Comet HaleBopp Pleiades Orion Sirius Aldebaran Capella Orion Mars Betelgeuse Rigel Observation is not Looking Observation is not Looking You ID: 931894
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Slide1
Introduction
to the
Sky
Slide2Slide3Comet Hale-Bopp
Pleiades
Orion
Sirius
Aldebaran
Capella
Slide4Slide5Orion
Mars
Betelgeuse
Rigel
Slide6“
Observation
”
is not
“
Looking
”
Slide7“
Observation
”
is not
“
Looking
”
"You
see
, Watson, but you do not observe."
--- Sherlock Holmes
Slide8“
Observation
”
is not
“
Looking
”Instead:
Study carefully, comprehensivelyRemember/record
Try to make connectionsIdentify systematic features
Slide9Motivations for Observing the Sky
Curiosity
Practical applications
Navigation
Time-keeping
Calendar-keeping
Fear, religious belief
E.g. Astrology
Slide10Polynesian Navigation
Slide11Slide12Sky worship/astrology
Egyptian Pharoh
Akhenaton and
family communing
with Sun God
(ca. 1350 BC)
Slide13Astronomical Measurements
Without
Telescopes
Angles (quantitative)
Sky
to Sky
Earth to SkyBrightnesses (crude)Colors,
Shapes (crude)Changes in above with time
Slide14Slide15
Isosceles triangle:
Slide16Units of Angular Measure
Slide17Naked Eye Instruments for Angular Measures
150 BC
1580 AD
Slide18Naked Eye Instruments for Angular Measures
150 BC
1580 AD
Limiting accuracy
~ resolution of human eye
~ 1 minute of arc
Slide19"Hand-y" Angle Measuring
(crude but useful for orientation)
Slide205 degrees
10 degrees
Ursa Major (The Big Dipper)
Slide21The Magnitude
System
(a brightness
ranking
)
Slide22Example: Range of magnitudes in Big Dipper
Slide23Star Colors (prism-dispersed image)
Slide24Slide25Slide26Puzzlah #9
If you go out at 9 PM on a clear night, turn to the south, and look up at the sky, you will see a certain group of bright stars. How will the location of those stars in the sky change if you come back at midnight or several weeks later?
(A) The locations of stars in the sky are always the same (they never change).
(B) The locations change during the night but are always the same at a given time of night.
(C) The locations change during the night and also change at a given time of night from month to month.
Slide27Puzzlah #9
If you go out at 9 PM on a clear night, turn to the south, and look up at the sky, you will see a certain group of bright stars. How will the location of those stars in the sky change if you come back at midnight or several weeks later?
(A) The locations of stars in the sky are always the same (they never change).
(B) The locations change during the night but are always the same at a given time of night.
(C) The locations change during the night and also change at a given time of night from month to month.
Slide28Puzzlah #10
During the day, the
Sun
moves from east to west across the sky. In which direction do the
stars
move after the Sun has set?
(A) The stars are stationary; they don't move
(B) West
(C) East
(D) North
(E) South
Slide29Puzzlah #10
During the day, the
Sun
moves from east to west across the sky. In which direction do the
stars
move after the Sun has set?
(A) The stars are stationary; they don't move
(B) West
(C) East
(D) North
(E) South
Slide30Main Actors in the Sky
Slide31STARS
Form background "reference frame"
About
2000-5000 visible
to naked
eye over whole sky
Patterns of bright stars seem
"fixed", unchanging
Move
"in lockstep" from East to
West
and return to same
position in sky after
23
h
56
m
Called the “diurnal motion”
Slide32Positions of stars in night sky at given time change systematically during the year
Slide33SUN
Brightest object (by far!)
Scattered sunlight masks
stars during day
Steady brightness
Slow, eastward motion
against stars,
1
o
per day
Returns to same position
after
365.25
days, or
one
year.
Slide34MOON
Second brightest object in
sky (but much fainter than sun)
Faster eastward motion
against
stars,
13
o per day
Dramatic change in (illuminated) shape or "phase" during cycleCycle takes
29.5 days to return to same phase.12 cycles per year Our "month" is based on lunar
cycles
Lunar Phases
Slide35Daily motions of Moon are easy to track
Slide36Planets
5 brighter
starlike
objects
that
move
with respect to
the stars.Mercury, Venus, Mars,
Jupiter, SaturnMerc, Venus always near
Sun. Others, up to 180o
away.
Motion is
slower
than Sun,
Moon.
Generally
eastward
, but
loops to west
Slide37"Retrograde Loop" in Mars Motion
Eastward
Slide38Other Phenomena Visible to Naked Eye
Meteors
Comets
Star clusters
Diffuse nebulae
Milky Way
External galaxies
}
Transient
Slide39Slide40Constellations
Constellations are the
patterns
formed by brighter stars on the sky
Patterns seem
fixed
(i.e. don't change over years)
Recognized for
millenia
, by all cultures
Associated with mythological figures, animals, instruments,
etc
Slide41Slide42Stick-Patterns
Slide43Official Names
Slide44"Classical" figures added
Slide45Greek amphora, ca. 400 BC, showing
Leo, Aquila, Hercules,
etc
Slide46Orion, Taurus,
Lepus
in a
classical
celestial atlas
.
Slide47Hevelius
,
Firmamentum
(1690)
Slide48Cellarius
,
Harmonia
Macrocosmica
, 1661
Slide49More modern
constellations
Bode, 1801
Slide50"Asterism"
Slide51"Asterism"
Winter Hexagon
Slide52"Official Constellations": 88 (est. 1930, IAU)
Boundaries of each well-defined
"
Zodiac
" = the 12 (13) constellations lying along the annual
path of Sun
through stars.
(Names widely recognized but NOT all bright.)
Modern Constellations
Slide53Significance of the Constellations?
Slide54Significance of the Constellations?
Not Much
Slide55Significance of the Constellations?
Not Much
Associations are
arbitrary
, man-made, culture-specific.
Not natural groupings
: stars are not necessarily close in 3D space. Shapes are specific to Earth's present location in galaxy.
Fainter stars don't participate in pattern
Constellations are
transient
because stars are all moving with respect to each other.
Used as convenient "address" for roughly locating objects in sky.
Slide56Modern star chart.
Fainter stars don't
participate in the
pattern.
Slide57Orion
Projected
View
3-D
Distribution
Slide58Motions in Big Dipper
Over 100,000 Years
Slide59Constellation Quiz
Two one-hour sessions offered M-R, 9 pm and 10 pm
Must reserve a place using on-line registration system
No special preparation needed
Bring a flashlight (red preferred), pencil, and clipboard (if you have one)
Cloudy or rainy weather will cancel the session
Check weather status after 6:30 pm at 924-7238
Slide60-- END --