Orbits And Gravity Flashcards
Why was Brahe limited in his research/discoveries
Brahe didn’t have the ability to analyze his data for the sun moon and planets and develop a better model than what Ptolemy had published. He was further inhibited because he was an extravagant and cantankerous fellow, and he accumulated enemies among government officials.
What did Brahe make continuous records of?
Brahe made a continuous record of the positions of the Sun, Moon, and planets for almost 20 years. His extensive and precise observations enabled him to note that the positions of the planets varied from those given in published tables, which were based on the work of Ptolemy.
Who discovered the laws of planetary motion?
Kepler
orbit
The path of an object through space is called its orbit
ellipse
oval (path the objects in space follow)
conic sections
A conic section, conic or a quadratic curve is a curve obtained from a cone’s surface intersecting a plane
major axis
The widest diameter of the ellipse
semimajor axis
is, the distance from the center of the ellipse to one end
eccentricity
how flat the ellipse is
In an ellipse, the sum of the distance from two special points inside the ellipse to any point on the ellipse is always the same. These two points inside the ellipse are called its ____
foci (singular: focus)
Kepler’s first law
the orbits of all the planets are ellipses.
orbital speed
the speed with which each planet moves along its ellipse,
Is the orbital speed consistent through 1 orbit?
No, Kepler discovered that the planet speeds up as it comes closer to the Sun and slows down as it pulls away from the Sun.
Why wasn’t Kepler satisfied after discovering his first 2 laws?
He wanted to know why the orbits of the planets were spaced as they are and to find a mathematical pattern in their movements—a “harmony of the spheres” as he called it.
How do we define a planet’s orbital period?
the time it takes a planet to travel once around the Sun.
Kepler’s third law
says that a planet’s orbital period squared is proportional to the semimajor axis of its orbit cubed,
Kepler’s second law
: The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time.
accelerate
to change velocity; to speed up, slow down, or change direction.
apparent magnitude
a measure of how bright a star looks in the sky; the larger the number, the dimmer the star appears to us
astrology
the pseudoscience that deals with the supposed influences on human destiny of the configurations and locations in the sky of the Sun, Moon, and planets
celestial equator
a great circle on the celestial sphere 90° from the celestial poles; where the celestial sphere intersects the plane of Earth’s equator
celestial poles
points about which the celestial sphere appears to rotate; intersections of the celestial sphere with Earth’s polar axis
celestial sphere
the apparent sphere of the sky; a sphere of large radius centered on the observer; directions of objects in the sky can be denoted by their position on the celestial sphere
circumpolar zone
those portions of the celestial sphere near the celestial poles that are either always above or always below the horizon
cosmology
the study of the organization and evolution of the universe
ecliptic
the apparent annual path of the Sun on the celestial sphere
epicycle
the circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle (the deferent)
geocentric
centered on Earth
heliocentric
centered on the Sun
horizon (astronomical)
a great circle on the celestial sphere 90° from the zenith; more popularly, the circle around us where the dome of the sky meets Earth
Who found a conceptual framework that completely explained the observations and rules assembled by Galileo,
Isaac Newton
Newton’s first law:
Every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force.
Newton’s second law:
The change of motion of a body is proportional to and in the direction of the force acting on it.
Newton’s third law:
For every action there is an equal and opposite reaction (or: the mutual actions of two bodies upon each other are always equal and act in opposite directions).
Newton’s first law is a restatement of one of Galileo’s discoveries, called the ________________________
conservation of momentum
What is Newton’s first law sometimes called?
law of inertia
What 3 factors does momentum depend on?
(1) speed—how fast a body moves (zero if it is stationary), (2) the direction of its motion, and (3) its mass—a measure of the amount of matter in a body,
velocity
describe the speed and direction of motion.
The momentum of a body can change only _____________________________
under the action of an outside influence.
acceleration
, the rate of change in an object’s velocity
The most profound of the rules newton discovered?
his 3rd
How does newton’s 3rd law relate to his other laws, while also introducing something diff?
it is a generalization of the first law, but it also gives us a way to define mass.
mass,
which is a measure of the amount of material within an object.
The volume
The volume of an object is the measure of the physical space it occupies.
