant planetary nebula white dwarf black dwarf

Deaths of Stars • Supernova – explosion of supergiant • Explosion creates heavy elements, lead, gold • Explosion creates new stars with material from old star (recycling!) • Neutron star – remains of supergiant • Smaller, denser than white dwarfs • Pulsar – spinning neutron star • Gives off pulses of radiation in the form of radio waves • Black hole – gravity so strong nothing can escape • Cannot be detected directly

The Lives of Stars Activity • Click the Active Art button to open a browser window and access Active Art about the lives of stars.

Pulsar • Pulsars are spinning neutron stars that emit steady beams of radiation.

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