what causes day and night
rotation of the earth on its axis
how does the sun appear to move in the sky in the course of a day
east to west because of earths rotation
what time of day does the sun transit the meridian
noon
what happens to the earth in one year
it orbits the sun one time
why do we have seasons
tilt of the earth's axis (not changing distance from the sun)
how is the earths axis tilted when we have summer in the northern hemisphere
with the north pole toward the sun
what season is it in the southern hemisphere when it is summer in the northern hemisphere
winter
winter begins
december 21 = nights longer than days
spring begins
march 21 = days and nights equal length
summer begins
june 21 = days longer than nights
fall begins
september 21 = days and nights equal length
what happens to the moon in 1 month
it moves once around the earth
what causes the phases of the moon
sun is lighting different fractions of the part of the moon that we see
what is the order of the phases of the moon
new - first quarter - full moon - third quarter - new
when is the full moon visible
only at night
when is the new moon visible
the new moon is visible during the day and sets at sunset
how are the sun earth and moon positioned when it is new moon
sun - moon - earth
seasons would not happen if...
the earths axis was not tilted
how are the sun earth and moon positioned when it is full moon
sun - earth - moon
what is a solar eclipse
moon blocking the suns light
how are the sun earth and moon positioned when it is a solar eclipse
sun - moon - earth
what is a lunar eclipse
earths shadow on the moon
how are the sun earth and moon positioned when it is a lunar eclipse and what phase is the moon in?
sun - earth - moon; full
why dont eclipses occur every month on earth
the moon orbits the earth in a different plane than the earth orbits the sun
constellation
big areas of sky = anything in that region is part of the constellation = there are 88 of them
are stars in the same constellations close to each other?
stars in the same constellation are likely to be at very different distances from us; not necessarily close to each other though they appear close projected on our sky
when is orion the hunter visible?
orion the hunter is visible in the winter because as the earth travles around the sun its nighttime side faces different regions of space
ecliptic
location of the sun with respect to the stars
zodiac constellations
along the orbit of the earth around the sun
the sun is inside a zodiac constellation at all times
in each one for a month each year during that time you cannot see that constellation since it is behind the sun all day and not on the nighttime side of earth
sun was in the constellation of your zodiac during
the month you were born (you can't see it at night at that time of year)
winter zodiac constellations
ones opposite the sun in the winter
summer zodiac constellations
ones opposite the sun in the summer
summer triangle
three prominent stars visible in the summertime
photon
a particle of light
what is the electromagnetic spectrum in order from high energy to low energy
gamma rays, x-rays, UV, optical, IR, radio
for radiation
energy high - frequency high - wavelength low
wavelengths of radio waves
meters and centimeters
wavelengths of visible light
angstroms (ten billionths of a meter)
wavelengths of xrays
even smaller
prism splits light into different colors by
bending different wavelengths by different angles
blackbody spectrum
higher temperature = more light = peak to shorter wavelength
what kinds of radiation get through the earth's atmosphere
optical and radio
continuous spectrum
light at all wavelengths
absorption lines
dark lines in spectrum at certain wavelengths; produced by gas cloud blocking light source; atom absorbs photon and electron moves from lower to higher level
emission lines
bright lines at specific wavelengths; produced by hot gas; atom emits photon and electron moves from higher to lover level
different chemical elements have different energy levels that
their electrons can occupy and thus give rise to different spectra
redshift
as source moves away the wavelength gets longer and lines in spectrum shift to the red, frequency decreases
blueshift
as source approaches the wavelength gets shorter and lines in spectrum shift to the blue, frequency increases
doppler effect
analogous effect for sound
reflecting telescopes
mirror
refracting telescopes
lens
important qualities of telescopes
light gathering power, angular resolution, and the quality of the instruments (magnification not so important)
telescopes collect light in proportion to the area of the mirrors:
area of circle proportional to diameter squared
a diameter 2 meter telescope collects 2x2=
4 times as much light as a 1 meter telescope 1x1= 1
angular resolution
can separate two nearby light sources with good angular resolution = earths atmosphere limits angular resolution "seeing" = makes stars twinkle
magnify
see more detail but also observe smaller area of the sky
telescopes above earths atmosphere are better because
certain kinds of radiation cannot get through atmosphere (x-ray, gamma-ray, UV, IR); give clearer images without atmospheric blurring, better seeing
telescopes above earths atmosphere are worse because
hard to get a very large collecting area launched into space
geocentric solar system
earth at center = ancient greek model
heliocentric solar system
sun at center = modern correct model
retrograde loop
planets move eastward from night to night then slows down and moves westward from night to night and then back to eastward. this happens for planets that orbit the sun slower than earth does so that as the earth overtakes them in their orbits they appear
newtons laws 1
an object at rest or in motion in a straight line as a constant speed will remain in that state unless acted upon by a force (if sun disappeared the earth would continue in the direction it was traveling in its orbit at that time)
newtons laws 2
the acceleration of a body due to a force will be in the same direction as the force with a magnitude directly proportional to its mass. force = mass x acceleration (smaller mass will move faster if same fore is applied to it.)
