Download Apparent size (apparent diameter)

Name:________________________________
Unit 9.1: Observations of celestial (sky) objects
1. Think of the sky as a dome.
2. The apparent path of the sun through the sky is an arc.
3. In the U.S. the sun, the moon, and all of the stars appear to rise from the ___________ horizon,
move through the southern sky, and set in the ___________________. (think daily motion disco)
4. The noon sun is ________________ at the zenith (overhead) anywhere in the continental U.S.
5. The noon sun can be found at the zenith on certain dates during the year only between 23.5N
(Tropic of ____________) and 23.5S (Tropic of ________________).
6. If we think of the sky as a dome above us:
a. The stars and planets seem to move counter-clockwise around ___________________.
b. The rate is approximately one revolution (360) per day or ____ per hour.
7. From NYS, the North Star (Polaris) is due north and half way between the horizon and the zenith
at _________ degrees altitude (same as latitude).
8. Constellations are imaginary patterns that help us to remember positions among the stars.
a. The distribution of stars is actually random.
b. The patterns are a human perception.
The Apparent Daily Motion of the Stars
To an observer in the United States, all stars appear to move from east to west in circular paths, or
along parts of circles called arcs. The rate of star rotation (really Earth’s rotation) is 360˚ (full
circle) every 24 hours…or 15˚ per hour. The center of rotation is very near the star of Polaris.
Polaris (North Star)
1. Polaris is the last star in the handle of the ___________ Dipper (Ursa Minor).
2. In the northern hemisphere, the direction towards Polaris is almost exactly due ______________.
3. Polaris is seen at the zenith when you are at the ___________ ____________ (altitude = 90).
4. Polaris is seen at the horizon when you are at the ___________________ (altitude = 0).
5. Polaris has an ___________ of 42 when you are in Washingtonville
 The latitude of Washingtonville is ____N.
Circumpolar Constellations (e.g. The Big Dipper)
1. Never rise or set
2. They “circle” Polaris always staying above the horizon
Star Trails: are made on an over
exposed photograph.
1. Take a picture at night.
2. Leave the camera’s shutter
open for hours.
3. Everything remaining still
(buildings, trees, etc.) will
look normal.
4. As the earth rotates, the
stars leave light trails on
the film.
Unit 9.2: Sun’s apparent path through the sky (Daily rotation – Latitude – Seasons):
1.
2.
3.
4.
Varies with the seasons and with _______________________
The points on the horizon of sunrise and sunset vary with the ___________________.
The length of daylight varies with the ____________ and with your __________________.
The noon sun is much higher in the sky during summer than in winter, but it never passes
directly _______________ (through the zenith) in the U.S.A.
5. The apparent motion of the sun and stars through the day is the result of the west to east
___________________________ (spinning) of the Earth.
The Apparent Daily
Motion of the Sun
To an observer the sun appears
to rise from east and set to
west. In fact it is the earth that
is rotating in the opposite
direction (from west to east).
WEST
EAST
Path of the sun’s apparent
motion in New York on the
solstices and equinoxes
 The strongest rays
from the sun are
those that are most
direct.
 On any given day the
sun’s rays are most
direct (intense) at
solar noon.
 As seasons change
from winter to
summer, the noon
position of the sun
gets ___________
and therefore more
direct (intense).
 As seasons change
from _________ to
____________ the
noon position of the
sun gets lower and
therefore ____ direct.
Unit 9.2: Sun’s apparent path through the sky (cont.):
Planetary Motions:
1. The planets share the daily apparent motion of the sun.
2. Sometimes, the outer planets exhibit retrograde motion as the Earth passes them on the inside.
Apparent Path of the Sun on June 21st
as seen by 4 different observers each at a different latitude
 This shows how each person sees the sun move from sunrise to sunset on June 21st.
 Notice the different apparent paths for the different latitudes.
 The zenith (Z) is the point in the sky directly over the observer’s head (90˚ altitude).
