On to Chapter 1
Figure 1.1
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Figure 1.5
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Figure 1.2
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Figure 1.3
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Figure 1.7
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Figure 1.8
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RADAR measures distances to planets.
RADAR works like SONAR or ECHOLOCATION
Astronomical Unit: unit of
measurement in solar system
• 1 Astronomical Unit (AU) = Earth to Sun
Distance
• 1 AU = 1.5 x 108 km (or about 93 million
miles)
RADAR measurements
• Groups of 2. One of you will be the RADAR pulse,
the other a scientist on Earth. RECORD YOUR
WORK IN AN ORGANIZED DATA TABLE.
• RADAR works because we know the speed light travels.
Because your "radar pulse" will not travel at the speed of
light, you need to find the actual speed of the "radar
pulse". The "radar pulse" should walk at an even,
repeatable speed, and the scientist should measure how
far the pulse travels in 5 seconds. Calculate the speed of
travel from the distance and the time.
RADAR measurements
• Now choose an object you want to measure the distance to.
The scientist gives the signal to begin, and the radar pulse
begins to travel toward the object. The scientist times the
"radar pulse's" trip (both going to the object and returning).
When the pulse comes to the object, it "bounces" off, and
travels back in the direction it came. The number of seconds
elapsed is the total time, T, taken for the pulse to travel out,
bounce off the object, and travel back again.
• The distance to the object, d, is given by:
d = s*(t/2)
Let’s do an example calculation.
• 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:
• Speed = distance/time
• 1 AU = 1.5 x 108 km
• RARAR travels at 300,000 km/s
http://astro.unl.edu/interactives/
Online ranking and sorting: Keplers
1st, 2nd, 3rd Laws; Force of Gravity 13 (including 3A-3D)
semi-minor axis
semi-major axis
2R
T is the time it takes to make 1 full revolution
Kepler’s Laws of planetary motion
3) Period(yrs)2 = semi-major axis (AU)3
What is the relationship between AU
and period?
Kepler’s Laws of planetary motion
3) Period(yrs)2 = semi-major axis (AU)3
What is the relationship between AU
and period?
Planetary years: Using data below
determine how old in Martian years
each group member would be.
Gravity. Newton used physics to
explain Kepler’s Laws.
Weight = mass x gravity
Mars has 0.38 the gravity Earth has.
What would you weigh on Mars?
Calculate this.
Which of the following best describes how you
would weigh on the Moon versus Earth?
•
•
•
•
You would weigh the same
You would weigh more on the moon
You would weigh less on the moon
You would have more mass on the moon, but
your weight would not change
Force of gravity depends on mass
and distance.
Distance follows the inverse
square law
If the distance between
two masses quadruples,
how much does the
gravitational force
between them lessen?