Astrophysics Notes

8/10/2019 Astrophysics Notes

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13;AstrophysicsAssessment Statements

E.1.1 Outline the general structure of the solar system

E.1.2 Distinguish between a stellar cluster and a constellation

E.1.3 Define a light year

E.1.4 Comare the relati!e distances between stars within a gala"y and between gala"ies# in terms of

order of magnitude

E.1.$ Describe the aarent motion of the stars% constellations o!er a eriod of a night and o!er a

eriod of a year and e"lain these obser!ations in terms of the rotation and re!olution of the

Earth

E.1.1

&lanets orbit the Sun in ellises and moons orbit lanets.

&lanet 'ass (elati!e to Earth (adius (elati!e to the Earth 'ean distance from the Sun )A*+

'ercury ,.,- ,.3 ,.3/

0enus ,.1 ,./ ,.2

Earth 1 1 1

'ars ,.11 ,.$3 1.$2

uiter 31 11.2 $.2

Saturn /2 /.$ /.$4

*ranus 12.$ 3. 1/.2

etune 1.1 3.$ 3,

ala"y iant assemblies of stars# gas# and dust held together by the gra!itational

forces they ha!e on each other. Our ala"y is called the 'il5y 6ay.rous of stars

Collection of stars including the sun

'il5y way contains about 1 billion stars

Asteroid Small minor lanet that drifts in the solar system# orbiting the sun.

Comet ra!itationally bound system of gala"ies%stars.'i"tures of roc5 and ice mo!ing in highly ellitical orbits around the sun.

As it is aroaching the sun# ice melts. 7ea!ing a bright trial of debris

which can be millions of 5ilometre long# ointing away from the Sun.

ebulae 8rom the 7atin word for 9cloud9. *sed to label all sorts of stuff in sace# that

are now 5nown as star cluster or gala"ies. :t is sometimes still used for aconcentration of gas and dust.

Star A fi"ed luminous oint in the night s5y that is a large# remote incandescent

body li5e the sun.

&lanet A celestial body mo!ing in an ellitical orbit around a star.


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'any asteroids are located between 'ars and uiter in a region 5nown as the asteroid belt.

E.1.2

Constellations

normally what we recall as the signs of the ;odiac

'odern astronomy uses it more as a grid in a celestial shere

rou of stars that seem to be close together because they are in a form of a recogni;able attern in

sace.

ear = distance light tra!els in one year.

1 light year ? 3., " 1,ms=1" 3-$ days " 24 hours " -, minutes " -, seconds ? /.4- " 1,1$m

E.1.4

(elati!e Distance =


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Clusters are groued into suerclusters

Suerclusters form into filaments# lea!es !ast !oids of emty sace in=between.

6hen loo5ing u in the s5y# loo5s li5e all stars rotate around it.Effect is because of the rotation of the Earth about its own a"is.

E"ercisesB

1. uiter# 'ars# Earth and etune

a+ 7ist these four lanets in order of increasing distance from the SunEarth# 'ars# uiter and etune.

b+ :ncreasing in diameter

'ars# Earth# etune and uiter

2 a+ si;e and temerature or big and fusion

13.2

E.2.1 State the the fusion is the main source of starsE.2.2 E"lain that# in a stable star )8or e"amle# our Sun+# there is an e@uilibrium between radiation

ressure and gra!itational ressure.

E.2.3 Define the 7uminosity of a star

E.2.4 Define aarent brightness and state how it is measured

E.2.$ Aly the Stefan=olt;mann law to comare the luminosities of different stars

E.2.- State 6ien9s dislacement law and aly it to e"lain the connection between the colour and

temerature of stars

E.2. E"lain how atomic sectra may be used to deduce chemical and hysical data for stars

E.2. Describe the o!erall classification system of sectral classes

E.2./ Describe the different tyes of star

E.2.1, Discuss the characteristics of sectroscoic and eclising binary stars

E.2.11 :dentify the general regions of star tyes on a ert;srung=(ussell )(+ diagram.

E.2.1

hydrogen is con!erted into helium.

Sun radiates an estimated 1,2-oules e!ery second

Sun loses an estimated 4.2- " 1,

E2.2a+ 8net? m " a

Acceleration ? ,


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E.2.3.

7uminosity is measured in watts

:t deends on both the surface temerature of the star and its radius or surface area.


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E.2.6

6ien9s 7aw

States that the ea5 wa!elength of the emission of a blac5 body is in!ersely roortional to its

temerature6ien9s dislacement law states that the higher the temerature the lower the wa!elength at which most

of the energy is radiated.

