Astronomy TEST 1
Eratosthenes
(Circle Lab) Measured the earths circumference with a stick at noon, sun shines straight down at wells in Syene but pillars in Alexandria casts shadows Measured the angle the sun is south of zenith (geometry with pillar height and shadow length) Angle = 1/15th of a full circle
What is the celestial sphere?
Projection of the Earth into space
The Earth's northern hemisphere is tilted toward the Sun in a. March b. June c. Sept d. Dec
b. June
A planet in retrograde motion a. rises in the west and sets in the east b. shifts westward with respect to the stars c. shifts eastward with respect to the stars d. will be at the north celestial pole e. will be exactly overhead no matter where you are on earth
b. shifts westward with respect to the stars
Galileo Galilei
-Italian Scientist and Scholar -Studied the motion of objects, but did not drop stones from the leaning tower of pisa -First one to look at the sky with telescope, 1609 -Saw craters and hills on the moon -Saw spots in the sun ; spots shifted in time -The moons of jupiter -Not everything orbits the moon, beginning of moon is not center of earth
Mystery of the Cosmos
-Keplers cosmic mystery: the spheres of the six planets nested in the five percent solids of pythagorus and plato -The outermost perfect solid is a cube
Epicycles
Planets move on small circles called epicycles
Nicolaus Copernicus
Polish physician and lawyer Revived Aristarchus' idea of Heliocentric Planets move in circular orbits around Sun Retrograde motion explained automatically -no need for epicycles and deferents, etc Measures relative size of planets
On which date would the North Pole not see the Sun at all? a. March 21 b. June 21 c. Sept 21 d. Dec 21
d. Dec 21
Which planet has the most axis tilt? a. Earth b. Mars c. Jupiter d. Uranus
d. Uranus
A solstice occurs a. in June and December b. when one of the poles is tilted toward the sun c. in between the equinoxes d. all of the above
d. all of the above
An equinox occurs a. halfway between solstices b. when the Earths North and South Poles are equally distant from the Sun c. all over the Earth at the same time d. all of the above
d. all of the above
Which planet would experience the least seasonal changes throughout its orbit around the sun? a. Earth b. Mars c. Jupiter d. Uranus
c. Jupiter
Beijing and Philadelphia have about the same latitude but very different longitudes. Therefore, tonight's night sky in these two places a. will look about the same b. will have completely different sets of constellations c. will have partially different sets of constellations
a. will look about the same
When it is summer in Australia, the season in the United States is a. winter b. summer c. spring
a. winter
The light year is a unit of... a. time b. distance c. speed d. weight e. age
b. distance
In which location could the Sun be observed at the zenith? a. a middle-north latitude b. the equator c. the North Pole d. none of the above
b. the equator
Parallax
the apparent displacement of an observed object due to a change in the position of the observer. Shift of far away stars wasn't visible from earth
Does this make sense: This morning i saw the full moon setting at about the same time the sun was rising.
this could be true because at that point, the moon and the sun are on opposite sides of the earth - the sunlight hits the moon directly.
Does this make sense: If the earths orbit were a perfect circle, we would not have seasons.
this makes sense because the season's are due to the axis tilt, not how close earth is to the sun.
Suppose you lived on the sun. Would you still see the moon go through phases as is orbited the earth.
we would not see the phases of the moon. it would be a constant full moon because we are on the source of light- it would always be illuminated from our point of view (the sun)
How is a light year defined?
A light year is the distance that the light will travel in 1 year (light has constant speed)
Some people still believe the Earth is flat. What proof would you offer to them that it is round?
Altitude of stars changes as you move North or South Length of shadows change as you go North or South
Does this make sense: I live in the US and during my first trip to Argentina i saw many constellations that I've never seen before
Could be true since it is a different location and more southern thus has a different view of the night sky.
Suppose a planet were found with an orbital period of 64 years. How might you estimate its distance from the Sun? If its orbit is circular, what is its radius?
