Transcript Bellringer - Madison County Schools

Bellringer
Which of the following is correct:
Earth orbits the sun
or
The sun orbits Earth
Earth in Space
Notes
Astronomy
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For thousands of years, Egyptian planting was ruled by
the annual flooding of the Nile river. Their entire culture
revolved around this act of nature, so predicting the
flooding was very important. Around 3000 BCE, people
noticed that the bright star Sirius first became visible in
the early morning sky every year shortly before the
floods would begin. They were able to use this knowledge
to prepare for the floods every year. The ancient
Egyptians were among the first to study the stars - the
first astronomers.
How Earth Moves
• Earth moves through space in two
major ways: rotation and revolution.
• Rotation is spinning. Earth rotates on
its axis. Earth’s axis is an imaginary
line through the North and South poles.
How Earth Moves
• Earth’s rotation causes day and night.
As Earth rotates from west to east the
sun appears to move across the sky.
The sun is not really moving as we see
it. Earth’s rotation makes it appear to
move. It takes Earth about 24 hours to
rotate once completely on its axis.
How Earth Moves
• Earth also moves around the sun. This
movement is called revolution.
Revolution is the movement of one
object around another.
• Earth revolves around the sun (Sol).
How Earth Moves
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The path that Earth follows around the
sun is called an orbit. Earth takes one
year to travel all the way around the sun
in its orbit.
The exact amount of time for one
complete revolution of Earth around Sol is
365.242 days.
Revolution = action (what it does)
Orbit = path (where it does it)
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Calendars
A calendar is a system of organizing time that defines the
beginning, length, and divisions of a year.
The Egyptians were one of the first cultures to develop a calendar
based on the star Sirius. It contained 12, 30-day months (based on
the lunar “moonth”) with a 5-day month at the end.
Remember that it actually takes 365.242 days to orbit the sun, not
an exact 365.
The Romans took the Egyptian calendar when it was conquered by
Alexander the Great and added a Leap Year every 4 years to
compensate for the difference between the Solar year and Calendar
year.
This still made the Roman calendar off my 11 minutes every year.
After a few centuries this added up, so Pope Gregory XIII dropped
10 days off of the year 1582. With a few more changes, he created
the calendar that we still use today. This is known as a Gregorian
The Seasons on
Earth
• Earth has seasons because its axis it
tilted as it revolves around the sun.
• Earth’s axis is tilted, or slanted.
• Earth is warmer near the equator than
near the poles.
The Seasons on
Earth
• Earth is tilted 23.5°. This means that at different
times of the year, the norther and souther
hemispheres can be either pointed 23.5°
towards the sun, or 23.5° away from the sun.
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In summer, Earth is tilted towards the sun. Day
is longer then night. Earth’s surface receives
more direct sunlight, and is therefore warmer.
In winter, Earth is tilted away from the sun.
Night is longer then day. Earth’s surface
receives less direct sunlight, and is therefore
cooler.
The Seasons on
Earth
• Summer and winter are caused by
Earth’s tilt as it revolves around the sun.
The change in seasons is not caused
by changes in Earth’s distance from the
sun. In fact, Earth is farthest from Sol
when it is summer in the Northern
Hemisphere.
Earth in June
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In June, the north end of Earth is tilted 23.5°
towards the sun. This means that the south end
of Earth is tilted 23.5° away from the sun.
In the north, this means more direct sunlight
and longer days. This adds up to more direct
heat during the summer months.
Conversely, the southern hemisphere receives
less direct sunlight and fewer hours of daylight
(longer nights). This means less heat is striking
the surface, making it winter south of the
Equator.
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Earth in December
In December, the north end of Earth is tilted
23.5° away from the sun. This means that the
south end of Earth is tilted 23.5° towards the
sun.
In the north, this means less direct sunlight and
shorter days. This adds up to less direct heat
during the winter months.
Conversely, the southern hemisphere receives
more direct sunlight and more hours of daylight
(longer days). This means more heat is striking
the surface, making it summer south of the
Equator.
Solstices and
Equinoxes
• June 21 - Longest day of the year in Northern
Hemisphere = Summer Solstice
• June 21 - Shortest day of the year in Southern
Hemisphere = Winter Solstice
• December 21 - Shortest day of the year in
Northern Hemisphere = Winter Solstice
• December 21 - Longest day of the year in
Southern Hemisphere = Summer Solstice
Solstices and
• March 21 - Equal amounts of day and night in both
Equinoxes
hemispheres (12
hours each). 1 of only 2 times of the
year where there is NO TILT wither towards or away
from the sun = Vernal Equinox in Northern
Hemisphere.
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March 21 = Autumnal Equinox in Southern
Hemisphere
September 22 - Equal amounts of day and night in both
hemispheres (12 hours each). 1 of only 2 times of the
year where there is NO TILT wither towards or away
from the sun = Autumnal Equinox in Northern
Hemisphere.
September 22 = Vernal Equinox in Southern