Transcript Moon - Humble ISD

Lecture Outlines
Introduction
Astronomy:
A Beginner’s Guide to the Universe
5th Edition
Chaisson / McMillan
© 2007 Pearson Prentice Hall
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Introduction
Exploring the Heavens
Units of the Introduction
The “Obvious” View
Earth’s Orbital Motion
The Motion of the Moon
The Measurement of Distance
Scientific Theory and the Scientific Method
What is Astronomy and how
do we use the celestial
sphere to study space?
What is Astronomy?
• Astronomy: study of the universe
• Universe
•Totality of all space, time, matter
and energy
•Solar system, stars, galaxies,
astrobiology, etc
• Actual science (physical)
•observations, data, facts
What is Astronomy?
• Astrology: study of the
movements and relative positions
of celestial bodies and their
supposed influence on human
affairs
• horoscopes, lunatics….
E.1 The “Obvious” View
• Earth is average – we don’t occupy
any special place in the universe
• Scales are very large: measure in
light-years, the distance light travels
in a year – about 10 trillion miles
THE BIGGEST STARS IN
THE UNIVERSE VIDEO
Celestial Sphere
Ancients used to think stars
moved around Earth
Stars’ apparent motion is
due to Earth’s rotation on
axis
Axis intersection points:
-North Celestial Pole
-South Celestial Pole
-Midway = Celestial Equator
Celestial Sphere
-Stars seem to be on the
inner surface of a sphere
surrounding the Earth
-They aren’t!!
-Use two-dimensional
spherical coordinates
(similar to latitude and
longitude) to locate sky
objects
E.1 Celestial Coordinates
• Declination:
•degrees north or south of celestial equator
(similar to latitude)
•Celestial Equator = 0° (0-90)
•Above CE = +X°; below CE = -X°
E.1 Celestial Coordinates
•Right ascension (RA):
•measured in hours, minutes, and seconds
eastward from position of Sun at vernal
equinox (similar to longitude; east-west)
E.1 Celestial Coordinates
Right ascension:
•Starting Line (0) = line from North star to
Sun on the vernal equinox (March 21)
•Maximum RA= 24 hrs
How does the Earth’s orbital motion
cause changes on Earth?
Revolution vs. Rotation
•Revolution: time it takes to orbit around an
object
•EXAMPLE
•Earth year: 365 ¼ days around the sun
(counterclockwise)
•Moon: ~27 1/3 days around Earth (cc)
Revolution vs. Rotation
•Rotation: time it takes to complete a turn on
its own axis
•EXAMPLE
•Earth day: 24 hours (counterclockwise)
•Moon: ~27 1/3 days (cc)
Synchronous Rotation
•Rotation time = Revolution time
•Always see same side of the moon!
E.2 Earth’s Orbital Motion
• Solar day•Daily cycle, noon to
noon, is diurnal motion
• 24 hours
• Sidereal day –
•Time it takes the stars to
be in the exact same
location
• 23 hrs 56 min
• “sidus”= star
E.2 Earth’s Orbital Motion
• Ecliptic is plane of Earth’s path around Sun
• at 23.5° to celestial equator
E.2 Earth’s Orbital Motion
•Northernmost point (above celestial equator) is
summer solstice
•Southernmost is winter solstice
• Points where path cross celestial equator are
vernal and autumnal equinoxes
E.2 Earth’s Orbital Motion
E.2 Earth’s Orbital Motion
•Summer solstice
•longest amount of daylight of year
•usually June 21
•first day of summer
•Winter solstice
•shortest amount of daylight of year
•usually Dec. 21 or 22
•first day of winter
E.2 Earth’s Orbital Motion
•Vernal equinox
•equal amount of daylight and dark
•usually March 20 or 21
•first day of spring
•Autumnal equinox
•equal amount of daylight and dark
•usually Sept. 21-23
•first day of fall
E.2 Earth’s Orbital Motion
•Seasons are caused by:
•Combination of day length
and sunlight angle due to
axis TILT
•Not distance from sun
•Perihelion- January 3
•Aphelion- July 4
E.2 Earth’s Orbital Motion
• Tropical year (Our calendar)
•Time from one vernal equinox to the next
•Follows seasons
•Sidereal year
•Time for Earth to orbit once around Sun,
relative to fixed stars
•Follows constellations
•In 13,000 years July and August will still be
summer, but Orion will be a summer
constellation
Watch the changing seasons
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Notice it is harder to tell in Southern Hemi. Because not as much land
E.2 Earth’s Orbital Motion
Precession: rotation of Earth’s axis itself;
makes one complete circle in about 26,000
years (like a top)
Essential Question
How does the motion of the moon cause us to
see different phases and different types of
eclipses?
