Download Guided notes part 1 - Duplin County Schools

22.2 Part 1 Note Guide
The Earth-Moon-Sun System
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People have always been fascinated by the changing positions of the ____________________________________
in the sky
Prehistoric people, for example, built __________________________________
The structure known as ___________________________________ was probably an attempt to better solar
predictions
At the beginning of ________________________________ in the Northern Hemisphere (the summer solstice on
June 21 or 22), the _________________________________________ comes up directly above the heel stone of
Stonehenge
Besides keeping this calendar, Stonehenge may also have provided a method of determining
________________________________
Motions of Earth
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The two main motions of Earth are _____________________________________________________________
Rotation is the ___________________________, or _______________________________, of a body on its axis
Revolution is the motion of a body, such as a _________________________________________________, along
a path around some point in space
For example, ___________________________ revolves around the sun, and the __________________________
revolves around Earth
Earth also has another very slow motion known as _________________________________, which is the slight
movement, over a period of __________________________________, of Earth’s axis
Rotation
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The main results of Earth’s rotation are ___________________________________________________
Earth’s rotation has become a standard method of measuring _____________________________ because it is so
dependable and easy to use
Each rotation equals about ___________________________________
We can _______________________________ Earth’s rotation in two ways, making two kinds of days
Most familiar is the ________________________________________________, the time interval from one noon
to the next, which averages about ______________________________
Noon is when the sun has reached its _________________________________, or highest point in the sky
The _____________________________________, on the other hand, is the time it takes for Earth to make one
complete rotation (_________________________________) with respect to a star other than our sun
The sidereal day is measured by the time required for a star to _________________________________ at the
identical position in the sky where it was observed the _______________________________________
The sidereal day has a period of ______________ hours, ______________ minutes, and _____________seconds
(measured in solar time), which is almost 4 minutes shorter than the mean solar day
This difference results because the direction to distant _________________________ barely changes because of
Earth’s slow _____________________________ along it orbit
The direction to the sun, on the other hand, changes by almost ________________________________ each day
In sidereal time, “_______________________” occurs four minutes earlier each day
Therefore, after six months, “_______________________” occurs at “_________________________”
Astronomers use sidereal time because the ____________________________ appear in the same position in the
sky every 24 _____________________________ hours
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Usually, an observatory will begin its sidereal day when the position of the _______________________________
is directly overhead
Revolution
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Earth revolves around the sun in an elliptical orbit at an average speed of _______________________ kilometers
per hour
Its average ______________________________ from the sun is 150 million kilometers
But because its orbit is an ellipse, Earth’s distance from the sun ___________________________
At _________________________________, Earth is closest to the sun—about ______________ million
kilometers away
Perihelion occurs about _______________________________ each year
At _________________________________, Earth is farthest from the sun—about ___________ million
kilometers away
Aphelion occurs about __________________________
So Earth is __________________________ from the sun in July and ___________________________ to the sun
in January
Because of Earth’s ________________________________________________ around the sun, each day the sun
appears to be displaced among the constellations at a distance equal to about twice its width, or
__________________
The apparent annual path of the sun against the backdrop of the celestial sphere is called the
____________________________
Generally, the ____________________________________________________ travel in nearly the same plane as
Earth
So their paths on the celestial sphere lie near the ____________________________
Earth’s Axis and Seasons
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The ______________________________________________ that connects Earth’s orbit with the celestial sphere
is called the plane of the ecliptic
From the reference plane, Earth’s axis of rotation is tilted about _________________________________
Because of Earth’s _____________________, the apparent _______________________ of the sun and the
_____________________________ equator intersect each other at an angle of 23.5 degrees
This angle, 23.5 degrees, is very important to Earth’s _________________________________
Because of the inclination of Earth’s axis to the plane of the ecliptic, Earth has its yearly cycle of
___________________________
When the apparent position of the ______________________ is plotted on the celestial sphere over a period of a
year’s time, its path intersects the celestial equator at ______________________ points
From a ____________________________ Hemisphere point of view, these intersections are called the spring
equinox (March ___________________) and autumn equinox (September ___________________)
On June 21 or 22, the date of the __________________________________________, the sun appears 23.5
degrees north of the celestial equator
Six months later, on December 21-22, the date of the _______________________________________________,
the sun appears 23.5 degrees south of the celestial equator
Precession
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A third and ________________________________________________________ of Earth is called precession
Earth’s ____________________________ maintains approximately the same angle of tilt
But the direction in which the axis ____________________________ continually changes
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As a result, the axis traces a ____________________________ on the sky
This movement is very similar to the wobble of a __________________________________________
At the present time, the axis points toward the bright star ______________________________
In the year ________________________, it will point toward the bright star _______________________, which
will then become the North Star
The period of precession is ______________________________________
By the year _______________________, __________________________ will once again be the North Star
Precession has only a minor effect on the ________________________________, because the angle of tilt
changes only slightly
It does, however, cause the positions of the seasons (________________________________________________)
to move slightly each year among the stars
Earth-Sun Motion
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In addition to its own movements, ___________________________ accompanies the sun as the entire solar
system speeds in the direction of the bright star ______________________ at 20 kilometers per second
Also, the sun, like other nearby stars, revolves around the ____________________________
This trip takes _________________________________ years to traverse at speeds approaching ______________
kilometers per second
The galaxies themselves are also in ______________________________
Earth is presently approaching one of its nearest galactic neighbors, the Great Galaxy in
_______________________________
The motions of Earth are _______________________________________________________, and its speed in
space is very great