Insolation Review:
1. The changing angle of insolation completes one full cycle per year.
a. Intensity of insolation (maximum at solar noon):
i. Solar noon insolation in the northern hemisphere increases from December 21st
through June 21st. This is opposite in the southern hemisphere.
ii. Solar noon insolation in the northern hemisphere decreases from June 21st through
December 21st. Again, this is opposite in the southern hemisphere.
b. Length of day: (change in number of hours of daylight animation)
i. Northern hemisphere: Length of daylight increases and darkness decreases from
December 21st through June 21st. This is opposite in the southern hemisphere.
ii. Northern hemisphere: Length of daylight decreases and darkness increases from
June 21st through December 21st. This is opposite in the southern hemisphere.
2. The angle of insolation completes one full cycle each day.
a. Insolation increases from sunrise to solar noon.
b. Insolation decreases from solar noon to sunset.
3. Combined the daily and yearly cycles of insolation and the result is…in the northern hemisphere
from December 21st through June 21st:
The shadow of a vertical post
a. Longer day = more hours of insolation each day
indicates how the angle of
b. Higher angle = more intense insolation each day
insolation varies during the
day…the higher the angle of
insolation, the shorter the
shadow and the greater the
intensity. Maximum angle and
intensity occur at solar noon.
Length of Day & Solar Insolation vs. Seasons
The angle at which the sun’s rays strike the Earth’s surface and the length of day change
throughout the year. In the Northern Hemisphere the longest day is June 21st (summer solstice). At
solar noon that day, the angle of insolation is also the greatest (the sun is highest in the sky). The
shortest day and the lowest angle of insolation in the Northern Hemisphere is December 21 (winter
solstice).
On the equinoxes the lengths of day and night are the same everywhere on Earth (Autumnal
Equinox: September 23rd – Vernal Equinox: March 21st). Equinox means equal day and equal night
(12 hours each). At the equator the length of day/night is 12 hours/12 hours all year round.
Solar Insolation & Length of Day vs. Seasons & Latitude
On first day of spring or fall, the most direct noon sun is located at the equator. Everyone will
have 12 hours of day and 12 hours of night.
+
On June 21st, the most direct noon sun is
located at the 23.5˚ N.
On Dec. 21st, the most direct noon sun is
located at the 23.5˚ S.
On June 21st, any location north of the Arctic Circle (66.5˚ N) will have 24 hours of daylight and
south of the Antarctic Circle (66.5˚ S) will have 24 hours of darkness. On Dec. 21st, the day/night
cycle is reversed for each location.
(Note: the equator always has 12 hours of day and 12 hours of night)
Geocentric model of the universe:
(Geo) Earth  (centric) centered
1. ______________ is the center of the
universe and is stationary.
2. The moon, sun, stars, and planets
revolve around ______________ in
crystal spheres.
3. Sunrise and sunset are caused by the
revolution of the sun around earth.
4. This model cannot explain the Coriolis
effect or the Foucault pendulum.
Heliocentric model of the universe:
(Helio) Sun  (centric) centered
1. The ______________ is the center of the
universe and is stationary.
2. The earth, stars, and planets revolve
around the _________ in circular orbits.
3. The moon revolves around the earth
4. The earth rotates on its axis once a day
making the sun “appear” to
_______________________________.
Today’s model of earth in space is most similar to the heliocentric model except:
1. The sun is the center of our solar system not the universe, and it rotates about an axis.
2. Earth rotates about an axis once every 24 hours.
3. Earth’s rotational axis is tilted _________ to a line perpendicular to its orbital plane
All terrestrial and celestial observations can be explained through current model.
UNIT 9-10: Astronomy
Apparent size (apparent diameter)
1. The closer a celestial object is, the larger it’s angular diameter
2. It appears larger because _________________________________________________________
At position A, the sun appears “yeah” big. As the Earth moves
further from the sun in its orbit (position B), the diameter of the
sun appears larger to us. The moon does the same thing.
Evidence that earth rotates
1. The Foucault pendulum
a. A free-swinging pendulum appears to
change direction because the _________ is
rotating.
b. The pendulum swings independently of
earth’s motions because of inertia.
2. The Coriolis effect: The deflection (curving) of
fluids to the ________ in the Northern Hemisphere
A rocket launched from the North
Pole on a course due south along the
meridian of Myrtle Beach, South
Carolina would appear to veer
westward and land near Dallas, Texas.
Actually the Earth is rotating from
west to east 15˚ each hour beneath the
flying rocket.
