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EVERYTHING
Thought Question:
If you could see stars during the day, this is what the sky
would look like at noon on a given day. The Sun is
near the stars of the constellation Gemini. Near
which constellation would you expect the Sun to be
located at sunset?
A. Leo
B. Cancer
C. Gemini
D. Taurus
E. Pisces
Thought Question
Which of the following describes when constellations are
visible from San Diego (if it is dark enough and the
clouds cooperate)?
A. You could observe any constellation tonight at midnight.
B. You could observe any constellation sometime during the
night.
C. You could observe any constellation on some night
during the next year.
D. Some constellations will never be visible from here.
CONSTELLATIONS: for
orienting ourselves in the sky:
NORTH
STAR
Being a Good
Astronomer
ATMOSPHERE
Complications in finding things:
•
Earth is a sphere (people in different places see different stars)
•
Earth rotates (stars continually move across sky)
•
Earth orbits the Sun (stars don’t appear in same place from
month to month)
•
Some of our targets are moving too…
Being a Good
Astronomer
LOW
ALTITUDE
HIGH
ALTITUDE
ATMOSPHERE
High in the sky is best because…
the more atmosphere you have to look through:
• the more light is blocked
• the more the colors are affected
Where in the Sky?
ZENITH
NORTH
STAR
E
N
NORTH
STAR
To describe position in sky,
need two coordinates:
• Altitude (ALT): angle
above horizon
0º: horizon
S
90º: zenith
W
E
N
W
• Direction (DIR): angle
clockwise from N
measured around horizon
0º: N
180º: S
S 90º: E
270º: W
Being a Good
Astronomer
ATMOSPHERE
Best telescopes usually scheduled months in advance:
• must be able to predict when an object will be up
• light from Sun, Moon should not interfere
Stars Move?
Thought Question
In the past, several TV shows (NBC Nightly News, The Daily
Show) had opening graphics which showed the Earth
spinning the wrong way. If you were watching Earth from
a stationary position out in space (as shown below), what
direction does it spin?
A. Left to right
B. Right to left
Celestial Sphere
Stars appear to move as
if attached to a sphere
rotating around Earth
• Celestial poles: above
Earth’s N and S poles
• Celestial equator:
directly above Earth’s
equator
Earth Surface Coordinates
NORTH POLE
90º N
EQUATOR
0º
SOUTH POLE
90º S
Celestial Coordinates
NORTH CELESTIAL
POLE
RIGHT
ASCENSION
LINES
NORTH CELESTIAL
POLE
CELESTIAL
EQUATOR
DECLINATION
LINES
SOUTH CELESTIAL
POLE
SOUTH CELESTIAL
POLE
Celestial Coordinates
north celestial pole
declination (DEC): like
latitude on Earth
north celestial pole: +90º
celestial equator: 0º
south celestial pole: -90º
right ascension (RA): like
longitude on Earth
BUT… counted in hrs, increases
toward east
The Sky from San Diego
circumpolar: stars that don’t rise
or set for a person
Most stars rise in east half of sky,
and set in west half:
LOOKING
NORTH
LOOKING
SOUTH
NORTH
CELESTIAL
POLE
E
S
N
W
HORIZON
Thought Question
If you watched the star pictured below from San Diego over
several hours, what would happen?
A. Its altitude and direction wouldn’t change.
B. Its altitude would change, but direction wouldn’t.
C. Its direction would change, but altitude wouldn’t.
D. Both its direction and altitude would change.
E
N
S
W
HORIZON
Using a
Telescope
A telescope pointing at
one ALT and DIR
doesn’t move
BUT a star’s ALT and
DIR both change
during night
• Is there a better way?