Motion of Earth and Sky - Guided Notes update
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Guided Notes – Motion of Earth and Sky
Your Name: Leah Walker
Please type or handwrite notes as you watch the video lecture and answer the
included questions.
Motion of Earth:
Earth is always in motion
Spin on axis: 1 day
Orbits the
sun
- 1 year
Precession of poles – 26,000 years
Sun orbits galaxy- 200 mil years, 200 km/s
Galaxy moving through space – 600 km/s
Earth rotates counterclockwise
Test Yourself – Moving Sky
Over the course of one night, an observer at any given location on Earth sees the constellations gradually
shift across the sky from east to west. This is caused primarily by:
A; the earth spins on its own axis
The Celestial Sphere:
An imaginary sphere of very large radius centered on an observer; the apparent
sphere of the sky.
Meridian
-The great circle on the celestial sphere that passes through an observer's zenith and
the north and south celestial poles.
celestial pole
is defined as the point in the celestial sphere directly above Earth's axis, i.e. North
Pole, South Pole, celestial equator
celestial equator
an imaginary plane that divides the celestial sphere into North and Southern
hemispheres. It represents an extension of Earth's equator onto the celestial sphere.
Your Turn
Date and Title of the images you viewed: The Once and Future Stars of Andromeda 10/7/23
How can you tell how long the exposure was for each picture?
Click or tap here to enter text.
How could you measure the latitude from where each picture was taken?
Click or tap here to enter text.
Test Yourself:
In the northern hemisphere, the stars rise in the East, set in the West and spin counter-clockwise around
the North celestial pole. In the southern hemisphere the stars rise in the
B; east, set in the west and spin clockwise around the south celestial pole.
Annual Motion:
earth orbits the sun once a year
stars position change throughout the year
The ecliptic
is the plane of Earth's orbit around the Sun. It is also the apparent path of the Sun
among the constellations in the course of a year.
Test Yourself – Orion
Orion is visible on winter evenings but not summer evenings because of
D; the location of the earth in its orbit
Your Turn – Aries
You are standing on Earth. It is noon and the Sun is between you and the constellation Aries.
A. Which direction in your sky is Aries?
The Sun moves westward in the sky every 6 hours, blocking a different constellation depending on the
time of year and the Sun's position along the ecliptic. Different constellations are visible at different
times of the year. Although the constellation Aries is located in the direction of the Sun at noon, it
cannot be seen during the daytime because of the Sun's brightness.
B. Which direction will it be in 6 hours?
As the Earth rotates, Aries changes its position in the sky every 6 hours. Aries moves towards the west in
the sky because the Earth rotates from west to east. Therefore, Aries will be visible in the western part of
the sky.
C. Which constellation will the Sun be blocking in 6 hours?
In 6 hours, the Sun will have moved further westward in the sky. This movement will cause the Sun to
block a different constellation. The constellation that the Sun will be blocking depends on the time of
year and the position of the Sun along the ecliptic. Different constellations are located along the ecliptic
at different times of the year.
D. Where will Aries be in your sky 6 months later at midnight?
In six months, at midnight, the position of Earth in its orbit will have changed, causing a shift in the
constellations visible in the night sky. Aries, which is along the path of the ecliptic, will also have
moved, resulting in a change in its position in the sky. However, the exact position of Aries will
depend on Earth's location in its orbit at that specific time. As a result of Earth's orbital motion
around the Sun, Aries will generally be in a different position in the sky during different times of the
year.
Seasons:
Seasons are caused by a combination of daily and annual motions.
The seasonal effects are different at different latitudes on Earth.
Every day of the year, the Sun is up half the time, so there are approximately 12 hours of
sunshine and 12 hours of night.
Spring: Begins on the spring equinox, which occurs around March 20th in the Northern
Hemisphere and around September 22nd in the Southern Hemisphere.
Summer: Begins on the summer solstice, which occurs around June 21st in the Northern
Hemisphere and around December 22nd in the Southern Hemisphere.
Fall: Begins on the fall equinox, which occurs around September 22nd in the Northern
Hemisphere and around March 20th in the Southern Hemisphere.
Winter: Begins on the winter solstice, which occurs around December 22nd in the Northern
Hemisphere and around June 21st in the Southern Hemisphere.
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Test Yourself – Seasons
Imagine a planet whose spin axis is perpendicular to its orbital plane. How would you describe its
seasons?
C; constant through the year
A solstice
is:
A solstice is a natural event that occurs twice a year when the sun reaches its highest or lowest point in
the sky at noon. This is marked by the longest and shortest days of the year. During a solstice, the sun
appears to stop moving in the sky, and its position is either at its furthest point north or south of the
Earth’s equator.
An equinox
is:
An equinox is a natural event that happens twice a year when the sun crosses the celestial equator. This
results in a day and night of roughly equal length.