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UNIT 9-10: Astronomy
Parallelism
 Earth’s axis always points in the same
direction with respect to the sun. At any given
position in Earth’s orbit, the rotational axis is
parallel to any other position in the orbit.
 Throughout Earth’s revolution around the sun,
Earth’s inclined axis and its parallelism are
important in the regular change of seasons and
the change in the length of day and night.
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UNIT 9-10: Astronomy
Universal Law of Gravitation:
1) Every object in the universe that has a mass generates _________________________.
2) Gravity keeps planets from shooting off into space.
3) Gravitational attraction (force) between two objects increases:
a) As mass increases (direct relationship)
b) As distance decreases (inverse relationship)
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UNIT 9-10: Astronomy
Name:________________________________
Orbital Facts: (Kepler’s Laws)
1. All orbits are __________________ with the primary located at one focus.
2. The Earth is a satellite of the ______ with the sun at the primary focus.
3. The _________ is a satellite of the Earth with the Earth at the ______________________ focus.
[ESRT1]
Eccentricity is measurement of
the “flatness” of an ellipse.
1. Be able to calculate the
eccentricity of an
ellipse.
2. Circle: e=0
Flat line: e=1
two
The speed of a satellite
1. Is inversely related to the distance from its primary focus.
2. For example, the _____________ the planet’s distance to the sun, the ___________ it moves.
a. Earth moves “fastest” in January when it is __________ to the sun.
b. Earth moves ____________ in ___________ when it is _____________ from the sun.
(Important: Earth’s seasons are caused by its revolution around the sun and the
tilt of earth’s axis, NOT by its changing distance to the sun!)
3. The outer planets take much longer to orbit the sun than the inner planets. Why?
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UNIT 9-10: Astronomy
Positions of Earth and Sun in our solar system
1) The Sun is NOT at the center of our solar system…it is located at one focus.
2) Earth’s orbit does NOT form a circle…it is a very slight oval (nearly a perfect circle). Earth’s
orbit has an eccentricity of 0.017…a perfect circle is e = 0.0
3) The Earth is closest to the Sun on January 3rd…called Perihelion.
a) Northern Hemisphere – Winter
b) Southern Hemisphere – Summer
4) The Earth is furthest from the Sun on July 4th …called Aphelion.
5) The average distance from Earth to the Sun is 93,000,000 miles.
The difference between 94.5 million and 91.5 million is only 3%.
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UNIT 9-10: Astronomy
6) Unit 10: Earth’s MOON
1. The moon revolves around the earth in an elliptical orbit.
2. The moons period of revolution is about 1 month.
3. The word “month” is from “month.”
“Don’t worry,
dear... Our moon is
just going through a
phase.”
Phases
1. The half of the moon facing the
sun is ALWAYS in light.
2. The half of the moon facing away
from the sun is ALWAYS in
dark.
3. A phase of the moon is OUR
view from Earth of the darkened
and lit-up sides of the moon.
4. Phases of the moon occur
because the changing relative
positions of the earth moon and
sun.
Tides
1. The ocean’s tides are
predictable, and are caused by
the gravitational attraction of
the moon, and to a lesser
extent, the sun.
2. Although the moon is less
massive, it is much closer than
the sun, and therefore has a
greater gravitational effect on
the tides than the sun.
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UNIT 9-10: Astronomy
Turn this page sideways to compare the relative positions of the Earth and Moon in space
to the lunar phase (or illuminated/darkened side of the moon that faces us here on Earth).
Moon’s Orbital Plane
The moon’s orbital plane
around the Earth is tilted
about 5˚ to Earth’s orbital
plane around the Sun.
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UNIT 9-10: Astronomy
Eclipses
1. Solar eclipse: Moon’s shadow is cast on to Earth’s surface (new moon) S – M - E
2. Lunar eclipse: Earth’s shadow falls on the moons surface (full moon) S – E – M
3. Eclipses are predictable and are caused by the alignment of the earth, sun and moon.
4. Eclipses (solar & lunar) DO NOT occur each month…because the moon’s orbital plane is tilted
5˚ to Earth’s orbital plane (as seen in the last diagram on page 17 of this study guide).