P^2=a^3 64^2 = a^3 a^3=4096 a= 16 AU
Where on the celestial sphere would you look for the planets?
The planets are found near the ecliptic or in the zodiac constellations
Which planet could be thought of as "upside down" compared to the others? a. Venus b. Earth c. Mars d. Jupiter
a. Venus
In which location would the day with the least sunlight be Dec 21? a. a middle-north latitude b. the equator c. the South Pole d. (all the locations have the least sunlight on that date)
a. a middle-north latitude
Kepler's third law a. relates a planets orbital period to the size of its orbit around the sun b. relates a body's mass to its gravitational attraction c. allowed him to predict when eclipses occur d. allowed him to measure the distance to nearby stars e. showed that the sun is much farther away than the moon
a. relates a planets orbital period to the size of its orbit around the sun
Extremes in the amounts of daylight and darkness occur at the a. solstices b. equinoxes c. both of the above depending on which hemisphere you are in d. none of the above
a. solstices
In the winter, Earth's axis points toward the star polaris. In the spring, a. the axis also points toward polaris b. the axis points toward Vega c. the axis points toward the sun
a. the axis also points toward polaris
The Inner Planets
Mercury - barren, Sun-scorched Venus - dense clouds of sulfuric acid Earth - water Mars - desert and huge canyons (water, possibility of life)
The pythagoreans universe
The earth and heavenly bodies are perfectly Sphere around a central fire invisible to the human eye 10 objects circled the central fire which included a counter-earth assumed to be there to account for eclipses
Ptolemy's Model
-Planets move on small circles --> epicycles -Epicycles move on big circles--> deferents -Deferents are centered on a point near but not on Earth -Adjusting sizes, rotation rates, etc. of these circles gave reasonable agreement between model and reality
Claudius Ptolemy
-Ptolemy of Alexandria -Built on ideas of Hipparchus -Still Earth Centered - Better accounts for retrograde motion -Ptolemy's ethereal spheres: -circle is perfect shape -Heavens are perfect -Music of the spheres -seventh heaven (moon, mercury, venus, sun, mars, jupiter, and saturn and the stars)
Aristarchus of Samos
-The size of the moon (75 years before Eratosthenes) -Compared the size of the Earth's shadow disk to Moon disk -Moon diameter= 35% of the Earth's diameter -Actual Value = 27% -looked at shadows on the moon -earth's curve wasn't as big as the moon, so bigger circle (earths) -the sun is so much bigger, must be the center? -Earth must be moving around the sun? -"but then the stars would shift"- no parallax -didnt see a shift so Earth is not moving (earth being center of universe got dismissed)
Johannes Kepler
-Tycho's assistant; came from a desperately poor background -Kepler's Cosmic Mystery -"inherited" Tycho's Notebooks -Very carefully analyzed records for mars and concluded that... -**mars and other planets move in elliptical orbits, not circular ones -**the sun is at the focus of the ellipse, not at its center
Kepler's Laws
1. All planets move in elliptical orbits, with the Sun at the focus of the ellipse 2. Line from the sun to a planet sweeps out equal areas in equal intervals of time 3. square of period (in years) = cube of orbit in size (in AU) P^2 = R^3
Aristotle
55-Sphere Universe - dominant for 1800 years -explained and predicted many of the observed motions of the stars and planets Earth did not come into being at one point but that it existed, unchanged for all eternity Believed Universe had a center (the earth) and its material part had an edge which ended in the fixed star sphere Beyond sphere of stars the universe continued into a spiritual realm where material things cannot be Conflict with Biblical description
The Earth, Our home (basic facts)
A Sphere - fact knows to ancient Greeks -Radius - 4000 miles Rotates - causes nights and days Has atmosphere - held by gravity Has magnetic field - deflects compass needles
The size of the earth - who and formula
Alexandria to Syene = 1/15th of all the way around the earth. (500 miles) Around the Earth = 50 X 500 miles = 25,000 miles Modern Value: 24,906 miles
How big is an astronomical unit?
