Lecture 2 - Distances, Sizes and Time

8/8/2019 Lecture 2 - Distances, Sizes and Time

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Lecture

2

:


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Time Item

7:00 7:50pm Sizes &DistancesintheSolarSystem

8:00 8:50pm Sizes &

Distances

beyond

the

Solar

System

9:00 9:30pm ReservedforCronyn projects


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Incaseyoudidntknow:theseprojectsareongoing: Clearskiesrequired!

Cronyn status:

htt : www.astro.uwo.ca cron nstatus.html


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Clickers:Last

week

not

enough

data

to

process.

e s ryaga n o ay.

WebCT quiz:justdoit.

Diagnostictest:

results

next

week.


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Earthhas

the

closest

encounter

with

Jupiter

until

. ,bigintheCronyn telescope!

MethaneinatmosphereofMarslastslessthana

.

.Andnow,byrequest,someselfpromotion.


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Whatsyourfavoritecolor? Textentryanswer!


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Today,wellsimplyhavealookattheBigPictureoftheUniverse:

Whatis

the

Solar

System,

the

Milky

Way,

the

Local

Group,galaxycluster??

Howbigarethings,howfarapart?HowandwheredoesEarthfitin?

Wewontreallyexplainhowweknowallthatwellsavethatfortheremainin lectures.

Weresettingthestagefortherestofthiscourse.


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,

andvisualize sizes

and

distances

in

the

Earth

MoonSuns stemandbe ondb usin scalemodels.

Youwill

be

able

to

ex ress

astronomical

distancesusinglighttraveltimes.

Youwillknowhowdifferentstructuralelements

ofthe

Universe

are

related

to

one

another.

Youwillbeabletocompareeventsinthehistoryo e n verse oaoneyearca en ar.


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Q:Do

Ihave

to

know

precise distances

between

, ,

: o,you on t avetomemor zeprec senumbers.However,youshouldknowaballpark

,shouldnowhowthesenumbersrelatetoeach

.


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Wellstart

from

Earth,

and

then

gradually

work

collectionsofobjects.

,togetagoodsenseofrelativesizesand

.


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Ascale

model

is

arepresentation

or

copy

of

an

sizeoftheobject.

,factor!!


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Sincemany

numbers

are

so

big

we

cant

really

,models.

bythesamefactor.

. .40,000kmapartbecome:

woo ec so 5an 10cm a are4mapar .


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Youdontneedto nows zestoseethatthe aresimilar!


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Diameter:12 2km.Youshouldapproximately12,000km.


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Wheninorbit,howfarawayistheSpaceShuttlefromEarth?

A. Afewkilometers.C. Afewthousandkilometers.D. Closetoamillionkilometers.E. Closetoabillionkilometers.


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EarthasseenfromtheSpaceShuttle/ISS


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Wheninorbit,howfarawayistheSpaceShuttlefromEarth?

A. Afewkilometers.C. Afewthousandkilometers.D. Closetoamillionkilometers.E. Closetoabillionkilometers.


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TheISSandtheshuttleasseenfrommoderatetelescope


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Equatorialdiameter

:12,756

km

qua or a c rcum erence:40,075 m

Around

the

world

is

about

a

400

hour

drive

a t esst an17 aysnonstop .

Convenientscalemodelfornow:

sca e

own

ya

actoro

50

m on

>diameterabout24cm

a ou es zeo a as e a .


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WithEarththesizeofabasketball,whereshouldweputtheInternationalSpaceStation?

A. 1cmabovethesurfaceC. 1mabovethesurfaceD. 10mabovethesurfaceE. 100mabovethesurface


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SpaceShuttle

/ISS

typically

flies

at

about

400

km

v e y50m on=0. cm

The

Hubble

Space

Telescope

at

about

1.2

cm


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Communicationsatellites

are

typically

in

earthinexactlyoneday.

Physicsrequiresthemtobeatanaltitudeof

,

Inourscalemodelthatwouldbe:71.6cm


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Howbig

would

the

moon

be?

owcou we gureou

Is

the

Moon

bigger

or

smaller

than

the

Sun? CloserorfurtherawaythantheSun?


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TheshadowoftheMoononEarthduringasolareclipse


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WithEarththesizeofabasketball,howbigshouldtheMoonbe?

A. AboutthesizeofasmallballbearingC. AboutthesizeofabaseballD. AboutthesizeofagrapefruitE. AboutthesizeoftheEarthitself


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Equatorialdiameter

=3,476

km

o noursca emo e s ecomesa ou 7cm.

