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Astronomy 1020, Unit 1B

by: Emily Mason

Astronomy 1020, Unit 1B Astronomy 1020

Marketplace > Clemson University > Astronomy 1020 > Astronomy 1020 Unit 1B
Emily Mason
Stellar Astronomy
Dr. Flower

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These notes cover the Learning Objectives posted on Blackboard for Unit 1B.
Stellar Astronomy
Dr. Flower
Study Guide
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This 6 page Study Guide was uploaded by Emily Mason on Monday January 25, 2016. The Study Guide belongs to Astronomy 1020 at Clemson University taught by Dr. Flower in Winter 2016. Since its upload, it has received 175 views.

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Date Created: 01/25/16
Unit 1B 0 BrightnessIntensity used to describe the amount of energy emitted each second Measured in ergsscmzor joulesSmz 0 Energy FluX the rate of ow of energy 0 Inverse Square Law brightness diminishes with the square of the distance 1 Brightness DC o Implies that if a star were 10 times farther away than we see it now it would appear 1 102 or 1 100 time as bright Or 100 times fainter 0 MagnitudeLuminosity a measure of the brightness of a star 0 The terms brightness and intensity are considered everyday terms where Magnitude and Luminosity are technical terms 0 Intrinsic Brightness the intrinsic brightness of a star is the energy uX at its surface 0 The energy from a star s surface is diminished as the square of the distance to the observer increases 0 In other words Intrinsic Brightness is the amount of light an object actually emits as opposed to how the object may look from Earth 0 Note intrinsic brightness varies on the object For instance the intrinsic brightness of a light bulb is its wattage 0 Apparent Brightness When the measured brightness at the Earth of any star depends of both intrinsic brightness and its distance 0 Photometer instrument used to measure the brightness of individual stars by electronically counting the number of photons from each star 0 Photons deliver energy so the intensity of light from a star is proportional to the number of photons it emits AKA the more photons the brighter the star 0 Apparent Magnitude m Groups Visible to the Naked Eye First Magnitude Stars m 1 Second Magnitude Stars m 2 Third Magnitude Stars m 3 Fourth Magnitude Stars m 4 Fifth Magnitude Stars m 5 999959quot 6 Sixth Magnitude Stars The faintest group 772 6 0 Calculating Magnitude Difference 0 Star Am1 0 Star B m 2 0 2 1 I l o The difference in magnitudes corresponds to a brightness factor of 2512 0 So since 2 1 1 the Star B is 2512 times fainter 39 If the difference of the magnitudes equaled 2 then it would be 5024 Or 2512 X 2 times fainter 0 Mgative Magnitudes the necessity for negative magnitudes arises because some objects including some stars are many time brighter than first magnitude stars Only negative magnitudes can represent the observed brightness ratios for these stars 0 Brightness Ratio Between 2 Stars Formula b1b2 2512m2 m1 0 AU represents Astronomical Units the mean distance from the center of the earth to the center of the sun 0 Light Year describes how far light travels in one year 0 1 Light Year 911 X 1012km 0 Light years represent both time and distance because it is used like a travel time such as 60 mph You can do 60 miles the distance in one hour time 0 Parsec A parsec is the distance a star would be at if its measured parallaX were 1 3600 degrees called an arcsecond o Abbreviated pc 0 1 parsec 1 pc 206265 AU 0 Light years to PC 1 Light year 030661pc 0 PC to light years 1 pc 326156 light years 0 Alpha Centauri closest star in the solar system 0 Distance of 43 light years from earth 0 Distance of 133 parsecs from earth 0 Distance of271400 AU 41 x 10A13 km from earth Parallax 3 de nitions 1 a name used to describe a method to obtain distances 2 an apparent motion of stars on the sky due to Earth39s orbital motion 3 an angle used in the distance estimation Measured in arcseconds Thumb Experiment You extend your arm and act like you re giving a thumbs up When you blink one eye then the other it looks like your thumb is moving back and forth This motion simulates parallax motion PARALLAX EQUATIONS 0 00000 The angle p is called the parallax angle or just the parallax The distance between the star and the sun is d The two equations in the drawing are two equivalent ways of determining the distance d from the measured parallax p The rst equation gives the distance measured in astronomical units the second in another unit the parsec p represents the parallax in arc seconds Star f d E eaasm 1 dpc Recall 1 parsec 1 pc 206265 AU 1 degree 60 arcminute 60 arcminute 1 degree 60 arcseconds 60 arcsecond 1 arcsecond 1 3600 degrees No known stars have parallaxes larger than 1quot and parallaxes are always measured in arcseconds 0 Planck Curves represent the supply of photons emitted by a star 0 Shows how the intensity of emitted radiation is distributed over the electromagnetic spectrum 0 Tend to rise steeply at short wavelengths reach a maximum then gradually decrease at longer wavelengths 0 Energy uX represents the total energy the star emits each second from each square meter of its surface 0 The amount of energy uX is dependent on temperature 0 Energy uX from a hotter star is greater than from a cooler star 10 g g 08 The Planck Curve of the hottest object g lies completely above the Planck Curve E 06 of both the cooler objects 5 D g 04 E 02 00 I l 0 500 1000 1500 2000 2500 3000 wavelength nm 0 Stefan Boltzmann Law gives the relationship between energy uX F and the temperature T of the surface of the star T represents the proportionality constant o me1 represents the amount of energy passing through a surface each second 0 Units joulescm2 or wattcm2 4 F total 39539 T 0 Wein s Law the mathematical relationship between the wavelength of the intensity maXimum and temperature See graph above as well 0 T represents the temperature of a radiating surface 0 Arm 2 waiveieiigiii of maximum emission iii meiere 0 Units meters or angstroms Home llmu T O Conversions 1 A 1010 m 0 Spectrographs prisms that disperse starlight into individual wavelengths 0 Absorption Spectra show dark lines on a continuous spectrum continuum O The dark lines represent individual wavelengths buy they are due to an absence of photons at those wavelengths O Occurs when atoms in cooler outer layers of a star absorb continuum photons emitted from the hot interior Every time an atom absorbs a photon an electron moves to a higher orbital 0 Emission Spectra eXhibit bright lines the colors of which indicate their wavelength O Occurs when atoms in a hot gas have electrons in orbitals farther away from the nucleus than normal or when it is in an excited state 0 Doppler Shift when motion causes the wavelengths of spectral lines to shift 0 Moves relative to us 0 Stars usually only shift only a fraction of an Angstrom O Blueshift is when the source is moving towards us Wavelengths become shorter O Redshift is when the source is moving away from us Wavelengths get longer 0 Represents the observed measured wavelength of an absorption or emission line in a spectrum source 0 Represents the measured wavelength of the same absorption emission line from a source at REST chugm wmlcae AA A x AA Wake Aogtgtgt elmH 39 CvihK Xlttl 377 bltgci fl i l 0 Radial Velocity the amount of velocity that is necessary to produce these Doppler Shifts Equation for Radial Velocity 0 Speed oflight c 3X105kms O The larger is the larger the larger the velocity V veloc j v r Xk C


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