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Bellwork
True or False:
1. Mirrors are used in some telescopes.
2. Telescopes are often located in humid
environments because water vapor in the
air enhances visibility of stars.
Bellwork
List the planets in order by the time it
takes to orbit the sun from fastest to
slowest.
 If the semimajor axis of Earth’s orbit is 150
million Km, what is the major axis? (use
pg. 81 for help)
 What 2 properties affect the force of
gravity?

Astronomy
Bellwork
What is astronomy?
Objective: Students will
describe the difference between
rotation and revolution in written
notes.
Astronomy is…

the study of the universe to include
moons, planets, stars, and other objects in
space
Beginnings of Astronomy
Have you ever asked yourself?

Why do the planets revolve around the
sun?

Why don’t they fly off into space?

Does something hold them in their paths?
Can you distinguish the
difference between rotation
and revolution?
Difference between rotation and
revolution.

Rotation


When an object in
space spins on it’s
axis
Earth’s rotation on it’s
axis causes day and
night

Revolution


The movement of one
object around another
Earth’s revolution
around the sun is
called a year.
Time Measurements
DAY (rotation)
– time it takes for a planet to rotate once around its own axis.
Earth – about every 24 hours
(23 hrs 56 min)
YEAR (revolution)
– time it takes for a planet to orbit once around the sun.
Earth – every 365.26 days
Sun
EPlanet
Why is there an extra day in
February every fourth year?

Earth’s orbit takes 365 ¼ days. To
account for the ¼ day we add an extra day
every fourth year. We call that year leap
year.
Why do we have seasons?

Earth has seasons because its axis it tilted
as it moves around the sun.
Seasons
– The tilt of the Earth’s axis causes the northern & southern
hemispheres to get different amounts of solar radiation causing the different
weather.
Solstice and Equinox

Solstice

Two days of the year
where the noon sun is
overhead at either
23.5 degrees south or
23.5 degrees north.

Equinox


Two days of the year
where neither
hemisphere is tilted
toward or away from
the sun
Equinox means “equal
night”
Sep 21,
2005
Dec 20,
2005
Mar 20,
2006
Jun 21,
2006
Sep 23,
2006
The amount of sunlight hitting different parts of the Earth changes as the Earth
moves around the Sun over a year.
Sep 21,
2005
Dec 20,
2005
Mar 20,
2006
Jun 21,
2006
Summer SOLSTICE
the one day of the year when the sunlight time is longest.
Sep 23,
2006
Sep 21,
2005
Dec 20,
2005
Mar 20,
2006
Jun 21,
2006
Sep 23,
2006
Winter SOLSTICE
the one day of the year when the sunlight time is shortest.
Sep 21,
2005
Dec 20,
2005
Mar 20,
2006
Jun 21,
2006
Sep 23,
2006
Spring EQUINOX
the one day between winter and summer when the sunlight time and night
time are of equal length.
Sep 21,
2005
Dec 20,
2005
Mar 20,
2006
Jun 21,
2006
Sep 23,
2006
Autumn EQUINOX
the one day between summer and winter when the sunlight time and night
time are of equal length.
Chapter 1 Section 1 Review
Why does Earth have day and night?
 Why does Earth have seasons?
 What is the difference between rotation
and revolution?
 What is leap year?

What is an
astronomical
unit?

AU – the distance
from the earth to
the sun. Approx.
150 million
kilometers
Kepler’s 3 Laws
What are
Kepler’s
laws of
motion?
-
The first law states that
orbits are elliptical.
-
An ellipse is a closed
curve in which the sum
of the distances from
the edge of the curve to
two points inside the
ellipse is always the
same.
-
The second says that
planets move faster
when they are closer to
the sun and slower the
farther away they are.
-
Mercury, the innermost
planet, takes only 88
days to orbit the Sun
but the outermost
planet (Pluto) requires
248 years to do the
same
What are
Kepler’s
laws of
motion?
What are
Kepler’s
laws of
motion?
-
The third explains the
relationship between
the period of revolution
and the semimajor axis
of the elliptical orbit.
-
Planets further from the
sun, such as Saturn,
take longer to orbit the
sun.
How does the
Law of Universal
Gravitation explain
how the objects in the
solar system revolve
around the Sun?
-Newton explained that
the force of gravity on
an object in the solar
system depends on
its mass and distance
from the sun.
-This force along with
the forward motion of
the object keeps it in
an elliptical orbit
around the sun.

Newton’s law of universal gravitation- The force
of gravity depends on the product of the masses
of the object divided by the square of the
distance between the objects.
Bellwork

List the planets in order by the time it
takes to orbit the sun from fastest to
slowest.

If the semimajor axis of Earth’s orbit is 150
million Km, what is the major axis? (use
pg. 81 for help)
Bellwork
List the planets in order by the time it
takes to orbit the sun from fastest to
slowest.
 If the semimajor axis of Earth’s orbit is 150
million Km, what is the major axis? (use
pg. 81 for help)
 What 2 properties affect the force of
gravity?