Your Turn: Saturn Seasons
A. What were the seasons on the different hemispheres of Saturn when this was taken?
North hemispheres: winter, obtain much sunlight tilting away from the sun.
South hemispheres: summer, because the south hemisphere had more direct sunlight.
B. How long does each season last?
Each season lasts about 7 years as it takes 29 years for Saturn to orbit the sun and each of the 4 seasons
divide these years and result is approx 7 year
C. What should the current season in the Southern hemisphere be?
The current season should be summer as it was reported around 2000 that Saturn was beginning winter.
When we add about 17 years then result is summer/fall to Saturn.
Motion of the Moon:
Synchronous rotation –
physical phenomenon in astronomy where a smaller body orbiting another
rotates on its own axis in roughly the same amount of time it takes to complete one orbit around the
larger body
The Moon moves eastward, rising later each day and passing through its phases: new, first
quarter, full, last quarter, and new again each month.
The Moon rotates on its own axis at the same rate that it orbits around Earth. That means we
always see the same side of the Moon from our position on Earth.
The orbit of the Moon is not a perfect circle but rather an ellipse with Earth at one of its foci.
Please fill in the appropriate phase name corresponding to the number on the Moon’s phases diagram
below.
1. New Moon
2. Waxing Moon
3. 1
st
Quarter
4. Waxing Gibbous
5. Full Moon
6. Waning Gibbous
7. 3
rd
Quarter
8. Waning Crescent
Test Yourself – Moon Phases
A friend exclaims that a few months ago she saw the full moon overhead at noon. Is this possible?
C; No the full moon is never overhead at noon
The moon spins at the same rate as it orbits.
Your Turn – Moon View
Imagine you are standing on the surface of the Moon, on the side facing Earth. Would you see the Sun
rise and set? Would you see Earth rise and set? Explain your answers.
From the surface of the Moon, you would have the opportunity to witness the Earth rising and setting,
just as we view the Moon from Earth. Earth would present itself as a stunning and ever-changing sight
against the backdrop of space. The lunar horizon would be the boundary for Earth's rise and fall. You
would be able to see the blue oceans and white clouds from the Moon's surface..
Eclipses:
Solar Eclipses:
A solar eclipse is a rare event in which the Moon comes between the Sun and Earth, causing the
Sun to be partially or completely blocked from view for people on Earth. There are three types of
solar eclipses: total, partial, and annular.
During a total solar eclipse, the Moon completely covers the Sun, while during a partial solar
eclipse, only part of the Sun is blocked. An annular solar eclipse happens when the Moon is too
far away from Earth to completely cover the Sun, creating a "ring of fire" effect.
It's important to note that solar eclipses can only occur during the new moon phase when the
Moon's orbit intersects with Earth's orbit around the Sun.
Test Yourself – Eclipse
A person on Earth sees a total solar eclipse. What would someone else standing on the side of the Moon
facing Earth see at this time? Earth’s
D; Day side with dark spot that moves across
Lunar Eclipses:
A lunar eclipse happens when the Moon goes through the Earth's shadow. This makes the Moon
look darker. A lunar eclipse only happens during a full moon phase when the Moon is closest to
the Earth's orbit. The Earth's shadow can be split into two parts: the umbra and penumbra. The
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umbra is where the Moon is completely covered, and the penumbra is where only some of the
Moon is covered.
There are three types of lunar eclipses: total, partial, and penumbral. A total eclipse happens
when the Moon goes entirely into Earth's umbra. A partial eclipse only happens when part of the
Moon goes into the umbra. A penumbral eclipse happens when the Moon goes through Earth's
penumbra. During a penumbral eclipse, the Moon looks slightly darker.
You can watch a lunar eclipse from anywhere on Earth where the Moon is visible during the
eclipse.
Motion of the Planets:
The motion of planets has been a topic of interest for astronomers for centuries. Johannes
Kepler, a German astronomer, derived three laws describing the motion of planets in the solar
system.
These laws are:
Law of Ellipses
: The orbit of a planet is an ellipse with the Sun at one of the two foci.
Law of Equal Areas
: A line segment joining a planet and the Sun sweeps out equal areas during
equal intervals of time.
Law of Harmonies:
The square of a planet’s orbital period is proportional to the cube of the
length of the semi-major axis of its orbit.
Kepler's three laws of planetary motion describe how planets move in our solar system.
The first law says that each planet moves around the Sun in an oval shape, with the Sun at one
of the ends.
The second law explains that planets move faster when they are closer to the Sun and slower
when they are farther away. This law also says that when a planet travels around the Sun, it
covers an equal amount of space in the same amount of time.
The third law shows that the periods of any two planets orbiting around the Sun are related to
their distances from the Sun.
Kepler's laws helped us understand how planets move, and they were the basis for Isaac
Newton's law of universal gravitation.