Astronomy Exam 1 - SCC
Terms in this set (67)
Determined the shape of the Earth. (Sphere) He said all objects fall straight down and if the Earth was flat, they would fall at an angle.
Determined the relative size of the Earth, Moon, and Sun. Was the first to deduce that the Earth must orbit the Sun.
Determined the physical size of the Earth.
Revised the observations of Aristarchus and discovered that the Earth experiences precession.
Developed the geocentric model using epicycles to explain retrograde motion.
Developed the heliocentric model. Correctly ordered planets about the Sun. The heliocentric model could explain retrograde motion without epicycles.
Observed nightly for 25 years.
Defined the three laws of planetary motion. Refined the heliocentric model.
Kepler's First Law of Planetary Motion
The planets orbit the Sun in elliptical orbits.
Kepler's Second Law
Law of Areas- the line joining planet and Sun sweeps equal areas in equal time units. A planets speed varies inversely with distance. (When a planet goes farther from the Sun, the speed decreases)
Kepler's Third Law
Harmonic Law- p= sidereal/orbital period in years a= semi major axis in AU ... p^2=a^3 P(Earth)= 1 year
a(Earth)= 1 AU 1=1 This means: The farther out a planet is form the Sun, the longer it takes to complete one orbit.
Made five observations that support the heliocentric model. 1)Venus shows places similar to moon's. Heliocentric/Copernican model predicts all phases. 2) Jupiter has four bright moons. (Io, Europa, Ganymede, Castillo) 3) Lunar features similar to Earth (mountains, craters, seas) 4) Sun is blemished with spots and rotates. 5) Galileo found with the milky way uncountable stars.
Describe Retrograde Motion, and discuss how it differs from the normal prograde motion of the planets.
Retrograde motion is the apparent backward motion (from E
to W) of the planets with respect to fixed stars.
Prograde motion is the apparent forward motion (from W to
E) of the planets with respect to fixed stars.
Kepler's three laws.
1. Planets orbit the sun in elliptical orbits.
2. The speed of a planet varies inversely with its
distance to the sun.
3. A planets orbital period is related to its
distance from the sun. (P2=a3)
how one would measure the Size of the Earth.
Measure the difference in the sizes of shadows in different
Describe the differences between the Geocentric versus the Heliocentric model for the solar system.
The geocentric model states that all planets orbit the Earth while the heliocentric model states that all planets orbit the sun. In the geocentric model, retrograde motion is explained using epicycles while the heliocentric model explains retrograde motion as an optical illusion resulting from the natural orbit of the
Explain why the Geocentric System uses epicycles when the Heliocentric does not.
In the geocentric model, it would be impossible to observe retrograde motion since the planets orbit the Earth. However, since the planets orbit the sun (not the Earth), retrograde motion can be observed as the Earth catches up to and then passes the planet.
Newton's three laws.
1. Conservation of Momentum: An object at rest or in motion at a constant velocity will remain in that state unless acted upon by an unbalanced external force.
2. Force Law: The acceleration a body experiences is related to the force acting on the object and the mass of the object.
3. When two objects interact, they exert an equal, but opposite in direction, force on each other.
Which exerts a stronger force on the Moon: the Sun or the Earth. Explain why and give an example of an observation to that supports your answer.
Although the Sun is more massive, the Earth is closer. Since it is the Earth that the Moon orbits (and not the Sun) we can conclude that the Moon feels a stronger pull from the Earth.
sun, its planets, moons, asteroids, comets
spherical, non luminous bodies that orbit a star and shine by reflected light
self-luminous ball of hot gas
Astronomical Unit - AU
1.5 x 10^8 km. the average distance from the sun to the Earth
Light year (ly)
the distance that light travels in one year, approximately 9.5 x 10^12 km or 63,000 AU.
great cloud of stars, gas, and dust held together by the combined gravity of all its matter.