An astronomical unit is 93 million miles 1 AU = 1.50 x 10^11 = 93 million miles
Pythagoreans- Pythagorus
Believed Universe could be understood with whole numbers
Greek Astronomy
Celestial Sphere
What are circumpolar stars? Are more stars circumpolar at the North Pole or the United States?
Circumpolar stars are stars that never set. Stars that are closest to the north pole are more circumpolar. For example, the big dipper is a circumpolar constellation because it is close to the north star.
What is the zodiac?
Constellations on the ecliptic
Tycho Brahe
Danish wealthy nobleman Built instruments of high accuracy (no telescopes yet) Made precise measurements of planet positions Observed a "new star" (supernova) - heavens are changeable! -showed no parallax; much farther than the planets Studied path of comet in 1577 The comet would have had to pass through many of the "perfect crystalline spheres Liked Copernicus' model but could not get over the "lack of stellar parallax" objection Comprised model - planets circle the sun, sun circles the earth
Does this make sense: The constellation orion didn't exist when my grandfather was a child.
Does not make sense because it takes many years for stars to form, and this statement only makes sense if he was a child after 1928 cause the constellation was named in 1928.
Deferents
Epicycles move on big circles called deferents Deferents are centered on a point near but not on Earth
Will a planet in retrograde motion rise in the east or west?
Everything always rises in the east and sets in the west due to Earth's rotation. Planets will appear to drift to the west with respect to the stars since they are much closer to use
The Moon's of Jupiter
Galileo saw moons of jupiter through the telescope, evidence of other centers of orbits... proves that not everything orbit earth.
The Sun (basic facts)
Gaseous (3 parts Hydrogen; 1 part Helium) Holds itself together by own gravity Holds earth and other planets in orbit Magnetic field - sunspots HOT - heated by nuclear reactions -surface temp = 6000 K -core temp = 15 million K Corona - outer atmosphere
What is a constellation?
Grouping of stars
Copernicus's Model
Ideas were not accepted Did not give much better agreement with observation than Ptolemy's -blame lies partly on choice of circle - the perfect circle Model implies parallax shift in star position but none seen Earth feels at rest; no sense of motion Authority of Aristotle and the Church - book was forbidden
Suppose Earth's axis had no tilt. Would we still have seasons?
If the earth's axis did not have a tilt we would not have seasons. The earth's tilt is the main cause of the seasons.
The Outer Planets
Jupiter - immense mass, lightening storms (powerful & long lasting) Saturn - ring system (trillions of ice fragments) Uranus - tilted axis Neptune - Methane Clouds Pluto - now a dwarf planet (didn't clear debris during formation)
What are latitude and longitude? Does the local sky vary with latitude? Does it vary with longitude?
Latitude lines run east to west and longitude runs north to south on the Earth. The local sky varies with location and where one is on the Earth. The local sky also varies with latitude for the same reason as well.
New Horizons at Pluto
Launched January 19, 206 Arrived: July 14, 2015 Highest launch speed - 36,373 mph Planned flybys of at least 2 Kuiper Belt objects 2016-2020
Juno at Jupiter
Launched: Aug 5, 2011 Arrival: July 6, 2016 Goal ~Understand origin and evolution of Jupiter ~Look for solid planetary core ~Map magnetic field ~Measure water and ammonia in deep atmosphere, ~Observe auroras
Suppose the stars were very much closer than they really are. How might that have made it easier for Aristarchus to persuade people that the earth moves around the sun?
Might have noticed the parallax of the stars
Early models of the universe
Moon, Venus , Sun, Mars... are mounted on separate nested, concentric spheres surrounding the central Earth
If the shape of the earths orbit was unaltered but its rotation axis was shifted so that it has no tilt, how would the seasons change?
No tilt would result in no seasons. The sun would reach the same altitude in the sky everyday.
Does this make sense: Last night the moon was so big that it stretched for a mile across the sky.
Not true because it is physically not big enough to stretch the sky.
