Astrophysics
Overview of the Astrophysics Unit
Planets and their size
Imagine Jupiter is the size of a basketball. Calculate the sizes of the other planets and find everyday objects
that are around the same size. They need to be common objects because we will need them for a model.
Put them all on a large table, in the correct order from the sun, and create small paper labels for them.
Distances from the Sun
0 AU
0 x 109 km
10 AU
1 x 109 km
20 AU
2 x 109 km
3 x 109 km
30 AU
4 x 109 km
A tediously accurate scale model of the solar system
Notice that the bottom diagram is a logarithmic scale, not a linear scale.
Scale video
Sizes of stars
Distance to nearest star
40 AU
5 x 109 km
6 x 109 km
Calculating distance, speed and time
Night and Day
sunlight
There are lots of YouTube clips explaining this:
https://www.youtube.com/results?search_query=sun+earth+day+night
Seasons
North ecliptic pole
North pole
Arctic circle
Tropic of Cancer
Equator
Tropic of Capricorn
Antarctic circle
Challenge
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Phases of the moon
This slide is northern-hemisphere-centric.
Ryo says: "The Moon Looks Different for
Different People. Check out these cool
images!"
Excellent Wikipedia resources
Scale model of the solar system
4,879
12,104
12,756
6,779
142,984
120,536
50,724
49,244
2,374
Scale model of the solar system
Phases of the moon animation
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Moon phases exercise
Image
Phase name
New moon
Starting with a new moon, draw/screenshot each of
these phases and put them in order in a table like
the one opposite.
Recall
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😃
Test your understanding
The Motion of the Stars
Constellations
Celestial Coordinates
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Parallax
Measuring the length of your arm using parallax 1
Distant
objects
A
B
V marked
on your
paper
X
Measuring the length of your arm using parallax 2
θ
θ
L
d
d
Measuring distances to stars
In the arm-length it is important to
understand how we got from the
V-shape diagram to the picture of a
triangle. Look at the following
diagrams carefully.
The diagram on the right shows
how exactly the same technique is
used to calculated distances to
nearby stars.
Definition of a parsec
1AU
L
θ
θ
2θ
Notes:
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1 arcsecond is 1/3600 of a degree.
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The white stars are "fixed" background stars. They are fixed because they are so far away that a parallax of 1 AU isn't enough to make
them seem to move.
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How do we measure that 2θ distance? Remember that when you look at the night sky, horizon to horizon is 180 degrees and each
degree is 60 arcminutes and each arcminute is 60 arcseconds. A tool called a sextant was used to measure angular separation.
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If talk of t and t + 6 months freaks you, just think of t as December and t + 6 months as June, or t = March and t + 6 months = September.
Measuring distances using stellar parallax
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Astronomical distances: key facts review
Parallax resources
Check out these parallax resources:
Excellent short video to see how parallax is used to
measure distances:
https://www.youtube.com/watch?v=Saw1Eg2iZaI
Parallax simulations:
1.
http://highered.mheducation.com/olcweb/cgi/pl
uginpop.cgi?it=swf::800::600::/sites/dl/free/007
2482621/78778/Parallax_Nav.swf::Stellar%20
Parallax%20Interactive
2.
http://astro.unl.edu/animationsLinks.html
3.
http://astro.unl.edu/classaction/animations/lun
arcycles/lunarapplet.html
What is out there
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Stellar evolution: The lifecycle of stars
Star life cycle summary
Stellar evolution: The lifecycle of stars
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* slight difference depending on stellar
mass. If in doubt, use of the term
‘pressure’ will suffice for all stars
The only element in the universe used to be
Hydrogen
Stellar evolution: Guiding questions
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The Doppler Effect
Redshift and Blueshift
Doppler Effect resources
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Redshift in the universe
Differences in
cosmological redshift
At time t=0, Galaxy A is at a distance of 2 from Earth. Galaxy B is at a distance of 6. At time t=1, the universe has expanded by
a factor of 2. Now Galaxy A is at a distance of 4 from Earth and Galaxy B is at a distance of 12 from Earth. Notice that this
means that the more distant galaxy will have "travelled" further in the same time. Hence we think of it as moving away faster.
Earth
A
A'
B
B'
Questions
This is how our closest neighbouring galaxy, Andromeda, would look if it were brighter.
Expanding space activity
Galaxy
Distance to the
Milky Way (before
expansion) /cm
Distance to the
Milky Way (after
expansion) /cm
Distance moved
/cm
A
B
C
Take the balloon, and use a pen to draw a wave along it.
1.
Blow up the balloon to represent the expansion of space. Observe
what happens to the wave.
2.
Answer the following questions (in complete sentences):
a.
Sketch the balloon before and after.
b.
How did the wavelength change when you blew up the balloon
c.
This effect is called ‘redshift’, because it shifts the light
from objects towards the red end of the spectrum. Explain
why.
Balloon Exercise Questions
Cosmic Microwave Background Radiation (CMBR)
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The Big Bang
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The Fate of the Universe
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Evidence for the Big Bang (assessment)
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That is the end of the
slides for this unit
Cosmic Microwave Background Radiation (CMBR)
The Big Bang
Cosmic Microwave Background Radiation (CMBR)
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Key terminology