8


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Wheredoweputthemooninourscalemodel :A. Atadistanceoflessthan70cmC. Atadistanceofabout7mD. Atadistanceofamorethan10m

Onecorrect

answer


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Thedistance

to

the

moon

is

384,399

km

ca e =7 9cmor7.7m

How

do

we

know

the

distance

??> nce po o: unar aser ang ng

Thisfigure

has

the

correct

scale

!!

30


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Pointlaser

to

mirror

on

the

moon

aser g sre ec e

Detect

laser

pulse

and

measure

time

between

r ng aseran etect ngt es gna

Thisisthenthelighttraveltime

Ifwe

know

the

speed

of

light,

we

can

calculate

thedistance

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c =299,792.458

km

/s

Youshouldknow:about300,000km/s

Thisistheabsolutefastestspeedpossibleinthe

Universe!

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LLRexperiments

observe

arrival

of

pulse

about

2.6

secondsafterfirin thelaser.

Withaspeedofabout300,000km/s,thiscorresponds

toadistance

of

780,000

km

Butthisistwice thedistancetothemoon(lighthastogothemoon,andthengetback)

o

rue

s ance

s

a

o

a ,

or

a ou

390,000

m Or:thedistancetothemoonisabout 1.3light

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LLRextremely

precise

oon s r ngawaya a ou 3. cmperyear

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Thephysical

size

of

the

Sun

is

about

400

times

.

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Howbigshouldthesunbeinourscalemodel?A. Diameterofabout30mC. Diameterabout500mD. Diameterabout1km

Onecorrect

answer

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Diameterabout

1,400,000

km

ca e =2 00cm=2 m

SunsdiameterislargerthantheMoonsorbit!

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Totalsolar

eclipse:theapparentsizethemoonarethesame!

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TheSunmustbeabout400timesfurtherawaythantheMoon

True/False

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Howfarawayisthisbigball?A. About100m C. About3km nearVictoriaPark,LondonOND. About20km

One

correct

answer

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Distanceto

the

sun

is

approximately

150

million

.

ThisisreferredtoasanAstronomicalUnit(AU)

mostcommon yuse ast e as s ordistancescalesinthesolarsystem

v e

y50

m on

=3

m

nour

sca e

mo e

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Iflighttravelsabitmorethan1secondfromtheMoontoEarth,thenhowlongdoessunlightneedtotraveltoreachEarth?

A. 1second.C. Abitmorethananhour.D. Manyhours.

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Usingthe

right

numbers,

you

can

find

that

it

Earth.

SoiftheSunwouldstopshiningrightnow,we

EarthSundistance:8lightminutes.

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Spaceis

not

as

far

away

as

you

think

when

,toOttawaorChicago!

MoonisnotasclosetotheEarthasyouthink!

ze

o

t e

un

s

arger

t an

oon s

or t

aroun

theEarth!

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Q:What

is

the

Solar

System?

: e o ar ys em s eco ec ono o ec s a orbitstheSun includingplanets,comets,

, Letsfocusonplanets.

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Distancesnot toscale!!

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Planet Distance(AU) Distanceinscalemodel Lighttravel timeMercury 0.4 AU 1.2 m 0 03.2min

Venus 0.7 AU 2.1km 0h05.8min

Earth 1.0

AU 3.0

km 0h

08.3

min

Mars 1.5 AU 4.5km 0h12.45min

Jupiter 5.2AU 15.6km 0h43min

. .

Uranus 20AU 60km 2h

40

min

Neptune 30AU 90 km 4h

Pluto 39AU 117km 5h20min

47


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Ourscale

model

that

worked

well

for

the

Earth

forlargerdistances..

48


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Insteadof

scaling

by

afactor

50

million,

lets

try

10

.

Sunisnowabout14cm grapefruitsized.

1 =150m on mcorrespon stoa out15meters.

stance

to

uto

:

a

a

ometer

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ApproximateSize or Distanceusinglight Scale model1(50million) Scalemodel2(10billion)distance(km) traveltime

Earth 12 2 2 cm 1mm

Moon 3,474 7cm 0.3mm

un 1,392,000 2 m 14cm

EarthMoon 384,000 1.3lightseconds

7m 4cm

SunEarth 150,000,000 8.3

light

minutes3km 15

cm

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WiththeSunthesizeofagrapefruit,howfarawayistheneareststar Proxima Centauri?

A. About3kmaway VictoriaPark,LondonON C. About1,000kmaway QuebecCityD. About4,000kmaway VancouverE. About15,000kmaway Sydney,Australia

51


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Insteadof

scaling

by

afactor

50

million,

lets

try

Sunisnowabout14cm grapefruitsized.

=meters.

DistancetoPluto:halfakilometer

Distanceto

Proxima Centauri

:4,400

km

!

T icaldistancebetweenstarsintheMilk Wa

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Stateof

the

art

spacecraft

:speed

abit

over

, .