How is volume measured?
in cubic units
density
is the mass divided by the volume.
angular momentum
a measure of the rotation of a body as it revolves around some fixed point
How is the angular momentum of an object defined?
The angular momentum of an object is defined as the product of its mass, its velocity, and its distance from the fixed point around which it revolves.
Why do the planets move in ellipses, not straight lines?
Because of gravity
Why do we know that gravity is what makes planets move in ellipses?
Everything must move in a straight line unless enacted by some other force, therefore, some force must be bending their paths.
Did Newton discover gravity?
No, but he did suggest that gravity wasn’t just something that existed on earth, and that it may might extend as far as the Moon and produce the force required to curve the Moon’s path from a straight line and keep it in its orbit. He further hypothesized that gravity is not limited to Earth, but that there is a general force of attraction between all material bodies. If so, the attractive force between the Sun and each of the planets could keep them in their orbits.
Who invented calculus and to explain what prob?
Isaac Newton, invented what we today call calculus to deal with the fact that force of gravity depends on distance in order for it’s conditions to be met
What causes acceleration?
forces
What does it mean “that gravity is a built in property of mass?”
Whenever there are masses in the universe, they will interact via the force of gravitational attraction.
Does gravity ever become 0?
No, It quickly gets weaker with distance, but it continues to act to some degree no matter how far away you get.
What does adding the mass term to Kepler’s equation allow us to use it in a new way?
It quickly gets weaker with distance, but it continues to act to some degree no matter how far away you get.
What do Newton’s universal law of gravitation and Kepler’s laws describe?
the motions of Earth satellites and interplanetary spacecraft as well as the planets.
the first artificial Earth satellite,
Sputnik,
Who’s laws describe the motions of Earth satellites and interplanetary spacecraft as well as the planets.
Newton’s universal law of gravitation and Kepler’s laws
What are some uses for satelites?
weather tracking, ecology, global positioning systems, communications, and military purposes, to name a few uses.
Why are the things low in earth’s orbit not indefinetely stable
because, as Earth’s atmosphere swells from time to time, a frictional drag is generated by the atmosphere on these satellites, eventually leading to a loss of energy and “decay” of the orbit.
The exploration of the solar system has been carried out largely by what?
robot spacecraft sent to the other planets.
What must craft do to achieve craft speed
, the speed needed to move away from Earth forever,
What does a spacecraft do as it comes close to it’s target?
As it comes close to its target, a spacecraft is deflected by the planet’s gravitational force into a modified orbit, either gaining or losing energy in the process.
What have actually been able to use a planet’s gravity to redirect a flyby spacecraft to a second target.
Spacecraft controller
How do we orbit a planet?
we must slow the spacecraft with a rocket when the spacecraft is near its destination, allowing it to be captured into an elliptical orbit.
all the planets exert gravitational forces upon one another. What does this cause?
These interplanetary attractions cause slight variations from the orbits than would be expected if the gravitational forces between planets were neglected.
star cluster
many stars all orbiting a common center
Why is it hard to calculate the motion of a star:
the other stars are also moving and thus changing the effect they will have on our star.
Do Kepler’s laws take into account gravitational effects of the other planets on the orbit?
no
Why is the effect of other bodies miniscule to affect the planet in our solar system’s orbit?
This is because these additional influences are very small in comparison with the dominant gravitational attraction of the Sun.
perturbations
disturbances).
What were scientists trying to discover when they discovered Neptune?
During the eighteenth and nineteenth centuries, mathematicians developed many elegant techniques for calculating perturbations, permitting them to predict very precisely the positions of the planets.
What was Uranus thought to be when it was initially discovered?
- When uncovered initially, it was thought to be a star
Who discovered Uranus to be a planet?
- Discovered to be a planet by William Herchell
Why did John Couch Adams hypothesize that Uranus was moving unpredictably?
The pull of a planet farther from the sun
The honor for the discovery of neptune is properly shared by who?
