Download One way to measure distance

One way to measure distance
Triangulation:
Measure baseline and
angles, and you can
calculate distance.
One way to measure distance
Stellar Parallax: The apparent
shift in position of a nearby
star relative to distant
background objects due to
Earth’s rotation
Parallax Lab:
Do Part 1 today as a group
Finish up part 2 at home
(up to part c) we’ll revisit this on Tuesday)
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?
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.
The parsec
Parallax angles measured
in arcseconds (1/3600 of
a degree).
Parsec = the distance to a
star with a parallax angle of
1 arc second. (~200,000 AU)
You observe two stars over the course of a year
(or more) and find that both stars have measurable
parallax angles. Star X has a parallax angle of 1
arcsecond.
Star Y has a parallax angle of ½ an arcsecond.
Which star is closer?
1.Star X
1.Star Y
1.Not enough information
You observe two stars over the course of a year
(or more) and find that both stars have measurable
parallax angles. Star X has a parallax angle of 1
arcsecond.
Star Y has a parallax angle of ½ an arcsecond.
Which star is closer?
1.Star X
1.Star Y
1.Not enough information
Resources
• http://astro.unl.edu/interactives/
• Online sorting and ranking:
– scale,
– scientific method
Lunar eclipses
KEY POINT: note the
alignment of Sun, Earth, moon
Why don’t eclipses occur every month?
KEY POINT: Earth and moon have different
orbital planes
Solar eclipse
KEY POINT: note the alignment of Sun, moon,
Earth
Chasing solar eclipses
• Consider Figure 0.18 on page 16 in your text.
This figure shows solar eclipse paths over a
world map. As a group, write a description of
which eclipse your group would most like to
observe together, where and when you would
go to observe it, and fully explain why you
selected the date and site you did.
Eclipse tracks, 2010 - 2030
Why don’t eclipses occur every month?
KEY POINT: Earth and moon have different
orbital planes
Earth’s Orbital Motion and seasons
Notice how the axis
always points in the
same direction
What direction does Earth
revolve around the Sun?
Figure 0.7
© 2013 Pearson Education, Inc.
Task #1: Use flashlight and ball-on-stick to represent
the Sun and Earth respectively. (For this
demonstration, keep the stick vertical.)
• How does the distribution of incoming
sunlight vary between the Equator and the
Poles? (Can you explain why the equator is
hotter than the poles?)
Task #2: Use flashlight and ball-on-stick to
represent the Sun and Earth respectively. (For this
demonstration, tilt the stick.)
• What effect does tilting the stick (Earth's axis)
have on the distribution of incoming solar
radiation?
• Use the model to show the relative positions
of Earth and Sun for our winter and summer.
• What happens when you rotate Earth on its
axis? What are you demonstrating?
Task #3: Demonstrate the annual orbit of Earth
around the Sun and use the model to explain:
• Why it can be winter in the U.S. when it is
summer in Australia;
• The contrasting positions of the Earth and Sun
for each season in the U.S.
• What happens to seasonal temperatures at
various locations if the tilt angle increases or
decreases?
Earth’s Orbital Motion: Precession
Phases of the moon
Go to moodle. Open the Phases of moon
activity.
Goto:
http://astro.unl.edu/interactives/
Work on:
Sorting and ranking:
Lunar sorting tasks 1-3
Seasons 1-5
Work together in groups until you
get 100% then move on
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Figure 0.4
© 2013 Pearson Education, Inc.
Figure 0.6b
© 2013 Pearson Education, Inc.
Figure 0.2
© 2013 Pearson Education, Inc.
Figure 0.3
© 2013 Pearson Education, Inc.
Figure 0.8
© 2013 Pearson Education, Inc.
Figure 0.9
© 2013 Pearson Education, Inc.
Phases of the Moon