newton laws 3
for every action there is an equal and opposite reaction (sun exerts force on planets and they orbit it = planets exert equal force on sun, but it only moves slightly because of its relatively large mass)
newtons law of universal gravitation
force of gravity proportional to (mass of object 1) x (mass of object 2) divided by distance between two objects squared
Question: What time do you think it will be when the Sun is on the meridian?
noon
What causes the Sun to follow a path from East to West across the sky?
the earth rotates counterclockwise
What season is it in Sydney, Australia in August?
winter
1. Smekz is a planet whose rotation axis is NOT tilted with respect to its orbital plane. What are the seasons like on our planet?
There would be no seasons
2. If your Earth had its orbit changed so that at all points along its orbit it was always the same distance from the Sun (circular orbit), how would this affect the seasons on Earth?
same as they are now
1. How does the number of hours of daylight change on Smekz from season to season?
A: Every day there are the same number of hours of daytime and nighttime.
2. On Earth, on which day do you expect the length of daytime to be roughly equal to the length of nighttime?
March 21
1. If you could see the Sun and the stars at the same time, what would you see during one of Earth's years?
C: The Sun is in front of a different group of stars every season.
2. What is the reason for the seasons on Earth?
C: Earth is tilted with respect to the Sun by about 23.5 degrees.
How much of the total surface area of the Moon is illuminated by Sunlight during the Full Moon phase?
one half
At approximately what time does the third quarter Moon rise?
midnight
Approximately two weeks after a Solar Eclipse, what phase will the Moon be in?
full
1. How often does Smekz experience a solar eclipse?
B: Once every orbit of its moon (its month).
2. What phase is Smekz's Moon experiencing today?
new
1. When will Smekz next experience a Lunar Eclipse?
D: 15 of its days from now.
2. Your Moon was Full on May 1, 2007. When will you expect it to next be in the First Quarter phase after this Full Moon?
B: May 22.
1. If we took you right now to Smekz's Moon, what phase would Smekz appear from the Moon? (Hint: You need to remember what phase Smekz's Moon is in today.)
Full Moon
2. At what time will Smekz's Moon set tonight?
Sunset
During what time of year is Orion most prominent in the sky over Pennsylvania?
Winter
One version of Orion's story goes that Scorpius was the scorpion that killed Orion, and now they are never found in the sky at the same time. What month is best to observe Scorpius?
July
1. From Earth, in which constellation might you find the planet Saturn?
Taurus
2. The constellation Virgo is halfway between Gemini and Sagittarius in the Zodiac. When is the best time to see Virgo in the night sky?
Spring
1. Why don't we see the constellation Orion all year?
D: As the Earth orbits the Sun, its nighttime side points to different constellations at different points along its orbit.
2. What does the constellation Cygnus consist of?
D: All of the stars and other objects that lie inside the agreed upon boundary lines.
