Download Earth in space

Earth in space
Topic 3
in Review Book
I. Celestial observations
All
of the objects in our sky
appear to be located on a
dome (hemisphere) that
encircles the earth
This dome is referred to as
the
celestial sphere
a. General Terms
1.
The horizon:
the imaginary line where
the earth appears to meet
the celestial sphere
2. The zenith:
the point on the celestial
sphere directly above an
observer…
90º above the horizon
3.
4.
Altitude: a vertical angle…
the angular distance above
the horizon
Declination: celestial lines of
latitude
The celestial equator is the
reference point
+ declination = north
- declination = south
Azimuth: a horizontal
angle:
the angular distance
measured clockwise from
due north.
6. Right Ascension: celestial
lines of longitude
5.
Right
ascension is labeled in
units of time…
it is given in hours (h),
minutes (m) and seconds (s)
and ranges from 0h 0m 0s to
24h 0m 0s
7.
a.
Constellations: groups of
stars that appear to form a
pattern in the sky
Some stars and
constellations are
circumpolar…
they seem to move in circles
around Polaris…
when photographed, they
create circular star trails
Circumpolar
motion occurs
because Polaris is directly
above our axis of rotation.
The farther north an
observer is located, the
greater the number of
circumpolar stars
Circumpolar motion
b.
c.
Stars/constellations change
their position in the sky
nightly due to the rotation of
the earth and…
seasonally because of the
revolution of the earth
We’ll talk more about these
motions in the next unit…so
stay tuned! 
d. Some Constellations you
should know:
i. The Big and Little Dippers:
 Seen on the horizon in the fall
at the zenith in the spring
The B.D. contains the pointer
stars to Polaris
ii.

Orion:
We only see it in the
winter during “prime time”
viewing
iii.

