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ASTRONOMY
• The study of celestial objects, space, and the
universe
• Considered one of the oldest disciplines of
science
• 3,000 – 4,000 years old
CELESTIAL MOTION
• The path a planet follows around the sun is
called an ?
ORBIT
• The orbital movement of a celestial body
around an object is called?
REVOLUTION
• The spinning or motion of a celestial body
around an axis is called?
ROTATION
HISTORY
• Utilized repeated observations of the night
sky with the naked eye
• Played a significant role in the development
of civilization, used to develop the calendar
and understand the seasons
HISTORY
• As civilization progressed astronomical
observatories were constructed
• Led to detailed maps of the night sky and
ideas about the motion of the planets, Sun,
Moon, and Earth.
ARISTOTLE
• Described the universe as a series of spheres
containing the planets and Sun rotating around the
Earth with the stars fixed against the background
• “Motionless Earth” idea based on the philosophical
idea that if you feel no motion there is no motion
• Constellations did not appear to change position or
size, no apparent parallax.
PARALLAX
• Is the change in the observed position of an
object due to the change in location of the
observer.
• Planets appeared to move position in the
night sky, while stars did not.
• Stars too far away for a noticeable change
in position with the naked eye
PTOLEMY
• 140 A.D., 5 centuries after Aristotle
• Developed a mathematical model based on
Aristotle’s teachings
• Ptolemaic/Geocentric Model
GEOCENTRIC MODEL
• Earth is fixed at or near
the center of the universe
• Planets and the Sun move
along a perfect circular
path
• Planets also follow a
circular path, epicycle,
that is centered along the
circular path around the
Earth
Abyss.uoregon.edu
COPERNICUS
• Challenged the Geocentric Model in the
1500’s
• Proposed the Heliocentric Model, planets
follow circular paths around the Sun, not
the Earth.
• Maintained classical concept of uniform
circular motion
HELIOCENTRIC MODEL
• Recognized as the
“Copernicus
Revolution”,
placing the Earth
along a similar
orbit to that of the
other planets.
• Helped explain
Retrograde
Motion
Stisci.edu
RETROGRADE MOTION
• When planets seem to move in the opposite
direction across the night sky
• Occurs because the planets move around the
Sun not the Earth
• The difference is speed also affects
Retrograde Motion but did not fit the
classical uniform circular models
Redorbit.com
KEPLER
• In the early 1600’s abandoned the classical
ideas of the circular and uniform motion of
the planets
• Studying the motions of Mars discovered
the planets move in an ellipse rather than a
circle
• Noticed that the speed of Mars was not
constant, but varied along its’ path
ELLIPSE
KEPLER’S LAWS OF
PLANETARY MOTION
1ST LAW Planets orbit the sun along an
elliptical path
• Ellipse is an oval-like shape drawn around
two focus points, foci. The distance from
one focus to any point on the ellipse and
then back to the other focus is a constant
• The closer the foci the more circular the
ellipse becomes, most planets are nearly
circular
KEPLER’S LAWS OF
PLANETARY MOTION
• 2nd LAW Planets move faster along their
elliptical path the closer they are to the sun
KEPLER’S LAWS OF
PLANETARY MOTION
3rd LAW The farther a planet is from the sun,
the longer it takes to complete the elliptical
orbit
• The semi-major axis is the average distance
from the planet to the sun
KEPLER’S LAWS
• All of the laws are empirical, based on
observation and data rather than theoretical
• Kepler never knew what held the planets
along their orbits or why they continued to
revolve around the sun
MODELS
• Used to display, represent, and demonstrate
the structure and behavior of the Cosmos
• Allow scientists to test and observe
behaviors on a smaller scale
• Models of our Solar System
TOOLS & TECHNOLOGY
• Astronomer’s study the light that reaches
Earth from distant objects in space
• Light is a form of electromagnetic
radiation
• Electromagnetic Radiation is a form of
wave-like energy emitted by the
acceleration of a charged particle by a force
ELECTROMAGNETIC
WAVES
• Do not require a medium, can travel in
space
• Travel at a speed of 300,000 km/s through
space, speed of light.
• Represents a spectrum of different
wavelengths
ELECTROMAGNETIC
SPECTRUM
R O Y
red
orange yellow
G.
green
B I
blue
indigo
V
violet
TELESCOPES
• Used to aid
astronomers in the
collection of light
normally not visible to
the naked eye.
• collect more light
• over a longer period of
time
• better image from
space
Popularmechanics.com
SATELITES & PROBES
• Atmosphere blocks certain wavelengths of
electromagnetic radiation
• Why does this matter?
Nasa.gov
How do they do it???
Nasa.gov
ORIGIN OF THE UNIVERSE
Big BANG Theory
1. Expansion of a single unstable dense
collection of matter and space
2. Gases, dust, particles and energy exploded
outward
3. Gases and particles cooled/condensed into
planets, stars, & galaxies
4. Matter and space still expanding out from
explosion
5. Red Shift demonstrates present day expansion
RED SHIFT EXPANSION
• Light observed from distant galaxies have light shifted
toward the red side of the spectrum.