EVERYTHING. All of the galaxies, stars, planets, etc.
well-defined regions on the sky, irrespective of the presence or absence of bright stars in these regions
we can take this idea of a shell of stars surrounding the Earth to describe the positions and motions of the objects in the sky. It is a scientific model of the sky, to which the stars appear to be attached. Because the Earth rotates Eastward, the celestial sphere appears to rotate West on its axis.
march 20; when spring begins; equinox means equal, when there are equal amounts of daylight and darkness. vernal - green.
Sept. 22 Autumn begins
June 22; Summer starts; Solstice means sun and stationary
Dec. 21 Winter starts
Why are winter days colder than summer days?
Because of the tilt of our planet, meaning: 1) the days get shorter in Winter (when the Northern Hemisphere is tilted away from the Sun) and 2) The Sun is lower in the sky during winter, which changes the angle of light hitting us and how much heat energy we get from it.
Earth at the center
Sun at the center
minor path; small circle, that rotates along the edge of a larger circle, the deferent, which enclosed a slightly off-center Earth
major circular path
a figure that can be drawn around two points, called the foci, in such a way that the distance from one focus to any point on the ellipse & back to the other focus equals a constant.
half of the longest diameter
e; half the distance between the foci divided by the semi major axis. it tells you its shape; if e is nearly equal to 1, the ellipse is very elongated. If e is close to 0, the ellipse is very circular.
Plato & the Perfect Heavens
Said all heavenly motions are uniform and circular because the most perfect geometrical form was the sphere; therefore, the perfect heavens must be made up of spheres rotating at constant rates and carrying objects around in circles.
epicycles of Mercury and Venus differed from Mars, Jupiter, and Saturn because the centers of the epicycles had to remain on the Earth-Sun line as the Sun circled Earth through the year.
acceleration of gravity
the rate at which a falling object changes its speed (9.8 m/s^2 at Earth's surface) & does not depend on the weight of the object.
a measure of a body's amount of motion, which is a combination of its velocity and mass
f=ma; an influence tending to change the motion of a body or produce motion or stress in a stationary body.
a change in velocity; must be caused by a force; its a change in speed, or direction, or both
a speed with a specific direction
an orbit around the Earth with an orbital period of one sidereal rotation period (approx. 24 hrs.)
the minimum speed needed for an object to "break free" from the gravitational attraction of a massive body. It is the speed at which the sum of an object's kinetic energy and its gravitational potential energy is equal to zero.
motions other than natural motion and had to be sustained by a force; best explained by Newtons first law- the conservation of momentum
Aristotle's explanation of gravity would not work if the Earth was not at the center of the universe because....
he said objects have a tendency to move towards their proper place in the cosmos and the things composed of earth, rock, soil, water, bone, flesh all tend to move downwards (explaining gravity). his explanation of gravity- why things fall down- works only if the center of the Earth is also the center of the universe.
the measure of the amount of matter a body contains
gravitational force acting on an object
size of sun: Earth
caused by the orbit of Earth around the Sun
the observed path of the Sun through the constellations (its tilted 23 degrees from the equator)
Have to do with the tilt, not the distance from the sun. We receive more hours of daylight (sunlight) during the summer (more direct sunlight). Earth is tilted with respect to its orbit around the sun.
build first observatories 6000 years ago; observed the motion of the celestial bodies in order to keep time.
wrong; led to wrong models; believed to be obvious and not "questioned;" like the geocentric universe and perfect heavens phenomenea
North celestial pole moves in a circle among the stars (spinning top); entire period takes 26,000 years
Discovered that all objects fall to the ground at the same rate regardless of weight. if a lighter object is falling slower, it is due to air resistance.
In the absence of collisions, an object at rest will remain at rest and an object in motion continues to move at the same speed in the same direction.
Said there must be an attractive force causing the planets to be continually deflected toward the sun. -pendulum swing
any motion that is not in a straight line experiences an acceleration. because objects that travel in a circle are not conserving momentum the object experiences a net force.
Would the larger or smaller object in a frictionless environment (with the same force exerted on each) experience a smaller acceleration?
The larger one
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