The Moon (basic facts)
Orbits Earth - held in orbit by earths gravity Distance - 240,000 miles Sphere -1/4 of Earth's radius -Mass much smaller --> weaker gravity -No atmosphere b/c no gravity
A Planet is discovered orbiting a nearby star once every 125 years. If the star is identical to the Sun, how could you find the planet distance from its star? If the planet's orbit is a perfect circle, how far from the star is the planet in AUs?
P^2 = a^3 125^2 = a^3 15625 = a^3 a=25
Suppose you received a message from aliens living on a planet orbiting a star identical to our sun. They say they live 4 times farther from their star than the earth is from the Sun. What is the length of their year compared to ours?
P^2 = a^3 P^2 - 4^3 P^2 = 64 P = 8 years
Observation with the Hubble Space Telescope revealed a planet about 16 AU from a star whose mass is the same as our suns mass. How long does it take the planet to orbit the Sun?
P^2 = a^3 P^2 = 16^3 P^2 = 4096 P=64 years
What is the ecliptic?
Path of the Sun through the sky
Calculate approximately how long it takes to travel from the Sun to Pluto.
Pluto is about 40 AU so... (1.50 X 10^11) X 40 = 6 X 10 ^12 which is 20000 seconds which is 333 minutes which is roughly 5-6 hours
What are the conditions needs for a solar or lunar eclipse?
Solar: the sun casts a shadow of the moon on earth (thus the sun in line with the moon then earth, also needs to be a new moon) Lunar: the sun casts a shadow of earth on the moon (all the sun sets onto the moon) ( the sun is in line with the earth and then the moon, also needs to be a full moon)
What do we mean by the apparent retrograde motion of the planets? why was it difficult for ancient astronomers to explain but easy for us to?
The "loop" we see planets do in the sky due to the fact of earth passing the planet in orbit. It looks as if it is going backwards. The apparent retrograde motion of the planes means that according the celestial view the planets will always move east but then will move back to the west. It is difficult for ancient astronomers to explain because they believed that the earth remained still (celestial view). They thought the earth was at the center of the solar system and remained still.
To what systems, in increasing order of size, does the Earth belong to?
The Earth --> the Solar system --> the milky way --> the local group, --> super cluster --> visible universe.
If you were standing on the Earth's equator, where would you look to see the North celestial pole? Could you see this pole from Australia?
The North Celestial Pole would lie on the horizon if you were on the equator (the north star gives your latitude). You can't see it from Australia
Briefly describe the moon's cycle of phases. Can you ever see a full moon at noon?
The moon has a cycle of phases and shifts positions against stars. Phases: New moon, waxing crescent, half moon, waxing gibbous, full moon, waning gibbous, half moon then waning crescent. A full cycle of the moon lasts 29 1/2 days You can never see a full moon at noon since the sun is illuminating the other side of the moon that we on earth cannot see.
Briefly describe what is special about the summer and winter solstices and the spring and fall equinoxes.
The summer and winter solstices: June 21st is the longest day of the year (sun is most direct in the northern hemisphere and never sets at the north pole) and December 21st is the shortest day of the year (sun is most direct in the southern hemisphere and never rises in the north pole). A solstice occurs two times a year when the sun is at its greatest distance from the celestial equator. The spring and fall equinoxes: the sun at these times crosses the celestial equator and have a day and night of equal length (12 hours) (north and south pole are of equal distance from the sun)
What causes the seasons?
The tilt of the Earth on its axis (23.5 degrees)
The Greeks - Early models of the universe (what did they think)
Universe is centered around Earth - Geocentric Earth was perfectly sphere Believed #10 was sacred
Why don't we see an eclipse at every new and full moon?
We don't see an eclipse at every new and full moon because it doesn't line up directly in front of the sun. the moons orbit around the earth isn't completely straight- it is at a tilt. The eclipses are rare because it needs to be in the correct phase and line up at the nodes (in line with earth and sun). Eclipses only happen when the sun hits one of the two nodes. Eclipses do not happen every month.
