ASTR 1120
General Astronomy:
Stars & Galaxies
Prof. Rosalba Perna
Goals of the day
• This Course
-
basic info review
• Order of Magnitude
Astronomy
– Reasonable estimates
TA:Thomas Rogers
• Size Scales
- getting used to astronomy
http://amalfi.colorado.edu/~rosalba/astro1120/astro1120.html
MAKE SURE TO GO OVER THE SYLLABUS (if you haven’t already done so)
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
• Light year
– Measuring distances in
astronomy
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
Required Text
The Cosmic Perspective
by Bennett et al., 2007, 5th ed
You can find
announcements,
assignments and
handouts, lecture notes,
and other useful things
there
Includes:
Access to textbook website
www.masteringastronomy.com,
Ebook (animations, etc), and
SkyGazer planetarium
software.
Grades will be shown on
You will need your own
`masteringastronomy’ account!
Most homeworks require it Course ID: ASTR11202009A
CULearn
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: 303-4920389) 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
observatory)
•
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
Clicker Test
• What class are you in?
• What is the nationality of your professor?
•
•
•
•
•
•
•
•
•
•
A) Freshman
B) Sophomore
C) Junior
D) Senior
E) Other
A) French
B) Spanish
C) Argentine
D) Italian
E) Greek
Reading Clicker Question
THE COSMIC CALENDAR
If the history of the entire universe was
condensed into a single year, the earliest
humans (hominids) would have appeared
about:
A.
B.
C.
D.
September 1
December 1
December 30
9 p.m. December 31 (3 hours before yearend)
E. 11:59:30 p.m. December 31 (30 seconds
before year-end)
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.
B.
C.
D.
E.
2
20
200
2000
Too many to count!
Start with known facts and
reasonable guesses
More reasonable estimates
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 long does it take to tune a piano?
– 3-4 hours?
= 2 tunings per day
• 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
Earth
Scales in the Universe:
our Cosmic Address
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)
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)
• 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)
• 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
3000 yr to counts all the stars in the MW, one per second
Solar system: dot ~20 meters away from center
•
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
of buildings in our
scale model) are
the largest
structures we see
• Observable
universe is about
size of Boulder
county on this scale
Which of these are the most
likely?
A.
B.
C.
D.
Two planets colliding
Two stars colliding
Two galaxies colliding
None of the above… there’s too much space!
In this image, each dot is an entire
galaxy
Clicker Question
Measuring cosmic distances
• Most useful measure is based on the speed
of 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
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 lightyears since its launch in 1989.
C. The globular cluster M13 is located 16,000 lightyears away from Earth.
D. The next generation of the Space Shuttle will be
able to travel 1.3 times the speed of light.
Measuring Distances with Light:
Not A: light-years measure distance, not time.
•
Earth-Moon = 1.5 light-seconds
•
Earth-Sun (a.k.a. astronomical unit, or AU) = 8 light-minutes
•
Solar system = light-hours
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.
• Nearest stars = several light-years
• Milky Way= 100,000 light-years = 105 ly
– Galactic Center is 28,000 light-years away
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.
B.
C.
D.
In the Solar System
From a close-by star in the Milky Way
In Andromeda, the nearest major galaxy
In a galaxy outside the local group
• Local group = several million light-years =106 ly
• Observable universe = 14 billion light-years = 1.4 x 1010
ly
• 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 lightyears 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!
Image of the Orion nebula, 1500 ly away
Look Back Time
What we SEE is always delayed by the speed of
light. In the classroom, our view of each other is
only 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)
When studying the Universe, it is
impossible to separate space and time
• 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
• 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.
Clicker Question
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.
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!