Toreachtheneareststars,wouldstillneedabout

,

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Iflight

takes

more

than

4years

to

travel

from

,Proxima Centauriasitwasmorethan4years

. Wecannotnowwhatthepresentdaysituationis

So:lookingfarther=lookingfurtherbackintime

s ronomyasa memac ne

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Say..thatsalot

stars

youve

got

there.

esun sas ar

Itsjustoneofabout300billionstarsinourMilkyay

a axy

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Sunis

about

28,000

lightyears from

the

center

of

.

DiameterofMW:about 100,000lightyears

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OurMilky

Way

is

fairly

close

to

other

galaxies

About30Galaxies,includingMagellanic Clouds,

,

li h

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1 li h r

LargeMagellanic Cloud

SN1987A

li h

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2 li h r

li h

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2 li h r

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200millionlightyears

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OurMilky

Way

is

one

of

at

least

100

billion

.

Soroughly1022 starsintheobservableUniverse

a out

as

muc

as

t ere

are

gra ns

o

san

on

a

beachesonEarth.

an

t a t s

on y

or

t at

part

o

t e

n verse

we

canactuallysee

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TheHubble

Deep

Field:

Empty

Space

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SolarSystem:

Sun

&

What

goes

around

spar o y ay a axy: a r y a collectionofbillionsofstars.

ga axypart

o

oca

roup:

ew

tens

o

galaxies,reasonableclosetogether

oca

roup

part

o

oca

uperc uster WhichispartoftheUniverse.

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Comparedto

sizes

of

objects,

distances

between

SotheUniverseismostlyempty!

ut

t e

n verse

sa so

area y

gp ace.

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Earthrotates

around

its

axis

(1

day)

r ear aroun esun 1year

OrbitsuninMilkyWay

Galaxies:expandinguniverse

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Rotationtakes

24

hour

, km

24hours.

whichmeanswetravelatabout1 6 0km/h!

Lowerspeeds

at

higher

latitudes

Rotationalvelocit =0at oles.

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Witharadius

of

150

million

km,

the

length

of

one

km.

,

billionkmperyear.

,

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Withrespect

to

local

neighbourhood

i.e.

the

Speedstypically70,000km/h

,

onlyslightlyontimescalesof10,000years.

: ,

Evenwiththatspeed,solarsystemhasonlycomp e e 2030or s.

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Withinlocal

Group

:random

velocities.

. .wellover300,000km/h

Universe

:

speedof

light.

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HubblesLaw:

the

further

away

agalaxy

is,

the

.

Soareweinthecenterofitall??

74

Notehowforallraisins,allother


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,

raisinsare

moving

away.

The

further

awaytheyare,thefastertheyaremovingaway!

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Weare

never

sitting

still!

pee sareenormous; yp ca y e argersca escorrespondtofasterspeeds!

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Becauseof

the

expansion

of

the

Universe,

we

can

Lightfromobjectsthatarefartherawayhasnot

theUniverse:

TheUniverse

has

an

observation

limit

:ahorizon

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Spaceitself

is

expanding

o ngswerec oser n epas ere sauniquemomentintimewheretheentire

. >BigBang,about14billionyearsago

so ow ongago st at

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Idea:compress

time

so

that

the

entire

lifetime

of

.

January1st :BigBang

ecem er31 ,

11:59:59pm:

r g t

now.

>Soonedaycorrespondstoabout40millionyears.

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Onthiscosmiccalendar,whendidthedinosaursbecomeextinct?

A. April1

st

ndC. November11thD. December30th

Onecorrectanswer

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About65

million

years

ago,

so

scaled

down

that

st,

midnight.

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Somewherein

February

:Milky

Way

forms

ep em er3 : ar orms a ou 4.5 onyearsold)

eptem er22 :

ar y

eon

eart .

Thatsquick!

ecem er31s ,11:5 pm: o ern umansevo ve

Entirehistoryofhumancivilization:thelastthirtyseconds.

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TheMW

galaxy

formed

shortly

after

the

Big

ButittookawhilebeforetheSolarSystem

LifeonEartharoseshortlyaftertheformationof

Butit

took

along

time

before

humans

appeared

on ep ane

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TheUniverse

is

abig,

big

place

s ancesareo eng gan ccompare os zes:theUniverseseemsmostlyempty,oratleast

Hierarchy:planets


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Howbig

is

an

Astronomical

Unit,

Light

year,

,.

Whataretypicalsizesanddistancesinthe

AgeoftheUniverse:about14billionyears

umans aven t eenaroun t at ong

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ReadChapter

2(see

lecture

guide

in

course

.

Lecture 2 - Distances, Sizes and Time

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