Unit 5: The Universe & Gravity 8th Grade

Electromagnetic Waves What is a vacuum? EM wave This energy is called EM radiation A place that is empty of all matter Space is nearly a vacuum Vibrating electric and magnetic fields Can move through vacuum or matter Move at the speed of light (300,000 km/s) Sun’s energy arrives on Earth as EM radiation Infrared, visible, and UV 62

Electromagnetic Spectrum Radio waves Microwaves Infrared rays Visible light Radio signals, WiFi Microwave ovens, cell phones, radar “Heat rays” Sun, heat lamps, thermogram Smallest part of the EM spectrum The only EM waves we can see ROYGBIV 62

Electromagnetic Spectrum Ultraviolet (UV) rays X-rays Gamma rays Kills cells (sunburn, cancer) Small amounts cause skin to make vitamin D Can penetrate most matter Bones/lead are dense and absorb x-rays Examine internal organs Very dangerous, but blocked from space by Earth’s atmosphere 62

Space Exploration How do we use radiation to explore space? Telescopes, satellites, and laser devices all use parts of the EM spectrum to help us gather information about space 64

Space Exploration 64 Telescopes Collect and focus forms of EM radiation coming from space Optical telescopes – visible light Radio telescopes – large, focus radio waves Spitzer Space telescope – takes infrared pics of space Chandra X-ray Observatory – in orbit, takes x-ray pics 64

Space Exploration 64 Satellites Hubble Space Telescope Some take photographs of Earth’s surface Made of pixels Used for mapping Some are used for global communication In orbit, flies near planets to take pictures of them in different types of light 64

Scale of the Universe 66 Universe Astronomers All of space and everything in it Contains billions of galaxies, which contain billions of stars Enormous beyond imagination Scientists that study astronomical bodies in the universe and radiation Study very large (galaxies) and very small (atoms) objects in space 66

Distance in Space 68 Scientific notation How do I write a number in scientific notation? Used to describe very large or very small numbers Sizes or distances Puts long numbers in a shorter form Add a decimal to the number to make it between 1 and 10 Count how many numbers follow the decimal and make it a power of 10 68

Distance in Space Light-year The distance light travels in one year 9.5 trillion kilometers Light is the fastest thing that exists 300,000 km/s 68

Astronomical Objects Nebula Galaxy Large cloud of gas and dust particles “Star nurseries” where new stars form Huge group of single stars, solar systems, star clusters, gas, and dust Held together by gravity 70

Astronomical Objects 70 Solar system Star Planet Contains one star and all planets that revolve around it Giant ball of gas Nuclear fusion Revolves around a star Rounded by gravity Some made of rock and metal, others made of liquids and gas 70

Astronomical Objects Moon Dwarf planet Orbits a planet AKA “satellite” Small planet that is not gravitationally dominant 70

Gravity Orbit Why don’t planets orbiting the sun fly off into space? The path of an object moving around another object in space The force of gravity holds them in place A force that attracts objects to each other 72

Gravity 72 Law of Universal Gravitation What two factors control the strength of gravity? Every object in the universe attracts every other object Mass – amount of matter in an object Distance – as distance increases, gravity decreases Mass does not change, but weight can change depending on location 72

Gravity How do we measure the strength of gravity? How does mass affect gravity? Weight – measures the force of gravity on an object Greater mass = greater gravitational pull = greater weight 72

Motion If the sun pulls on Earth, why doesn’t Earth crash into the sun? Why do objects stay in orbit? Inertia – an object resisting a change in motion. Greater mass = greater inertia = more difficult to start or stop The force of gravity and inertia combined keeps objects in orbit 76

Formation of Planets, Stars, and Solar Systems How do astronomical objects form? Solar systems Accretion – gravity brings materials together and slowly builds them up Begin as clouds of hydrogen, helium, rock, ice Gravity pulls the materials together Cloud begins to rotate and forms a spinning disk 78

Formation of Planets, Stars, and Solar Systems Material in spinning disk pulled toward center Gasses tightly packed from accretion = greater temperature and pressure Causes hydrogen atoms to fuse together to form helium (nuclear fusion) 78

Formation of Planets, Stars, and Solar Systems What keeps solar systems together? Other rock, ice, and gasses in the spinning disk begin to pull together The gravity of the center star 78

Star Properties – Color, Temperature, and Size How do stars produce electromagnetic energy? How do astronomers classify stars? Through the process of nuclear fusion Using characteristics including color, temperature, size, composition, and brightness 82

Star Properties – Color, Temperature, and Size How do scientists know the surface temperature of a star? Using the color of the star Red stars = coolest (3,200⁰C) Yellow = medium (5,500⁰C) Blue = hottest (over 20,000⁰C) 82

Star Properties – Color, Temperature, and Size Size of stars Giants or supergiants = very large stars, larger than our sun White dwarfs = small, about the size of Earth Neutron stars = very small, about 12.5 miles in diameter 82

Star Properties – Composition and Brightness How do scientists know what stars are made of (composition)? Using a spectrograph – breaks light into colors and produces an image of a spectrum Each gas element in a star absorbs a specific wavelength of light The wavelengths that were absorbed show up as thin lines on the spectrum Lines create a unique pattern 84

Star Properties – Composition and Brightness What are stars made of? Which two factors do scientists use to determine the brightness of a star? Most stars are about 73% hydrogen, 25% helium, and 2% other elements Size and temperature Apparent brightness = how bright a star appears from Earth Absolute brightness = how bright stars would be if they were all the same distance from Earth Apparent brightness + distance from Earth 84

The Sun 86 Does the sun have layers like the earth? What features can you see on the sun? Yes, but no solid surface 3 interior layers 3 atmospheric layers Solar flares – powerful eruptions of gas from the sun into space Solar prominences – huge loops of gas that connect two sunspot areas 86

The Sun What features can you see on the sun (cont.)? Sunspots - dark areas “spots” on the sun’s surface Caused by spots of gas that are cooler than the other gas around them Cooler gas gives off less light, so the spots appear darker 86

The Sun How often do sunspots appear? Do sunspots move? They appear in a cycle Number of sunspots rises and falls every 11 years Yes, we can track the movement of sunspots Different sections of the sun rotate at different speeds 86