Astronomy Chapter 1
What are four things Sir Isaac Newton did?
- Almost single handedly developed Calculus - Discovered the principle of gravitational attraction - Investigated certain properties of light - Used Galileo's insight
What are 8 key characteristics of Aristotle's Geocentric Model?
- Earth is stationary - Earth is at the center of the Universe - All "heavenly objects" orbited the Earth - The Universe has two parts: The heavens which are perfect and unchanging and the Earth, which is imperfect and changing - Earth was too heavy to move through space and bad things would happen if it did - There was no parallax "proving" the earth was stationary - Day and Night was simply the sun moving around the earth - Heavenly bodies moved around Earth in perfect circles, prograde (forward/East) at uniform speeds - They could not explain retrograde motions of planets
What were six significant parts of the heliocentric model?
- Sun is at the center of the universe - We were just another planet - The Moon orbits the Earth - Copernicus still used epicyclic motion - The eastward spin of the earth accounted for the apparent westward motion of the celestial sphere - Retrograde was natural this way
What is Mars' eccentricity?
.093 (basically .01) (basically circular) you can see why they thought it was circular
What are the steps of the Scientific Method?
1) Start with an observation or and idea 2) Suggest a hypothesis 3) Make a prediction 4) Perform a test, experiment, or additional observation 5a) If the test does not support the hypothesis, revise the original hypothesis or choose a new one. (Return to step 2) 5b) If the test supports the hypothesis, make additional predictions and test them (Return to Step 3)
What were the implications of Galileo spotting moons revolving around Jupiter?
1) This was the first time bodies were seen orbiting other bodies besides the earth. This discovery showed that there could be other centers of motion 2) The classical belief was that if the Earth moved, then Earth would lose its moon, but Jupiter was moving and it still had its moons... so the earth could move too and not lose its moon 3) The relationship between Jupiter and its moons could be seen as a small-scale model of the Sun and its planets... This was not seen as proof for the heliocentric universe, but it was seen as part of the argument
How long is the lunar cycle?
29.5 days
What is the Gravitational Constant?
6.667 x 10^-11 Meters cubed per second squared kilograms G
What did Brahe observe in 1572?
A "new star" (really a supernova)
What did Tycho Brahe believe in?
A Geocentric universe
What was the probable purpose of Stonehenge?
A calendar
What did Brahe observe in 1577
A comet
What is a paradigm?
A commonly accepted set of scientific ideas and assumptions
What do today's scientists refer to gravity as?
A field
What is Gravity?
A force between any two objects having mass
What is momentum?
A measure of an object's amount of motion
What is a hypothesis?
A proposed reasonable explanation based on what is known so far. Tested through observation and experimentation.
What is the scientific method? (Not the steps)
A sequence of steps for systematically analyzing scientific problems in a way that leads to verifiable results.
What is a Natural Law?
A theory that has been refined, tested and confirmed so often that scientists have overwhelming confidence in it. Natural laws are the most fundamental principles of scientific knowledge.
What did Newton call gravity?
Action at a distance
What is an AU?
An Astronomical Unit The orbital radius of the Earth and Sun 93,000,000 miles 9.296x10^7
What is a Catastrophic hypothesis/theory?
An explanation for natural processes/events that depends on dramatic and unlikely events Ex. The extinction of the dinosaurs 65 million years ago is attributed to an impact by an object 10-14 km in diameter.
What is an Evolutionary hypothesis/theory?
An explanation for natural processes/events that involves gradual changes that occur over a period of time. Ex. Slow, continual processes that build up mountains
What is a Theory?
An idea that is widely applicable and confirmed by abundant evidence.
Who first came up with the Heliocentric model? (like legit first one) BONUS: Why?
Aristarchus Aristotle was too influential on everyone
Who developed the second main model of the Universe and what was it called?
Aristotle (student of Plato) developed the Geocentric Universe
What other discovery did Brahe make that contradicted Aristotle? and why? (1577)
Aristotle said the comets were atmospheric phenomena, however Brahe observed a parallax on the comet, but the parallax put the comet farther out in the universe than the moon. This again represented a change in the celestial sphere...
Do the horns of the moon point towards or away from the sun?
Away from the sun
Describe the two types of orbits.
Bound (closed) orbits (GM/r)^.5 = Vcirc Ex. Moon falling around earth Bonus: Geosynchronous orbit is where an object is falling directly over a certain point on earth Unbound (open) orbits (2GM/r)^.5 = Vesc Ex. Voyager
Where were the stars originally?
Celestial Sphere
If objects have different masses, where is the center of mass?
Closer to the more massive object
What is the difference between and inelastic and an elastic collision?
