Transcript pptx - Faculty Virginia

Introduction to the Sky
Capella
Sirius
Aldebaran
Orion
Pleiades
Comet Hale-Bopp
Orion
Mars
Betelgeuse
Rigel
“Observation” is not “Looking”
“Observation” is not “Looking”
"You see, Watson,
but you do not observe."
--- Sherlock Holmes
“Observation” is not “Looking”
Instead:
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Study carefully, comprehensively
Remember/record
Try to make connections
Identify systematic features
Motivations for Observing the Sky
• Curiosity
• Practical applications
– Navigation
– Time-keeping
– Calendar-keeping
• Fear, religious belief
– E.g. Astrology
Polynesian Navigation
Sky worship/astrology
Egyptian Pharoh
Akhenaton and
family communing
with Sun God
(ca. 1350 BC)
Astronomical Measurements
Without Telescopes
• Angles (quantitative)
– Sky to Sky
– Earth to Sky
• Brightnesses (crude)
• Colors, Shapes (crude)
• Changes in above with time
Isosceles triangle:
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Units of Angular Measure
Naked Eye Instruments for Angular Measures
150 BC
1580 AD
Naked Eye Instruments for Angular Measures
Limiting accuracy
~ resolution of human eye
~ 1 minute of arc
150 BC
1580 AD
"Hand-y" Angle Measuring
(crude but useful for orientation)
10 degrees
5 degrees
Ursa Major (The Big Dipper)
The Magnitude System
(a brightness ranking)
Example: Range of magnitudes in Big Dipper
Star Colors (prism-dispersed image)
Puzzlah #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.
Puzzlah #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.
Puzzlah #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
Puzzlah #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
Main Actors in the Sky
STARS
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 23h56m
Called the “diurnal motion”
Positions of stars in night sky at given time
change systematically during the year
SUN
Brightest object (by far!)
Scattered sunlight masks
stars during day
Steady brightness
Slow, eastward motion
against stars, 1o per day
Returns to same position
after 365.25 days, or
one year.
Lunar Phases
MOON
Second brightest object in
sky (but much fainter than sun)
Faster eastward motion against
stars, 13o per day
Dramatic change in (illuminated)
shape or "phase" during cycle
Cycle takes 29.5 days to return
to same phase.
12 cycles per year
Our "month" is based on lunar
cycles
Daily motions of Moon are easy to track
Planets
5 brighter starlike objects
that move with respect to
the stars.
Mercury, Venus, Mars,
Jupiter, Saturn
Merc, Venus always near
Sun. Others, up to
180o away.
Motion is slower than Sun,
Moon.
Generally eastward, but
loops to west
"Retrograde Loop" in Mars Motion
Eastward
Other Phenomena Visible to Naked Eye
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Meteors
Transient
Comets
Star clusters
Diffuse nebulae
Milky Way
External galaxies
Constellations
• 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
Stick-Patterns
Official Names
"Classical" figures added
Greek amphora, ca. 400 BC, showing
Leo, Aquila, Hercules, etc
Orion, Taurus,
Lepus in a
classical
celestial atlas.
Hevelius, Firmamentum (1690)
Cellarius, Harmonia Macrocosmica, 1661
More modern
constellations
Bode, 1801
"Asterism"
"Asterism"
Winter Hexagon
Modern Constellations
• "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.)
Significance of the Constellations?
Significance of the Constellations?
Not Much
Significance 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.
Modern star chart.
Fainter stars don't
participate in the
pattern.
Orion
Projected
View
3-D
Distribution
Motions in Big Dipper
Over 100,000 Years
Constellation 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
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