1. What is the significance of the stars in the Summer Triangle?
E: They are three of the brightest stars in the summer sky.
2. When is the best time for you to be able to see the constellation that is your sign of the Zodiac?
E: At midnight six months after your birthday.
If you were going to design a camera to detect the animal that is getting into your garbage cans in the middle of the night, you would want it to:
detect infrared light
1. Star A is 4000 K, and Star B is 8000 K. Which of the following is true about these two stars?
E: Star A will give off less total light than Star B
2. Why can gamma-rays be used to treat cancer patients?
C: They carry a lot of energy and can actually kill cancerous cells.
1. Why do incandescent light bulbs feel so hot?
A: They emit a lot of infrared light.
2. What do you expect the spectrum of an object that is 1,000,000 Kelvin to be like?
A: It should peak at X-ray wavelengths.
1. Why do firemen use infrared cameras to look into smoke filled buildings?
E: They can see through the smoke to look for people inside the room.
2. I detect a star giving off more ultraviolet light than green light. What property of the star can I estimate with this information?
B: Its temperature
A star is a hot, dense gas surrounded by a cooler, low density atmosphere. What type of spectrum will a star create?
absorption spectrum
Why does a neon light appear red?
C: It gives off an emission spectrum with mostly red spectral lines.
Why does this gas cloud in the constellation Orion appear red?
D: The cloud must be made of some element or elements that give off red emission lines.
1. The electrons in a cloud of hydrogen gas are making the transition from excited states to the ground state. What does the spectrum of this cloud of gas look like?
C: It will consist of a few bright emission lines at very specific wavelengths.
2. The spectrum of an oxygen lamp looks different than the spectrum of a sodium lamp because:
C: each atom has a unique set of electron orbits
1. One of the lines of Hydrogen has a wavelength of 486.1 nm. If a cloud of Hydrogen gas is moving towards us at 100 km/sec, what will we detect?
A: An emission line in the cloud's spectrum with a wavelength shorter than 486.1 nm.
2. I take the spectrum of a bright source of light in space and find it has absorption lines due to helium. What is the source of the helium lines in the spectrum?
D: There is a cloud of gas containing helium between us and the light source.
1. An electron in a sodium atom absorbs a photon of light and moves to the first excited state. What will happen next?
B: The electron will eventually emit a photon with the same energy as the one it absorbed.
2. How do we know that interstellar gas clouds contain Oxygen?
E: They give off emission line spectra that have lines with the same wavelengths as Oxygen does on Earth.
When you magnify an object with a telescope, what else happens to your view of the sky?
B: Your field of view gets smaller, so you can only see a small area of sky.
If the Hubble Space Telescope's opening is only 1/4 the size of the Keck Telescope, among the biggest telescopes presently on the surface of Earth, which of the following is true?
B: The Keck telescope can observe objects fainter than Hubble.
Since the Hubble Space Telescope is in orbit around the Earth but the Keck telescope is on Mauna Kea in Hawaii, which of the following is true?
A: The Hubble will be able to take sharper images than Keck.
If you had 1 billion dollars of NASA's money to fund a telescope, which would you choose?
E: A combination x-ray and gamma-ray telescope in space.
1. The faintness of an object that a telescope can observe is mostly determined by the?
A: diameter of the opening of the telescope
2. In what ways does a 5 meter telescope outperform a 1 meter telescope?
B: Its images are 25 times brighter than a 1 meter.
1. Even the largest ground-based telescopes have resolution restrictions imposed by:
C: atmospheric blurring of images
2. Our atmosphere is completely transparent to ? and ? radiation, which enables observations of these wavelengths from the ground. All other wavelengths must be observed from space.
E: visible / radio
1. Compared to Keck, Hubble Space Telescope has:
D: better resolution but worse light gathering power
2. What is the primary difference between a refracting telescope and a reflecting telescope?
C: A refractor uses a lens to gather light, while a reflector uses a mirror.
From our point of view on Earth, how do the planets appear to move compared to the stars?
D: The Planets sometimes drift eastward and sometimes westward with respect to the stars.
