Transcript An Earth-Centered Universe

Clickers!
• Grab the Clicker which
corresponds to your Astro 2 ID
number (EX: If your Astro 2 ID
number is 3460 grab the clicker
which has “60” on it)
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Department
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Announcements
• Remember to attend third hour!
– Which Third Hour you are assigned are posted online
– IMPORTANT NOTE: 3RD HOUR DOES NOT FULFILL A LAB
REQUIREMENT: IT IS SIMPLY THE 3RD HOUR OF THE LECTURE
• Astro labs: Astro 11 and Astro 14
– Bring the 3rd hour sheets (found in the Astro 10 Handbook)!
• Homework – Assignment 01 is due on next Friday by Noon!
– Homework assignments from MasteringAstronomy at
http://www.masteringastronomy.com
– Do Assignment 00 to get used to the style of online homework
• Remember your 4-digit Astro 10 ID number
– That was the number printed on the yellow cards
– Put this on 3rd hour assignments and any else you turn in
• We’ll be practicing the use of the “clickers”
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Department
Fall Semester
2
The Sky
An Earth-Centered Perspective
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Department
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Lecture 2: Patterns in the Sky
Describing positions
• Representing position with coordinates:
–Flat surface: 2 dimensions
• coordinate system of this room
• coordinate system of Rocklin
–Surface of a sphere: 2 dimensions
• coordinate system of Earth
• coordinate system of the Sky
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Lecture 2: Patterns in the Sky
Position on the Earth
E-1
• Describe with the Terrestrial
Coordinate system: longitude-latitude
–Points of reference: North pole, equator
–Two angular coordinates: latitude,
longitude
–Zero point of longitude: prime meridian
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Lecture 2: Patterns in the Sky
Angles
Measuring the Positions of Objects on Spheres
• A minute of arc (arcmin or ´) is one-sixtieth (1/60) of
a degree of arc.
• A second of arc (arcsec or ´´) is one-sixtieth (1/60) Arcmin
arcsec
of a minute of arc.
• A fist held at arm’s length yields an angle of about
10°.
• A little finger held at arm’s length yields an angle of Fist &
Finger
about 1°.
• Angular separation, measured from the observer, is
the angle between two objects in the sky.
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Angular sep.
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Lecture 2: Patterns in the Sky
Position in the Sky - I
Horizon
system
• Describe with the horizon system
–Two angular coordinates: altitude, azimuth
–Points of reference: zenith, horizon
Horizon
system2
–Zero point: north
• meridian stretches from north to zenith to south
–But this won’t work as a permanent
designation!!!! Why?
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Lecture 2: Patterns in the Sky
Position in the Sky - II
CS
• Positions: Use the Equatorial Coordinate
System on the Celestial Sphere
CS
Hor
Celestial sphere is the sphere of heavenly objects
that seems to center on the observer.
Celestial pole is the point on the celestial sphere
directly above a pole of the Earth. In the Northern
Hemisphere one can see the north celestial pole
directly above the North Pole. In the Southern
Hemisphere the south celestial pole sits above the
South Pole.
© Sierra College Astronomy
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CS
ship
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Fig
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Lecture 2: Patterns in the Sky
Position in the Sky - III
CE
• Two angular coordinates: declination, right
ascension
– Points of reference: north celestial pole,
celestial equator
– Zero point: vernal equinox
• The Altitude of the celestial pole above the
horizon is equal to your Latitude
Dec
RA
01-03
Fig
1-19
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Lecture 2: Patterns in the Sky
trails
Position in the Sky - IV
CS
• Stellar motion: “Stars are fixed on the celestial
sphere, which rotates from east to west (on a
minute-by-minute basis) completing one full
turn each sidereal day.”
– This is called diurnal motion
CS
ship
CS
CosmEss
• The circular region around the north celestial
pole in which stars never set is referred to as
the North Circumpolar Region.
