Electromagnetic Spectrum Making Waves Waves begin with vibrations

Electromagnetic Spectrum

Making Waves • Waves begin with vibrations and transfer energy • There are two types of waves: – Compressional--such as sound waves, require a medium to transfer energy – Transverse--such as light waves, can travel through a vacuum (space)

Electromagnetic Wave • A transverse wave that transfers electric & magnetic waves. • It consists of vibrating electric & magnetic fields that move through space at the speed of light (300, 000 km per second). • Produced by charged particles

Electromagnetic Waves

Electromagnetic waves cont. Electromagnetic radiation: the energy transferred through space by EM waves • Travels through empty space • Doesn’t require a medium • This is why we can see the sun & stars •

§ All electromagnetic waves travel at the same speed in a vacuum, but have DIFFERENT wavelengths & DIFFERENT frequencies.

Wavelength & Frequency • Wavelength: the distance between the crest of one wave & the crest of the next wave • Frequency: number of wavelengths repeating during a unit of time

• Wavelength & Frequency • As wavelength decreases, the frequency INCREASES. • Waves with longest wavelengths = lowest frequency AND have less energy • Waves with shortest wavelengths=highest frequency AND more energy

Electromagnetic Spectrum § Tg. The complete range of electromagnetic waves placed in order of increasing frequency § Made up of: radio waves, infrared rays, visible light, ultraviolet rays, X-rays & gamma rays

Radio Waves • the longest wavelengths in the electromagnetic spectrum • used by radios, TV, cell phones

Microwaves • shorter than radio waves but longer than infrared • used by microwave ovens, cell phones, tv, weather radar • transmits information over long distances

Radar • Stands for “radio detection and ranging” • uses reflected radio waves to detect objects & measure their distance & speed • Used in police radar guns

Infrared • between microwaves & visible light on the EMS • we experience this type of infrared radiation every day in the form of heat • Uses: remote controls, infrared imaging

Visible Light • • the only electromagnetic waves we can see appear as the colors of the rainbow (ROY G BIV) Have shorter wavelengths, higher frequency than infrared Things that appear red = longest wavelength Things that appear violet = shortest wavelength. As the wavelengths decrease, other colors are visible Visible light that appears white is a mixture of the other colors

Ultraviolet • • shorter wavelengths than visible light (carry more energy) produced by the sun, blocked by the ozone causes sunburns, skin cancer, damage eyes Good use: vitamin D (for bones/teeth)

X-rays • • smaller wavelengths & higher energy than ultraviolet waves the ozone blocks all x-rays from space X-rays can go through most matter Used by doctors to diagnose & treat health problems

Gamma Ray • the smallest wavelengths & the most energy of any other wave (highest frequency) • generated by radioactive atoms & in nuclear explosions • Most penetrating of all EM waves • used to kill cancerous cells (radiation)

Stars

Classifying Stars • • Color and Temperature: color indicates surface temperature Cooler stars appear RED. Hot stars are BLUE & about 20, 000 degrees C Our sun is yellow & about 5, 500 degrees C

Size of stars § SStars can be small, medium or large. § Our Sun is a medium sized star. § Large stars are called super giants or giant stars. Ex. Betelgeuse

Classifying Stars • Chemical composition: most are about 73% H, 25% He, & 2% other • Spectrograph: a device that breaks light into colors and produces an image of the resulting spectrum. • Since different gases absorb different wavelengths, we can identify what gases are in a star.

Measurement • Light year: the distance that light travels in one year, about 9. 5 trillion kilometers • Parallax: the apparent change in position of an object when you look at it from different places

How a star is born • Nebula: a large cloud of gas and dust spread out in an immense volume • Protostar: a contracting cloud of gas & dust with enough mass to form a star. Earliest stage of a star’s life.