A hot obGect emits radiation across a broad range and there is a ea5 in intensity at a articularwa!elength. 8or a hotter body# the ea5 is at a higher intensity and shorter wa!elength.

*seful for the determining the temeratures of hot radiant obGects such as stars# and indeed for a

determination of the temerature of any radiant obGect whose temerature is far abo!e that of itssurroundings.

6hen the temerature of a blac5body radiator increases# the o!erall radiated energy increases and the

ea5 of the radiation cur!e mo!es to shorter wa!elengths.

E.2.7

6e can deduce both chemical and hysical data about stars from their absortion sectra.

Can determine the chemical comosition and find the surface temerature.Can gain information about the seed and direction of motion of stars from an analysis of their sectra#

using the doler effect

Doler Effect

:f a source of wa!es is mo!ing towards us# their fre@uency is shifted uwards.


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is increased and the fre@uency is shifted down.

(ed Shifted

:f a star is mo!ing away from earth# the light wa!es reaching us are more saced out and theirabsortion lines will shift to longer wa!elengths.


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bigger7argest structures in the uni!erse# although they

are not that massi!e.

6hite dwarfs Small and ha!e low luminosity.


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/J of stars ? re# !iants and super!iants. 8rom Stefan=olt;mann 7aw we can see that their high

luminosity and lo% temperature means that they must ha!e a "ery lar!e area = they are therefore

giants.

WHITE DWARFS are !ery hot but not luminous# therefore they are much smaller than their

counterarts on the main se@uence.


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p =aralla" angle

E.3.2

heparallaxangle can be measured by obser!ing changes in the star9s osition o!er a eriod of a year.

6e can use trigonometry to wor5 out the distance of the star from the Earth )as we 5now the distancebetween the Earth and the Sun+.


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E.3.3

he paralla: an!les or stars are !reater #istances are too small to measure accurately.


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&olaris 1.//

a5ed eye limit -

&luto 1$.1

ubble sacetelescoe

31

E.3.6

A%solute of a star as the aarent magnitude it would ha!e if it were 1, c from Earth.

A star which aears to be bright could either be a star with low luminosity not too far away from

Earth# or a !ery much brighter more distant star.


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are !ery inaccurate.

E.3.13


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E.4./ Define the term critical densityby reference to a flat model of the de!eloment of the uni!erse.

E.4.1, Discuss how the density of the uni!erse determines he de!eloment of the uni!erse

E.4.11 Discuss roblems associated with determining the density of the uni!erse

E.4.12 State that the current scientific e!idence suggests that the uni!erse is oen

E.4.13 Discuss and e"amle of the international nature of recent astrohysics research

E.4.14 E!aluate arguments related to in!esting significant resources into researching the nature of the

uni!erse.

E.4.1

@e$tons &o#el o the uni"erse


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its wa!elength decreases.

Astronomers use Doler shifts to calculate recisely how fast stars and other astronomical obGects

mo!e toward or away from Earth. :n 1/2,s Edwin ubble and 'ilton umanson realised that thesectra of distant gala"ies showed a redshift# which means that they are mo!ing away from Earth. So# if

gala"ies are mo!ing away from each other then it they may ha!e been much closer together in the ast

Singularity= the logical e"tension to this idea is that at some time in the ast e!erything in the uni!erse

must ha!e all been located at one oint.

ig ang *ni!erse began 13. billion years ago# with an e"losion.

E.4.5

C' first obser!ed inad!ertently by &en;ias and 6ilson in 1/-$. (adiation was acting as a source of

e"cess noise in a radio recei!er they were building. :nitially# the radiation was thought to be some sort

of contamination and they tried to remo!e it by cleaning the recei!er. T"e cosmic micro&a!e

'ac#ground radiation is a #ind of ec"o of t"e (ig (ang still resonating around t"e uni!erse.

E.4.6

Fensi*as an# Gilson oun# that the intensity o the ra#iation that they recei"e#) ro& all

#irections) ha# a $a"elen!th in the &icro$a"e re!ion. Ghen they plu!!e# this $a"elen!th into

Giens #isplace&ent la$ they found that it ga!e a temerature of 2. I# and we 5now that 2.I is the

temerature of the ambient uni!erse so C' radiation ro!ides e"cellent suort for the ig angmodel.


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lat uni"erseB 9.

E.4.13


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Useful &e' lin#s

httB%%hysics=astronomy.Ghu.edu%grous%astro%

httB%%www.astronomynow.com%news%n1,,$%24setia%

E.4.14

Summari-e t"e arguments for and against astrop"ysics researc"

B,

*nderstanding the nature of the uni!erse hels shed light on hilosohical @uestions such as Why are

%e here< and/s there other intelligent life in the unierse

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