01-03
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Fig
1-19
Lecture 2: Patterns in the Sky
Motions of the Stars in California
• East: stars rise, altitude increases, azimuth
increases
• South: stars rise and set, altitude increases
and decreases, azimuth increases
• West: stars set, altitude decreases,
California
azimuth increases
paths
• North: stars neither rise nor set, but rotate
around a pole (circumpolar motion);
altitude and azimuth both alternately
increase and decrease
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Lecture 2: Patterns in the Sky
Pole
Differences in Latitude
• Consider a star on eastern point of horizon
• Equator: straight up (altitude increases,
Equator
azimuth unchanged)
• California: up at an angle (altitude and
azimuth increase)
40 N
Latitude
• North pole: horizontal motion (altitude
unchanged, azimuth increases)
© Sierra College Astronomy
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Look up into the sky
Looking High Southeast, 9:30PM, early September
Vega
LYRA
Albireo
AQUILA
Northern Cross
Summer Triangle
SAGGITA
Altair
Deneb
CYGNUS
DELPHINUS
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Lecture 2: Patterns in the Sky
The Celestial Sphere
Constellations
Constellation (from the Latin, meaning “stars
together”) is an area of the sky containing a
pattern of stars named for a particular object,
animal or person.
The earliest constellations were defined by the
Sumerians as early as 2000 B.C.
Summer
The 88 constellations used today were
Winter
established by international agreement.
Asterisms are unofficial arrangements of
stars. (Ex: Big Dipper, Pleiades, Northern Cross)
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Lecture 2: Patterns in the Sky
The Sun’s Motion: How Long Is A Year?
• The Sun appears to move constantly
eastward among the stars (on a day-today basis).
• The time the Sun takes to return to the
same place among the stars is about
365.24 days.
• Consequently, the stars rise about 4
minutes earlier each day.
Ecliptic
Sun’s
path
SC001
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Lecture 2: Patterns in the Sky
The Sun’s Motion: How Long Is A Year?
CE
The Ecliptic
Ecliptic
• The celestial equator is a line on the celestial on CS
sphere directly above the Earth’s equator.
Sun’s
• The ecliptic is the apparent path of the Sun path
on the celestial sphere.
• The zodiac is the band that lies 9° on either Ecliptic
on Map
side of the ecliptic on the celestial sphere and
contains the constellations through which the
Sun passes.
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Lecture 2: Patterns in the Sky
Solstices and Equinoxes
Ecliptic
on CS
• As the Sun marches on the ecliptic it encounters 4
special points
• Equinoxes: The 2 intersections of ecliptic and
Ecliptic
celestial equator
– Vernal (March 20)
– Autumnal (Sept 22)
Seasons
• Solstices: The 2 extremes in declination of ecliptic
– Summer (June 21)
– Winter (Dec 21)
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Lecture 2: Patterns in the Sky
The Length of a Day
Solar
sidereal
ground
• Sidereal Day – The length of the day with
respect to the stars. It is 3 min. 56 sec. Solar Day
Vs.
SHORTER than the solar day.
Sidereal Day
• Solar Day – The length of the day
measured with respect to the sun. It varies
from day to day and is about 24 hours.
Solar
• All clocks measure the day as a 24 hour
period. This is called the mean solar
day.
Sidereal
space
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SKIP?
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Lecture 2: The Moon
The Moon’s Phases
phases
phasePicture
• Elongation is the angle of the Moon (or planet)
from the Sun in the sky.
phases2
• Phases of the Moon - The changing
appearance of the Moon during its cycle are
caused by the relative positions of the Earth,
Moon, and Sun (different elongations).
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• The phases follow the sequence of new Moon,
waxing crescent, first quarter, waxing gibbous,
full Moon, waning gibbous, third (or last) quarter,
waning crescent, back to new Moon.
• Web tool: http://www.calvin.edu/~lmolnar/moon
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Department
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Waxing Phases
FQ
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Department
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Full Moon, Waning Phases and New Moon
FM
TQ
NM
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Lecture 2: The Moon
Rotation and Revolution
• The rotation and revolution period of the
Moon are exactly equal and can be
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explained by the law of universal gravitation.
• Rotation is the spinning of an object about Revolution
Rotation
an axis that passes through it.
• Revolution is the orbiting of one object
Scale and
around another.
Rotation
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Lecture 2: The Moon
phases2
When and where can you see the Moon?