• The shift toward “red” is due to an increase in wavelength
due to the DOPPLER EFFECT
UNIVERSE
GALAXIES
SOLAR
SYSTEMS
MILKY WAY GALAXY
• “via lactae” latin for Milky Way
• “Milky” band appearance created by diskshape of our galaxy viewed from within
• Millions of stars and planets, including our
solar system
• All orbit the proposed “black-hole” center
Our Solar System
• Formed by a Solar Nebula
(4.6 bya)
• Hot dense center of cloud
condenses into the Sun
• Disk-like cloud of gases
surrounding Sun has various
regions of temperature
• Different elements cool,
condense, and combine in
different regions
Universetoday.com
THE SUN
• Largest object in
our solar system
• 99% of the mass
of our solar
system
• Large mass
= strong
gravitational
force, resulting
in the orbits of
all the planets
GRAVITY
• Gravitational force is a force of attraction
dependent on the mass and distance
between two objects.
• Described by Sir Issac Newton in 1687 as
the Law of Universal Gravitation
THE SUN
• The sun’s energy comes from Nuclear
Fusion
• Nuclear Fusion – small light nuclei
(hydrogen atoms) are combined to form
larger nuclei (helium atoms) resulting in the
release of ENERGY
• E = mc2
NUCLEAR FUSION
SUN’S ATMOSPHERE
• Photosphere
– 6,000 K
– Surface, yellow-color
• Chromosphere
– 30,000 K
– Only visible during solar eclipse, reddish
• Corona
– 1- 2 million K
– Only visible during solar eclipse, white
– Solar Winds
SOLAR WIND
• Originate in the
Corona
• Stream of
charged atoms
known as “ions”
• Collide with
Earth’s magnetic
field creating the
Auroras.
Harvard.edu
Nationalgeographic.com
SOLAR ACTIVITY
• Changes in the Sun’s
atmosphere
• 11 year cycles
• Sunspots and Solar
Flares
• Interfere with phone,
TV, and radio
reception
• Affects climate on
Earth
Nasa.gov
INNER PLANETS
– terrestrial planets
– dense, small, have
solid rocky
surfaces, metal
cores
OUTER PLANETS
– Jovian Planets
– less dense, large, gaseous, thick
atmosphere
“My Very Eager Mother
Just Served Us Noodles”
• 3rd planet from the Sun
• Nearly circular orbit
• Moderately dense
atmosphere
– 78% Nitrogen 21% Oxygen
– Greenhouse Effect
• Water
– Solid, Liquid, Gas
EARTH
EARTH’S MOTION
• Rotation
– Earth rotates around an axis
– Night and Day
– 24 hours
• Revolution
– Earth revolves around the Sun, Heliocentrism
– Seasons
– 365 days = 1 year
EARTH’S ROTATION
•
•
•
•
•
Rotates along a tilted axis, 23.5o
Rotates West to East
Mean Solar Day = 24 hours
15o / hour rotation
The “day” is getting longer due to tidal
friction
• inertia
Astro.psu.edu
EARTH’S ROTATION
• Precession – a slow gradual change in the
orientation of a rotational axis
• “wobble of a top”
• Due to the gravitational influences of the
Sun, Moon, and other celestial bodies.
• Would it affect Polaris, the North Star?
Geography.hunter.cuny.edu
EARTH’S ROTATION
• The gravitational forces of the Sun and
Moon vary over time
• Creates a variation in the speed of
precession.
• Variation in gravitational forces and the
speed of precession create a NUTATION of
the Earth’s axis
EARTH’S ROTATION
• Nutation – a
slight variation
in the precession
of the Earth’s
rotation
• From nutare,
latin for “to nod”
• “nodding” due to
the Moon
Ucar.edu
EARTH’S REVOLUTION
• Revolves around the Sun in an almost
circular orbit
• 1 AU = 150 million km
• one revolution = 365 days
• one revolution = one orbital period
• Seasons
• Hemisphere that tilts towards the
Sun has summer
• (more direct sunlight)
• Hemisphere that tilts away from the
Sun  has winter
• (less direct sunlight)
• summer solstice: longest sunlight
hours of the year
• June 21st-first day of summer
• winter solstice: shortest sunlight hours
of the year
• Dec. 21st- first day of winter
• spring equinox: equal amounts of
day/night hours
• March 21st- first day of spring
• fall equinox: equal amounts of
day/night
• Sept. 21st- first day of fall
EARTH’S REVOLUTION
• The Earth does not revolve around the
center of the Sun!
• The Earth revolves around the center of
mass of the Solar System
• This center of mass which objects orbit is
called the barycenter
• The barycenter of the Solar System lies
within the Sun
Barewalls.com
Lhup.edu
THE MOON
• Earth’s only
natural satellite
• Moon’s diameter
27% of the
Earth’s diameter
• Impact Theory – formed by a collision
between Mars-sized object and the proto-Earth
Universetoday.com
Nasa.gov
THE MOON
• Synchronous Rotation – the Moon’s rotational
period is equal to it’s orbital period.
• 1 rotation = 1 revolution
• One complete revolution or “orbital period” is
27.3 days
• Lunar Month 29.5 days due to position in relation
to the Sun
THE MOON’S GRAVITY
• Gravitational influence on Earth decreases
the “bulge” along the equator
• Gravitational
influence on the
oceans, creating
the tides.
Lhup.edu
TIDES
• Due to the gravitational influence of the
Moon and the Sun
• Moon and Sun pull in perpendicular
directions, Neap tides.
• Moon and Sun pull in same/opposite
directions, Spring tides.
ECLIPSES
• Moon passes directly between the Sun and
the Earth blocking our view of the Sun
Solar Eclipse
• Moon passes through the Earth’s shadow
Lunar Eclipse
Nasa.gov
Why are solar and lunar eclipses so rare????