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UNIT 9-10: Astronomy
Our Star (called: the Sun)
1) The sun is an average star.
2) The Earth is just one small planet orbiting a typical star among billions in the universe.
3) Sunspots:
a) are visible from earth.
b) are cool, dark patches on the sun’s surface.
c) occur when the sun’s magnetic field loops up and out of the solar surface cooling down that area.
d) increase and decrease in frequency following an 11-year cycle between maximum and minimum.
The Universe is:
1. EVERYTHING: all space, matter, and energy that is in existence.
2. more than 10 billion years old.
The Milky Way and other galaxies
1. Most stars are found in massive groups
called galaxies.
2. There are over 200 billion stars just in
our galaxy, and over 80 billion galaxies
in the universe.
Distances in Space
1. One a.u. (astronomical unit) = 93
million miles (average distance between
the earth and sun)
2. One light year = the distance light can
travel in one year
a. Speed of light = 186,282 miles
per second
b. Number of seconds in a year =
31,536,000
c. 186,282 X 31,536,000 =
5,874,589,200,000 miles (5.9 X
1012 miles)
d. 6 million miles per hour (mph)
e. The light we see left the sun’s
surface about 8 minutes and 18
seconds ago.
3. When we look at distant stars, we look
back in time.
a. Proxima Centauri is the next
closes star to earth = 4.3 light
years.
b. When you look at Proxima
Centauri in the night sky you are
looking at the light it emitted
from its surface about 4 years, 2
months and 20 days ago.
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UNIT 9-10: Astronomy
Just for fun…
Distance to the Sun (at perihelion) = 91,400,000 miles
Speed of Light = 670,615,200 miles per hour
One light year = 5,874,589,152,000 miles
Years to Sun at 60 Miles per Hour = about 173 years
Distance to Proxima Centauri = 25,260,733,354,000 miles
Light Years to Proxima Centauri = 4.3 light years
Days to Proxima Centauri = 1569.5 days (at speed of light)
Years to Proxima Centauri at 60 MPH = 48,060,756 years
Distance to nearest Galaxy = 1,174,917,830,400,000,000 miles
Light Years to nearest Galaxy = 200,000 light years
Days to nearest Galaxy = 73,000,000 (at light speed)
Years to nearest Galaxy at 60 MPH = 2,235,384,000,000 years
http://www.ecstaticfuturist.com/perspective.html
Bang
Origin of the universe and solar system: Big
Theory
(Theory: an explanation for some phenomenon based on observation, experimentation, and reasoning.)
1. All matter in the universe was once concentrated into a very small space.
2. This matter exploded outward (hence: Big Bang) 10-20 billion years ago.
3. The explosion created hydrogen (the simplest element)
4. The universe began to evolve with clouds of hydrogen contracting to form new stars.
5. We can observe the expansion and evolution of the universe continuing today.
Words that begin with “Spect”
1. The electromagnetic spectrum (EMS) is the array of energy given off by a star.
2. The visible light spectrum is the part of the EMS our eyes can see….
 white light (red, orange, yellow, green, blue, indigo, violet)
3. A spectroscope is a scientific instrument that breaks up light from a star into its component
colors in order to identify which elements are present in that star.
4. A spectral line is a bright or dark line found in the spectrum of some radiant sources.
5. A dark line spectrum from a star:
 is like a fingerprint or barcode.
 tells us the composition, temperature, and motion of a star.
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UNIT 9-10: Astronomy
Doppler effect: is a change in the wavelength of energy (shorter or longer) caused by the direction of
that energy with respect to the observer.
 If the source of energy is moving away the wavelength gets longer.
 If the source of the energy is moving closer the wavelength gets shorter.
Evidence for the Big Bang Theory
1. Red shift (Doppler effect): supports the expanding universe theory
a. light from very distant galaxies is observed through a spectroscope.
b. their dark line spectra (barcodes) are shifted to the red side.
2. Cosmic background radiation
a. Sensitive radio receivers pick up radiation from all directions.
b. This is the “noise” of the explosive birth of the universe.
