Exam #1
Study Guide
(Note this is not all the information you need to know
for the test, these are just SOME of the main points)
Moon Phases
• Moon is always ½ illuminated by the Sun, and the sunlit
side ALWAYS faces the sun
• New Moon is when the moon is between the Earth and
Sun, it is highest in the sky at noon. The New Moon is
the only time a solar eclipse can happen.
• Full Moon rises at sunset, and sets at sunrise. A lunar
eclipse can happen during a full moon.
• Waxing (“increasing”)
• Waning (“decreasing”)
• Order: New Moon, Waxing crescent, first quarter moon,
waxing gibbous, full moon, waning gibbous moon, third
quarter, waning crescent --- REPEAT next month
Eclipses
• Lunar eclipse- occurs when the earth
“shades” the Moon as it passes between
the moon and sun, during a full moon
• Solar eclipse- occurs when the moon
passes in front of the sun, blocking the sun
from view from earth, during a new moon
Newton’s Laws
• 1. the law of inertia, a body remains at rest, or moves in
a straight line at a constant speed unless acted upon by
a net outside force. (an outside force would be
something exerted on the body other than your body
itself)
• 2. F=ma the acceleration of an object is proportional to
the net outside force acting on the object. (the harder
you push on an object, the greater the resulting
acceleration)
• 3. Whenever one body exerts a force on a second body,
the second body exerts an equal and opposite force on
the first body. (Standing on the ground, you weigh 110
pounds, the floor is pushing up 110 pounds, equal force)
Newton’s law of Gravity
•
•
•
•
•
Fgravity = G (m1m2/r2)
G = gravitational contast
m = masses of the two objects
r = the distance between the two
Ex: How much would you weigh on a
planet that has the same mass as Earth
but has ¼ the radius (r)?
– (Answer on next slide)
ANSWER
• You would weight 4 times more than you
do on Earth
Gravity
• Newton’s law of gravity explains
why the planet rotate the sun in
a elliptical manner without
falling out their orbits
Diurnal motion
• Diurnal- means having a period of ONE day
• Stars rise in the east, and set in the west
• The diurnal, or daily motion of the stars occurs
b/c the earth rotates once a day around an axis
from the north pole to the south pole
• The stars will slowly shift throughout the year,
approximately FOUR minutes EARLIER each
night.
– This is because of the rotation of the Earth around the
Sun
Seasons
•
•
•
•
•
•
The sun heats the Earth’s surface
The closer the sun the warmer the surface
It is NOT Earth’s orbital eccentricity that effects the seasons
The seasons are caused by the 23 ½ degree tilt of the earth
The sun stays high in the midday sky in summer
The sun is low (not as direct) in the midday in the winter
• March 21- sun crosses northward across celestial
equator at the vernal equinox and marks beginning
of spring,
• -Sep. 22- sun moves southward across celestial
equator called autumnal equinox
Retrograde motion of planets
• When observed from one night to the next, a planet appears to move from
West to East against the background stars most of the time.
• Sometimes it will appear to reverse direction. For a short time, it moves
from East to West against the background constellations.
• This reversal is known as retrograde motion. All planets exhibit this
behavior as seen from Earth. It is due to the relative motion of Earth and
the planet.
Blackbody radiation
• A perfect blackbody does not reflect any light
at all, it absorbs all light. The Sun is an
example of blackbody radiation
• The higher an objects temperature, the
shorter the wavelength (Wein’s Law)
• Stefan- Boltzmann law states that a
blackbody radiates electromagnetic waves
with a total energy flux (F) directly
proportional to the fourth power of the Kelvin
temperature (T) of the object
• Engery flux is how rapidly energy is flowing out of the
object
• The amount of energy emitted by a blackbody depends
on both its temperature and its surface area (the larger
the object, the more heat it will radiate)
The Sun is like a Blackbody
Question
• If you double the temperature of an object
from 300K to 600K, what would be the
energy emitted from the object’s surface
each second?
Answer
• Each second would increase by a factor of
2, therefore 24= 16 (Stefan-Boltzmann
law)
Telescopes
• A refracting Telescope- consists of a large
diameter objective lens witha long
focal length and a small eyepiece lens of
short focal length. the eyepiece lens
magnifies the image formed by the objective
lens in its focal plane.
(astrnomers want to view an image so they
add a second lens to magnify the image
formed in the focal plane, called a refracting
telescope or refracting)
Telescopes continued…
• Angular resolution- The angular resolution of a telescope indicates
the
sharpness of the telescopes image. To determine the angular
resolution of a
telescope pick out two adjacent stars whose separate images are
barely
discernible the angle between the stars is the telescopes angular
resolution,
the smaller that angle the finer the details can be seen and the finer
the
image.