• The Moon is bright enough to be seen easily in
the daytime
• When and where the moon is in the sky is
completely determined by the elongation angle
(i.e. phase)
– EX: a first quarter moon should be crossing the
meridian at sunset
• There are certain phase combinations that
cannot be seen at certain times
– EX: a waxing crescent high in the sky cannot be
seen at 1 AM
– EX: A full moon cannot be seen at noon
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Department
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Lecture 2: The Moon
The Moon’s Phases
• Phase age is the number of days past new
(1st Quarter ≈ 7.5 days etc.).
• A sidereal period is the amount of time
phases
required for one revolution (or rotation) of a
celestial object with respect to the distant
stars.
• A sidereal revolution of the Moon takes
about 27 1/3 days.
Synodic
And
Sidereal
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Lecture 2: The Moon
The Moon’s Phases
Synodic
• A synodic period is the time interval
And
between successive similar alignments of a Sidereal
celestial object with respect to the Sun.
• A synodic revolution of the Moon takes
about 29 1/2 days
• Lunar month is the Moon’s synodic period,
or the time between successive phases
(e.g. new moon to new moon): 29d12h44m2s.
© Sierra College Astronomy
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Lecture 2: The Moon
Eclipses
• Eclipses occur when the shadow of one
Anatomy
celestial object falls on the surface of
of an
another celestial object (solar and lunar eclipse
eclipses).
• Umbra is the portion of a shadow that
Eclipse
receives no direct light from the light source. Types
• Penumbra is the portion of a shadow that
receives direct light from only part of the light
source.
© Sierra College Astronomy
Department
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Lecture 2: The Moon
Lunar Eclipses
Geom
Types of Lunar Eclipses
• Penumbral lunar eclipse is an eclipse of
the Moon in which the Moon passes
through the Earth’s penumbra but not
Lunar
through its umbra.
Types
• Partial lunar eclipse is an eclipse of the
Moon in which only part of the Moon
passes through the umbra of the Earth’s
shadow.
© Sierra College Astronomy
Department
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Lecture 2: The Moon
Lunar Eclipses
• Total lunar eclipse is an eclipse of the
Moon in which the Moon is completely in Lunar
Types
the umbra of the Earth’s shadow.
• A total eclipse of the Moon is never totally
Red
dark because some light is refracted
toward the Moon by the Earth’s
atmosphere. Most of this refracted light
Red
reaching the Moon is red; the blue
portion has been scattered out.
Total Lunar
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Lecture 2: The Moon
Solar Eclipses
Types
Total
Solar Pic
• Solar eclipse is an eclipse of the Sun in
which light from the Sun is blocked by the
Moon.
• Total solar eclipse is an eclipse in which
light from the normally visible portion of the Total
Sun (the photosphere) is completely blocked
by the Moon.
Umbral
• The corona - the outer atmosphere of the Width
Sun - is visible during a total solar eclipse.
06-19C
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Department
Path
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Lecture 2: The Moon
Solar Eclipses
Annular
Solar Pic
The Partial Solar Eclipse
• Partial solar eclipse: only part of the Sun’s
disk is covered by the Moon.
The Annular Eclipse
• Annular Eclipse is an eclipse in which the
Moon is too far from Earth for its disk to
cover that of the Sun completely, so the
outer edge of the Sun is seen as a ring or
annulus.
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Department
Annular
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Lecture 2: The Moon
Solar and Lunar Eclipses
Earthmoon
• Eclipses does not occur at each full and new Moon
because the Moon’s orbital plane is tilted 5° to the
Earth’s orbital plane.
• An eclipse season is a time of the year during nodes
which a solar and lunar eclipses are possible.
• Only during the two (or three) eclipse seasons that
occur each year are the Earth and Moon positioned
so that the Moon or the Earth will falls on the other
to create an eclipse.
• 1 or 2 solar and 1 or (2 or 0) lunar eclipses occur
each eclipse season (maximum of 3 of both types)
• Viewing of eclipses is dependent on observer
location (more so for solar than lunar)
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Lecture 7: The Earth-Moon System
Solar and Lunar Eclipses
• Upcoming Lunar Eclipses
•
•
•
•
Total: 2007 Mar 03 (~15:20 PST)
Total: 2007 Aug 28 (~3:40 PDT)
Total: 2008 Feb 21 (~19:30 PST)
Partial: 2008 Aug 16 (~14:10 PDT)
Total
Solar
Annular
Solar
• Upcoming Solar Eclipses
• Partial: 2007 March 19 (E. Asia, Alaska)
• Partial: 2007 Sept 11 (Southern S. America,
Antarctica)
• Annular: 2008 Feb 08 (Antarctica, e Australia, N.
