Basics of Astronomy
Astronomy
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Tackles some fundamental questions
What is our place in the universe?
How did we get here?
Are we alone?
Astronomy vs. Astrology
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_________- the pseudo-science that studies how the
motion of the stars and planets affect peoples lives.
Available daily in your horoscope.
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_________– The science of probing the universe to derive the
properties of celestial objects and the laws under which the
universe operates.
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• Astrology contributed to Astronomy since the
position of the Sun, Moon, and stars was
needed to determine a person’s sign.
• Planets, Sun, and Moon move in a band around
the sky known as the______.
• Babylonians divided the zodiac into 12
sections. (the “signs”)
• Different cultures may have different divisions.
Constellations
Configuration of stars named in honor of
mythological characters or great heroes
Today 88 constellations are recognized
Constellations divide the sky into units, like
state boundaries in the United States
The brightest stars in a constellation are
identified in order of their brightness by the
letters of the Greek alphabet – alpha, beta,
and so on
Location of celestial objects
• Although incorrect, the
______________________ is a useful way
of looking at the sky.
• Equatorial system of location
• A coordinate system that divides the celestial
sphere
• Similar to the latitude-longitude system that is
used on Earth's surface
Terms
• ________________– an imaginary plane
extending from Earth’s equator out to the
celestial sphere.
• ___________– the angular distance north or
south of the celestial equator. Similar to
latitude on Earth.
Terms
• _______________– the angular distance
measured eastward along the celestial
equator from the position of the vernal
equinox. Similar to Earth’s longitude.
• ______________– point in the sky where
the Sun crosses the celestial equator at the
onset of spring.
Planetary Motions
• ________– Turning of a body on its axis.
(Earth 24 hours)
• __________– motion of a body around
some point in space. (Earth 1 year)
• ___________
• ___________
• ___________
Earth’s Rotation
______________– Time interval from
zenith to zenith of the Sun at a location.
• ____________ – Time interval for Earth to
make one complete rotation (360°) with
respect to another star, not the Sun.
Earth’s Revolution
• Average speed (66,000 mph)
• Average Distance from Sun ( __ million
miles = 1 AU)
• Distance at perihelion (91.5 million miles)
• Distance at aphelion (94.5 million miles)
• Tilt on axis and revolution are reasons for
seasons.
http://www.ioncmaste.ca/homepage/resources/web_resources/CSA_Astro9/files/multimedia/unit3/reasons_seasons/re
asons_seasons.swf
Earth’s Revolution
• _________– The apparent annual path of
the Sun against the backdrop of the celestial
sphere.
• _____________________ – the imaginary
plane that connects Earth’s orbit with the
celestial sphere.
Plane of Ecliptic vs. Celestial Equator
Milankovitch Theory
• Milutin Milankovitch
• Formulated a mathematical model to
explain changes in Earth’s climate during
the Pleistocene.
• Model is based on variations in Earth’s orbit
and the amount of incoming solar radiation
available at various times.
Elements of Milankovitch Model
• __________ – Variations in the elliptical
nature of Earth’s orbit.
• _______ – Changes in the angle of tilt of
Earth with its orbit.
• _________ – Wobbling of the Earth on its
axis.
Eccentricity (~100,000 y)
Obliquity (~41,000 y)
Precession (~26,000 y)
Precession
• Very slow Earth movement
• Direction in which Earth's axis points continually
changes. Currently points toward Polaris.
• In 13,000 years, winter in the Northern Hemisphere
will occur when Earth is farthest from the Sun
(aphelion), will have summer when Earth is closest
to the Sun (perihelion). Exact opposite of today.
http://www.onr.navy.mil/Focus/spacesciences/animation/observingsky/precession.swf
Fig. 2.16, p. 52
What does that mean?
• Northern Hemisphere summers will be
warmer. Montreal in summer then will feel
like Washington D.C. now.
• Northern Hemisphere winters will be colder
than present.
• Southern Hemisphere is opposite, cooler
summers, warmer winters.
Additional Motions
• Sun and solar system is moving toward the
star Vega.
• Solar system revolves around the galaxy.
• Milky Way is moving, approaching the
Great Galaxy in Andromeda.
Earth-Sun relations
Earth motions
• _________ on its axis
• _________ around the Sun
Seasons
• Result of
• Changing Sun angle
• Changing length of daylight
Fig. 2.17, p. 53
Daily paths of the Sun at
40º N latitude
Relationship of sun angle and
solar radiation received on Earth
Earth-Sun relations
Seasons
• Caused by Earth's changing orientation to the
Sun
• Axis is inclined 23½º
• Axis is always pointed in the same direction
• Special days (Northern Hemisphere)
• _______ solstice
• June 21-22
• Sun's vertical rays are located at the Tropic of
Cancer (23½º N latitude)
Relationship of sun angle to the
path of solar radiation
Earth-Sun relations
Seasons
• Special days (Northern Hemisphere)
• _______ solstice
• December 21-22
• Sun's vertical rays are located at the Tropic of
Capricorn (23½º S latitude)
• ___________ equinox
• September 22-23
• Sun's vertical rays are located at the Equator (0º
latitude)
Earth-Sun relations
Seasons
• Special days (Northern Hemisphere)
• ________________ equinox
• March 21-22
• Sun's vertical rays are located at the Equator (0º
latitude)
Earth-Sun relationships
Characteristics of the solstices
and equinoxes
Earth—Moon Interactions
• Average distance from Earth to the Moon is
238,329 miles.
• Moon orbit is elliptical.
• Interactions of Earth, Moon and Sun cause
familiar phenomena…eclipses, phases of
the Moon.
Moon Phases
Phases of the Moon
• When viewed from above the North Pole, the
Moon orbits Earth in a counterclockwise
(eastward) direction
• The relative positions of the Sun, Earth, and
Moon constantly change
• ____________ are a consequence of the motion
of the Moon and the sunlight that is reflected
from its surface
Phases of the Moon
Earth – Moon Movements
• Earth-Moon
• _________ month
• Cycle of the phases
• Takes 29 1/2 days
• ___________ month
• True period of the Moon's revolution around
Earth
• Takes 27 1/3 days
Motions of the Earth-Moon
system
• Earth-Moon
• The difference of two days between the synodic and
sidereal cycles is due to the Earth-Moon system also
moving in an orbit around the Sun
• Moon's period of rotation about its axis and its
revolution around Earth are the same, 27 1/3
days
• Causes the same lunar hemisphere to always face
Earth (tidally locked)
Eclipse
• Simply shadow effects that were first understood
by the early Greeks
• ________– Central completely dark part
of a shadow produced during an eclipse.
• _________– portion of a shadow from
which only part of the light source is
blocked.
Eclipses
• Two types of eclipses
• Solar eclipse (eye of god)
• Moon moves in a line directly between Earth
and the Sun
• Can only occur during the __________ phase
Solar Eclipse
Solar Eclipse Mythology
• Thought a dragon or demon was devouring
the sun. Would bang pots, drums, shoot
guns to frighten spirit away.
• In Tahiti, thought of as a divine cosmic
“love-making”.
• Said to have stopped the battle and led to
peace between the Medians and the Lydians
in 585 BC.
Lunar Eclipse
• Moon moves within the shadow of Earth
• Only occurs during the _________ phase
• For any eclipse to take place, the Moon must be
in the plane of the ecliptic at the time of new- or
full-Moon
• Because the Moon's orbit is inclined about 5
degrees to the plane of the ecliptic, during most
of the times of new- and full-Moon the Moon is
above or below the plane, and no eclipse can
occur
• The usual number of eclipses is _____ per year
Lunar Eclipse
Lunar Eclipse