#### Transcript Day-13

```Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-13
Course Announcements
•
How is the sunset/sunrise observing going?
•
Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at
7:30pm – at the Observatory.
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Total lunar eclipse: Sun.-Mon. 9/27-28
•
•
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Weather dependent, if clear, we’ll be setup at the
Here’s the important information
I will collect the L-T workbooks on Friday.
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Make sure your name is in it.
Kepler’s First Law: The orbit of a planet about
the Sun is an ellipse with the Sun at one focus.
Kepler’s Second Law: A line joining a planet and
the Sun sweeps out equal areas in equal intervals
of time.
Lecture – Tutorial
nd
Kepler’s 2 Law: pg 21
 Work with a partner!
 Read the instructions and questions carefully.
another.
 Come to a consensus answer you both agree on.
another group.
 If you get really stuck or don’t understand what the
According to Kepler’s second law, a
planet with an orbit like Earth’s would:
A. move faster when further from the Sun.
B. move slower when closer to the Sun.
C. experience a dramatic change in orbital speed
from month to month.
D. experience very little change in orbital speed
over the course of the year.
E. none of the above.
Kepler’s second law says “a line joining a planet
and the Sun sweeps out equal areas in equal
amounts of time.” Which of the following
statements means nearly the same thing?





A. Planets move fastest when they are moving toward the
Sun.
B. Planets move equal distances throughout their orbit of
the Sun.
C. Planets move slowest when they are moving away from
the Sun.
D. Planets travel farther in a given time when they are
closer to the Sun.
E. Planets move the same speed at all points during their
orbit of the Sun.
THIRD LAW
 The size of the orbit determines the orbital period
 planets that orbit near the Sun orbit with shorter periods than
planets that are far from the Sun
p = ~ 12 years
p = 1 year
THIRD LAW
The size of the orbit determines the orbital period
planets that orbit near the Sun orbit with shorter periods
than planets that are far from the Sun
MASS DOES NOT MATTER
Both have p = 1 year
THIRD LAW
 The size of the orbit determines the
orbital period
 planets that orbit near the Sun orbit with shorter
periods than planets that are far from the Sun
3
a
=
AU
2
P
years
MATH TOOLS 3.2
 Kepler’s third law in its simplest form utilizes
nonstandard units—the periods are in years,
while the distances are in AU.
 The relationship does not change if standard
units are used.
 The equation is just more complicated.
 Consequences:
• Distant planets take
longer to orbit the
Sun.
• Distant planets travel
at slower speeds.
```