ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies

Prof. Rosalba Perna

TA:Thomas Rogers

http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html

MAKE SURE TO GO OVER THE SYLLABUS (if you haven’t already done so)

Goals of the dayGoals of the day• This Course

- basic info review

• Order of MagnitudeAstronomy– Reasonable estimates

• Size Scales

- getting used to astronomy

• Light year– Measuring distances in

astronomy

Who should take this course?Who should take this course?

•• No prerequisites,No prerequisites,

aimed at aimed at non-sciencenon-science

majorsmajors

•• No lab creditNo lab credit

•• Moderate amounts ofModerate amounts of

quantitative workquantitative work

(algebra)(algebra)

•• More quantitativeMore quantitative

course course –– ASTR 1040 ASTR 1040

MATH REVIEW SESSION:

Will you attend it?

A.YES

B. NO

In the process of coordinating with other classes

Course InformationCourse Information

COURSE WEB PAGECOURSE WEB PAGE::http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html

You can findYou can find

announcements,announcements,

assignments andassignments and

handouts, lecture notes,handouts, lecture notes,

and other useful thingsand other useful things

therethere

GradesGrades will be will be shown onshown onCULearnCULearn

Required TextRequired Text

The Cosmic PerspectiveThe Cosmic Perspective by Bennett et al., 2007, 5by Bennett et al., 2007, 5thth ed ed

Includes:Includes:

Access to textbook websiteAccess to textbook website

www.masteringastronomywww.masteringastronomy.com.com,,

Ebook Ebook (animations, etc), and(animations, etc), and

SkyGazer SkyGazer planetariumplanetarium

software.software.

You will need your You will need your ownown

`masteringastronomy`masteringastronomy’’ account!account!

Most Most homeworks homeworks requirerequire it it Course ID: ASTR11202009A

How to succeed in this courseHow to succeed in this course

• PUT IN THE TIME:

3 credits at CU = 6-9hours outside of theclassroom

•• Read the textbookRead the textbooksections as assigned insections as assigned inclass, discuss withclass, discuss withfriends, do friends, do homeworkshomeworks,,come tocome to

classclass

• Come see us during officehours!

Come talk with usCome talk with us

•• Prof.Prof. Rosalba Perna Rosalba Perna’’ss office hours::

Tue: 1pm-2pm; Tue: 1pm-2pm; ThTh: 1pm-3pm in: 1pm-3pm inJILA Tower 506AJILA Tower 506A (phone: 303-492- (phone: 303-492-0389) 0389) rosalba@coloradorosalba@colorado..eduedu

•• TA Thomas RogersTA Thomas Rogers office hours:

Wed, Fri:Wed, Fri: 2pm-3:30pm in Duane D1B312pm-3:30pm in Duane D1B31

(phone: 720-308-9382).(phone: 720-308-9382).

Thomas. Thomas.Rogers@coloradoRogers@colorado..eduedu

•• Or call or email (any of us) to makeOr call or email (any of us) to makean appointment!an appointment!

Observatory NightsObservatory Nights• Starting Wed Sept 2nd at

8:30pm, then about every 2weeks

• Sommers-BauschObservatory (next to Fiske):16” and 18” telescopes

• Not mandatory, but you canget extra credit towards yourgrade (Fill out summarysheet available atobservatory)

• Signup required on CULearnwebsite

ClickersClickers

GRADED clicker questions will start NEXT WEEK.

Remember to bring your clicker to class always.

Clicker questions TODAY UNGRADED.

Clicker TestClicker Test

• What class are you in?

• A) Freshman

• B) Sophomore

• C) Junior

• D) Senior

• E) Other

Clicker TestClicker Test

• What is the nationality of your professor?