Summer Triangle:
We only see it in the
summer during “prime
time” viewing
The Big Bang
B. Origin of the universe
The Big Bang theory:
There is scientific evidence
that supports that
approximately 14 billion
years ago, the universe was
a dense concentration of
matter that
expanded explosively…
At this time:
all matter and space was
created and moved outward
in all directions at the speed
of light (300 million m/sec),
masses of gas cooled and
condensed and…
stellar systems formed.
 Evidence of the Big Bang
includes:
1. The uniform age of all of the
galaxies
2. Weak electromagnetic
radiation from the explosion
(cosmic background
radiation) has been
detected
C. The fate of the universe
In
1929, Edwin Hubble
examined the spectra of
distant galaxies
He compared the spectral
lines of far away galaxies to
those of nearby stars
Hubble
knew that when a light
source is moving away from an
observer it’s wavelength
becomes longer…
This results in a shift of its
spectrum towards the red end
conversely, when a light source
moves towards an observer,
there is a shift towards the blue
end of the spectrum
He
found that the nearby stars
had spectral lines similar to
those expected.
But he found that the distant
galaxies showed spectral lines
shifted to the red end of the
spectrum
The
shift towards the red end
of the spectrum indicated that
distant galaxies are moving
away from the earth…
If the shift had been towards
the blue end of the spectrum,
the galaxies would be moving
towards the earth
Hubble’s law
Galaxies
are retreating from
us at a speed proportional to
their distance from us
The expanding universe theory
 proposes
that the universe is
expanding so that objects
(galaxies) move away from one
another
 The galaxies aren’t
expanding…just the spaces
between them
D. Classification of stars
Stars
are classified based on
spectral analysis of their light
This information is organized
on a chart called a
Hertzsprung-Russell diagram
See ESRT page 15
The
H-R diagram is based
upon the relationship
between the luminosity
(brightness) of a star and its
temperature
In general…hot stars tend to
be blue/white and bright…
cool stars tend to be
red/yellow and not as bright
When a star varies from
this generalization, an
inference can be made
regarding where it is in its
life cycle
E. The Life of A Star
Stars
begin as clouds of gas
or dust that gets pulled
together by a developing
force of gravity. As the force
of gravity builds, and the star
becomes hotter, fusion
begins to take place.
Fusion
creates an outward
force that is in opposition to
the inward pull of gravity.
These forces, and how
balanced they are, determine
the life of a star.
Smaller
stars last longer than
massive stars…
Bigger stars are hotter and
undergo fusion much faster …
therefore, the balance
between the forces is upset
sooner.
Nova
Nebula
Red Giant
White
dwarf
Main
Sequence
Star
Black
Hole
Super
Giant
Protostar
Once fuel
begins to
diminish,
the
equilibrium
Is
disrupted
Super
Nova
F. Distances to Stars
The
sun is the closest star to
earth
It is 150,000,000 km away
This distance is equal to
1 Astronomical Unit (AU)
The
next nearest star is
Alpha Centauri
It is ~ 40 trillion km away
This would be ~ 266,666 AU
To
make stellar distances
more manageable, we
convert distances to light
years
This is the distance light
travels in one year!!!
Light
12
9.5x10
travels
km/year
Which is 9,500,000,000,000
(9.5 trillion) km/year
Alpha Centauri is 4.35 ly from
Earth
It
takes the light from the sun
8 minutes and 20 seconds to
reach Earth
Another
unit of distance is a
parsec
Parsec stands for
1 second of parallax
Parallax is the apparent shift
in the position of one star in
relationship to another star
This is equal to 3.26 ly
G. Stellar Brightness
1.
Luminosity is the actual
(true) brightness of a star
This is dependent upon
size:
the larger the star, the more
luminous it tends to be
and temperature:
The hotter the star, the more
luminous it tends to be
2.
Apparent magnitude is how
bright a star appears to an
observer on Earth
This is influenced by the
distance between a star
and the observer
As
distance increases,
the apparent brightness
decreases
This is reported as a
numerical value:
Brighter stars have lower
apparent magnitudes.
Apparent
magnitude can be
reported in negative
numbers
A star with an apparent
magnitude of 6 is the faintest
that can be seen with an
unaided eye
3.
Absolute magnitude is the
brightness a star would
have if it was located 32.6
ly from Earth
This eliminates the effect
that distance has on the
apparent magnitude of a
star
This
is a comparative
brightness and can be used
to determine the relative
distances between stars and
the earth.
H. Galaxies and the Universe
A
galaxy is a system that
contains billions of stars
There are at least a billion
billion galaxies in our
universe
The
sun is located in the
Milky Way galaxy
and is only one star among
100 billion stars!
Neighboring Galaxies
Magellanic
Clouds
the closest galaxies
They are only visible from
the Southern Hemisphere
Andromeda
Galaxy
the closest galaxy visible
from the Northern
Hemisphere
1. Types of galaxies
Galaxies are classified based
upon their shape
 Spiral galaxies:
consist of a central nucleus
with “arms” that trail behind
while the galaxy rotates
The Milky Way is a spiral
galaxy
100,000 ly across
ii.
iii.
Elliptical galaxies:
range in shape from nearly
spherical to lens shaped
Irregular galaxies:
do not have any specific
shape.
The stars are spread
unevenly throughout the
galaxy
II. Our solar system
Consists of:
1 star
8 planets
61 (and counting) natural satellites
thousands of asteroids
millions of meteoroids
numerous comets
Which
all travel through
space in paths called orbits
that are
ellipses with the sun at one
of the foci
a. Models of the universe
1.
Geocentric model:
Earth-centered
Proposes that the earth is
stationary at the center of
the universe
and all of the celestial
objects (sun, moon, planets,
stars) revolve around it.
2. Heliocentric model
Sun-centered
In 1543, Copernicus published a
paper proposing that the sun
was stationary and everything
revolved around it.
Galileo supported this theory
through telescopic observations
3. Evidence of
heliocentrism
a.
Circumpolar motion of
stars:
provides evidence of the
earth’s rotation.
If the earth did not rotate,
star trails would not be
created
b.
Foucault pendulum:
Also provides evidence of
the earth’s rotation.
Jean Foucault created a
free-swinging pendulum
that knocked down
standing pegs which led to
his conclusion that the
earth rotates
Foucault Pendulum
Foucault pendulum 2
c.
Coriolis Effect
The deflection of a freemoving substance to the
right in the Northern
Hemisphere and to the
left in the Southern
Hemisphere due to the
rotation of the earth
d.
Retrograde motion:
The apparent backwards
motion of a planet against
the backdrop of stars.
This is due to the
variations in rates of
revolution
III. Orbital geometry
A. Kepler’s laws of planetary
motion describe the motions
of the planets in their orbits
around the sun.
1. First law
The
planets move in orbit
around the sun in a path that
is an ellipse with the sun at
one of the foci
An
ellipse is a closed curve
that ranges in shape from a
perfect circle to a straight line.
Eccentricity is a measure of
the “out-of-roundness” of an
ellipse
It ranges in value from 0
(perfect circle) to 1 (straight
line)
As
the distance between the
foci increases, eccentricity
increases and the ellipse
becomes more oval
Length of the major axis
Distance between the foci
Now you try!
Calculate eccentricity:
f
3.7 cm
9.2 cm
f
E
= dbf
lma
E = 3.7 cm
9.2 cm
E = 0.40
2. Second law
An
imaginary line joining the
planet to the sun will sweep
out equal areas in equal
amounts of time
Since
the orbit of each planet
is an ellipse with some
degree of eccentricity,
the distance between the
planet and the sun will vary
throughout its revolution
 Kepler’s
law says that the areas
covered each day by the planet
will be the same, but the
distance traveled will differ
This results in variations in the
velocity of revolution
When
the planet is closer to
the sun,
the distance to travel is
greater,
so the velocity has to be
greater
When
the planet is farther
from the sun,
the distance to travel is less,
so the velocity is less
In summary
Orbital
velocity is
Greatest when the planet is
closest to the sun
and
least when the planet is
farthest from the sun
D
C
A
B
A = perihelion
= closest to the sun
C = aphelion
= farthest from the sun
3. Third law
A
planet’s period of revolution is
directly related to its distance
from the sun
as distance from the sun
increases
period of revolution increases
This
difference in rate of
revolution results in
retrograde motion
which is seen when the earth
passes a planet farther from it
causing it to look like it is going
backwards
B. Gravitational attraction
Sir
Isaac Newton stated
Every object in the universe
is attracted to every other
object in the universe.
This attraction is called
gravity
Force of gravity α m1 m2
d2
Changing distance would have the
greatest effect on gravity
Increasing
mass
Increases gravity
Increasing distance
Decreases gravity