A STAR is born…
1. Gravity causes huge clouds of hydrogen gas and cosmic dust to contract in on itself.
2. This squeezing generates great heat.
3. When hot enough nuclear fusion occurs.
a. Two hydrogen atoms slam into each other and “fuse” together.
b. Helium is created from this fusion.
c. Electromagnetic energy is released.
All stars are not created equal…
1. Stars differ greatly in mass.
a. The more mass of hydrogen a star has, the greater its rate of nuclear fusion.
b. Increase nuclear fusion and a star burns much hotter and faster.
c. Massive stars live hard and die young.
2. Stars differ greatly in luminosity (true brightness).
a. Luminosity is the brightness of stars compared to the brightness of our Sun.
b. Just because a star looks brighter in the night sky does NOT mean it is.
c. More luminous stars may look dimmer than other stars because they are further away.
d. Luminosity corrects for differences in distance.
3. Stars differ greatly in temperature.
a. The color of a star depends on the temperature it is burning at (Blue=hot, Red=cool).
b. Our Sun is a yellow star of average mass, size, and temperature.
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UNIT 9-10: Astronomy
Classifying stars: The Hertzsprung-Russell Diagram
(See RT 15 Luminosity and Temperature of Stars)
1. Stars are classified based on their temperature and luminosity.
2. Plotted on a graph, most stars fall close to a line called the main sequence.
a. If you plotted peoples weight and height, most points would fall close to a line, the “main
sequence.”
b. (in other words, most people are of average height and weight)
The significance of main sequence stars
1. All main sequence stars are undergoing nuclear fusion.
2. A stars place on the main sequence is determined solely by its mass.
a. Mass determines color, temperature, and luminosity for main sequence stars.
b. Our Sun is of average temperature and average brightness.
The significances of stars NOT on the main sequence
1. Used up most or all of its hydrogen.
2. Are in the process of dying.
a. Red Giants…dying stars (huge, but not very dense, very bright, but cool)
b. White dwarfs…dead star (tiny – size of earth, but very dense, very dim, but very hot)
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UNIT 9-10: Astronomy
Our solar system
1. Formed about five billion years ago from a giant cloud of hydrogen gas and debris.
2. Gravity caused this cloud to contract and spin.
3. Most of the material fell to the center, heated up, and ignited a fusion reaction.
4. The debris combined to form the four inner, rocky planets.
5. Leftover gas combined to form the four outer gas giant planets.
Planets differ from stars:
1. Planets are cold and shine by reflecting sunlight.
2. Stars generate their own light through nuclear fusion reactions.
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UNIT 9-10: Astronomy
Planetary characteristics: affected by each planet’s proximity to the sun.
1. The Terrestrial planets are small, rocky, and dense.
a. Mercury, Venus, Earth, and Mars are all similar in size and rocky composition.
b. Formed by collecting leftover debris (collisions & contraction = heat & melting).
c. Melting during formation allowed the liquid plant to separate out into layer (different
densities).
2. The Jovian planets are large, gaseous, and of low density.
a. Jupiter, Saturn, Uranus, and Neptune have a similar gaseous composition.
b. Formed by collecting leftover gasses (contraction = heat but not enough for fusion).
c. Jupiter has more mass than all other planets combined.
d. If Jupiter had more mass it could have become another star.
e. Jupiter gives off more energy than it receives form the Sun.
3. Asteroids, comets and meteors are leftover components of our solar system’s formation.
a. Impact events have been correlated with mass extinction and global climatic change.
b. Impact craters can be identified in Earth’s crust.
c. Asteroids: Composed of iron and/or rock
i. Located mostly in a belt between the orbits of Mars and Jupiter (asteroid belt).
ii. Tens of thousands in number
iii. Called planetesimals (“minor planets”) – may be a destroyed planet
d. Meteors: range in size from huge to dust
i. Small solid particles in space that can be caught and pulled down to Earth by its
gravity.
ii. As they heat by the friction of Earth’s atmosphere, they burn up producing streaks
of light.
iii. If they survive to strike Earth’s surface, they are called meteorites.
e. Comets
i. Form a cloud that surrounds the solar system called the Oort cloud.
ii. Comets are huge balls of dirty, rocky ice.
iii. Comets that escape the Oort cloud are pulled by the Sun’s gravity.
iv. Many are caught in an elliptical orbit around the Sun.
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