Life Spans • Low mass star: 200 billion years • Medium mass star: 10 billion years – Our sun is estimated to be 4. 6 billion years • High mass star: 10 million years

Life Cycle of a medium sized star Low/medium mass nebula L/Med. Mass star Red Giant Planetary Nebula White Dwarf Black dwarf

Life cycle of a high mass star High mass nebula High mass star supergiant Supernova neutron star OR black hole

Phases of Death • When stars begin to run out of fuel, the core shrinks and the outer portion expands • Eventually, the outer parts grow larger and drift out into space creating a planetary nebula.

Phases • White dwarf: the blue-white core of the star that is left behind • Supernova: results from an exploding supergiant and can form a nebula which has the potential for new stars

Phases • Neutron stars: the remains of a supergiant and can have a mass three times that of the sun but the size of a city • Pulsars: radio waves emitted by neutron stars that are spinning

Phases • Black hole: has gravity so strong that not even light can escape. These can be detected by other objects’reaction when near a black hole.

Galaxies and the Universe • Clusters of stars: • All the stars in a cluster formed from the same nebula at about the same time & the same distance from Earth.

Clusters • 2 Types of clusters: • 1. Open: disorganized, loose appearance contains no more than 1000 stars; a lot of bright super giants & lots of gas & dust •

• 2. Globular: large groupings of older stars; round & densely packed with stars; some may contain more than a million stars

• Galaxies: enormous swarms of stars, gas, dust & dark matter held together by gravity • Our solar system is in the _________ Galaxy. • The MWG is one of a billion galaxies in the universe (that have been observed)!!

Types of Galaxies 1. spiral: pinwheel shaped, young stars are found on the arms, older stars found in the nucleus Ex. Milky Way

• 2. Elliptical: oldest & largest galaxies, smooth & oval shaped • 3. Irregular: don’t have a distinct shape, may be young galaxies that haven’t formed or 2 gal. colliding

Milky Way Galaxy • Contains more than 200 billion stars • About 100, 000 light years wide • Sun orbits the galaxy’s core every 240 million years.

Origins of the Universe • 3 common theories about the origin: • 1. Steady state theory: the universe has always been the same & will NEVER change • Not a readily accepted theory based on scientific evidence • 2. Oscillating Model: expansion of the Universe began & everything moved outward, but over time, expansion slowed & the matter moved back in (think of a slinky), then it repeated over and over

• 3. BIG BANG THEORY: everything started with a BANG……. Most widely accepted theory, matter clumped together to form H & He

Our Expanding Universe • The Doppler Shift explains how we are expanding: • If a star is moving towards Earth, the wavelengths are compressed & you see the spectrum BLUE. • If a star is moving away from Earth, the light wavelengths are stretched out & you see the spectrum in RED.

The Red Shift-Hubble Law • In 1929, Edwin Hubble published a paper about light from other galaxies. • All galaxies beyond the Local Group (our group of galaxies) show a red shift in their spectrum, this shows they are moving away from us. • The universe is EXPANDING!!!!

Dark Energy • The universe is accelerating due to dark energy. • Dark energy: force causing the galaxies to be moving far apart at a faster rate

How long does it take for the light from stars to be visible here on Earth? • • Other stars are so much farther away that it is convenient to express the distance to them in units of the distance traveled by light in one year. This unit is called a light year. The next closest star to us is Proxima Centauri. This star is 4. 3 light years away which means that light from it takes 4. 3 years to reach us. Our galaxy is about 100, 000 light years across. This means that it can take tens of thousands of years for light from some stars in our galaxy to reach us. For stars that we can see in nearby galaxies it can take millions of years. The farthest objects we can see are quasars. They are so distant that the light we see from them today left billions of years ago.

• So when we look up at the stars we are looking back in time. This is useful for astronomers because when we look at very distant objects we can see what the Universe was like a long time ago.

Future of the Universe 3 possibilities: • 1. all stars will run out of fuel & burn out, the universe will be cold & dark • 2. force of gravity will pull the galaxies back together (“Big Crunch”), all matter would be crushed into a black hole • 3. universe will keep on EXPANDING

Age of our Universe • About 13. 7 billion years old • Scientists know this from measurements of how fast the galaxies are moving away from us AND cosmic background radiation (thermal energy leftover from the big bang)