Zealand)
• Total: 2008 Aug 01 (ne N. America, Europe, Asia)
© Sierra College Astronomy
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© Sierra College Astronomy
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© Sierra College Astronomy
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Lecture 2: Patterns in the Sky
The Equation of Time
• The correction to get true solar time is
done with the equation of time. This
is the amount of time added to (or
subtracted from) the sun’s time (due
to elliptical orbit of Earth).
D-36
SKIP
– See Sky Gazer’s Almanac
• The analemma is a graphical
representation of this as well.
© Sierra College Astronomy
Department
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Lecture 2: Patterns in the Sky
The Length of the Day
• The world is divided up into (more than) 24
time zones.
• In most countries Daylight Savings Time Time zones
(or Summer Time) is used to allow for more
daylight hours when most people are active.
• The International Date Line is defined as
the position on the earth where the current
day ends and the next day begins (add a day
traveling west).
© Sierra College Astronomy
Department
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Lecture 2: Patterns in the Sky
International and Astronomical Time
• To indicate time internationally (and astronomically),
we use one specified (Standard) time zone
• The time zone along the prime meridian is used and
the time there is called Greenwich Mean Time (GMT)
or Universal Time (UT) or Zulu (Z)
• In the Pacific Standard Time Zone (PST) we are eight
hours behind UT  PST + 8 = UT
– Pacific Daylight Time (PDT): PDT + 7 = UT
• Astronomers use a 24-hour clock (like military time;
e.g. 20:00 = 8 pm)
© Sierra College Astronomy
Department
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Lecture 2: Patterns in the Sky
The Length of the Year
• Many types of years may be defined
• Calendar, Sidereal, Anomalistic, Tropical
How many
days
on the
calendar?
How long does
it take for the
Sun to appear to
go around the
celestial
Sphere?
How long
between
successive
perihelion
passages?
© Sierra College Astronomy
Department
How long is it
Between
successive
Vernal
equinoxes?
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Lecture 2: Patterns in the Sky
Observation: The Planets
• Five planets are visible to the naked
eye: Mercury, Venus, Mars, Jupiter,
Saturn.
• Planets lack the simple, uniform motion
of the Sun and Moon.
• These planets always stay near the
ecliptic.
• Mercury and Venus never appear very
far from the position of the Sun in the
sky. Thus their elongation is small.
© Sierra College Astronomy
Department
79
dome
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Lecture 2: Patterns in the Sky
Observation: The Planets
• The early observers noted several planetary
configurations
Inferior
Configs
– Opposition: when a planet and Sun appear in the
opposite part of the sky (Elongation = 180°)
• Only happens for Mars, Jupiter, Saturn
Superior
Configs
– Conjunction: when the planet and Sun appear together
in the sky (Elongation = 0°)
– Greatest Elongation: when Mercury or Venus reaches a
maximum elongation angle during a particular apparition
• The time it took a planet to return to a particular
configuration (e.g. conjunction, opposition) was
called the synodic period.
© Sierra College Astronomy
Department
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Lecture 2: Patterns in the Sky
Observation: The Planets
• Planets sometimes stop their eastward
(direct or prograde) motion and move
westward against the background of stars.
This is called retrograde motion.
– Mars, Jupiter, Saturn do this near opposition
– Mercury and Venus do this near every other
conjunction
– The would be the most difficult motion to
account for when modeling the solar system
© Sierra College Astronomy
Department
Retrograde
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Retrograde
Ptolemaic
Model
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Ptolemy, Mars
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Ptolemy,
Mercury and
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Venus
CANIS MINOR
Procyon
Looking
up into the
sky
Betelguese
Winter Triangle
Belt
ORION
Rigel
Sirius
CANIS MAJOR
Looking South, 9PM, early February