Adams and Le Verrier
Reasons for Uranus’s “disobeideint” movement
Neptune’s gravitational pull
angular momentum
the measure of the motion of a rotating object in terms of its speed and how widely the object’s mass is distributed around its axis
aphelion
the point in its orbit where a planet (or other orbiting object) is farthest from the Sun
apogee
the point in its orbit where an Earth satellite is farthest from Earth
asteroid belt
the region of the solar system between the orbits of Mars and Jupiter in which most asteroids are located; the main belt, where the orbits are generally the most stable, extends from 2.2 to 3.3 AU from the Sun
astronomical unit (AU)
the unit of length defined as the average distance between Earth and the Sun; this distance is about 1.5 × 108 kilometers
density
the ratio of the mass of an object to its volume
eccentricity
in an ellipse, the ratio of the distance between the foci to the major axis
ellipse
a closed curve for which the sum of the distances from any point on the ellipse to two points inside (called the foci) is always the same
escape speed
the speed a body must achieve to break away from the gravity of another body
focus
(plural: foci) one of two fixed points inside an ellipse from which the sum of the distances to any point on the ellipse is constant
gravity
the mutual attraction of material bodies or particles
Kepler’s first law
each planet moves around the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse
Kepler’s second law
the straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time
Kepler’s third law
the square of a planet’s orbital period is directly proportional to the cube of the semimajor axis of its orbit
major axis
the maximum diameter of an ellipse
mass
a measure of the amount of material within an object
momentum
the measure of the amount of motion of a body; the momentum of a body is the product of its mass and velocity; in the absence of an unbalanced force, momentum is conserved
Newton’s first law
every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force
orbit
the path of an object that is in revolution about another object or point
orbital period (P)
the time it takes an object to travel once around the Sun
orbital speed
the speed at which an object (usually a planet) orbits around the mass of another object; in the case of a planet, the speed at which each planet moves along its ellipse
perigee
the point in its orbit where an Earth satellite is closest to Earth
perihelion
the point in its orbit where a planet (or other orbiting object) is nearest to the Sun
perturbation
a small disturbing effect on the motion or orbit of a body produced by a third body
satellite
an object that revolves around a planet
semimajor axis
half of the major axis of a conic section, such as an ellipse
velocity
the speed and direction a body is moving—for example, 44 kilometers per second toward the north galactic pole
Why do the patterns of the stars in our sky look the same from year to year?
The stars in our sky actually move rapidly relative to us—thousands of kilometers per hour—but are so far away that it takes a long time for this motion to make a noticeable change in the patterns in the sky
Can two stars in a constelation be very far away from each other?
yes
Constellation Sagittarius is best seen during the evenings of August and September, but not January evenings because of
the location of earth in it’s orbit
The line that divides the sky into the east and west parts is called the
meridian
Under what circumstances can you find the sun above or below the ecliptic?
never
Beijing and Philadelphia have about the same latitude but very different longitudes. Therefore, tonight’s night sky in these two places
will look the same
What makes the North Star, Polaris, special?
It appears very near the north celestial pole.
What is a circumpolar star?
a star that always remains above your horizon
You are standing on Earth’s North Pole. Which way is Polaris, the North star?
on the northern horizon
When traveling North from the United States into Canada, you’ll see the North Star (Polaris) getting ________.
higher in the sky
He discovered that Jupiter has moons.
Galileo
Kepler’s third law, P2 = a3, means that:
-a planet’s period does not depend on the eccentricity of its orbit
-all orbits with the same semimajor axis have the same period
-planets that are farther from the Sun move at slower average speeds than nearer planets
-the period of a planet does not depend on its mass
Venus orbits the Sun at a slower average speed than Mercury. Which of Kepler’s law can one derive this statement from?
3rd
Kepler’s second law, which states that as a planet moves around its orbit it sweeps out equal areas in equal times, means that:
a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
Suppose a comet orbits the Sun on a highly eccentric orbit with an average (semimajor axis) distance of 1 AU. How long does it take to complete each orbit, and how do we know?
One year, which we know from Kepler’s third law.
According to Kepler’s second law, as a planet moves closer to the sun in its orbit,
it speeds up
From the fact that virtually every galaxy is moving away from us and more distant galaxies are moving away from us at a faster rate than closer ones, we conclude that
the universe is expanding
The term observable universe refers to
that portion of the universe that we can see in principle, given the current age of the universe
Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case, ________.
we are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2
