Goals of the day Stars & Galaxies This Course - basic info - - PowerPoint PPT Presentation

ASTR 1120 General Astronomy: Stars & 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 day

• This Course
• basic info review
• Order of Magnitude

Astronomy

– Reasonable estimates

• Size Scales
• getting used to astronomy
• Light year

– Measuring distances in astronomy

Who should take this course?

• No prerequisites,

aimed at non-science majors

• No lab credit
• Moderate amounts of

quantitative work (algebra)

• More quantitative

course – ASTR 1040

MATH REVIEW SESSION:

Will you attend it? A.YES

• B. NO

In the process of coordinating with other classes

Course Information

COURSE WEB PAGE:

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

You can find announcements, assignments and handouts, lecture notes, and other useful things there Grades will be shown on

CULearn

Required Text

The Cosmic Perspective

by Bennett et al., 2007, 5th ed Includes: Access to textbook website www.masteringastronomy.com, Ebook (animations, etc), and SkyGazer planetarium software. You will need your own `masteringastronomy’ account! Most homeworks require it Course ID: ASTR11202009A

How to succeed in this course

• PUT IN THE TIME:

3 credits at CU = 6-9 hours outside of the classroom

• Read the textbook

sections as assigned in class, discuss with friends, do homeworks, come to class

• Come see us during office

hours!

Come talk with us

• Prof. Rosalba Perna’s office hours:

Tue: 1pm-2pm; Th: 1pm-3pm in JILA Tower 506A (phone: 303-492- 0389) rosalba@colorado.edu

• TA Thomas Rogers office hours:

Wed, Fri: 2pm-3:30pm in Duane D1B31 (phone: 720-308-9382).

Thomas.Rogers@colorado.edu

• Or call or email (any of us) to make

an appointment!

Observatory Nights

• Starting Wed Sept 2nd at

8:30pm, then about every 2 weeks

• Sommers-Bausch

Observatory (next to Fiske): 16” and 18” telescopes

• Not mandatory, but you can

get extra credit towards your grade (Fill out summary sheet available at

• bservatory)
• Signup required on CULearn

website

Clickers

GRADED clicker questions will start NEXT WEEK. Remember to bring your clicker to class always.

Clicker questions TODAY UNGRADED.

Clicker Test

• What class are you in?
• A) Freshman
• B) Sophomore
• C) Junior
• D) Senior
• E) Other

Clicker 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 was condensed into a single year, the earliest humans (hominids) would have appeared 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 seconds

before year-end)

Reading Clicker Question

THE COSMIC CALENDAR

Order of Magnitude Astronomy

• 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 magnitude Astronomy How many piano tuners are there in Boulder County?

• A. 2
• B. 20
• C. 200
• D. 2000
• E. Too many to count!

Start with known facts and reasonable guesses

Population 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 reasonable estimates

• How long does it take to tune a piano?

– 3-4 hours? = 2 tunings per day

Scales in the Universe:

• ur Cosmic Address

Earth

Sun/Solar System Milky Way Galaxy Local Group Local Supercluster

Scale 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 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 (with solar system in Boulder)

• There is essentially nothing in between!!

New 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 stars

1 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 Another Scale for Everything Else

• Galaxies are 10” paper

plates

• Milky Way and nearest

neighbor Andromeda) are 5 meters apart

• Galaxy groups and

clusters contain 10’s to 1000’s of galaxies

• Superclusters 50

meters across (size

• f 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 most 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 distances

• Most useful measure is based on the speed
• f 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 following sentences makes sense? (the

• thers 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 faster than the speed of 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 space

arrived today which was sent from planet Buff on the day you were born. The friendly aliens sending you the birthday message 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 10

and 90 years old. Objects at distances between 10 and 90 light-years away from us are relatively close-by stars in the 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 delayed image. In looking out into space, we are looking back in time!

Look Back Time

What we SEE is always delayed by the speed of

• light. In the classroom, our view of each other is
• nly 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

• ur 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 is impossible to separate space and time

Last night we saw a bright supernova explode in the Andromeda galaxy (the other big galaxy in the local group). The remnants from such explosions disperse in about 10,000 years.

• A. The supernova remnant still exists now, and

we will watch it disperse over the next 10,000 Earth years.

• B. In reality, the supernova remnant has already

dispersed, but we will watch it disperse over the next 10,000 Earth years.

• C. The image of the supernova dispersing will not

reach us for another 2 million years.

• D. We will never see the supernova remnant

because it has already dispersed.

Clicker Question

• Answer: B
• This galaxy is millions of light-years away

from us. The light left the galaxy millions of years ago and only arrived yesterday. In the intervening time, the supernova remnant has dispersed and no longer exists today. But the light that left on the day after the explosion will arrive here today and we can see that.

Discussed so far

• Cosmic Distances
• Light-Year vs Year
• Look Back Time

Make sure to become familiar with these concepts!

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!