SLIDE 1 ASTR 1120 ASTR 1120 General Astronomy: General Astronomy: Stars & Galaxies Stars & Galaxies
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)
SLIDE 2 Goals of the day 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
SLIDE 3 Who should take this course? Who should take this course?
No prerequisites, aimed at aimed at non-science non-science majors majors
No lab credit
Moderate amounts of quantitative work quantitative work (algebra) (algebra)
More quantitative course course – – ASTR 1040 ASTR 1040
SLIDE 4 MATH REVIEW SESSION:
Will you attend it? A.YES
In the process of coordinating with other classes
SLIDE 5
Course Information Course Information
COURSE WEB PAGE COURSE WEB PAGE: :
http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html
You can find You can find announcements, announcements, assignments and assignments and handouts, lecture notes, handouts, lecture notes, and other useful things and other useful things there there Grades Grades will be will be shown on shown on
CULearn CULearn
SLIDE 6 Required Text Required Text
The Cosmic Perspective The Cosmic Perspective
by Bennett et al., 2007, 5 by Bennett et al., 2007, 5th
th ed
ed Includes: Includes: Access to textbook website Access to textbook website www.masteringastronomy www.masteringastronomy.com .com, , Ebook Ebook (animations, etc), and (animations, etc), and SkyGazer SkyGazer planetarium planetarium software. software. You will need your You will need your own
`masteringastronomy `masteringastronomy’ ’ account! account! Most Most homeworks homeworks require require it it Course ID: ASTR11202009A
SLIDE 7 How to succeed in this course How to succeed in this course
3 credits at CU = 6-9 hours outside of the classroom
Read the textbook sections as assigned in sections as assigned in class, discuss with class, discuss with friends, do friends, do homeworks homeworks, , come to come to class class
- Come see us during office
hours!
SLIDE 8 Come talk with us Come talk with us
- Prof.
- Prof. Rosalba Perna
Rosalba Perna’ ’s s
: Tue: 1pm-2pm; Tue: 1pm-2pm; Th Th: 1pm-3pm in : 1pm-3pm in JILA Tower 506A JILA Tower 506A (phone: 303-492- (phone: 303-492- 0389) 0389) rosalba@colorado rosalba@colorado. .edu edu
TA Thomas Rogers office hours:
Wed, Fri: Wed, Fri: 2pm-3:30pm in Duane D1B31 2pm-3:30pm in Duane D1B31 (phone: 720-308-9382). (phone: 720-308-9382).
Thomas. Thomas.Rogers@colorado Rogers@colorado. .edu edu
- Or call or email (any of us) to make
Or call or email (any of us) to make an appointment! an appointment!
SLIDE 9 Observatory Nights Observatory Nights
8:30pm, then about every 2 weeks
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
SLIDE 10
Clickers Clickers
GRADED clicker questions will start NEXT WEEK. Remember to bring your clicker to class always.
Clicker questions TODAY UNGRADED.
SLIDE 11 Clicker Test Clicker Test
- What class are you in?
- A) Freshman
- B) Sophomore
- C) Junior
- D) Senior
- E) Other
SLIDE 12 Clicker Test Clicker Test
- What is the nationality of your professor?
- A) French
- B) Spanish
- C) Argentine
- D) Italian
- E) Greek
SLIDE 13 If the history of the entire universe was If the history of the entire universe was condensed into a condensed into a single year single year, the earliest , the earliest humans (hominids) would have appeared humans (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 seconds
before year-end)
Reading Reading Clicker Question Clicker Question
SLIDE 14
THE COSMIC CALENDAR THE COSMIC CALENDAR
SLIDE 15 Order of Magnitude Order of Magnitude Astronomy 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?
SLIDE 16 More on order of magnitude More on order of magnitude Astronomy Astronomy How many piano tuners are How 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!
SLIDE 17 Start with Start with known facts and known facts and reasonable reasonable guesses 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
SLIDE 18 More reasonable More reasonable estimates estimates
- How long does it take to tune a piano?
– 3-4 hours? = 2 tunings per day
2 piano tunings day x 5 days week x 50 weeks year = 500 piano tunings year tuner
10,000 piano tunings year 500 piano tunings year tuner = 20 tuners
SLIDE 19 Scales in the Universe: Scales in the Universe:
- ur Cosmic Address
- ur Cosmic Address
Earth
Sun/Solar System Milky Way Galaxy Local Group Local Supercluster
SLIDE 20 Scale models of the Universe Scale models of the Universe
- Scale Sun as a grapefruit (1:10,000,000,000)
SLIDE 21
- Earth = tip of ball point
pen, 15 meters (49 feet)
– Moon = 4 cm away from earth
pen, 23 meters (75 feet)
meters (255 feet)
What about distances from the Sun on the same scale?
SLIDE 22 Moving out of the solar system 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 Alaska (with solar system in Boulder)
- There is essentially nothing in between!!
SLIDE 23 New New 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 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
SLIDE 24 Yet Another Yet Another Scale for Everything Scale for Everything Else Else
plates
neighbor Andromeda) are 5 meters apart
clusters contain 10’s to 1000’s of galaxies
SLIDE 25
meters across (size
scale model) are the largest structures we see
universe is about size of Boulder county on this scale
In this image, each dot is an entire galaxy
SLIDE 26 Which of these are the most Which 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!
SLIDE 27 Measuring cosmic distances 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
SLIDE 28 Light-year: which of the following Light-year: which of the following sentences makes sense? (the sentences makes sense? (the
- thers are nonsense)
- 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
SLIDE 29
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.
SLIDE 30 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
SLIDE 31
- 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
SLIDE 32 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
SLIDE 33
- 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
SLIDE 34
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 Our image of the universe is a delayed image image. In looking out into space, In looking out into space, we are we are looking looking back in time! back in time!
SLIDE 35 Look Back 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)
SLIDE 36
Image of the Orion nebula, 1500 ly away
SLIDE 37
galaxy spreads across 100,000 years of time
we SEE NOW as different from what may EXIST now When studying the Universe, it is When studying the Universe, it is impossible to separate space and time impossible to separate space and time
SLIDE 38 Last night we saw a bright supernova explode in Last night we saw a bright supernova explode in the Andromeda galaxy (the other big galaxy in the Andromeda galaxy (the other big galaxy in the local group). The remnants from such the 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, 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
SLIDE 39
- 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.
SLIDE 40 Discussed so far Discussed so far
- Cosmic Distances
- Light-Year vs Year
- Look Back Time
Make sure to become familiar with these concepts!
SLIDE 41
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!