• A) French

• B) Spanish

• C) Argentine

• D) Italian

• E) Greek

If the history of the entire universe wasIf the history of the entire universe was

condensed into a condensed into a single yearsingle year, the earliest, the earliest

humans (hominids) would have appearedhumans (hominids) would have appeared

about:about:

A. September 1

B. December 1

C. December 30

D. 9 p.m. December 31 (3 hours before year-end)

E. 11:59:30 p.m. December 31 (30 secondsbefore year-end)

ReadingReading Clicker QuestionClicker Question

THE COSMIC CALENDARTHE COSMIC CALENDAR

Order of MagnitudeOrder of Magnitude

AstronomyAstronomy

• Astronomy frequently deals with very BIG

numbers

• When dealing with really big quantities, the

small details become trivial

– For example, when we say that the nearest galaxy

is 2 million (2,000,000) light-years away, does it

really matter if its actually 2,000,001? 2,000,100?

– How far is it to drive from here to Los Angeles?

(centimeters won’t matter…)

What’s a factor of ! between friends?

More on order of magnitudeMore on order of magnitude

AstronomyAstronomy

How many piano tuners areHow many piano tuners are

there in Boulder County?there in Boulder County?

A. 2

B. 20

C. 200

D. 2000

E. Too many to count!

Start withStart with known facts andknown facts and

reasonablereasonable guessesguessesPopulation of Boulder County?

– ~300,000 people

• How many people have a piano?– 1 in 30?

• Could be off but probably not by much!

• How many pianos?– ~10,000 pianos in Boulder County

• How often do you need to tune a piano?– Once a year??

10,000 piano tunings/year

More reasonableMore reasonable estimatesestimates

• How long does it take to tune a piano?

– 3-4 hours?

= 2 tunings per day

!

2 piano tunings

dayx

5 days

weekx

50 weeks

year=

500 piano tunings

yeartuner

!

10,000 piano tunings

year

500

piano tunings

yeartuner

= 20 tuners

Scales in the Universe:Scales in the Universe:

our Cosmic Addressour Cosmic AddressEarth

Sun/Solar

System

Milky Way

Galaxy

Local Group

Local

Supercluster

Scale models of the UniverseScale models of the Universe

• Scale Sun as a grapefruit (1:10,000,000,000)

• Earth = tip of ball point

pen, 15 meters (49 feet)

– Moon = 4 cm away from

earth

• Mars = tip of ball point

pen, 23 meters (75 feet)

• Jupiter = marble, 78

meters (255 feet)

What about distances from the

Sun on the same scale?

Moving out of the solar systemMoving out of the solar system

• On this scale, the nearest stars would

be a system formed by a cantaloupe, a

small apple and a kiwi fruit, located in

the middle of Alaska Alaska (with solar system

in Boulder)

• There is essentially nothing in between!!

NewNew Scale for the Galaxy: Scale for the Galaxy:

• Stars are microscopic - located a few mm apart

• Milky Way galaxy is 100 meters in diameter,

contains 100,000,000,000’s (100’s of billions) of

stars1 to 10^19 scale - MW=100 m

Solar system: dot ~20 meters away from center

3000 yr to counts all the stars in the MW, one per second

Yet AnotherYet Another Scale for Everything Scale for Everything

ElseElse• Galaxies are 10” paper

plates

• Milky Way and nearestneighbor Andromeda)are 5 meters apart

• Galaxy groups andclusters contain 10’s to1000’s of galaxies

• Superclusters 50

meters across (size

of buildings in our

scale model) are

the largest

structures we see

• Observable

universe is about

size of Boulder

county on this scale

In this image, each dot is an entire

galaxy

Which of these are the mostWhich of these are the most

likely?likely?

A. Two planets colliding

B. Two stars colliding

C. Two galaxies colliding

D. None of the above… there’s too much space!

Measuring cosmic distancesMeasuring cosmic distances

• Most useful measure is based on the speedof light = 300,000 km/sec– Light-year = the distance light travels in a year

= ~ 10 trillion kilometers = 1016 m

• Like saying “I live 30 min from Boulder”

• Constant speed for light traveling in space

• Nothing travels faster through space

Light-year: which of the followingLight-year: which of the following

sentences makes sense? (thesentences makes sense? (the

others are nonsense)others are nonsense)

A. We’ll wait light-years before Mars is as close as

it is tonight.

