Reminder and Announcement
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Classroom changed! Watanabe 415
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Come talk to Nick or Chao-Ling after class if you
have any question about Mastering Astronomy
Mastering Astronomy HW0 due this Friday
Mastering Astronomy HW1 is available today, due
next Tuesday
What we learned yesterday
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Idea about Science and Astronomy
a bit useful math for Astronomy
relative size and distance of Earth, Moon and the
Sun
What are we going to learn today
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Build some idea about scales of Astronomical
objects
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How do we describe the size/distance scale of
these objects
OUR PLACE IN THE UNIVERSE?
What is our
Cosmic Address?
Our place in the Universe?
Class Action!
Your friends, Roy and Mike, rulers of
Omicron Persei 8, want to send you a
postcard via the Cosmic Postal Service.
The CPS is very strict about complete
addresses on all mail! Help them by using
all seven of the terms in the box to
complete your cosmic address — put them
in order, from smallest to largest:
Our place in the Universe?
Do this yourselves (no discussion)
Write down your answers on the worksheet
complete your cosmic address — put them
in order, from smallest to largest:
Dear Friend,
We hear that you are taking
astronomy this semester, eh? Just
keep your telescopes pointed away
from Perseus!! Heh, just kidding.
We just got back from a quick trip
up the Perseus Arm to the Bulge —
we saw some gorgeous nebulae along
the way.
Things here on omicron Per 8 are the
same as usual - 200˚C and lots of
hydrocarbon haze. At least we’re
getting stellar panels installed next
month to help lower our energy bill!
Write back soon,
Lrrr & Ndnd
TO:
your name: __________________________
your street: __________________________
your city: __________________________
your state: __________________________
your country: __________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
Earth
The Local Group
The Milky Way
The Orion Arm
The Solar System
The Universe
The Virgo Supercluster
OUR PLACE IN THE UNIVERSE?
What is our
Cosmic Address?
Our place in the Universe?
Answer
Orion arm
Our place in the Universe?
Answer
Our place in the Universe?
Honolulu
Hawaii
2680 Woodlawn Drive
Honolulu, Hawaii, USA
96822-1839
USA
Our place in the Universe?
20 miles
1
Honolulu
Hawaii
300 miles
15
2680 Woodlawn Drive
Honolulu, Hawaii, USA
96822-1839
2500 miles
USA
125
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Describe our “cosmic address”
Earth
Radius = 6370 km
Earth-Sun
Earth - Sun average distance = 145,980,000 km = 1.4598 x 108 km
= 20000 Earth radii
= 1 Astronomical Unit (AU)
At the scale of the Solar System distances are
described in terms of the Astronomical Unit or AU.
Solar System
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Earth is the third
planet from the sun
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The solar system
consists of the Sun
and other
astronomical objects.
Light Travel Time
Light travels at 3 x 105 km/sec through the
vacuum of space.
We can use how long does it take for light to
travel from point A to B as a measure of the
distance from point A to B.
Milky Way Galaxy
Orion arm
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The Milky Way is the
galaxy in which the
solar system is
contained.
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It is a spiral galaxy
Contains 300 billion
stars.
Milky Way Galaxy
Orion arm
Disk radius = 3.162 x 109 AU
= 50,000 ly
Disk thickness = 1,000 ly
Local Group
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The Local Group is
the group of galaxies
that includes Milky
Way.
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It has ~50 galaxies
It has a binary
distribution
Local Group
Distance to Andromeda
(M31)
= 2.5 x 106 ly
Virgo Supercluster
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The Virgo
Supercluster is a
irregular supercluster
that includes the
Local Group
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It has ~100 galaxy
group and clusters
Virgo Supercluster
Diameter = 2 x 108 ly
The Universe
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The Universe is
commonly defined as
the totality of
everything that
exists.
The Universe
9.3 x 1010 ly across
13.3 billion years old
Lecture Tutorial
• Break up into groups of 2-3
– NO MORE THAN 3
• In your group, work through the following:
-Looking at Distant Objects (pages
131-132): Question 1 to 8
– Discuss the answers – don’t be silent!
• I will be roaming around if you need help…
• If your group finishes, check your answers
with another group