Download (arc- seconds).

Welcome Back
This should be the
NASA Astronomy pic of
NASA
the day
Weekly Schedule
Today
Finish Black box lab
Scale of the Universe
Measuring Distances
in Space
Parallax Lab
Next Tuesday
HW 0, 1 due on
Mastering Astronomy
Quiz # 1
Seasons
Moon Phases
Eclipses
The Scale of the Universe
Power of 10
Typical
Dog:
~ 1 meter
Orders of Magnitude
Trees:
~ 10 meters
Whales:
100 meteres
= 10 x 10 meters
Typical Small
Mountain
~ 1000 meters
= 10x10 x10 meters
= 1 kilometer
= 103 meters
~ 10000 meters
= 10x10 x10 x 10 meters
= 10 kilometers
= 104 meters
From Three
Sisters to
Mt. Hood:
~ 100,000
meters
=100 km
~ 105 meters
Oregon ~106 meters
=1,000,000 meters
The U.S. ~107
=10,000,000 meters
Approx. one
quarter the
way around
the planet:
108
meters
=100,000,000
meters
Approx.
one
quarter
the way
around
our Sun:
109
meters
=1,000,000,
000 meters
A new star and planetary
system being born:
1012 meters
=1,000,000,000,000 meters
A star that
exploded ten
years ago:
~1014 meters
=100,000,000,000,000 meters
The Eagle Nebula:
~1019 meters
=10,000,000,000,000,000,000 meters
A galaxy like ours:
~1021 meters
=1,000,000,000,000,000,000,000 meters
A collection of galaxies
~1022 meters
=100,000,000,000,000,000,000 meters
=1,000,000,000,000,000,000,000 meters
The deepest we’ve peered into our
24
Universe: ~10 meters
1012
1,000,000,000,000 Tera-
T
109
1,000,000,000
Giga-
G
106
1,000,000
Mega- M
103
1,000
Kilo-
100
1
k
100
1
10-1
.1
deci-
d
10-2
.01
centi-
c
10-3
.001
milli-
m
10-6
.000001
micro- 
10-9
.000000001
nano-
n
10-12
.000000000001 pico-
p
How do we measure the
distance to Nearby objects
in the Universe?
RADAR measures distances to planets.
RADAR works like SONAR or
ECHOLOCATION
RADAR. Let’s do an example
together.
A radar signal is transmitted from Earth,
bounced off Venus, and returns to Earth in
300 seconds.
How far away is Venus in km and AU from
Earth?
You need to know:
Velocity = distance/time
1 AU = 1.5 x 108 km (distance from Earth to
Sun)
Light travels at 300,000 km/s
Another one.
How long would a radar signal take
to complete a round trip journey
from Earth to Jupiter if they are 4.2
AU apart?
Another way to measure distance
Triangulation:
Measure baseline
and angles, and you
can calculate
distance.
Another way to measure distance
Stellar Parallax: The
apparent shift in position
(measured in degrees) of a
nearby star relative to
distant background objects
due to Earth’s rotation
Demonstration. Close one eye and hold your
hand at arms length, pointing the tip of your
index finger at me. Close one eye then open
the other. What happens?
Now move your finger closer to your
face and blink back and forth again.
What happens? (i.e. What’s the relationship
between angle and distance?)
Pretend your eyes represent Earth’s orbit six months apart.
Your nose is the Sun. Your finger is a nearby star. I am a
distant star or galaxy.
Parallax Demo
The parsec
Parallax angles measured
in arcseconds.
Parsec = the distance to
a star with a parallax
angle of 1 arc second.
(~200,000 AU)
Arc Second?
• Full circle contains 360
(degrees).
• Each degree contains 60
(arc-minutes).
• Each arc-minute
contains 60 (arcseconds).
• Angular size of an
object depends on actual
size and distance away.
The parsec
Parallax angles measured
in arcseconds.
Parsec = the distance to
a star with a parallax
angle of 1 arc second.
(~200,000 AU)
Still don’t get it???
Let’s do the lab and
then tonight go to the
Study space on MA and
do the self guided
tutorial on Parallax