B. The Galileo spacecraft has traveled 30 light-

years since its launch in 1989.

C. The globular cluster M13 is located 16,000 light-

years away from Earth.

D. The next generation of the Space Shuttle will be

able to travel 1.3 times the speed of light.

Clicker Question

Not A: light-years measure distance, not time.

Not B: Light travels 1 light-year in 1 year.Nothing travels faster than light!

C: correct!

Not D: Same as B. Nothing can travel fasterthan the speed of light.

Measuring Distances with Light:Measuring Distances with Light:

• Earth-Moon = 1.5 light-seconds

• Earth-Sun (a.k.a. astronomical unit, or AU) = 8 light-minutes

• Solar system = light-hours

• Nearest stars = several light-years

• Milky Way= 100,000 light-years = 105 ly– Galactic Center is 28,000 light-years away

• Local group = several million light-years =106 ly

• Observable universe = 14 billion light-years = 1.4 x 1010

ly

Clicker Question

• A radio message from outer spacearrived today which was sent from planetBuff on the day you were born. Thefriendly aliens sending you the birthdaymessage live:

A. In the Solar System

B. From a close-by star in the Milky Way

C. In Andromeda, the nearest major galaxy

D. In a galaxy outside the local group

• Answer: you are probably between 10and 90 years old. Objects at distancesbetween 10 and 90 light-years awayfrom us are relatively close-by stars inthe Milky Way.

• The solar system is light-hours in size

• The Local group is millions of light-years in size

Over astronomical distances, even light

takes a lot of time (from a human’s

perspective!) to travel between the stars

This means that what we SEE in the distant

universe is light that has traveled a long

time.

Our image of the universe is a delayedOur image of the universe is a delayed

imageimage.

In looking out into space,In looking out into space, we arewe are looking looking

back in time!back in time!

Look Back TimeLook Back Time

What we SEE is always delayed by the speed oflight. In the classroom, our view of each other isonly about 10-5 seconds old, so we barely notice

(10-5 sec = 0.00001 sec)

Satellite communications - noticeable delays

The image of the Sun is _____ old?

Analogy: what we “hear” is delayed by the speed of sound - more familiar in

our everyday lives (e.g. lightening-thunder delay)

Image of the Orion nebula, 1500 ly away

• The image of a

galaxy spreads

across 100,000

years of time

• Try to think of what

we SEE NOW as

different from what

may EXIST now

When studying the Universe, it isWhen studying the Universe, it is

impossible to separate space and timeimpossible to separate space and time

Last night we saw a bright supernova explode inLast night we saw a bright supernova explode in

the Andromeda galaxy (the other big galaxy inthe Andromeda galaxy (the other big galaxy in

the local group). The remnants from suchthe local group). The remnants from such

explosions disperse in about 10,000 years.explosions disperse in about 10,000 years.

A. The supernova remnant still exists now, andwe will watch it disperse over the next 10,000Earth years.

B. In reality, the supernova remnant has alreadydispersed, but we will watch it disperse overthe next 10,000 Earth years.

C. The image of the supernova dispersing will notreach us for another 2 million years.

D. We will never see the supernova remnantbecause it has already dispersed.

Clicker Question

• Answer: B

• This galaxy is millions of light-years awayfrom us. The light left the galaxy millions ofyears ago and only arrived yesterday. Inthe intervening time, the supernovaremnant has dispersed and no longerexists today.

But the light that left on the day after theexplosion will arrive here today and wecan see that.

Discussed so farDiscussed so far

• Cosmic Distances

• Light-Year vs Year

• Look Back Time

Make sure to become familiar with these concepts!

For next class meeting, reading..For next class meeting, reading..

….remains on the entire Ch. 1

Make sure you familiarize yourself

also with the (more mathematical) material in the boxes.

Make sure you have completed the (UNGRADED)

Tutorial on Mastering Astronomy.

IF you have problems, please let us know!