animated GIF created by Antonio Cidadao
E.3 Motion of the Moon
•Half of moon’s
surface is ALWAYS
illuminated by the
sun!!!
•Wax-grow
•Right edge
•Wane-shrink
•Left edge
Motion of the Moon
Lunar Phases
animated GIF created by Antonio Cidadao
E.3 Motion of the Moon
•Synodic month
•29.5 days to go
through whole
cycle of phases
•Phases -different
amounts of sunlit
portion being
visible from Earth
•Sidereal month
•Time to make full
360° around Earth
(orbital time)
•27.3 days
Moon Features
•Natural Satellite
•Gravity causes tides
•Maria
• Most obvious darkened
areas
•Craters
•Circular, bowl shaped holes
•Formed by impacts long ago
•No erosion forces
•Atmosphere, water, wind
Lunar Phases
Waxing crescent
Waxing crescent – 1st
quarter – waxing gibbous
Waxing gibbous
Full – waning gibbous
Waning gibbous – waning
crescent
Waning crescent-new moon
Photo from: http://aa.usno.navy.mil/graphics/Moon_phases.jpg
Motion of the Moon
•Eclipse:
•When the sun or moon is blocked to an
observer on Earth for a short period of time
(minutes or hours)
•Caused by shadows of Earth or Moon
•Umbra- darkest part of the shadow
•Penumbra- lightest part of the shadow
•Lunar eclipse:
• Moon is blocked
•Solar eclipse:
• Sun is blocked
Motion of the Moon
Lunar eclipse:
• Earth is between Moon and Sun
• Only occurs during full moon phase
When the Earth’s shadow covers the Moon, we have a lunar eclipse
3 types of Lunar Eclipses
1. Penumbral
2. Partial
3. Total
3 types of Lunar Eclipses
•Penumbral lunar eclipse
•the Moon only passes through the
penumbra of Earth’s shadow
3 types of Lunar Eclipses
•Partial lunar eclipse
•part of the Moon passes through the
umbra of Earth’s shadow
3 types of Lunar Eclipses
•Total lunar eclipse
•the entire Moon passes through the umbra
of Earth’s shadow (turns red)
Total Lunar Eclipes Time Lapse Video
*Next Total Lunar Eclipse not until April 15, 2014*
Why is the Moon red during an eclipse?
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Atmosphere filters some sunlight and
allows it to reach the Moon’s surface
Blue light is removed
Remaining light is red or orange
Bent or refracted so that a small fraction
of it reaches the Moon
Exact appearance depends on dust and
clouds in the Earth’s atmosphere
E.3 Motion of the Moon
Solar eclipse:
• Moon is between Earth and Sun
• New Moon
• 3 types
1. Partial
2. Total
3. Annular
Solar Eclipse
http://www.hermit.org/eclipse/why_solar.html
E.3 Motion of the Moon
Partial
•part of Sun is
blocked
•Seen by
people located
in the
penumbral
shadow
E.3 Motion of the Moon
•Total
•entire sun is blocked
•Corona becomes
visible
•Low density cloud of
plasma with
•higher transparency
than the inner layers
•“Diamond Ring” effect
“Diamond Ring” Effect Before Totality
Begins
In the last seconds before totality begins, the remaining bit of
Sun resembles a dazzling jewel as the ring-like corona appears.
Photo of a Total Solar Eclipse
http://sunearthday.nasa.gov/2006/multimedia/gal_008.php
Credit: Fred Bruenjes
Total Solar Eclipse from Antarctica
It’s possible to see a total eclipse from anywhere on
Earth. This image was shot in Antarctica in 2003.