The circular shape of the earths shadow on the moon led early astronomers to conclude that a. the earth is a sphere b. the earth is at the center of the solar system c. the earth must be a rest d. the moon must orbit the sun e. the moon is a sphere
a. the earth is a sphere
If there is going to be a total lunar eclipse tonight, then you know that a. the moon's phase is full b. the moon's phase is new c. the moon is unusually close to earth
a. the moon's phase is full
The north celestial pole is 35 degrees above your northern horizon. This tells you that a.you are at latitude 35 degrees North b. you are at a longitude 35 degrees north c. you are at latitude 35 degrees south
a. you are at latitude 35 degrees North
On which date would the Sun appear its lowest when observed from the equator? a. March 21 b. June 21 c. Sept 21 d. none of the above
b. June 21
Which planet should have seasons most similar to Earth's? a. Venus b. Mars c. Jupiter d. Uranus
b. Mars
When we see saturn going through a period of apparent retrograde motion it means, a. saturn is temporarily moving backward in its orbit of the sun b. earth is passing saturn in its orbit, with both planet on the same side of the sun c. saturn and earth must be on opposite sides of the earth
b. earth is passing saturn in its orbit, with both planet on the same side of the sun
If the sun rises precisely due east, a.you must be located at the earths equator b. it must be the day of either the spring or fall equinox c. it must be the day of the summer solstice
b. it must be the day of either the spring or fall equinox
Which location gets the most sunlight over the entire year? a. the poles b. the equator c. midlatitudes d. throughout the whole year, all locations receive the same amount of sunlight
b. the equator
Which location has the least variation in the daily amount of sunlight throughout the year? a. a middle-north latitude b. the equator c. the North Pole d. the South Pole
b. the equator
A week after the full, the moon's phase is a. first quarter b. third quarter c. new
b. third quarter
You write your home address in the order of street, town, state, and so on. Suppose you were writing your cosmic address in a similar manner. Which of the following is the correct order? a. Earth, Milky Way, Solar System, Local Group b. Earth, Solar System, Local Group, Milky Way c. Earth, Solar System, Milky Way, Local Group d. Solar System, Earth, Local Group, Milky Way e. Solar System,Local Group, Milky Way, Earth
c. Earth, Solar System, Milky Way, Local Group
When the Earth's northern hemisphere is tilted toward the Sun, it is a. summer b. winter c. summer in the northern hemisphere and winter in the southern hemisphere d. winter in the northern hemisphere and summer in the southern hemisphere
c. summer in the northern hemisphere and winter in the southern hemisphere
In which location would there be a day where the sun is up for 24 hours straight? a. a middle-north latitude b. the equator c. the North Pole d. (that can never be observed)
c. the North Pole
On which date would a location in Australia observe the midday Sun at its highest altitude for the year? a. March 21 b. June 21 c. Sept 21 d. Dec 21
d. Dec 21
On which date would the Sun appear its highest when observed from the South Pole? a. March 21 b. June 21 c. Sept 21 d. none of the above
d. none of the above
What would an observer on the South Pole observe on March 21? a. 24 hours on sunlight b. 24 hours of darkness c. sunrise d. sunset
d. sunset
If you were standing at the earths North Pole, which of the following will be directly overhead? a. the celestial equator b. the ecliptic c. the zodiac d. the north celestial pole e. the sun
d. the north celestial pole
Neither of the Earth's hemispheres is tilted closer to the sun in a. March b. June c. Sept d. two of the above
d. two of the above
Galileo used his observations of the changing phases of Venus to demonstrate that a. the sun moves around the earth b. the universe is infinite in size c. the earth is a sphere d. the moon orbits the earth e. Venus follows an orbit around the sun rather than around the earth
e. Venus follows an orbit around the sun rather than around the earth
Which of the following astronomical system is/are held together by gravity? a. the sun b. the solar system c. the milky way d. the local group e. all of them are
e. all of them are
Galilean Moons
the four largest moons of jupiter, evidence of life perhaps on these moons: Io, Europa, Ganymede, and Callisto