One factor limiting angular resolution is diffraction which is the
tendency of
light waves to spread out when they are confined to a small area like
the lens
or mirror of a telescope.
Magnification
• The amount of magnification depends on the focal length of the
primary and the eyepiece (The smaller the eyepiece, the
greater the magnification)
• A hot opaque body (blackbody)
produces a smooth
continuous spectrum
– Example: stars
• A cool transparent gas in front
of a source of a continuous
spectrum produces an
absorption-line spectrum
– Example – planetary
atmospheres, solar photosphere
and chromosphere
• A hot transparent gas radiates
an emission-line spectrum
(against a dark background)
– Example: the solar corona
Kirchoff’s Laws
Ancient Astronomers
Ancient astronomers knew
that the earth was a
sphere and believed it was
the center of the universe
• Aristotle dismissed the
heliocentric system he saw
because he saw no
parallax
• Believed the heavens were
unchangeable
Copernicus
• (1473-1543) –
Polish scientist
who Reproposed
heliocentric
theory and put
the Sun at the
center, but still
believed the
orbits of the
planets were
circles +
epicycles
• Heliocentric
Model
Ptolemaic system
• Thought of by Ptolemy. Ptolemy (127- 145ad) Egypt -Used the concept of Epicycles to explain
the motion of the Sun and planets
• Said that each planet moved in a small circle, or
an epicycle, whose center turns in a larger circle
(the deferent), rotating counterclockwise
• Theory is flawed!
Tycho Brahe
• (1546-1601), Danish
• -Observed a supernova, and
periodic comets
• – Proof that the stars and planets are not
constant, as the ancient astronomers
believed
• -Best pre-telescope observer
Galileo
•
•
•
•
•
•
•
•
•
•
•
(1564-1642), Italian
-Used telescope to view Jupiter’s moons, lunar mountains, and
sunspots
– Phases of Venus
• Experiments on motion
– Including attempts to measure the speed of light
– Famous gravity experiment using the leaning tower of Pisa
-Galileo also discovered four moons, now called the Galilean
satellites, orbiting Jupiter
Phases of Venus- Galileo’s observations of Venus’s gibbous (“fullish”) phase definitively ruled out Ptolemy’s geocentric model
Galileo discovered that the higher an object is dropped, the greater its
speed when it reaches the ground
- All falling objects near the surface of the Earth have the same
acceleration (9.8 m/s2)
-The acceleration of gravity on the surface of other solar-system
bodies depends on their mass and radius
Kepler’s Laws
•
1. The orbits are ellipses
–
–
–
•
2. A planet’s speed varies as it moves around its elliptical orbit
–
–
•
- The planets move about the sun in elliptical orbits with the Sun
at one foci of the ellipse
- The Semi-major axis is ½ the “long” width of the ellipse
- Eccentricity – a measure of how oblong an ellipse is.
- The Planet sweeps out equal areas of the elliptical orbit, in equal
time intervals
- The planet moves fastest when it is closest to the Sun and
slowest when it is farthest away
3. The orbital period of a planet is related to the size of its
orbit
–
–
–
–
–
–
–
- The square of a planet’s period (P) is proportional
- To the cube of its semi-major axis (a).
- The farther a planet is from the sun, the longer it
takes to go around the sun
P2 = A3
P= period (in years)
A= semi- major axis (in AU)
only applies to planetary motion about the sun
Isaac Newton
•
•
•
•
(1642 – 1727)
Developed the Laws of Motion
Discovered the law of gravity
Used physics to derive Kepler’s 3rd Law
Units
• Common Units Used:
• Distance- AU for between planets, 1AU=distance from
earth to sun
•
Km- size of features on planets
• Mass- kg
• *mass is different from weight, weight is force exerted by
gravity
• Speed- km/s
•
Speed of light:
3 x 108 m/s
• Temperature- Kelvin, Centigrade, and Fahrenheit
• Distance Traveled= speed x time
• D=vt
Planet order
• Layout of the Solar System starting from sun- Mercury, Venus ,
Earth , Mars , Jupiter , Saturn , Uranus , Neptune , Pluto
Terrestrial planets
• The first four are Terrestrial Planets which
are set apart because they are
small, rocky materials containing iron,
oxygen, silicon, magnesium, nickel, and
sulfur. with high density.
Jovian planets
• The outer four are the Jovian Planets
which are large and mostly composed of
helium and hydrogen are have a low
density.
Question
• What does it take for a planet to have
active volcanoes?
Answer
• -requires heat hot after planet formed
- Big planets cool slower
- Big terrestrial planets are active
longer
- Fewer craters
- more likely to have active volcanoes
Question
• What does a planet need to have an
atmosphere?
Answer
• -Requires Gas
-gas must be cool enough to not escape
-must have enough gravity
-Big cool planets are more likely to have
an atmosphere