The Earth is approximately 6400 km in radius. If you were in orbit in the Space Shuttle 150 km above the Earth, the force of gravity you feel from the Earth would be:
A: slightly weaker than when you are standing on Earth
The force of gravity by the Sun keeps the planets in orbit around it, but how do the planets affect the Sun?
B: They exert an equally strong pull on the Sun, causing it to move slightly.
1. If the Earth was moved twice as close to the Sun, how would the force of gravity by the Sun on the Earth change?
A: It would be four times stronger.
2. What did Newton's Law of Universal Gravitation tell us about how gravity works?
D: The force of gravity from the Sun will be stronger on a larger mass object.
1. If I apply exactly the same amount of force to a pebble and a boulder, what will happen?
C: The pebble will move faster.
2. What would happen to the Earth if the Sun's gravity turned off instantaneously?
E: It would continue to move in a line in the same direction it was moving when the gravity turned off.
1. How can you observe a retrograde loop of Mars?
E: Over the course of a few months, the planet will appear to change directions with respect to the stars.
2. Why does retrograde motion of the planets happen?
E: When Earth overtakes a planet in its orbit, the planet will appear to move backwards for a short time.
Orion the hunter
green clouds, ancients believed his belt to be the back of a turtle where all three stars symbolize a god to be true, one red star, one blue star, hunts the lion
Cygnus the swan
lies in the milky way during the summer you can see it, northern cross, one of the triangle stars is in it's tail. my head is a double star one blue but pale, one nebula was born from a stars death trap, see it in the summer winter it is not
ursa major the great bear
very well known constellation never sets in the northern sky, native americans and greeks wrote legends about it, one points to the north start
Scorpius the Scorpion
across the sky from great orion, he killed the person who hunted the lion, my alpha star so large and red rivals the red planet, near the center of the milky way, My star clusters send many a ray To Earth, revealing sights so wondrous!
compare the frequency of an xray with that of visible light
the xray has a larger frequency than visible light
a solar eclipse can occur only
during a new moon
how do the stars move over the course of a night
east to west
eclipses are rare because
the orbital planes of the moon and of the earth are different
what moon phase cannot be seen at midnight
new
how long would one need to observe a star on a 10 meter telescope to collect the same amount of light as one collects in one hour on a 5 meter telescope
15minutes
if you view a hotstar through a cool cloud of gas what sort of spectrum will you see
absorption
a mountain top is a good location for optical and infrared telescopes
because the site is above much of the atmosphere
how is the angular resolution of a telescope defined
its ability to see detail in an object
if a planet with half the mass of earth was in earths orbit around the sun how would the force between that planet and the sun compare to the force between the earth and the sun
the force between the new planet and the sun would be half as much
which one of the following is true
infrared radiation has a longer wavelength than blue light
an emission line is produced
an electron passes from a higher to a lower level energy level
which of the following is true
an absorption spectrum appears as a continuous spectrum interrupted by a series of dark lines
retrograde motion is
the motion of the planets changing from east to west to test to east and back
what is emitted from an atom when one of its electrons makes a transition from a higher energy state to a lower energy state
photon
radio waves can travel large distances without interference because
they have a longer wavelength than visible light
if the earth's north polar axis always tilted 23.5 degrees toward the sun, but the earth was still rotating about this axis once each day
it would be winter in the southern hemisphere
day and night are due to
the rotation of the the earth
what is the relationship between wavelength and frequency
if the frequency increases the wavelength decreases
during a full moon where is the moon relative to the sun and the earth
on the opposite side of the earth from the sun
if the moon is full on january 10 when is the next time we will see a new moon
january 24
when is the summer solstice in the southern hemisphere
around december 21st
as compared to a cool star a hotter star emits
shorter wavelength higher frequency bluer color
the glowing embers of a fire are emitting most of their energy in the
infrared
the distance between tow massive objects quadruples by what factor is the gravitational force between them changed
one forth
more mass =
more gravity
larger separation =
less gravity