Download Optional HW Assignments SUN-EARTH

SUN-EARTH-MOON SYSTEM
Tools of Astronomy
The Moon
The Sun-Earth-Moon System
TEST DATE:
OPT. HW DUE:
Optional HW Assignments
III.
SUN-EARTH-MOON
A. Motions of Earth
• Rotation – spinning of a body on an imaginary
axis.
Explains day/night cycles. Sun rise, Moon rise,
Constellations moving across sky
• Day Length
- Solar day – noon to noon. 24 hrs
- Siderial day – 1 complete rotation on axis in
reference to a distant star. 23h. 56 m Due to
Earth’s motion in its orbit.
B Annual Motions
 Plane of Earth’s orbit called the ecliptic plane
As viewed from a rotating Earth, the Sun &
planets appear to move across the sky along a
line. This line or path is called the ecliptic.
 Revolution –one body orbits around another
body.
- Siderial period – time it takes a planet to
orbit the sun in reference to a distant star.
- Earth’s sidereal period is 365.25 days.
The most reasonable explanation is that Earth is
tilted 23.5 o.
This is the cause of Earth’s seasons
Some have suggested that distance is the cause,
but this was shown not to be true by the results
of the Apparent Size of the Sun activity.
According to the data from the activity, Earth is
closest to the sun in January and furthest from
the sun in July. The distance difference is
relatively small, only about 3 million miles.
 Seasonal Cycle
- Due to Earth’s Tilt 23.5 degrees on its axis
Axis has a fixed orientation in space.
Result: As it orbits, Earth’s N
hemisphere is angled toward sun and
then away. Same for the S. Hemisphere.
Part of year neither is angled toward
sun. Earth experience seasons.
Summer Solstice – June. 21
Begins the summer season in northern hemisphere
Earth’s northern hemisphere is tilted toward the sun.
Sun appears higher in the sky for most of northern
hemisphere and cause the time between rise and set to
be longer.
At our latitude we experience: about 14 .5 hrs of
daylight & 9.5 hrs of night
People north of 66.5o experience 24 hr of daylight.
Opposite conditions in the southern hemisphere.
- AutumnEquinox (northern hemisphere)Sept. 22 or 23
Begins the fall season in the northern hemisphere.
Opposite season in southern hemisphere.
Earth’s axial tilt is neither toward or away from sun. It is
as if Earth has no tilt.
Sun noon altitude of 90o (directly overhead) occurs at
the equator (0o latitude)
Everyone on Earth experiences about 12 hrs of daylight
& 12 hrs of night.
•Winter Solstice Dec. 21/22
-Winter
Solstice Dec. 21/22
Begins the winter season in northern hemisphere
Earth’s northern hemisphere is tilted away from the
sun.
Receives less direct rays from sun.
Everyone north of this latitude experiences shorter
daylight hours
At our latitude we experience: about 9 .5 hrs of
daylight & 14.5 hrs of night
People north of 66.5o experience 24 hr of night.
Opposite conditions in the southern hemisphere.
-Vernal
(spring) Equinox Mar. 22 or 23
Begins the spring season in norther hemisphere.
Same conditions as autumn equinox
Test Essay Question
You are at a social gathering and overhear someone
announce that the Earth experiences season because its
distance from the sun varies. He adamantly asserts that
winter occurs because we are further from the sun than
during summer.
Please explain to him that he is incorrect and that you can
provide very convincing quantitative evidence against his
assertion.
Not only that but you can provide quantitative evidence for
what the real cause of our winter and summer.
You can give 3 strong pieces of evidence that
strongly suggests Earth’s Axis Is Tilted.
1. The Sun’s noon altitude changes cyclically during the
year. Highest during summer to lowest during winter
and back to highest in summer.
2. Earth’s poles experience 24 hours of either daylight or
darkness during their respective summer and winter.
Only explanation is that Earth axis is tilted.
3. The opposite conditions occur at the same latitude in the
southern hemisphere
Assignment
Finish Apparent Size of Sun Questions
& turn in.
Assgn. Packet
Vocab. 12-17
Sec. III. Sun-Earth Moon 1-14
Will Check Assgn. Packet on Block
Day
 Lunar Phases
- The duration of the Phase Cycle is 29.5
days (synodic month)
- Lunar Orbit Affects How Much We See:
Phases
Lunar Orbit Affects How Much We See: Phases
PHASES OF THE MOON PRACTICE
https://www.youtube.com/watch?v=kgbK2FZFFdw
 Eclipses - one object passing between two
other objects
- Overview
Eclipses create 2 shadow
Umbra – darker, inner shadow
Penumbra – lighter, outer shadow
Usually no more than 4-7 solar & lunar eclipses
each year. Why?
Because the Moon orbits Earth on a different
orbital plane than the Earth-Sun plane.
- Solar Eclipse
The Moon casts a shadow on the Earth
Occurs only during a new moon phase
Last about 7.5 minutes
Sketch of Solar Eclipse
Only those within the umbra experience total
eclipses.
Shadow path is no more than 150 miles wide
People in penumbra see a partial solar eclipse
Total Solar Eclipses (2008-2035)
Lunar Eclipse
The Earth casts a shadow on the Moon
Occurs only during a full moon phase
Lasts several hours
Everyone on the side facing the moon can see it
Sketch of Lunar Eclipse
ASSIGNMENT
FINISH ASSIGNMENT PACKET – Don’t forget the
vocabulary on p. 2
Work on Opt. HW – some easy points.
Study for Phases Mastery on Monday.
Work on your Test Essay about the seasons.