2 28.1 A CLOSER LOOK AT LIGHTLight is a form of electromagnetic radiation, which is energy that travels in waves.Waves of energy travel at 300,000 km/sec (speed of lightEx: radio waves and x-rays
3 Electromagnetic radiation waves are arranged into a continuum call the electromagnetic spectrum. Wide range of wavelengthsLong wavelengths with low frequencies at one end, short wavelengths with high frequencies at the other endWavelength measured crest to crest/trough to troughFrequency the number of that crests of the same wavelength that pass a point in one second.
4 Scientists study the visible light portion of the electromagnetic spectrum. Spectra of a stars allow for astronomers to learn about the star’s elements and motion.Spectra studied using a spectroscope
5 Three types of visible spectra Continuous spectrum: unbroken band of colors, emitting all colors of visible lightEmission spectrum: unevenlyspace of lines of different colors,emitting light of only someWavelengthsAbsorption spectrum: dark lines thatcross a continuous spectrum.
6 Doppler Effect - change in the wavelength of sound due to motion between the object and the receiver.
7 Doppler effect applies to lights as well as sound. Shift of the emission spectra can indicate if the object is moving towards or away from EarthShift towards red end of spectrum, object moving away Earth – RedshiftShift towards blue end of spectrum, object moving towards Earth - BlueshiftDoppler effect determined that the universe is expanding
8 TELESCOPESOptical Telescopes – gather far more light than an unaided eye and magnify imagersReflectingUses one lens at back to gather and focus lightImage reflected on to a small mirror and then the eye pieceRefractingUses two lensesLens at the front gathers lightEyepiece magnifies image
9 Radio Telescopes = big satellite dishes Use to detect energy waves at frequencies lower than visible lightOtherUsually satellites in spaceGamma rayBackground radiationX-rayHubble (infrared)
10 28.2 Stars and Their Characteristics Observation of stars has been going on for over 5000 yearsThe grouping of stars are called constellationsConstellationsonly appear together as viewed from Earth; from a different angle they do not look like the constellation
11 Constellations (continued) Constellations will change shape over thousands of years due to the universe expandingMove across the sky from east to west (though Earth rotates west to east)
12 North Star – Current is Polaris Sits directly over the North poleDoes not move to the naked eyeVery powerful tool for navigationDue to Precession, Polaris will not always be the “North Star”
13 The Constellations that dominate the night sky change from month to month. This is the result of the Earth’s change in position as it orbits the Sun.
14 Distances to stars and other objects in space Astronomical Unit (AU) - the distance from Earth to the Sun (150 million kilometers)Light year - the distance light travels in one year (9.5 trillion kilometers)It is a distance measurementExample light-years means that the light we see has been traveling for 4.2 years before we can see it (4.2 X 9.5 trillion km)Parallax - change in an object’s direction due to a change in the observer’s positionParsec short for “parallax second” equal to light-years.
15 ParallaxThe further the object from the viewer, the less the parallax shift.
16 Stars Elements No two stars have the same proportions of elements Hydrogen ~69%Helium ~29%Heavier elements ~2%light that radiates is dependent on composition and temperature, this differs in every starStar spectrum is its fingerprint
17 Mass, Size and Temperature Stars vary greatly in masses, size and temperatureCannot observe directly so we are estimating what the mass might beGravitational effect on bodies around the star help with estimating its massStar mass is expressed as multiples of the mass of our Sun (which has a stellar mass of 1)Size varies more than massSmallest stars are smaller than EarthLargest have diameters more than 2000 times that of our SunStars differ even more in densityBetelguese is about one ten-millionth of our SunOne star is so dense that one teaspoon would weight more than a ton on Earth
19 Temperature of stars vary Range of color emitted is dependent on the surface temperatureCool stars are redEx. Betelguese with a surface temperature of 3000oCMid-temperatures are yellowEx. The Sun with a surface temperature of 5500oCHot stars are blueEx. SirusHarvard Spectral Classification Scheme - group stars by temperature and color
21 Luminosity = brightness of a star Dependent on size and temperature of the starIf two stars are the same size the hotter star would be more luminousApparent magnitude - how bright a star appearsDoes not factor in distanceAbsolute magnitude - how bright the star would be if all stars were the same distance from Earth (10 parsec)
22 Variable stars -show a variation in brightness Cepheid variables are yellow supergiant stars with a cycle of brightness ranging from days.Most have a cycle of 5 days.Nonpulsating star change in brightness due to fact that it is more than one star.
23 28.3 LIFE CYCLE OF STARSHertzsprung-Russell (H-R) diagram – shows luminosity, temperature, and stages in the life cycle of the starsMain Sequence – 90% of stars run in a band from upper left to bottom right of diagramGiants & Supergiants – more luminous, found above main sequenceWhite dwarfs – near the end of their lives, below main sequence, glowing stellar core
25 Life cycle of a star like our Sun A star begins its life in a cloud of gas ( mostly Hydrogen) and dust called a nebulanebula condenses, becomes denser, temp. increases becomes a protostar fusion begins and star is “born”Hydrogen in core continues to fuse into heliumWhen hydrogen “runs out”, fusion occurs outside the core and the star expands (giant)Gas layers are blown away and the carbon-oxygen core is left (a white dwarf)
26 Life cycle of a Massive Star Begins like our sunInstead of a carbon-oxygen core forming, an iron nuclei forms, and the star expands to 100x the size of our sun (supergiant)Iron nuclei absorbs energy and collapses (supernova)Massive star remnants become a Neutron Star or Black Hole
28 Galaxies and the Universe Universe –everything that exists, 10 billion-20 billion years oldGalaxy – group of stars held together by gravity3 types:We live in the Milky Way Galaxy ( a spiral galaxy)Elliptical Galaxy- concentrated, spherical shapeIrregular Galaxy – smaller, fainter, spread unevenly
30 Origin of the UniverseBig Bang Model – explains the history of the universe from a fraction of a second AFTER it came into being up to present timeEvidence supporting it = distance between galaxies is increasing (universe is expanding)Edwin Hubble found redshifts in the spectra of the galaxiesCosmic background radiation found with radio telescopes