E.3 Motion of the Moon
•Annular•Moon is too far from Earth for total (umbra
doesn’t reach surface of Earth)
•Forms a ring
•No corona visible
http://sunearthday.nasa.gov/2006/multimedia/gal_010.php; photos taken by Fred Espenak
Annular Solar Eclipse
http://www.hermit.org/eclipse/why_solar.html
Solar Eclipse
This is a photo
taken from the
former Soviet
space station
MIR. It
shows the
shadow of the
Moon falling on
the Earth in
1999. Anyone
under the
shadow saw a
solar eclipse.
E.3 Motion of the Moon
•Eclipses don’t occur every month because Earth’s
and Moon’s orbits are not in the same plane
•5° tilt compared to ecliptic
E.3 Motion of the Moon
Eclipse tracks, 2000 - 2020
Constellations and parallax
•How do astronomers identify stars, name
stars and calculate their distances?
Constellations
• Patterns of stars in the sky that’s “relative”
distance doesn’t change
• Most visible in Northern Hemisphere
named after mythological heroes and
animals by Greek astrologers
• Different constellations visible at night
during different times of year; appear to
move from east to west during night
• 88 total constellations
•Still used to specify large areas of the sky
Locating a star
• Easiest way: specify constellation then rank in
order of brightness using Greek alphabet
• Alpha (α)- Brightest star
• Beta (β)- Second brightest
• Method can only be used with naked eye since
limited number of letters
The “Obvious” View
Stars that appear close in the sky may not
actually be close in space:
Earth’s Orbital Motion
12 constellations Sun moves through during the
year are called the zodiac
The Measurement of Distance
Triangulation:
measure baseline
and angles, can
calculate distance
The Measurement of Distance
The Measurement of
Distance
Parallax: similar to
triangulation, but look at
apparent motion of object
against distant background
from two vantage points
Larger parallax= closer the
object
Smaller parallax= farther the
object
Measuring with Parallax
1. Ruler, tape, cardboard, scissors
2. Cut out both pieces along dashed line
3. Fold up arrows on dotted lines
4. Stick pushpin through both pieces and
cardboard
5. Select a colored target
6. Make a perpendicular baseline taping ruler
to desk
Measuring with Parallax
1. Put EYE ARROW on one end of baseline
2. Line up EYE ARROW, REFERENCE ARROW and
REFERENCE POINT (corner)-gunsight
3. Pivot TARGET ARROW until it is aligned with EYE
ARROW and TARGET OBJECT (scale piece should
NOT move, only the pointer)
4. Read “Angle to Target object” and put on
worksheet as “Target Angle 1”
5. Repeat previous steps from opposite side of the
baseline and write down Angle in “Target angle 2”
6. Complete calculations (Baseline=30 cm)
Scientific Theory and the
Scientific Method
What is a Scientific theory and how is it
developed?
Scientific Theory and the
Scientific Method
Scientific theories:
• must be testable
• must be continually tested
• should be simple
• should be elegant
Scientific theories can be proven wrong, but
they can never be proven right with 100%
certainty
Scientific Theory and the Scientific
Methods
• Observation leads to theory
explaining it
• Theory leads to predictions
consistent with previous
observations
• Predictions of new
phenomena are observed. If
the observations agree with
the prediction, more
predictions can be made. If
not, a new theory can be
made.
Summary of the Introduction
• Astronomy: study of the universe
•Stars can be imagined to be on inside of celestial
sphere; useful for describing location
• Plane of Earth’s orbit around Sun is ecliptic; at
23.5° to celestial equator
• Angle of Earth’s axis causes seasons
• Moon shines by reflected light, has phases
• Solar day ≠ sidereal day, due to Earth’s rotation
around Sun
Summary of the Introduction
• Synodic month ≠ sidereal month, also due to
Earth’s rotation around Sun
• Tropical year ≠ sidereal year, due to
precession of Earth’s axis
• Distances can be measured through
triangulation and parallax
•Eclipses of Sun and Moon occur due to
alignment; only occur occasionally as orbits
are not in same plane
• Scientific method: observation, theory,
prediction, observation, …