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Transcript
The Celestial Sphere
•
•
•
•
Model describing the sky. (Glass bowl over the Earth)
Pretend that the stars are attached to it
Celestial Meridian: Line North to South.
Zenith: Spot straight up.
Celestial Sphere
• The sun and stars rise
from East to West.
• What causes this?
• Earth’s Rotation
• What star is that?
• North Star (Polaris)
Finding Your Latitude
• Find the Big Dipper.
• Use Pointing stars.
• Measure angle from
ground to the North
Star.
• That angle is your
latitude.
North Star from different latitudes
• At the North Pole,
where is the North
Star in the sky?
• Answer: Straight up!
• At the Equator, where
is the North Star in
the sky?
• Answer: On the
Horizon!
Right Ascension (RA)
•
Corresponds to longitude, but
different units are used.
•
Instead of 360°, a circle is
broken into 24 hours of right
ascension.
•
So, 360° = 24 h R.A., 15° = 1
h R.A., and 1° = 4 min R.A.
Right ascension increases
from west to east (note that we
are looking at the exterior of
the celestial sphere in the
above picture).
Declination (Dec)
• Corresponds to
latitude - relative to
the celestial equator
(0° dec).
• Circles of constant
declination are all
parallel to the
celestial equator
• With the two numbers
of declination and
right ascension, the
position of any object
in the sky can be
precisely described.
Ecliptic
• Stars are fixed
relative to each other.
• The Sun traces out a
circle on the celestial
sphere called the
ecliptic.
• Ecliptic is tilted at an
angle of 23.5° with
respect to the
celestial equator.
The Ecliptic & Zodiac
First Point of Aries
Cardinal Directions
• Why is East & West
switched?
Equatorial Starmaps
Reading a Map
•
•
•
•
•
Key – Different objects
Magnitude
Identify Zodiac
Plotting RA & Dec. of stars
Plot a moving or wandering object over
time.