Download Chaper 1 part b

In order to more easily locate objects in the sky, we
divide the sky into regions named after familiar
patterns of stars called constellations.
constellations.
Ancient constellations were
imaginary pictures outlined
by familiar patterns of stars.
Modern astronomers divide the sky into
88 official constellations or regions of
space, many of which contain the
ancient star patterns.
Some Common Guides to Finding Constellations
Using the “Big Dipper”
Dipper” as a guide
The “Summer Triangle”
Triangle”
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The “Winter Triangle”
Triangle”
Astronomers describe the universe as an imaginary
sphere surrounding the earth on which all objects in
the sky can be located, called the CELESTIAL SPHERE.
SPHERE.
! As viewed from Earth, the
celestial sphere appears to rotate
arouns two axis points, the north
and south celestial poles,
poles, which
are located directly above the
Earth’’s poles.
Earth
!Between these is the celestial
equator, which divides the
celestial sphere into northern and
southern hemispheres.
!We define the position of an
object on the celestial sphere
using two coordinates, right
ascension and declination
declination..
Cyclic motions of the Sun and stars in our sky
are due to motions of the Earth
1. ROTATION=the spin of the Earth on its axis. It takes one
day for the Earth to complete one rotation.
2. REVOLUTION=the movement of the Earth in orbit around
the sun. It takes one year for the Earth to complete one
revolution.
3. PRECESSION=the slow conical (top-like) motion of the
Earth’
Earth’s axis of rotation. It takes 26,000 years for the Earth
to complete one cycle of precession.
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The apparent westward motion of the Sun,
Moon, and stars across our sky each day is
caused by Earth’
Earth’s rotation.
rotation.
At middle latitudes, we see the Sun, Moon, and many of the stars
first come into view moving upward, rising at some point along the
eastern horizon. Then, they appear to arc across the sky. Finally,
they disappear somewhere along the western horizon.
We generalize this motion to make statements such as, “ The Sun
rises in the east and sets in the west.”
west.”
However, not all stars in our sky rise and set, and different latitudes
view the movements of the stars differently.
The stars near the poles of the celestial
sphere (shown here) move in trails that
circle the pole and never set. They are
called circumpolar
circumpolar..
The view of the stars movement
depends on our latitude.
NORTH
POLE
EQUATOR
MIDDLE
LATITUDES
Different parts of the world experience different times of day as the Earth
rotates.
TIME ZONES which can be used to calculate the time of day in any given
part of the world.
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The Earth also revolves around the Sun, which changes our view of the stars.
From our perspective, the Sun
appears to move through the
stars along a special path
called the ecliptic.
From an outside view, we see
the Earth revolve around the
Sun. We define the plane of the
Earth’’s orbit as the ecliptic plane.
Earth
We can see how different stars appear at different times of day by looking at
the position of the Sun against the backdrop of stars. The side of the Earth
facing the Sun is experiencing “ day,
day,”” while the side of the Earth turned away
from the Sun is experiencing “night.
night.””
SEPTEMBER
MARCH
Seasons are caused because the Earth’
Earth’s axis is tilted and as the Earth
revolves around the Sun, different parts of the Earth receive more direct
sunlight (summer), while other parts of the Earth receive sunlight which is
more spread out (winter).
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