Energy is released in inelastic collisions Energy is not released in elastic collisions
What is the Law of Universal Gravitation?
Every two particles of matter in the universe will attract each other with a force that depends on the product of their masses and the inverse square of the distance between them Force of Gravity = (GMm)/r^2
Which theories do scientists typically prefer? (With some exceptions)
Evolutionary theories
What is Newton's Third Law?
For every action, there is an equal but opposite reaction - Force always comes in pairs - in each pair, the forces are the same size - Forces will have opposite directions because they are vectors - This law applies to all forces
What was Galileo first to do?
He had heard of a discovery that two lenses could be used to magnify distant objects, and he was the first to build the astronomical telescope to study the heavens
Beginning in 1610, what did Galileo do?
He made important astronomical discoveries that had implications for both Ptolemaic and Copernican theories
What did Galileo think of the Tychonic System?
He rejected it as an unnecessary hybrid. The copernican model was simple and Occam's razor says the the Tychonic system is bad news bears.
What did Galileo observe about Venus? implications?
He saw phases just like the moon. This would mean that for a 'Full Venus' it would have to be on the other side of the sun. This meant that Ptolemy was wrong in having venus always between the sun and earth and it meant Venus orbited the sun
Why was Kepler legit? (Too legit to quit) (2 L 2 Q)
He used MATH
What came after the Geocentric Universe Model?
Heliocentric Model
What is a a proposed reasonable explanation based on what is known so far, which must be tested through observation and experimentation?
Hypothesis
What are two implications of the Cosmological Principle?
If scientists can understand the local behavior of nature, then they can extrapolate this behavior to the universe at large. Information carried by light from a distant part of the universe can be reliably interpreted based on our understanding of nature locally.
If two objects have the same mass, where is the center of mass?
In the middle between the objects
What properties does gravity have?
It is an attractive force always acting along a straight line between objects it is a mutual force that acts on both bodies It can act on multiple bodies at the same time The farther apart the objects are, the weaker the force of gravity becomes on both of them. However, it is never zero.
What was significant about Kepler discovering Mars' orbit?
It started the idea of elliptical orbits It started the idea of non-uniform rotations basically KEPLER DISPROVED UNIFORM CIRCULAR MOTION
Who decided on what an AU is?
Kepler
What is Newton's First Law?
Law of Inertia - A body continues at rest or in uniform motion in a straight line unless acted upon by some force. - The natural path is not a circle, its a straight line - A force is necessary to bend a path - A force is a push or pull
What type of parallax did Brahe observe?
Lunar Parallax
What did Brahe and his assistants do?
Make naked-eye observations of the positions of the Sun, Moon, planets and stars (Very accurate, given the time)
What did Kepler accomplish in just 5 years by just working the mathematical data?
Mars' orbit
What did Galileo end up studying more in depth later in life? What was the significance of this?
Motion and actions of forces on bodies This was the first example of experimental science He had to abandon the authority of the ancients for this, devise his own experiments, and draw his own conclusions. His results were off because of friction, however he could imagine an infinite frictionless plane and worked out the law of inertia
Who was credited for being the "first" one to come up with the heliocentric model?
Nicolas Copernicus
Was Earth originally considered a planet?
No
Who was Johannes Kepler?
One of Tycho Brahe's assistants
What happened when Brahe moved to Prague in 1597 to become the Imperial Mathematician of the Holy Roman Empire?
One of the assistants hired was Johannes Kepler. And when Brahe died in 1601, Kepler "inherited" all of Brahe's notes and observations
What is Newton's refined version of Kepler's Third Law?
P^2 = 4 pi^2 a^3 / GM M = Mass of the system added together
What is Peri and Ap for various bodies?
Perihelion is close to the sun Aphelion is far from the sun Perigee is close to Earth Apogee is far from Earth Perijove is close to Jupiter Apojove is far from Jupiter (Semi-Major Axis lengths)
What was the name of the idea that the heavens must be made up of perfect spheres rotating at uniform speeds while carrying objects around in circles?
Principle of Uniform Circular Motion
What were five characteristics of the second (sort of third) version of the Geocentric model and who made it?
Ptolemy made it 500 years later - Ptolemy made Aristotle's model mathematical - To help predict planets and stuff, he made the planets move in an epicyclic manner (circles doing circles) - Epicyclic motion accounted for retrograde - It wasn't super precise - It lasted 1000 years (until the 16th Century)
What is Retrograde and Prograde?
Retrograde - Backwards - Westward Prograde - Forwards - Eastward (When compared against background stars)
What was the perfect geometric form according to Plato? And what was the significance of this?
Sphere. The heavens are perfect so they must be made up of perfect spheres rotating at uniform speeds while carrying objects around in circles.
What was the first Universe model made up of?
Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn
What did Galileo see when looking at the sun? and what were the implications?
Sunspots. - This showed that the sun was not perfect... making it just another celestial body - He was able to see that the sun rotated at just less than a month... if the sun could rotate, so could earth
What kind of rotation is the moon in with the Earth?
Synchronous Rotation The moon is tidally locked with earth
What discovery did Brahe make that contradicted Aristotle? and why? (1572)
The "new star" (supernova) that he observed. This was a change in the heavens so it must have occurred below the sphere of the moon, however he did not observe parallax so it must lie outside the sphere of the moon... perhaps on the celestial sphere itself...?
What did Kepler believe in? (which universe model)
The Copernican heliocentric universe
What is the Cosmological Principle?
The Cosmological principle states that on a large scale the universe looks the same everywhere - There is nothing unique about Earth's place in the cosmos - Generally, the cosmological principle assumes that matter and energy over the same physical laws everywhere
What is a lunar eclipse?
The Earth blocks the light from the sun to the moon and the moon will be red from the light bent around the earth
What model did Tycho Brahe put forth? and what did it consist of?
The Tychonic System It was still geocentric (moon and sun revolved around the earth), but all other planets revolved around the sun. Motion was still uniform circular motion
What was the significance of the first sighting of the star Sirius in the pre-dawn sky?
The ancient Egyptians had it timed with the flooding of the nile.
What is Kepler's Second Law?
The areas swept in a given time period are equal
What is the center of mass?
The balance point of a system of masses. Objects orbit about the center of mass
What were three things Ptolemy's model of the universe included?
The earth was at the center It contained epicycles the planets were moving in uniform circular motion
What happens as eccentricity approaches zero?
The ellipse approaches a circle
What did Tyco Brahe build?
The first modern European observatory (on and island off the danish coast)
What did Galileo observe when looking at Jupiter?
The four largest moons and their orbital periods (innermost moons had short periods and as you go out, they get proportionally longer)
What did Galileo Galilei believe in?
The heliocentric universe
What is the Umbra?
The inner core of the shadow where no light is received
What is the diameter of an ellipse?
The length of the Major Axis
What is the radius of an ellipse?
The length of the Semi-Major Axis
What is the terminator?
The line that separates the illuminated portion of the Moon from the dark portion.
What is a solar eclipse?
The moon passes in front of the sun, blocking out the sun itself, leaving only the corona to be seen from earth.
Why don't we see two eclipses a month?
The moon's orbit is tipped about 5 degrees so it doesn't always match up. The moon crosses the ecliptic twice per month, these points are called nodes
What was the closest thing Galileo observed with the telescope and what did he discover? Implications?
The moon, and he discovered that the surface was very imperfect (actually looked very similar to earth with the valleys and mountains and flat areas). These observations showed the moon to be another imperfect celestial body, and it went a long way in confirming that Earth was just another celestial body
What is Newton's Second Law?
The net force on an object is equal to the mass of the object multiplied by the acceleration of the object F=ma
What is Kepler's first law?
The orbit of a planet is an ellipse with the sun at one focus.
What is the Penumbra?
The outer area of a shadow where it is only partially shaded
What is the average distance from the sun of an elliptical revolution?
The radius (Semi-Major Axis)
What is Kepler's Third Law?
The square of the Period of the Orbit in Earth years is equal to the Cube of the Semi-Major Axis in AU p^2 = a^3 The farther the planet is from the sun, the longer its orbit is
What is Cosmology?
The study of nature, origin, and the evolution of the universe.
What are the two conditions that must be met in order for an eclipse to occur?
The sun must be near a node and the moon must be crossing the same node or the other node
What was the 99 years of astronomy?
These were the years between Copernicus' death and Galileo's death. This marked the transition from ancient astronomy to copernicus' revolutionary theory. This was also the period that science was 'invented' as a way of understanding nature
Why does the small moon block out the large Sun?
They both have an angular diameter of .5 degrees. The sun is ~400x larger but ~400x further
What are the three types of solar eclipses?
Total - An observer will see only the corona of the sun and will only happen in the path of totality and can at most last seven and a half minutes partial - This is where the moon covers part of the sun Annular - This is where the moon is slightly farther away because of its orbit and it creates an annular ring where you can see the edge of the sun
How was it possible for them to discover Mars' orbit?
Tycho Brahe's accurate measurements
Did Aristotle consider the Earth imperfect and changeable?
Yes
How much later each day does the moon rise?
about 1 hour later
What is Earth's escape velocity?
about 11km/s or 24,600 mph
How do you calculate e? (Eccentricity)
e = .5 [(distance between foci) / (semi-major axis)] e = half of the long thing divided by the short thing
